Imported Upstream version 2.18.0
[platform/upstream/git.git] / refs / files-backend.c
index c041d4b..a9a066d 100644 (file)
 #include "../cache.h"
+#include "../config.h"
 #include "../refs.h"
 #include "refs-internal.h"
+#include "ref-cache.h"
+#include "packed-backend.h"
 #include "../iterator.h"
 #include "../dir-iterator.h"
 #include "../lockfile.h"
 #include "../object.h"
 #include "../dir.h"
-
-struct ref_lock {
-       char *ref_name;
-       struct lock_file *lk;
-       struct object_id old_oid;
-};
-
-struct ref_entry;
-
-/*
- * Information used (along with the information in ref_entry) to
- * describe a single cached reference.  This data structure only
- * occurs embedded in a union in struct ref_entry, and only when
- * (ref_entry->flag & REF_DIR) is zero.
- */
-struct ref_value {
-       /*
-        * The name of the object to which this reference resolves
-        * (which may be a tag object).  If REF_ISBROKEN, this is
-        * null.  If REF_ISSYMREF, then this is the name of the object
-        * referred to by the last reference in the symlink chain.
-        */
-       struct object_id oid;
-
-       /*
-        * If REF_KNOWS_PEELED, then this field holds the peeled value
-        * of this reference, or null if the reference is known not to
-        * be peelable.  See the documentation for peel_ref() for an
-        * exact definition of "peelable".
-        */
-       struct object_id peeled;
-};
-
-struct files_ref_store;
-
-/*
- * Information used (along with the information in ref_entry) to
- * describe a level in the hierarchy of references.  This data
- * structure only occurs embedded in a union in struct ref_entry, and
- * only when (ref_entry.flag & REF_DIR) is set.  In that case,
- * (ref_entry.flag & REF_INCOMPLETE) determines whether the references
- * in the directory have already been read:
- *
- *     (ref_entry.flag & REF_INCOMPLETE) unset -- a directory of loose
- *         or packed references, already read.
- *
- *     (ref_entry.flag & REF_INCOMPLETE) set -- a directory of loose
- *         references that hasn't been read yet (nor has any of its
- *         subdirectories).
- *
- * Entries within a directory are stored within a growable array of
- * pointers to ref_entries (entries, nr, alloc).  Entries 0 <= i <
- * sorted are sorted by their component name in strcmp() order and the
- * remaining entries are unsorted.
- *
- * Loose references are read lazily, one directory at a time.  When a
- * directory of loose references is read, then all of the references
- * in that directory are stored, and REF_INCOMPLETE stubs are created
- * for any subdirectories, but the subdirectories themselves are not
- * read.  The reading is triggered by get_ref_dir().
- */
-struct ref_dir {
-       int nr, alloc;
-
-       /*
-        * Entries with index 0 <= i < sorted are sorted by name.  New
-        * entries are appended to the list unsorted, and are sorted
-        * only when required; thus we avoid the need to sort the list
-        * after the addition of every reference.
-        */
-       int sorted;
-
-       /* A pointer to the files_ref_store that contains this ref_dir. */
-       struct files_ref_store *ref_store;
-
-       struct ref_entry **entries;
-};
-
-/*
- * Bit values for ref_entry::flag.  REF_ISSYMREF=0x01,
- * REF_ISPACKED=0x02, REF_ISBROKEN=0x04 and REF_BAD_NAME=0x08 are
- * public values; see refs.h.
- */
-
-/*
- * The field ref_entry->u.value.peeled of this value entry contains
- * the correct peeled value for the reference, which might be
- * null_sha1 if the reference is not a tag or if it is broken.
- */
-#define REF_KNOWS_PEELED 0x10
-
-/* ref_entry represents a directory of references */
-#define REF_DIR 0x20
-
-/*
- * Entry has not yet been read from disk (used only for REF_DIR
- * entries representing loose references)
- */
-#define REF_INCOMPLETE 0x40
-
-/*
- * A ref_entry represents either a reference or a "subdirectory" of
- * references.
- *
- * Each directory in the reference namespace is represented by a
- * ref_entry with (flags & REF_DIR) set and containing a subdir member
- * that holds the entries in that directory that have been read so
- * far.  If (flags & REF_INCOMPLETE) is set, then the directory and
- * its subdirectories haven't been read yet.  REF_INCOMPLETE is only
- * used for loose reference directories.
- *
- * References are represented by a ref_entry with (flags & REF_DIR)
- * unset and a value member that describes the reference's value.  The
- * flag member is at the ref_entry level, but it is also needed to
- * interpret the contents of the value field (in other words, a
- * ref_value object is not very much use without the enclosing
- * ref_entry).
- *
- * Reference names cannot end with slash and directories' names are
- * always stored with a trailing slash (except for the top-level
- * directory, which is always denoted by "").  This has two nice
- * consequences: (1) when the entries in each subdir are sorted
- * lexicographically by name (as they usually are), the references in
- * a whole tree can be generated in lexicographic order by traversing
- * the tree in left-to-right, depth-first order; (2) the names of
- * references and subdirectories cannot conflict, and therefore the
- * presence of an empty subdirectory does not block the creation of a
- * similarly-named reference.  (The fact that reference names with the
- * same leading components can conflict *with each other* is a
- * separate issue that is regulated by verify_refname_available().)
- *
- * Please note that the name field contains the fully-qualified
- * reference (or subdirectory) name.  Space could be saved by only
- * storing the relative names.  But that would require the full names
- * to be generated on the fly when iterating in do_for_each_ref(), and
- * would break callback functions, who have always been able to assume
- * that the name strings that they are passed will not be freed during
- * the iteration.
- */
-struct ref_entry {
-       unsigned char flag; /* ISSYMREF? ISPACKED? */
-       union {
-               struct ref_value value; /* if not (flags&REF_DIR) */
-               struct ref_dir subdir; /* if (flags&REF_DIR) */
-       } u;
-       /*
-        * The full name of the reference (e.g., "refs/heads/master")
-        * or the full name of the directory with a trailing slash
-        * (e.g., "refs/heads/"):
-        */
-       char name[FLEX_ARRAY];
-};
-
-static void read_loose_refs(const char *dirname, struct ref_dir *dir);
-static int search_ref_dir(struct ref_dir *dir, const char *refname, size_t len);
-static struct ref_entry *create_dir_entry(struct files_ref_store *ref_store,
-                                         const char *dirname, size_t len,
-                                         int incomplete);
-static void add_entry_to_dir(struct ref_dir *dir, struct ref_entry *entry);
-
-static struct ref_dir *get_ref_dir(struct ref_entry *entry)
-{
-       struct ref_dir *dir;
-       assert(entry->flag & REF_DIR);
-       dir = &entry->u.subdir;
-       if (entry->flag & REF_INCOMPLETE) {
-               read_loose_refs(entry->name, dir);
-
-               /*
-                * Manually add refs/bisect, which, being
-                * per-worktree, might not appear in the directory
-                * listing for refs/ in the main repo.
-                */
-               if (!strcmp(entry->name, "refs/")) {
-                       int pos = search_ref_dir(dir, "refs/bisect/", 12);
-                       if (pos < 0) {
-                               struct ref_entry *child_entry;
-                               child_entry = create_dir_entry(dir->ref_store,
-                                                              "refs/bisect/",
-                                                              12, 1);
-                               add_entry_to_dir(dir, child_entry);
-                               read_loose_refs("refs/bisect",
-                                               &child_entry->u.subdir);
-                       }
-               }
-               entry->flag &= ~REF_INCOMPLETE;
-       }
-       return dir;
-}
-
-static struct ref_entry *create_ref_entry(const char *refname,
-                                         const unsigned char *sha1, int flag,
-                                         int check_name)
-{
-       struct ref_entry *ref;
-
-       if (check_name &&
-           check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
-               die("Reference has invalid format: '%s'", refname);
-       FLEX_ALLOC_STR(ref, name, refname);
-       hashcpy(ref->u.value.oid.hash, sha1);
-       oidclr(&ref->u.value.peeled);
-       ref->flag = flag;
-       return ref;
-}
-
-static void clear_ref_dir(struct ref_dir *dir);
-
-static void free_ref_entry(struct ref_entry *entry)
-{
-       if (entry->flag & REF_DIR) {
-               /*
-                * Do not use get_ref_dir() here, as that might
-                * trigger the reading of loose refs.
-                */
-               clear_ref_dir(&entry->u.subdir);
-       }
-       free(entry);
-}
-
-/*
- * Add a ref_entry to the end of dir (unsorted).  Entry is always
- * stored directly in dir; no recursion into subdirectories is
- * done.
- */
-static void add_entry_to_dir(struct ref_dir *dir, struct ref_entry *entry)
-{
-       ALLOC_GROW(dir->entries, dir->nr + 1, dir->alloc);
-       dir->entries[dir->nr++] = entry;
-       /* optimize for the case that entries are added in order */
-       if (dir->nr == 1 ||
-           (dir->nr == dir->sorted + 1 &&
-            strcmp(dir->entries[dir->nr - 2]->name,
-                   dir->entries[dir->nr - 1]->name) < 0))
-               dir->sorted = dir->nr;
-}
-
-/*
- * Clear and free all entries in dir, recursively.
- */
-static void clear_ref_dir(struct ref_dir *dir)
-{
-       int i;
-       for (i = 0; i < dir->nr; i++)
-               free_ref_entry(dir->entries[i]);
-       free(dir->entries);
-       dir->sorted = dir->nr = dir->alloc = 0;
-       dir->entries = NULL;
-}
-
-/*
- * Create a struct ref_entry object for the specified dirname.
- * dirname is the name of the directory with a trailing slash (e.g.,
- * "refs/heads/") or "" for the top-level directory.
- */
-static struct ref_entry *create_dir_entry(struct files_ref_store *ref_store,
-                                         const char *dirname, size_t len,
-                                         int incomplete)
-{
-       struct ref_entry *direntry;
-       FLEX_ALLOC_MEM(direntry, name, dirname, len);
-       direntry->u.subdir.ref_store = ref_store;
-       direntry->flag = REF_DIR | (incomplete ? REF_INCOMPLETE : 0);
-       return direntry;
-}
-
-static int ref_entry_cmp(const void *a, const void *b)
-{
-       struct ref_entry *one = *(struct ref_entry **)a;
-       struct ref_entry *two = *(struct ref_entry **)b;
-       return strcmp(one->name, two->name);
-}
-
-static void sort_ref_dir(struct ref_dir *dir);
-
-struct string_slice {
-       size_t len;
-       const char *str;
-};
-
-static int ref_entry_cmp_sslice(const void *key_, const void *ent_)
-{
-       const struct string_slice *key = key_;
-       const struct ref_entry *ent = *(const struct ref_entry * const *)ent_;
-       int cmp = strncmp(key->str, ent->name, key->len);
-       if (cmp)
-               return cmp;
-       return '\0' - (unsigned char)ent->name[key->len];
-}
-
-/*
- * Return the index of the entry with the given refname from the
- * ref_dir (non-recursively), sorting dir if necessary.  Return -1 if
- * no such entry is found.  dir must already be complete.
- */
-static int search_ref_dir(struct ref_dir *dir, const char *refname, size_t len)
-{
-       struct ref_entry **r;
-       struct string_slice key;
-
-       if (refname == NULL || !dir->nr)
-               return -1;
-
-       sort_ref_dir(dir);
-       key.len = len;
-       key.str = refname;
-       r = bsearch(&key, dir->entries, dir->nr, sizeof(*dir->entries),
-                   ref_entry_cmp_sslice);
-
-       if (r == NULL)
-               return -1;
-
-       return r - dir->entries;
-}
-
-/*
- * Search for a directory entry directly within dir (without
- * recursing).  Sort dir if necessary.  subdirname must be a directory
- * name (i.e., end in '/').  If mkdir is set, then create the
- * directory if it is missing; otherwise, return NULL if the desired
- * directory cannot be found.  dir must already be complete.
- */
-static struct ref_dir *search_for_subdir(struct ref_dir *dir,
-                                        const char *subdirname, size_t len,
-                                        int mkdir)
-{
-       int entry_index = search_ref_dir(dir, subdirname, len);
-       struct ref_entry *entry;
-       if (entry_index == -1) {
-               if (!mkdir)
-                       return NULL;
-               /*
-                * Since dir is complete, the absence of a subdir
-                * means that the subdir really doesn't exist;
-                * therefore, create an empty record for it but mark
-                * the record complete.
-                */
-               entry = create_dir_entry(dir->ref_store, subdirname, len, 0);
-               add_entry_to_dir(dir, entry);
-       } else {
-               entry = dir->entries[entry_index];
-       }
-       return get_ref_dir(entry);
-}
-
-/*
- * If refname is a reference name, find the ref_dir within the dir
- * tree that should hold refname.  If refname is a directory name
- * (i.e., ends in '/'), then return that ref_dir itself.  dir must
- * represent the top-level directory and must already be complete.
- * Sort ref_dirs and recurse into subdirectories as necessary.  If
- * mkdir is set, then create any missing directories; otherwise,
- * return NULL if the desired directory cannot be found.
- */
-static struct ref_dir *find_containing_dir(struct ref_dir *dir,
-                                          const char *refname, int mkdir)
-{
-       const char *slash;
-       for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
-               size_t dirnamelen = slash - refname + 1;
-               struct ref_dir *subdir;
-               subdir = search_for_subdir(dir, refname, dirnamelen, mkdir);
-               if (!subdir) {
-                       dir = NULL;
-                       break;
-               }
-               dir = subdir;
-       }
-
-       return dir;
-}
+#include "../chdir-notify.h"
 
 /*
- * Find the value entry with the given name in dir, sorting ref_dirs
- * and recursing into subdirectories as necessary.  If the name is not
- * found or it corresponds to a directory entry, return NULL.
+ * This backend uses the following flags in `ref_update::flags` for
+ * internal bookkeeping purposes. Their numerical values must not
+ * conflict with REF_NO_DEREF, REF_FORCE_CREATE_REFLOG, REF_HAVE_NEW,
+ * REF_HAVE_OLD, or REF_IS_PRUNING, which are also stored in
+ * `ref_update::flags`.
  */
-static struct ref_entry *find_ref(struct ref_dir *dir, const char *refname)
-{
-       int entry_index;
-       struct ref_entry *entry;
-       dir = find_containing_dir(dir, refname, 0);
-       if (!dir)
-               return NULL;
-       entry_index = search_ref_dir(dir, refname, strlen(refname));
-       if (entry_index == -1)
-               return NULL;
-       entry = dir->entries[entry_index];
-       return (entry->flag & REF_DIR) ? NULL : entry;
-}
 
 /*
- * Remove the entry with the given name from dir, recursing into
- * subdirectories as necessary.  If refname is the name of a directory
- * (i.e., ends with '/'), then remove the directory and its contents.
- * If the removal was successful, return the number of entries
- * remaining in the directory entry that contained the deleted entry.
- * If the name was not found, return -1.  Please note that this
- * function only deletes the entry from the cache; it does not delete
- * it from the filesystem or ensure that other cache entries (which
- * might be symbolic references to the removed entry) are updated.
- * Nor does it remove any containing dir entries that might be made
- * empty by the removal.  dir must represent the top-level directory
- * and must already be complete.
+ * Used as a flag in ref_update::flags when a loose ref is being
+ * pruned. This flag must only be used when REF_NO_DEREF is set.
  */
-static int remove_entry(struct ref_dir *dir, const char *refname)
-{
-       int refname_len = strlen(refname);
-       int entry_index;
-       struct ref_entry *entry;
-       int is_dir = refname[refname_len - 1] == '/';
-       if (is_dir) {
-               /*
-                * refname represents a reference directory.  Remove
-                * the trailing slash; otherwise we will get the
-                * directory *representing* refname rather than the
-                * one *containing* it.
-                */
-               char *dirname = xmemdupz(refname, refname_len - 1);
-               dir = find_containing_dir(dir, dirname, 0);
-               free(dirname);
-       } else {
-               dir = find_containing_dir(dir, refname, 0);
-       }
-       if (!dir)
-               return -1;
-       entry_index = search_ref_dir(dir, refname, refname_len);
-       if (entry_index == -1)
-               return -1;
-       entry = dir->entries[entry_index];
-
-       memmove(&dir->entries[entry_index],
-               &dir->entries[entry_index + 1],
-               (dir->nr - entry_index - 1) * sizeof(*dir->entries)
-               );
-       dir->nr--;
-       if (dir->sorted > entry_index)
-               dir->sorted--;
-       free_ref_entry(entry);
-       return dir->nr;
-}
+#define REF_IS_PRUNING (1 << 4)
 
 /*
- * Add a ref_entry to the ref_dir (unsorted), recursing into
- * subdirectories as necessary.  dir must represent the top-level
- * directory.  Return 0 on success.
+ * Flag passed to lock_ref_sha1_basic() telling it to tolerate broken
+ * refs (i.e., because the reference is about to be deleted anyway).
  */
-static int add_ref(struct ref_dir *dir, struct ref_entry *ref)
-{
-       dir = find_containing_dir(dir, ref->name, 1);
-       if (!dir)
-               return -1;
-       add_entry_to_dir(dir, ref);
-       return 0;
-}
+#define REF_DELETING (1 << 5)
 
 /*
- * Emit a warning and return true iff ref1 and ref2 have the same name
- * and the same sha1.  Die if they have the same name but different
- * sha1s.
+ * Used as a flag in ref_update::flags when the lockfile needs to be
+ * committed.
  */
-static int is_dup_ref(const struct ref_entry *ref1, const struct ref_entry *ref2)
-{
-       if (strcmp(ref1->name, ref2->name))
-               return 0;
-
-       /* Duplicate name; make sure that they don't conflict: */
-
-       if ((ref1->flag & REF_DIR) || (ref2->flag & REF_DIR))
-               /* This is impossible by construction */
-               die("Reference directory conflict: %s", ref1->name);
-
-       if (oidcmp(&ref1->u.value.oid, &ref2->u.value.oid))
-               die("Duplicated ref, and SHA1s don't match: %s", ref1->name);
-
-       warning("Duplicated ref: %s", ref1->name);
-       return 1;
-}
+#define REF_NEEDS_COMMIT (1 << 6)
 
 /*
- * Sort the entries in dir non-recursively (if they are not already
- * sorted) and remove any duplicate entries.
+ * Used as a flag in ref_update::flags when we want to log a ref
+ * update but not actually perform it.  This is used when a symbolic
+ * ref update is split up.
  */
-static void sort_ref_dir(struct ref_dir *dir)
-{
-       int i, j;
-       struct ref_entry *last = NULL;
-
-       /*
-        * This check also prevents passing a zero-length array to qsort(),
-        * which is a problem on some platforms.
-        */
-       if (dir->sorted == dir->nr)
-               return;
-
-       QSORT(dir->entries, dir->nr, ref_entry_cmp);
-
-       /* Remove any duplicates: */
-       for (i = 0, j = 0; j < dir->nr; j++) {
-               struct ref_entry *entry = dir->entries[j];
-               if (last && is_dup_ref(last, entry))
-                       free_ref_entry(entry);
-               else
-                       last = dir->entries[i++] = entry;
-       }
-       dir->sorted = dir->nr = i;
-}
+#define REF_LOG_ONLY (1 << 7)
 
 /*
- * Return true if refname, which has the specified oid and flags, can
- * be resolved to an object in the database. If the referred-to object
- * does not exist, emit a warning and return false.
+ * Used as a flag in ref_update::flags when the ref_update was via an
+ * update to HEAD.
  */
-static int ref_resolves_to_object(const char *refname,
-                                 const struct object_id *oid,
-                                 unsigned int flags)
-{
-       if (flags & REF_ISBROKEN)
-               return 0;
-       if (!has_sha1_file(oid->hash)) {
-               error("%s does not point to a valid object!", refname);
-               return 0;
-       }
-       return 1;
-}
-
-/*
- * Return true if the reference described by entry can be resolved to
- * an object in the database; otherwise, emit a warning and return
- * false.
- */
-static int entry_resolves_to_object(struct ref_entry *entry)
-{
-       return ref_resolves_to_object(entry->name,
-                                     &entry->u.value.oid, entry->flag);
-}
-
-typedef int each_ref_entry_fn(struct ref_entry *entry, void *cb_data);
+#define REF_UPDATE_VIA_HEAD (1 << 8)
 
 /*
- * Call fn for each reference in dir that has index in the range
- * offset <= index < dir->nr.  Recurse into subdirectories that are in
- * that index range, sorting them before iterating.  This function
- * does not sort dir itself; it should be sorted beforehand.  fn is
- * called for all references, including broken ones.
+ * Used as a flag in ref_update::flags when the loose reference has
+ * been deleted.
  */
-static int do_for_each_entry_in_dir(struct ref_dir *dir, int offset,
-                                   each_ref_entry_fn fn, void *cb_data)
-{
-       int i;
-       assert(dir->sorted == dir->nr);
-       for (i = offset; i < dir->nr; i++) {
-               struct ref_entry *entry = dir->entries[i];
-               int retval;
-               if (entry->flag & REF_DIR) {
-                       struct ref_dir *subdir = get_ref_dir(entry);
-                       sort_ref_dir(subdir);
-                       retval = do_for_each_entry_in_dir(subdir, 0, fn, cb_data);
-               } else {
-                       retval = fn(entry, cb_data);
-               }
-               if (retval)
-                       return retval;
-       }
-       return 0;
-}
-
-/*
- * Load all of the refs from the dir into our in-memory cache. The hard work
- * of loading loose refs is done by get_ref_dir(), so we just need to recurse
- * through all of the sub-directories. We do not even need to care about
- * sorting, as traversal order does not matter to us.
- */
-static void prime_ref_dir(struct ref_dir *dir)
-{
-       int i;
-       for (i = 0; i < dir->nr; i++) {
-               struct ref_entry *entry = dir->entries[i];
-               if (entry->flag & REF_DIR)
-                       prime_ref_dir(get_ref_dir(entry));
-       }
-}
-
-/*
- * A level in the reference hierarchy that is currently being iterated
- * through.
- */
-struct cache_ref_iterator_level {
-       /*
-        * The ref_dir being iterated over at this level. The ref_dir
-        * is sorted before being stored here.
-        */
-       struct ref_dir *dir;
+#define REF_DELETED_LOOSE (1 << 9)
 
-       /*
-        * The index of the current entry within dir (which might
-        * itself be a directory). If index == -1, then the iteration
-        * hasn't yet begun. If index == dir->nr, then the iteration
-        * through this level is over.
-        */
-       int index;
-};
-
-/*
- * Represent an iteration through a ref_dir in the memory cache. The
- * iteration recurses through subdirectories.
- */
-struct cache_ref_iterator {
-       struct ref_iterator base;
-
-       /*
-        * The number of levels currently on the stack. This is always
-        * at least 1, because when it becomes zero the iteration is
-        * ended and this struct is freed.
-        */
-       size_t levels_nr;
-
-       /* The number of levels that have been allocated on the stack */
-       size_t levels_alloc;
-
-       /*
-        * A stack of levels. levels[0] is the uppermost level that is
-        * being iterated over in this iteration. (This is not
-        * necessary the top level in the references hierarchy. If we
-        * are iterating through a subtree, then levels[0] will hold
-        * the ref_dir for that subtree, and subsequent levels will go
-        * on from there.)
-        */
-       struct cache_ref_iterator_level *levels;
-};
-
-static int cache_ref_iterator_advance(struct ref_iterator *ref_iterator)
-{
-       struct cache_ref_iterator *iter =
-               (struct cache_ref_iterator *)ref_iterator;
-
-       while (1) {
-               struct cache_ref_iterator_level *level =
-                       &iter->levels[iter->levels_nr - 1];
-               struct ref_dir *dir = level->dir;
-               struct ref_entry *entry;
-
-               if (level->index == -1)
-                       sort_ref_dir(dir);
-
-               if (++level->index == level->dir->nr) {
-                       /* This level is exhausted; pop up a level */
-                       if (--iter->levels_nr == 0)
-                               return ref_iterator_abort(ref_iterator);
-
-                       continue;
-               }
-
-               entry = dir->entries[level->index];
-
-               if (entry->flag & REF_DIR) {
-                       /* push down a level */
-                       ALLOC_GROW(iter->levels, iter->levels_nr + 1,
-                                  iter->levels_alloc);
-
-                       level = &iter->levels[iter->levels_nr++];
-                       level->dir = get_ref_dir(entry);
-                       level->index = -1;
-               } else {
-                       iter->base.refname = entry->name;
-                       iter->base.oid = &entry->u.value.oid;
-                       iter->base.flags = entry->flag;
-                       return ITER_OK;
-               }
-       }
-}
-
-static enum peel_status peel_entry(struct ref_entry *entry, int repeel);
-
-static int cache_ref_iterator_peel(struct ref_iterator *ref_iterator,
-                                  struct object_id *peeled)
-{
-       struct cache_ref_iterator *iter =
-               (struct cache_ref_iterator *)ref_iterator;
-       struct cache_ref_iterator_level *level;
-       struct ref_entry *entry;
-
-       level = &iter->levels[iter->levels_nr - 1];
-
-       if (level->index == -1)
-               die("BUG: peel called before advance for cache iterator");
-
-       entry = level->dir->entries[level->index];
-
-       if (peel_entry(entry, 0))
-               return -1;
-       oidcpy(peeled, &entry->u.value.peeled);
-       return 0;
-}
-
-static int cache_ref_iterator_abort(struct ref_iterator *ref_iterator)
-{
-       struct cache_ref_iterator *iter =
-               (struct cache_ref_iterator *)ref_iterator;
-
-       free(iter->levels);
-       base_ref_iterator_free(ref_iterator);
-       return ITER_DONE;
-}
-
-static struct ref_iterator_vtable cache_ref_iterator_vtable = {
-       cache_ref_iterator_advance,
-       cache_ref_iterator_peel,
-       cache_ref_iterator_abort
-};
-
-static struct ref_iterator *cache_ref_iterator_begin(struct ref_dir *dir)
-{
-       struct cache_ref_iterator *iter;
-       struct ref_iterator *ref_iterator;
-       struct cache_ref_iterator_level *level;
-
-       iter = xcalloc(1, sizeof(*iter));
-       ref_iterator = &iter->base;
-       base_ref_iterator_init(ref_iterator, &cache_ref_iterator_vtable);
-       ALLOC_GROW(iter->levels, 10, iter->levels_alloc);
-
-       iter->levels_nr = 1;
-       level = &iter->levels[0];
-       level->index = -1;
-       level->dir = dir;
-
-       return ref_iterator;
-}
-
-struct nonmatching_ref_data {
-       const struct string_list *skip;
-       const char *conflicting_refname;
-};
-
-static int nonmatching_ref_fn(struct ref_entry *entry, void *vdata)
-{
-       struct nonmatching_ref_data *data = vdata;
-
-       if (data->skip && string_list_has_string(data->skip, entry->name))
-               return 0;
-
-       data->conflicting_refname = entry->name;
-       return 1;
-}
-
-/*
- * Return 0 if a reference named refname could be created without
- * conflicting with the name of an existing reference in dir.
- * See verify_refname_available for more information.
- */
-static int verify_refname_available_dir(const char *refname,
-                                       const struct string_list *extras,
-                                       const struct string_list *skip,
-                                       struct ref_dir *dir,
-                                       struct strbuf *err)
-{
-       const char *slash;
-       const char *extra_refname;
-       int pos;
-       struct strbuf dirname = STRBUF_INIT;
-       int ret = -1;
-
-       /*
-        * For the sake of comments in this function, suppose that
-        * refname is "refs/foo/bar".
-        */
-
-       assert(err);
-
-       strbuf_grow(&dirname, strlen(refname) + 1);
-       for (slash = strchr(refname, '/'); slash; slash = strchr(slash + 1, '/')) {
-               /* Expand dirname to the new prefix, not including the trailing slash: */
-               strbuf_add(&dirname, refname + dirname.len, slash - refname - dirname.len);
-
-               /*
-                * We are still at a leading dir of the refname (e.g.,
-                * "refs/foo"; if there is a reference with that name,
-                * it is a conflict, *unless* it is in skip.
-                */
-               if (dir) {
-                       pos = search_ref_dir(dir, dirname.buf, dirname.len);
-                       if (pos >= 0 &&
-                           (!skip || !string_list_has_string(skip, dirname.buf))) {
-                               /*
-                                * We found a reference whose name is
-                                * a proper prefix of refname; e.g.,
-                                * "refs/foo", and is not in skip.
-                                */
-                               strbuf_addf(err, "'%s' exists; cannot create '%s'",
-                                           dirname.buf, refname);
-                               goto cleanup;
-                       }
-               }
-
-               if (extras && string_list_has_string(extras, dirname.buf) &&
-                   (!skip || !string_list_has_string(skip, dirname.buf))) {
-                       strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
-                                   refname, dirname.buf);
-                       goto cleanup;
-               }
-
-               /*
-                * Otherwise, we can try to continue our search with
-                * the next component. So try to look up the
-                * directory, e.g., "refs/foo/". If we come up empty,
-                * we know there is nothing under this whole prefix,
-                * but even in that case we still have to continue the
-                * search for conflicts with extras.
-                */
-               strbuf_addch(&dirname, '/');
-               if (dir) {
-                       pos = search_ref_dir(dir, dirname.buf, dirname.len);
-                       if (pos < 0) {
-                               /*
-                                * There was no directory "refs/foo/",
-                                * so there is nothing under this
-                                * whole prefix. So there is no need
-                                * to continue looking for conflicting
-                                * references. But we need to continue
-                                * looking for conflicting extras.
-                                */
-                               dir = NULL;
-                       } else {
-                               dir = get_ref_dir(dir->entries[pos]);
-                       }
-               }
-       }
-
-       /*
-        * We are at the leaf of our refname (e.g., "refs/foo/bar").
-        * There is no point in searching for a reference with that
-        * name, because a refname isn't considered to conflict with
-        * itself. But we still need to check for references whose
-        * names are in the "refs/foo/bar/" namespace, because they
-        * *do* conflict.
-        */
-       strbuf_addstr(&dirname, refname + dirname.len);
-       strbuf_addch(&dirname, '/');
-
-       if (dir) {
-               pos = search_ref_dir(dir, dirname.buf, dirname.len);
-
-               if (pos >= 0) {
-                       /*
-                        * We found a directory named "$refname/"
-                        * (e.g., "refs/foo/bar/"). It is a problem
-                        * iff it contains any ref that is not in
-                        * "skip".
-                        */
-                       struct nonmatching_ref_data data;
-
-                       data.skip = skip;
-                       data.conflicting_refname = NULL;
-                       dir = get_ref_dir(dir->entries[pos]);
-                       sort_ref_dir(dir);
-                       if (do_for_each_entry_in_dir(dir, 0, nonmatching_ref_fn, &data)) {
-                               strbuf_addf(err, "'%s' exists; cannot create '%s'",
-                                           data.conflicting_refname, refname);
-                               goto cleanup;
-                       }
-               }
-       }
-
-       extra_refname = find_descendant_ref(dirname.buf, extras, skip);
-       if (extra_refname)
-               strbuf_addf(err, "cannot process '%s' and '%s' at the same time",
-                           refname, extra_refname);
-       else
-               ret = 0;
-
-cleanup:
-       strbuf_release(&dirname);
-       return ret;
-}
-
-struct packed_ref_cache {
-       struct ref_entry *root;
-
-       /*
-        * Count of references to the data structure in this instance,
-        * including the pointer from files_ref_store::packed if any.
-        * The data will not be freed as long as the reference count
-        * is nonzero.
-        */
-       unsigned int referrers;
-
-       /*
-        * Iff the packed-refs file associated with this instance is
-        * currently locked for writing, this points at the associated
-        * lock (which is owned by somebody else).  The referrer count
-        * is also incremented when the file is locked and decremented
-        * when it is unlocked.
-        */
-       struct lock_file *lock;
-
-       /* The metadata from when this packed-refs cache was read */
-       struct stat_validity validity;
+struct ref_lock {
+       char *ref_name;
+       struct lock_file lk;
+       struct object_id old_oid;
 };
 
-/*
- * Future: need to be in "struct repository"
- * when doing a full libification.
- */
 struct files_ref_store {
        struct ref_store base;
-       struct ref_entry *loose;
-       struct packed_ref_cache *packed;
-};
+       unsigned int store_flags;
 
-/* Lock used for the main packed-refs file: */
-static struct lock_file packlock;
+       char *gitdir;
+       char *gitcommondir;
 
-/*
- * Increment the reference count of *packed_refs.
- */
-static void acquire_packed_ref_cache(struct packed_ref_cache *packed_refs)
-{
-       packed_refs->referrers++;
-}
+       struct ref_cache *loose;
 
-/*
- * Decrease the reference count of *packed_refs.  If it goes to zero,
- * free *packed_refs and return true; otherwise return false.
- */
-static int release_packed_ref_cache(struct packed_ref_cache *packed_refs)
-{
-       if (!--packed_refs->referrers) {
-               free_ref_entry(packed_refs->root);
-               stat_validity_clear(&packed_refs->validity);
-               free(packed_refs);
-               return 1;
-       } else {
-               return 0;
-       }
-}
-
-static void clear_packed_ref_cache(struct files_ref_store *refs)
-{
-       if (refs->packed) {
-               struct packed_ref_cache *packed_refs = refs->packed;
-
-               if (packed_refs->lock)
-                       die("internal error: packed-ref cache cleared while locked");
-               refs->packed = NULL;
-               release_packed_ref_cache(packed_refs);
-       }
-}
+       struct ref_store *packed_ref_store;
+};
 
 static void clear_loose_ref_cache(struct files_ref_store *refs)
 {
        if (refs->loose) {
-               free_ref_entry(refs->loose);
+               free_ref_cache(refs->loose);
                refs->loose = NULL;
        }
 }
@@ -967,224 +86,103 @@ static void clear_loose_ref_cache(struct files_ref_store *refs)
  * Create a new submodule ref cache and add it to the internal
  * set of caches.
  */
-static struct ref_store *files_ref_store_create(const char *submodule)
+static struct ref_store *files_ref_store_create(const char *gitdir,
+                                               unsigned int flags)
 {
        struct files_ref_store *refs = xcalloc(1, sizeof(*refs));
        struct ref_store *ref_store = (struct ref_store *)refs;
+       struct strbuf sb = STRBUF_INIT;
 
-       base_ref_store_init(ref_store, &refs_be_files, submodule);
+       base_ref_store_init(ref_store, &refs_be_files);
+       refs->store_flags = flags;
+
+       refs->gitdir = xstrdup(gitdir);
+       get_common_dir_noenv(&sb, gitdir);
+       refs->gitcommondir = strbuf_detach(&sb, NULL);
+       strbuf_addf(&sb, "%s/packed-refs", refs->gitcommondir);
+       refs->packed_ref_store = packed_ref_store_create(sb.buf, flags);
+       strbuf_release(&sb);
+
+       chdir_notify_reparent("files-backend $GIT_DIR",
+                             &refs->gitdir);
+       chdir_notify_reparent("files-backend $GIT_COMMONDIR",
+                             &refs->gitcommondir);
 
        return ref_store;
 }
 
 /*
- * Downcast ref_store to files_ref_store. Die if ref_store is not a
- * files_ref_store. If submodule_allowed is not true, then also die if
- * files_ref_store is for a submodule (i.e., not for the main
- * repository). caller is used in any necessary error messages.
+ * Die if refs is not the main ref store. caller is used in any
+ * necessary error messages.
  */
-static struct files_ref_store *files_downcast(
-               struct ref_store *ref_store, int submodule_allowed,
-               const char *caller)
+static void files_assert_main_repository(struct files_ref_store *refs,
+                                        const char *caller)
 {
-       if (ref_store->be != &refs_be_files)
-               die("BUG: ref_store is type \"%s\" not \"files\" in %s",
-                   ref_store->be->name, caller);
-
-       if (!submodule_allowed)
-               assert_main_repository(ref_store, caller);
+       if (refs->store_flags & REF_STORE_MAIN)
+               return;
 
-       return (struct files_ref_store *)ref_store;
+       BUG("operation %s only allowed for main ref store", caller);
 }
 
-/* The length of a peeled reference line in packed-refs, including EOL: */
-#define PEELED_LINE_LENGTH 42
-
-/*
- * The packed-refs header line that we write out.  Perhaps other
- * traits will be added later.  The trailing space is required.
- */
-static const char PACKED_REFS_HEADER[] =
-       "# pack-refs with: peeled fully-peeled \n";
-
 /*
- * Parse one line from a packed-refs file.  Write the SHA1 to sha1.
- * Return a pointer to the refname within the line (null-terminated),
- * or NULL if there was a problem.
+ * Downcast ref_store to files_ref_store. Die if ref_store is not a
+ * files_ref_store. required_flags is compared with ref_store's
+ * store_flags to ensure the ref_store has all required capabilities.
+ * "caller" is used in any necessary error messages.
  */
-static const char *parse_ref_line(struct strbuf *line, unsigned char *sha1)
+static struct files_ref_store *files_downcast(struct ref_store *ref_store,
+                                             unsigned int required_flags,
+                                             const char *caller)
 {
-       const char *ref;
-
-       /*
-        * 42: the answer to everything.
-        *
-        * In this case, it happens to be the answer to
-        *  40 (length of sha1 hex representation)
-        *  +1 (space in between hex and name)
-        *  +1 (newline at the end of the line)
-        */
-       if (line->len <= 42)
-               return NULL;
+       struct files_ref_store *refs;
 
-       if (get_sha1_hex(line->buf, sha1) < 0)
-               return NULL;
-       if (!isspace(line->buf[40]))
-               return NULL;
+       if (ref_store->be != &refs_be_files)
+               BUG("ref_store is type \"%s\" not \"files\" in %s",
+                   ref_store->be->name, caller);
 
-       ref = line->buf + 41;
-       if (isspace(*ref))
-               return NULL;
+       refs = (struct files_ref_store *)ref_store;
 
-       if (line->buf[line->len - 1] != '\n')
-               return NULL;
-       line->buf[--line->len] = 0;
+       if ((refs->store_flags & required_flags) != required_flags)
+               BUG("operation %s requires abilities 0x%x, but only have 0x%x",
+                   caller, required_flags, refs->store_flags);
 
-       return ref;
+       return refs;
 }
 
-/*
- * Read f, which is a packed-refs file, into dir.
- *
- * A comment line of the form "# pack-refs with: " may contain zero or
- * more traits. We interpret the traits as follows:
- *
- *   No traits:
- *
- *      Probably no references are peeled. But if the file contains a
- *      peeled value for a reference, we will use it.
- *
- *   peeled:
- *
- *      References under "refs/tags/", if they *can* be peeled, *are*
- *      peeled in this file. References outside of "refs/tags/" are
- *      probably not peeled even if they could have been, but if we find
- *      a peeled value for such a reference we will use it.
- *
- *   fully-peeled:
- *
- *      All references in the file that can be peeled are peeled.
- *      Inversely (and this is more important), any references in the
- *      file for which no peeled value is recorded is not peelable. This
- *      trait should typically be written alongside "peeled" for
- *      compatibility with older clients, but we do not require it
- *      (i.e., "peeled" is a no-op if "fully-peeled" is set).
- */
-static void read_packed_refs(FILE *f, struct ref_dir *dir)
+static void files_reflog_path(struct files_ref_store *refs,
+                             struct strbuf *sb,
+                             const char *refname)
 {
-       struct ref_entry *last = NULL;
-       struct strbuf line = STRBUF_INIT;
-       enum { PEELED_NONE, PEELED_TAGS, PEELED_FULLY } peeled = PEELED_NONE;
-
-       while (strbuf_getwholeline(&line, f, '\n') != EOF) {
-               unsigned char sha1[20];
-               const char *refname;
-               const char *traits;
-
-               if (skip_prefix(line.buf, "# pack-refs with:", &traits)) {
-                       if (strstr(traits, " fully-peeled "))
-                               peeled = PEELED_FULLY;
-                       else if (strstr(traits, " peeled "))
-                               peeled = PEELED_TAGS;
-                       /* perhaps other traits later as well */
-                       continue;
-               }
-
-               refname = parse_ref_line(&line, sha1);
-               if (refname) {
-                       int flag = REF_ISPACKED;
-
-                       if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
-                               if (!refname_is_safe(refname))
-                                       die("packed refname is dangerous: %s", refname);
-                               hashclr(sha1);
-                               flag |= REF_BAD_NAME | REF_ISBROKEN;
-                       }
-                       last = create_ref_entry(refname, sha1, flag, 0);
-                       if (peeled == PEELED_FULLY ||
-                           (peeled == PEELED_TAGS && starts_with(refname, "refs/tags/")))
-                               last->flag |= REF_KNOWS_PEELED;
-                       add_ref(dir, last);
-                       continue;
-               }
-               if (last &&
-                   line.buf[0] == '^' &&
-                   line.len == PEELED_LINE_LENGTH &&
-                   line.buf[PEELED_LINE_LENGTH - 1] == '\n' &&
-                   !get_sha1_hex(line.buf + 1, sha1)) {
-                       hashcpy(last->u.value.peeled.hash, sha1);
-                       /*
-                        * Regardless of what the file header said,
-                        * we definitely know the value of *this*
-                        * reference:
-                        */
-                       last->flag |= REF_KNOWS_PEELED;
-               }
+       switch (ref_type(refname)) {
+       case REF_TYPE_PER_WORKTREE:
+       case REF_TYPE_PSEUDOREF:
+               strbuf_addf(sb, "%s/logs/%s", refs->gitdir, refname);
+               break;
+       case REF_TYPE_NORMAL:
+               strbuf_addf(sb, "%s/logs/%s", refs->gitcommondir, refname);
+               break;
+       default:
+               BUG("unknown ref type %d of ref %s",
+                   ref_type(refname), refname);
        }
-
-       strbuf_release(&line);
 }
 
-/*
- * Get the packed_ref_cache for the specified files_ref_store,
- * creating it if necessary.
- */
-static struct packed_ref_cache *get_packed_ref_cache(struct files_ref_store *refs)
+static void files_ref_path(struct files_ref_store *refs,
+                          struct strbuf *sb,
+                          const char *refname)
 {
-       char *packed_refs_file;
-
-       if (*refs->base.submodule)
-               packed_refs_file = git_pathdup_submodule(refs->base.submodule,
-                                                        "packed-refs");
-       else
-               packed_refs_file = git_pathdup("packed-refs");
-
-       if (refs->packed &&
-           !stat_validity_check(&refs->packed->validity, packed_refs_file))
-               clear_packed_ref_cache(refs);
-
-       if (!refs->packed) {
-               FILE *f;
-
-               refs->packed = xcalloc(1, sizeof(*refs->packed));
-               acquire_packed_ref_cache(refs->packed);
-               refs->packed->root = create_dir_entry(refs, "", 0, 0);
-               f = fopen(packed_refs_file, "r");
-               if (f) {
-                       stat_validity_update(&refs->packed->validity, fileno(f));
-                       read_packed_refs(f, get_ref_dir(refs->packed->root));
-                       fclose(f);
-               }
+       switch (ref_type(refname)) {
+       case REF_TYPE_PER_WORKTREE:
+       case REF_TYPE_PSEUDOREF:
+               strbuf_addf(sb, "%s/%s", refs->gitdir, refname);
+               break;
+       case REF_TYPE_NORMAL:
+               strbuf_addf(sb, "%s/%s", refs->gitcommondir, refname);
+               break;
+       default:
+               BUG("unknown ref type %d of ref %s",
+                   ref_type(refname), refname);
        }
-       free(packed_refs_file);
-       return refs->packed;
-}
-
-static struct ref_dir *get_packed_ref_dir(struct packed_ref_cache *packed_ref_cache)
-{
-       return get_ref_dir(packed_ref_cache->root);
-}
-
-static struct ref_dir *get_packed_refs(struct files_ref_store *refs)
-{
-       return get_packed_ref_dir(get_packed_ref_cache(refs));
-}
-
-/*
- * Add a reference to the in-memory packed reference cache.  This may
- * only be called while the packed-refs file is locked (see
- * lock_packed_refs()).  To actually write the packed-refs file, call
- * commit_packed_refs().
- */
-static void add_packed_ref(struct files_ref_store *refs,
-                          const char *refname, const unsigned char *sha1)
-{
-       struct packed_ref_cache *packed_ref_cache = get_packed_ref_cache(refs);
-
-       if (!packed_ref_cache->lock)
-               die("internal error: packed refs not locked");
-       add_ref(get_packed_ref_dir(packed_ref_cache),
-               create_ref_entry(refname, sha1, REF_ISPACKED, 1));
 }
 
 /*
@@ -1192,28 +190,21 @@ static void add_packed_ref(struct files_ref_store *refs,
  * (without recursing).  dirname must end with '/'.  dir must be the
  * directory entry corresponding to dirname.
  */
-static void read_loose_refs(const char *dirname, struct ref_dir *dir)
+static void loose_fill_ref_dir(struct ref_store *ref_store,
+                              struct ref_dir *dir, const char *dirname)
 {
-       struct files_ref_store *refs = dir->ref_store;
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ, "fill_ref_dir");
        DIR *d;
        struct dirent *de;
        int dirnamelen = strlen(dirname);
        struct strbuf refname;
        struct strbuf path = STRBUF_INIT;
        size_t path_baselen;
-       int err = 0;
 
-       if (*refs->base.submodule)
-               err = strbuf_git_path_submodule(&path, refs->base.submodule, "%s", dirname);
-       else
-               strbuf_git_path(&path, "%s", dirname);
+       files_ref_path(refs, &path, dirname);
        path_baselen = path.len;
 
-       if (err) {
-               strbuf_release(&path);
-               return;
-       }
-
        d = opendir(path.buf);
        if (!d) {
                strbuf_release(&path);
@@ -1224,7 +215,7 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
        strbuf_add(&refname, dirname, dirnamelen);
 
        while ((de = readdir(d)) != NULL) {
-               unsigned char sha1[20];
+               struct object_id oid;
                struct stat st;
                int flag;
 
@@ -1239,29 +230,19 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
                } else if (S_ISDIR(st.st_mode)) {
                        strbuf_addch(&refname, '/');
                        add_entry_to_dir(dir,
-                                        create_dir_entry(refs, refname.buf,
+                                        create_dir_entry(dir->cache, refname.buf,
                                                          refname.len, 1));
                } else {
-                       int read_ok;
-
-                       if (*refs->base.submodule) {
-                               hashclr(sha1);
-                               flag = 0;
-                               read_ok = !resolve_gitlink_ref(refs->base.submodule,
-                                                              refname.buf, sha1);
-                       } else {
-                               read_ok = !read_ref_full(refname.buf,
-                                                        RESOLVE_REF_READING,
-                                                        sha1, &flag);
-                       }
-
-                       if (!read_ok) {
-                               hashclr(sha1);
+                       if (!refs_resolve_ref_unsafe(&refs->base,
+                                                    refname.buf,
+                                                    RESOLVE_REF_READING,
+                                                    &oid, &flag)) {
+                               oidclr(&oid);
                                flag |= REF_ISBROKEN;
-                       } else if (is_null_sha1(sha1)) {
+                       } else if (is_null_oid(&oid)) {
                                /*
                                 * It is so astronomically unlikely
-                                * that NULL_SHA1 is the SHA-1 of an
+                                * that null_oid is the OID of an
                                 * actual object that we consider its
                                 * appearance in a loose reference
                                 * file to be repo corruption
@@ -1274,11 +255,11 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
                                                 REFNAME_ALLOW_ONELEVEL)) {
                                if (!refname_is_safe(refname.buf))
                                        die("loose refname is dangerous: %s", refname.buf);
-                               hashclr(sha1);
+                               oidclr(&oid);
                                flag |= REF_BAD_NAME | REF_ISBROKEN;
                        }
                        add_entry_to_dir(dir,
-                                        create_ref_entry(refname.buf, sha1, flag, 0));
+                                        create_ref_entry(refname.buf, &oid, flag));
                }
                strbuf_setlen(&refname, dirnamelen);
                strbuf_setlen(&path, path_baselen);
@@ -1286,9 +267,24 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
        strbuf_release(&refname);
        strbuf_release(&path);
        closedir(d);
+
+       /*
+        * Manually add refs/bisect, which, being per-worktree, might
+        * not appear in the directory listing for refs/ in the main
+        * repo.
+        */
+       if (!strcmp(dirname, "refs/")) {
+               int pos = search_ref_dir(dir, "refs/bisect/", 12);
+
+               if (pos < 0) {
+                       struct ref_entry *child_entry = create_dir_entry(
+                                       dir->cache, "refs/bisect/", 12, 1);
+                       add_entry_to_dir(dir, child_entry);
+               }
+       }
 }
 
-static struct ref_dir *get_loose_refs(struct files_ref_store *refs)
+static struct ref_cache *get_loose_ref_cache(struct files_ref_store *refs)
 {
        if (!refs->loose) {
                /*
@@ -1296,59 +292,32 @@ static struct ref_dir *get_loose_refs(struct files_ref_store *refs)
                 * are about to read the only subdirectory that can
                 * hold references:
                 */
-               refs->loose = create_dir_entry(refs, "", 0, 0);
-               /*
-                * Create an incomplete entry for "refs/":
-                */
-               add_entry_to_dir(get_ref_dir(refs->loose),
-                                create_dir_entry(refs, "refs/", 5, 1));
-       }
-       return get_ref_dir(refs->loose);
-}
+               refs->loose = create_ref_cache(&refs->base, loose_fill_ref_dir);
 
-/*
- * Return the ref_entry for the given refname from the packed
- * references.  If it does not exist, return NULL.
- */
-static struct ref_entry *get_packed_ref(struct files_ref_store *refs,
-                                       const char *refname)
-{
-       return find_ref(get_packed_refs(refs), refname);
-}
+               /* We're going to fill the top level ourselves: */
+               refs->loose->root->flag &= ~REF_INCOMPLETE;
 
-/*
- * A loose ref file doesn't exist; check for a packed ref.
- */
-static int resolve_packed_ref(struct files_ref_store *refs,
-                             const char *refname,
-                             unsigned char *sha1, unsigned int *flags)
-{
-       struct ref_entry *entry;
-
-       /*
-        * The loose reference file does not exist; check for a packed
-        * reference.
-        */
-       entry = get_packed_ref(refs, refname);
-       if (entry) {
-               hashcpy(sha1, entry->u.value.oid.hash);
-               *flags |= REF_ISPACKED;
-               return 0;
+               /*
+                * Add an incomplete entry for "refs/" (to be filled
+                * lazily):
+                */
+               add_entry_to_dir(get_ref_dir(refs->loose->root),
+                                create_dir_entry(refs->loose, "refs/", 5, 1));
        }
-       /* refname is not a packed reference. */
-       return -1;
+       return refs->loose;
 }
 
 static int files_read_raw_ref(struct ref_store *ref_store,
-                             const char *refname, unsigned char *sha1,
+                             const char *refname, struct object_id *oid,
                              struct strbuf *referent, unsigned int *type)
 {
        struct files_ref_store *refs =
-               files_downcast(ref_store, 1, "read_raw_ref");
+               files_downcast(ref_store, REF_STORE_READ, "read_raw_ref");
        struct strbuf sb_contents = STRBUF_INIT;
        struct strbuf sb_path = STRBUF_INIT;
        const char *path;
        const char *buf;
+       const char *p;
        struct stat st;
        int fd;
        int ret = -1;
@@ -1358,10 +327,7 @@ static int files_read_raw_ref(struct ref_store *ref_store,
        *type = 0;
        strbuf_reset(&sb_path);
 
-       if (*refs->base.submodule)
-               strbuf_git_path_submodule(&sb_path, refs->base.submodule, "%s", refname);
-       else
-               strbuf_git_path(&sb_path, "%s", refname);
+       files_ref_path(refs, &sb_path, refname);
 
        path = sb_path.buf;
 
@@ -1385,7 +351,8 @@ stat_ref:
        if (lstat(path, &st) < 0) {
                if (errno != ENOENT)
                        goto out;
-               if (resolve_packed_ref(refs, refname, sha1, type)) {
+               if (refs_read_raw_ref(refs->packed_ref_store, refname,
+                                     oid, referent, type)) {
                        errno = ENOENT;
                        goto out;
                }
@@ -1424,7 +391,8 @@ stat_ref:
                 * ref is supposed to be, there could still be a
                 * packed ref:
                 */
-               if (resolve_packed_ref(refs, refname, sha1, type)) {
+               if (refs_read_raw_ref(refs->packed_ref_store, refname,
+                                     oid, referent, type)) {
                        errno = EISDIR;
                        goto out;
                }
@@ -1470,8 +438,8 @@ stat_ref:
         * Please note that FETCH_HEAD has additional
         * data after the sha.
         */
-       if (get_sha1_hex(buf, sha1) ||
-           (buf[40] != '\0' && !isspace(buf[40]))) {
+       if (parse_oid_hex(buf, oid, &p) ||
+           (*p != '\0' && !isspace(*p))) {
                *type |= REF_ISBROKEN;
                errno = EINVAL;
                goto out;
@@ -1489,9 +457,7 @@ out:
 
 static void unlock_ref(struct ref_lock *lock)
 {
-       /* Do not free lock->lk -- atexit() still looks at them */
-       if (lock->lk)
-               rollback_lock_file(lock->lk);
+       rollback_lock_file(&lock->lk);
        free(lock->ref_name);
        free(lock);
 }
@@ -1506,10 +472,10 @@ static void unlock_ref(struct ref_lock *lock)
  *
  * If the reference doesn't already exist, verify that refname doesn't
  * have a D/F conflict with any existing references. extras and skip
- * are passed to verify_refname_available_dir() for this check.
+ * are passed to refs_verify_refname_available() for this check.
  *
  * If mustexist is not set and the reference is not found or is
- * broken, lock the reference anyway but clear sha1.
+ * broken, lock the reference anyway but clear old_oid.
  *
  * Return 0 on success. On failure, write an error message to err and
  * return TRANSACTION_NAME_CONFLICT or TRANSACTION_GENERIC_ERROR.
@@ -1521,7 +487,7 @@ static void unlock_ref(struct ref_lock *lock)
  *
  * but it includes a lot more code to
  * - Deal with possible races with other processes
- * - Avoid calling verify_refname_available_dir() when it can be
+ * - Avoid calling refs_verify_refname_available() when it can be
  *   avoided, namely if we were successfully able to read the ref
  * - Generate informative error messages in the case of failure
  */
@@ -1540,7 +506,7 @@ static int lock_raw_ref(struct files_ref_store *refs,
        int ret = TRANSACTION_GENERIC_ERROR;
 
        assert(err);
-       assert_main_repository(&refs->base, "lock_raw_ref");
+       files_assert_main_repository(refs, "lock_raw_ref");
 
        *type = 0;
 
@@ -1549,7 +515,7 @@ static int lock_raw_ref(struct files_ref_store *refs,
        *lock_p = lock = xcalloc(1, sizeof(*lock));
 
        lock->ref_name = xstrdup(refname);
-       strbuf_git_path(&ref_file, "%s", refname);
+       files_ref_path(refs, &ref_file, refname);
 
 retry:
        switch (safe_create_leading_directories(ref_file.buf)) {
@@ -1564,7 +530,8 @@ retry:
                 * another reference such as "refs/foo". There is no
                 * reason to expect this error to be transitory.
                 */
-               if (verify_refname_available(refname, extras, skip, err)) {
+               if (refs_verify_refname_available(&refs->base, refname,
+                                                 extras, skip, err)) {
                        if (mustexist) {
                                /*
                                 * To the user the relevant error is
@@ -1577,7 +544,8 @@ retry:
                        } else {
                                /*
                                 * The error message set by
-                                * verify_refname_available_dir() is OK.
+                                * refs_verify_refname_available() is
+                                * OK.
                                 */
                                ret = TRANSACTION_NAME_CONFLICT;
                        }
@@ -1603,10 +571,9 @@ retry:
                goto error_return;
        }
 
-       if (!lock->lk)
-               lock->lk = xcalloc(1, sizeof(struct lock_file));
-
-       if (hold_lock_file_for_update(lock->lk, ref_file.buf, LOCK_NO_DEREF) < 0) {
+       if (hold_lock_file_for_update_timeout(
+                           &lock->lk, ref_file.buf, LOCK_NO_DEREF,
+                           get_files_ref_lock_timeout_ms()) < 0) {
                if (errno == ENOENT && --attempts_remaining > 0) {
                        /*
                         * Maybe somebody just deleted one of the
@@ -1626,7 +593,7 @@ retry:
         */
 
        if (files_read_raw_ref(&refs->base, refname,
-                              lock->old_oid.hash, referent, type)) {
+                              &lock->old_oid, referent, type)) {
                if (errno == ENOENT) {
                        if (mustexist) {
                                /* Garden variety missing reference. */
@@ -1667,10 +634,9 @@ retry:
                                goto error_return;
                        } else if (remove_dir_recursively(&ref_file,
                                                          REMOVE_DIR_EMPTY_ONLY)) {
-                               if (verify_refname_available_dir(
-                                                   refname, extras, skip,
-                                                   get_loose_refs(refs),
-                                                   err)) {
+                               if (refs_verify_refname_available(
+                                                   &refs->base, refname,
+                                                   extras, skip, err)) {
                                        /*
                                         * The error message set by
                                         * verify_refname_available() is OK.
@@ -1702,16 +668,13 @@ retry:
 
                /*
                 * If the ref did not exist and we are creating it,
-                * make sure there is no existing packed ref whose
-                * name begins with our refname, nor a packed ref
-                * whose name is a proper prefix of our refname.
+                * make sure there is no existing packed ref that
+                * conflicts with refname:
                 */
-               if (verify_refname_available_dir(
-                                   refname, extras, skip,
-                                   get_packed_refs(refs),
-                                   err)) {
+               if (refs_verify_refname_available(
+                                   refs->packed_ref_store, refname,
+                                   extras, skip, err))
                        goto error_return;
-               }
        }
 
        ret = 0;
@@ -1726,85 +689,9 @@ out:
        return ret;
 }
 
-/*
- * Peel the entry (if possible) and return its new peel_status.  If
- * repeel is true, re-peel the entry even if there is an old peeled
- * value that is already stored in it.
- *
- * It is OK to call this function with a packed reference entry that
- * might be stale and might even refer to an object that has since
- * been garbage-collected.  In such a case, if the entry has
- * REF_KNOWS_PEELED then leave the status unchanged and return
- * PEEL_PEELED or PEEL_NON_TAG; otherwise, return PEEL_INVALID.
- */
-static enum peel_status peel_entry(struct ref_entry *entry, int repeel)
-{
-       enum peel_status status;
-
-       if (entry->flag & REF_KNOWS_PEELED) {
-               if (repeel) {
-                       entry->flag &= ~REF_KNOWS_PEELED;
-                       oidclr(&entry->u.value.peeled);
-               } else {
-                       return is_null_oid(&entry->u.value.peeled) ?
-                               PEEL_NON_TAG : PEEL_PEELED;
-               }
-       }
-       if (entry->flag & REF_ISBROKEN)
-               return PEEL_BROKEN;
-       if (entry->flag & REF_ISSYMREF)
-               return PEEL_IS_SYMREF;
-
-       status = peel_object(entry->u.value.oid.hash, entry->u.value.peeled.hash);
-       if (status == PEEL_PEELED || status == PEEL_NON_TAG)
-               entry->flag |= REF_KNOWS_PEELED;
-       return status;
-}
-
-static int files_peel_ref(struct ref_store *ref_store,
-                         const char *refname, unsigned char *sha1)
-{
-       struct files_ref_store *refs = files_downcast(ref_store, 0, "peel_ref");
-       int flag;
-       unsigned char base[20];
-
-       if (current_ref_iter && current_ref_iter->refname == refname) {
-               struct object_id peeled;
-
-               if (ref_iterator_peel(current_ref_iter, &peeled))
-                       return -1;
-               hashcpy(sha1, peeled.hash);
-               return 0;
-       }
-
-       if (read_ref_full(refname, RESOLVE_REF_READING, base, &flag))
-               return -1;
-
-       /*
-        * If the reference is packed, read its ref_entry from the
-        * cache in the hope that we already know its peeled value.
-        * We only try this optimization on packed references because
-        * (a) forcing the filling of the loose reference cache could
-        * be expensive and (b) loose references anyway usually do not
-        * have REF_KNOWS_PEELED.
-        */
-       if (flag & REF_ISPACKED) {
-               struct ref_entry *r = get_packed_ref(refs, refname);
-               if (r) {
-                       if (peel_entry(r, 0))
-                               return -1;
-                       hashcpy(sha1, r->u.value.peeled.hash);
-                       return 0;
-               }
-       }
-
-       return peel_object(base, sha1);
-}
-
 struct files_ref_iterator {
        struct ref_iterator base;
 
-       struct packed_ref_cache *packed_ref_cache;
        struct ref_iterator *iter0;
        unsigned int flags;
 };
@@ -1857,7 +744,6 @@ static int files_ref_iterator_abort(struct ref_iterator *ref_iterator)
        if (iter->iter0)
                ok = ref_iterator_abort(iter->iter0);
 
-       release_packed_ref_cache(iter->packed_ref_cache);
        base_ref_iterator_free(ref_iterator);
        return ok;
 }
@@ -1872,24 +758,16 @@ static struct ref_iterator *files_ref_iterator_begin(
                struct ref_store *ref_store,
                const char *prefix, unsigned int flags)
 {
-       struct files_ref_store *refs =
-               files_downcast(ref_store, 1, "ref_iterator_begin");
-       struct ref_dir *loose_dir, *packed_dir;
-       struct ref_iterator *loose_iter, *packed_iter;
+       struct files_ref_store *refs;
+       struct ref_iterator *loose_iter, *packed_iter, *overlay_iter;
        struct files_ref_iterator *iter;
        struct ref_iterator *ref_iterator;
+       unsigned int required_flags = REF_STORE_READ;
 
-       if (!refs)
-               return empty_ref_iterator_begin();
-
-       if (ref_paranoia < 0)
-               ref_paranoia = git_env_bool("GIT_REF_PARANOIA", 0);
-       if (ref_paranoia)
-               flags |= DO_FOR_EACH_INCLUDE_BROKEN;
+       if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN))
+               required_flags |= REF_STORE_ODB;
 
-       iter = xcalloc(1, sizeof(*iter));
-       ref_iterator = &iter->base;
-       base_ref_iterator_init(ref_iterator, &files_ref_iterator_vtable);
+       refs = files_downcast(ref_store, required_flags, "ref_iterator_begin");
 
        /*
         * We must make sure that all loose refs are read before
@@ -1897,64 +775,63 @@ static struct ref_iterator *files_ref_iterator_begin(
         * condition if loose refs are migrated to the packed-refs
         * file by a simultaneous process, but our in-memory view is
         * from before the migration. We ensure this as follows:
-        * First, we call prime_ref_dir(), which pre-reads the loose
-        * references for the subtree into the cache. (If they've
-        * already been read, that's OK; we only need to guarantee
-        * that they're read before the packed refs, not *how much*
-        * before.) After that, we call get_packed_ref_cache(), which
-        * internally checks whether the packed-ref cache is up to
-        * date with what is on disk, and re-reads it if not.
+        * First, we call start the loose refs iteration with its
+        * `prime_ref` argument set to true. This causes the loose
+        * references in the subtree to be pre-read into the cache.
+        * (If they've already been read, that's OK; we only need to
+        * guarantee that they're read before the packed refs, not
+        * *how much* before.) After that, we call
+        * packed_ref_iterator_begin(), which internally checks
+        * whether the packed-ref cache is up to date with what is on
+        * disk, and re-reads it if not.
         */
 
-       loose_dir = get_loose_refs(refs);
-
-       if (prefix && *prefix)
-               loose_dir = find_containing_dir(loose_dir, prefix, 0);
-
-       if (loose_dir) {
-               prime_ref_dir(loose_dir);
-               loose_iter = cache_ref_iterator_begin(loose_dir);
-       } else {
-               /* There's nothing to iterate over. */
-               loose_iter = empty_ref_iterator_begin();
-       }
-
-       iter->packed_ref_cache = get_packed_ref_cache(refs);
-       acquire_packed_ref_cache(iter->packed_ref_cache);
-       packed_dir = get_packed_ref_dir(iter->packed_ref_cache);
+       loose_iter = cache_ref_iterator_begin(get_loose_ref_cache(refs),
+                                             prefix, 1);
 
-       if (prefix && *prefix)
-               packed_dir = find_containing_dir(packed_dir, prefix, 0);
+       /*
+        * The packed-refs file might contain broken references, for
+        * example an old version of a reference that points at an
+        * object that has since been garbage-collected. This is OK as
+        * long as there is a corresponding loose reference that
+        * overrides it, and we don't want to emit an error message in
+        * this case. So ask the packed_ref_store for all of its
+        * references, and (if needed) do our own check for broken
+        * ones in files_ref_iterator_advance(), after we have merged
+        * the packed and loose references.
+        */
+       packed_iter = refs_ref_iterator_begin(
+                       refs->packed_ref_store, prefix, 0,
+                       DO_FOR_EACH_INCLUDE_BROKEN);
 
-       if (packed_dir) {
-               packed_iter = cache_ref_iterator_begin(packed_dir);
-       } else {
-               /* There's nothing to iterate over. */
-               packed_iter = empty_ref_iterator_begin();
-       }
+       overlay_iter = overlay_ref_iterator_begin(loose_iter, packed_iter);
 
-       iter->iter0 = overlay_ref_iterator_begin(loose_iter, packed_iter);
+       iter = xcalloc(1, sizeof(*iter));
+       ref_iterator = &iter->base;
+       base_ref_iterator_init(ref_iterator, &files_ref_iterator_vtable,
+                              overlay_iter->ordered);
+       iter->iter0 = overlay_iter;
        iter->flags = flags;
 
        return ref_iterator;
 }
 
 /*
- * Verify that the reference locked by lock has the value old_sha1.
- * Fail if the reference doesn't exist and mustexist is set. Return 0
- * on success. On error, write an error message to err, set errno, and
- * return a negative value.
+ * Verify that the reference locked by lock has the value old_oid
+ * (unless it is NULL).  Fail if the reference doesn't exist and
+ * mustexist is set. Return 0 on success. On error, write an error
+ * message to err, set errno, and return a negative value.
  */
-static int verify_lock(struct ref_lock *lock,
-                      const unsigned char *old_sha1, int mustexist,
+static int verify_lock(struct ref_store *ref_store, struct ref_lock *lock,
+                      const struct object_id *old_oid, int mustexist,
                       struct strbuf *err)
 {
        assert(err);
 
-       if (read_ref_full(lock->ref_name,
-                         mustexist ? RESOLVE_REF_READING : 0,
-                         lock->old_oid.hash, NULL)) {
-               if (old_sha1) {
+       if (refs_read_ref_full(ref_store, lock->ref_name,
+                              mustexist ? RESOLVE_REF_READING : 0,
+                              &lock->old_oid, NULL)) {
+               if (old_oid) {
                        int save_errno = errno;
                        strbuf_addf(err, "can't verify ref '%s'", lock->ref_name);
                        errno = save_errno;
@@ -1964,11 +841,11 @@ static int verify_lock(struct ref_lock *lock,
                        return 0;
                }
        }
-       if (old_sha1 && hashcmp(lock->old_oid.hash, old_sha1)) {
+       if (old_oid && oidcmp(&lock->old_oid, old_oid)) {
                strbuf_addf(err, "ref '%s' is at %s but expected %s",
                            lock->ref_name,
                            oid_to_hex(&lock->old_oid),
-                           sha1_to_hex(old_sha1));
+                           oid_to_hex(old_oid));
                errno = EBUSY;
                return -1;
        }
@@ -1985,28 +862,35 @@ static int remove_empty_directories(struct strbuf *path)
        return remove_dir_recursively(path, REMOVE_DIR_EMPTY_ONLY);
 }
 
+static int create_reflock(const char *path, void *cb)
+{
+       struct lock_file *lk = cb;
+
+       return hold_lock_file_for_update_timeout(
+                       lk, path, LOCK_NO_DEREF,
+                       get_files_ref_lock_timeout_ms()) < 0 ? -1 : 0;
+}
+
 /*
  * Locks a ref returning the lock on success and NULL on failure.
  * On failure errno is set to something meaningful.
  */
-static struct ref_lock *lock_ref_sha1_basic(struct files_ref_store *refs,
-                                           const char *refname,
-                                           const unsigned char *old_sha1,
-                                           const struct string_list *extras,
-                                           const struct string_list *skip,
-                                           unsigned int flags, int *type,
-                                           struct strbuf *err)
+static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
+                                          const char *refname,
+                                          const struct object_id *old_oid,
+                                          const struct string_list *extras,
+                                          const struct string_list *skip,
+                                          unsigned int flags, int *type,
+                                          struct strbuf *err)
 {
        struct strbuf ref_file = STRBUF_INIT;
        struct ref_lock *lock;
        int last_errno = 0;
-       int lflags = LOCK_NO_DEREF;
-       int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
+       int mustexist = (old_oid && !is_null_oid(old_oid));
        int resolve_flags = RESOLVE_REF_NO_RECURSE;
-       int attempts_remaining = 3;
        int resolved;
 
-       assert_main_repository(&refs->base, "lock_ref_sha1_basic");
+       files_assert_main_repository(refs, "lock_ref_oid_basic");
        assert(err);
 
        lock = xcalloc(1, sizeof(struct ref_lock));
@@ -2016,9 +900,10 @@ static struct ref_lock *lock_ref_sha1_basic(struct files_ref_store *refs,
        if (flags & REF_DELETING)
                resolve_flags |= RESOLVE_REF_ALLOW_BAD_NAME;
 
-       strbuf_git_path(&ref_file, "%s", refname);
-       resolved = !!resolve_ref_unsafe(refname, resolve_flags,
-                                       lock->old_oid.hash, type);
+       files_ref_path(refs, &ref_file, refname);
+       resolved = !!refs_resolve_ref_unsafe(&refs->base,
+                                            refname, resolve_flags,
+                                            &lock->old_oid, type);
        if (!resolved && errno == EISDIR) {
                /*
                 * we are trying to lock foo but we used to
@@ -2028,22 +913,22 @@ static struct ref_lock *lock_ref_sha1_basic(struct files_ref_store *refs,
                 */
                if (remove_empty_directories(&ref_file)) {
                        last_errno = errno;
-                       if (!verify_refname_available_dir(
-                                           refname, extras, skip,
-                                           get_loose_refs(refs), err))
+                       if (!refs_verify_refname_available(
+                                           &refs->base,
+                                           refname, extras, skip, err))
                                strbuf_addf(err, "there are still refs under '%s'",
                                            refname);
                        goto error_return;
                }
-               resolved = !!resolve_ref_unsafe(refname, resolve_flags,
-                                               lock->old_oid.hash, type);
+               resolved = !!refs_resolve_ref_unsafe(&refs->base,
+                                                    refname, resolve_flags,
+                                                    &lock->old_oid, type);
        }
        if (!resolved) {
                last_errno = errno;
                if (last_errno != ENOTDIR ||
-                   !verify_refname_available_dir(
-                                   refname, extras, skip,
-                                   get_loose_refs(refs), err))
+                   !refs_verify_refname_available(&refs->base, refname,
+                                                  extras, skip, err))
                        strbuf_addf(err, "unable to resolve reference '%s': %s",
                                    refname, strerror(last_errno));
 
@@ -2056,48 +941,22 @@ static struct ref_lock *lock_ref_sha1_basic(struct files_ref_store *refs,
         * refname, nor a packed ref whose name is a proper prefix of
         * our refname.
         */
-       if (is_null_oid(&lock->old_oid) &&
-           verify_refname_available_dir(refname, extras, skip,
-                                        get_packed_refs(refs),
-                                        err)) {
-               last_errno = ENOTDIR;
-               goto error_return;
-       }
-
-       lock->lk = xcalloc(1, sizeof(struct lock_file));
-
-       lock->ref_name = xstrdup(refname);
-
- retry:
-       switch (safe_create_leading_directories_const(ref_file.buf)) {
-       case SCLD_OK:
-               break; /* success */
-       case SCLD_VANISHED:
-               if (--attempts_remaining > 0)
-                       goto retry;
-               /* fall through */
-       default:
-               last_errno = errno;
-               strbuf_addf(err, "unable to create directory for '%s'",
-                           ref_file.buf);
+       if (is_null_oid(&lock->old_oid) &&
+           refs_verify_refname_available(refs->packed_ref_store, refname,
+                                         extras, skip, err)) {
+               last_errno = ENOTDIR;
                goto error_return;
        }
 
-       if (hold_lock_file_for_update(lock->lk, ref_file.buf, lflags) < 0) {
+       lock->ref_name = xstrdup(refname);
+
+       if (raceproof_create_file(ref_file.buf, create_reflock, &lock->lk)) {
                last_errno = errno;
-               if (errno == ENOENT && --attempts_remaining > 0)
-                       /*
-                        * Maybe somebody just deleted one of the
-                        * directories leading to ref_file.  Try
-                        * again:
-                        */
-                       goto retry;
-               else {
-                       unable_to_lock_message(ref_file.buf, errno, err);
-                       goto error_return;
-               }
+               unable_to_lock_message(ref_file.buf, errno, err);
+               goto error_return;
        }
-       if (verify_lock(lock, old_sha1, mustexist, err)) {
+
+       if (verify_lock(&refs->base, lock, old_oid, mustexist, err)) {
                last_errno = errno;
                goto error_return;
        }
@@ -2113,200 +972,34 @@ static struct ref_lock *lock_ref_sha1_basic(struct files_ref_store *refs,
        return lock;
 }
 
-/*
- * Write an entry to the packed-refs file for the specified refname.
- * If peeled is non-NULL, write it as the entry's peeled value.
- */
-static void write_packed_entry(FILE *fh, char *refname, unsigned char *sha1,
-                              unsigned char *peeled)
-{
-       fprintf_or_die(fh, "%s %s\n", sha1_to_hex(sha1), refname);
-       if (peeled)
-               fprintf_or_die(fh, "^%s\n", sha1_to_hex(peeled));
-}
-
-/*
- * An each_ref_entry_fn that writes the entry to a packed-refs file.
- */
-static int write_packed_entry_fn(struct ref_entry *entry, void *cb_data)
-{
-       enum peel_status peel_status = peel_entry(entry, 0);
-
-       if (peel_status != PEEL_PEELED && peel_status != PEEL_NON_TAG)
-               error("internal error: %s is not a valid packed reference!",
-                     entry->name);
-       write_packed_entry(cb_data, entry->name, entry->u.value.oid.hash,
-                          peel_status == PEEL_PEELED ?
-                          entry->u.value.peeled.hash : NULL);
-       return 0;
-}
-
-/*
- * Lock the packed-refs file for writing. Flags is passed to
- * hold_lock_file_for_update(). Return 0 on success. On errors, set
- * errno appropriately and return a nonzero value.
- */
-static int lock_packed_refs(struct files_ref_store *refs, int flags)
-{
-       static int timeout_configured = 0;
-       static int timeout_value = 1000;
-       struct packed_ref_cache *packed_ref_cache;
-
-       assert_main_repository(&refs->base, "lock_packed_refs");
-
-       if (!timeout_configured) {
-               git_config_get_int("core.packedrefstimeout", &timeout_value);
-               timeout_configured = 1;
-       }
-
-       if (hold_lock_file_for_update_timeout(
-                           &packlock, git_path("packed-refs"),
-                           flags, timeout_value) < 0)
-               return -1;
-       /*
-        * Get the current packed-refs while holding the lock.  If the
-        * packed-refs file has been modified since we last read it,
-        * this will automatically invalidate the cache and re-read
-        * the packed-refs file.
-        */
-       packed_ref_cache = get_packed_ref_cache(refs);
-       packed_ref_cache->lock = &packlock;
-       /* Increment the reference count to prevent it from being freed: */
-       acquire_packed_ref_cache(packed_ref_cache);
-       return 0;
-}
-
-/*
- * Write the current version of the packed refs cache from memory to
- * disk. The packed-refs file must already be locked for writing (see
- * lock_packed_refs()). Return zero on success. On errors, set errno
- * and return a nonzero value
- */
-static int commit_packed_refs(struct files_ref_store *refs)
-{
-       struct packed_ref_cache *packed_ref_cache =
-               get_packed_ref_cache(refs);
-       int error = 0;
-       int save_errno = 0;
-       FILE *out;
-
-       assert_main_repository(&refs->base, "commit_packed_refs");
-
-       if (!packed_ref_cache->lock)
-               die("internal error: packed-refs not locked");
-
-       out = fdopen_lock_file(packed_ref_cache->lock, "w");
-       if (!out)
-               die_errno("unable to fdopen packed-refs descriptor");
-
-       fprintf_or_die(out, "%s", PACKED_REFS_HEADER);
-       do_for_each_entry_in_dir(get_packed_ref_dir(packed_ref_cache),
-                                0, write_packed_entry_fn, out);
-
-       if (commit_lock_file(packed_ref_cache->lock)) {
-               save_errno = errno;
-               error = -1;
-       }
-       packed_ref_cache->lock = NULL;
-       release_packed_ref_cache(packed_ref_cache);
-       errno = save_errno;
-       return error;
-}
-
-/*
- * Rollback the lockfile for the packed-refs file, and discard the
- * in-memory packed reference cache.  (The packed-refs file will be
- * read anew if it is needed again after this function is called.)
- */
-static void rollback_packed_refs(struct files_ref_store *refs)
-{
-       struct packed_ref_cache *packed_ref_cache =
-               get_packed_ref_cache(refs);
-
-       assert_main_repository(&refs->base, "rollback_packed_refs");
-
-       if (!packed_ref_cache->lock)
-               die("internal error: packed-refs not locked");
-       rollback_lock_file(packed_ref_cache->lock);
-       packed_ref_cache->lock = NULL;
-       release_packed_ref_cache(packed_ref_cache);
-       clear_packed_ref_cache(refs);
-}
-
 struct ref_to_prune {
        struct ref_to_prune *next;
-       unsigned char sha1[20];
+       struct object_id oid;
        char name[FLEX_ARRAY];
 };
 
-struct pack_refs_cb_data {
-       unsigned int flags;
-       struct ref_dir *packed_refs;
-       struct ref_to_prune *ref_to_prune;
+enum {
+       REMOVE_EMPTY_PARENTS_REF = 0x01,
+       REMOVE_EMPTY_PARENTS_REFLOG = 0x02
 };
 
 /*
- * An each_ref_entry_fn that is run over loose references only.  If
- * the loose reference can be packed, add an entry in the packed ref
- * cache.  If the reference should be pruned, also add it to
- * ref_to_prune in the pack_refs_cb_data.
- */
-static int pack_if_possible_fn(struct ref_entry *entry, void *cb_data)
-{
-       struct pack_refs_cb_data *cb = cb_data;
-       enum peel_status peel_status;
-       struct ref_entry *packed_entry;
-       int is_tag_ref = starts_with(entry->name, "refs/tags/");
-
-       /* Do not pack per-worktree refs: */
-       if (ref_type(entry->name) != REF_TYPE_NORMAL)
-               return 0;
-
-       /* ALWAYS pack tags */
-       if (!(cb->flags & PACK_REFS_ALL) && !is_tag_ref)
-               return 0;
-
-       /* Do not pack symbolic or broken refs: */
-       if ((entry->flag & REF_ISSYMREF) || !entry_resolves_to_object(entry))
-               return 0;
-
-       /* Add a packed ref cache entry equivalent to the loose entry. */
-       peel_status = peel_entry(entry, 1);
-       if (peel_status != PEEL_PEELED && peel_status != PEEL_NON_TAG)
-               die("internal error peeling reference %s (%s)",
-                   entry->name, oid_to_hex(&entry->u.value.oid));
-       packed_entry = find_ref(cb->packed_refs, entry->name);
-       if (packed_entry) {
-               /* Overwrite existing packed entry with info from loose entry */
-               packed_entry->flag = REF_ISPACKED | REF_KNOWS_PEELED;
-               oidcpy(&packed_entry->u.value.oid, &entry->u.value.oid);
-       } else {
-               packed_entry = create_ref_entry(entry->name, entry->u.value.oid.hash,
-                                               REF_ISPACKED | REF_KNOWS_PEELED, 0);
-               add_ref(cb->packed_refs, packed_entry);
-       }
-       oidcpy(&packed_entry->u.value.peeled, &entry->u.value.peeled);
-
-       /* Schedule the loose reference for pruning if requested. */
-       if ((cb->flags & PACK_REFS_PRUNE)) {
-               struct ref_to_prune *n;
-               FLEX_ALLOC_STR(n, name, entry->name);
-               hashcpy(n->sha1, entry->u.value.oid.hash);
-               n->next = cb->ref_to_prune;
-               cb->ref_to_prune = n;
-       }
-       return 0;
-}
-
-/*
- * Remove empty parents, but spare refs/ and immediate subdirs.
- * Note: munges *name.
+ * Remove empty parent directories associated with the specified
+ * reference and/or its reflog, but spare [logs/]refs/ and immediate
+ * subdirs. flags is a combination of REMOVE_EMPTY_PARENTS_REF and/or
+ * REMOVE_EMPTY_PARENTS_REFLOG.
  */
-static void try_remove_empty_parents(char *name)
+static void try_remove_empty_parents(struct files_ref_store *refs,
+                                    const char *refname,
+                                    unsigned int flags)
 {
+       struct strbuf buf = STRBUF_INIT;
+       struct strbuf sb = STRBUF_INIT;
        char *p, *q;
        int i;
-       p = name;
+
+       strbuf_addstr(&buf, refname);
+       p = buf.buf;
        for (i = 0; i < 2; i++) { /* refs/{heads,tags,...}/ */
                while (*p && *p != '/')
                        p++;
@@ -2314,188 +1007,208 @@ static void try_remove_empty_parents(char *name)
                while (*p == '/')
                        p++;
        }
-       for (q = p; *q; q++)
-               ;
-       while (1) {
+       q = buf.buf + buf.len;
+       while (flags & (REMOVE_EMPTY_PARENTS_REF | REMOVE_EMPTY_PARENTS_REFLOG)) {
                while (q > p && *q != '/')
                        q--;
                while (q > p && *(q-1) == '/')
                        q--;
                if (q == p)
                        break;
-               *q = '\0';
-               if (rmdir(git_path("%s", name)))
-                       break;
+               strbuf_setlen(&buf, q - buf.buf);
+
+               strbuf_reset(&sb);
+               files_ref_path(refs, &sb, buf.buf);
+               if ((flags & REMOVE_EMPTY_PARENTS_REF) && rmdir(sb.buf))
+                       flags &= ~REMOVE_EMPTY_PARENTS_REF;
+
+               strbuf_reset(&sb);
+               files_reflog_path(refs, &sb, buf.buf);
+               if ((flags & REMOVE_EMPTY_PARENTS_REFLOG) && rmdir(sb.buf))
+                       flags &= ~REMOVE_EMPTY_PARENTS_REFLOG;
        }
+       strbuf_release(&buf);
+       strbuf_release(&sb);
 }
 
 /* make sure nobody touched the ref, and unlink */
-static void prune_ref(struct ref_to_prune *r)
+static void prune_ref(struct files_ref_store *refs, struct ref_to_prune *r)
 {
        struct ref_transaction *transaction;
        struct strbuf err = STRBUF_INIT;
+       int ret = -1;
 
        if (check_refname_format(r->name, 0))
                return;
 
-       transaction = ref_transaction_begin(&err);
-       if (!transaction ||
-           ref_transaction_delete(transaction, r->name, r->sha1,
-                                  REF_ISPRUNING | REF_NODEREF, NULL, &err) ||
-           ref_transaction_commit(transaction, &err)) {
-               ref_transaction_free(transaction);
+       transaction = ref_store_transaction_begin(&refs->base, &err);
+       if (!transaction)
+               goto cleanup;
+       ref_transaction_add_update(
+                       transaction, r->name,
+                       REF_NO_DEREF | REF_HAVE_NEW | REF_HAVE_OLD | REF_IS_PRUNING,
+                       &null_oid, &r->oid, NULL);
+       if (ref_transaction_commit(transaction, &err))
+               goto cleanup;
+
+       ret = 0;
+
+cleanup:
+       if (ret)
                error("%s", err.buf);
-               strbuf_release(&err);
-               return;
-       }
-       ref_transaction_free(transaction);
        strbuf_release(&err);
-       try_remove_empty_parents(r->name);
+       ref_transaction_free(transaction);
+       return;
 }
 
-static void prune_refs(struct ref_to_prune *r)
+/*
+ * Prune the loose versions of the references in the linked list
+ * `*refs_to_prune`, freeing the entries in the list as we go.
+ */
+static void prune_refs(struct files_ref_store *refs, struct ref_to_prune **refs_to_prune)
 {
-       while (r) {
-               prune_ref(r);
-               r = r->next;
+       while (*refs_to_prune) {
+               struct ref_to_prune *r = *refs_to_prune;
+               *refs_to_prune = r->next;
+               prune_ref(refs, r);
+               free(r);
        }
 }
 
-static int files_pack_refs(struct ref_store *ref_store, unsigned int flags)
+/*
+ * Return true if the specified reference should be packed.
+ */
+static int should_pack_ref(const char *refname,
+                          const struct object_id *oid, unsigned int ref_flags,
+                          unsigned int pack_flags)
 {
-       struct files_ref_store *refs =
-               files_downcast(ref_store, 0, "pack_refs");
-       struct pack_refs_cb_data cbdata;
-
-       memset(&cbdata, 0, sizeof(cbdata));
-       cbdata.flags = flags;
+       /* Do not pack per-worktree refs: */
+       if (ref_type(refname) != REF_TYPE_NORMAL)
+               return 0;
 
-       lock_packed_refs(refs, LOCK_DIE_ON_ERROR);
-       cbdata.packed_refs = get_packed_refs(refs);
+       /* Do not pack non-tags unless PACK_REFS_ALL is set: */
+       if (!(pack_flags & PACK_REFS_ALL) && !starts_with(refname, "refs/tags/"))
+               return 0;
 
-       do_for_each_entry_in_dir(get_loose_refs(refs), 0,
-                                pack_if_possible_fn, &cbdata);
+       /* Do not pack symbolic refs: */
+       if (ref_flags & REF_ISSYMREF)
+               return 0;
 
-       if (commit_packed_refs(refs))
-               die_errno("unable to overwrite old ref-pack file");
+       /* Do not pack broken refs: */
+       if (!ref_resolves_to_object(refname, oid, ref_flags))
+               return 0;
 
-       prune_refs(cbdata.ref_to_prune);
-       return 0;
+       return 1;
 }
 
-/*
- * Rewrite the packed-refs file, omitting any refs listed in
- * 'refnames'. On error, leave packed-refs unchanged, write an error
- * message to 'err', and return a nonzero value.
- *
- * The refs in 'refnames' needn't be sorted. `err` must not be NULL.
- */
-static int repack_without_refs(struct files_ref_store *refs,
-                              struct string_list *refnames, struct strbuf *err)
+static int files_pack_refs(struct ref_store *ref_store, unsigned int flags)
 {
-       struct ref_dir *packed;
-       struct string_list_item *refname;
-       int ret, needs_repacking = 0, removed = 0;
-
-       assert_main_repository(&refs->base, "repack_without_refs");
-       assert(err);
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE | REF_STORE_ODB,
+                              "pack_refs");
+       struct ref_iterator *iter;
+       int ok;
+       struct ref_to_prune *refs_to_prune = NULL;
+       struct strbuf err = STRBUF_INIT;
+       struct ref_transaction *transaction;
 
-       /* Look for a packed ref */
-       for_each_string_list_item(refname, refnames) {
-               if (get_packed_ref(refs, refname->string)) {
-                       needs_repacking = 1;
-                       break;
-               }
-       }
+       transaction = ref_store_transaction_begin(refs->packed_ref_store, &err);
+       if (!transaction)
+               return -1;
 
-       /* Avoid locking if we have nothing to do */
-       if (!needs_repacking)
-               return 0; /* no refname exists in packed refs */
+       packed_refs_lock(refs->packed_ref_store, LOCK_DIE_ON_ERROR, &err);
 
-       if (lock_packed_refs(refs, 0)) {
-               unable_to_lock_message(git_path("packed-refs"), errno, err);
-               return -1;
-       }
-       packed = get_packed_refs(refs);
+       iter = cache_ref_iterator_begin(get_loose_ref_cache(refs), NULL, 0);
+       while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
+               /*
+                * If the loose reference can be packed, add an entry
+                * in the packed ref cache. If the reference should be
+                * pruned, also add it to refs_to_prune.
+                */
+               if (!should_pack_ref(iter->refname, iter->oid, iter->flags,
+                                    flags))
+                       continue;
 
-       /* Remove refnames from the cache */
-       for_each_string_list_item(refname, refnames)
-               if (remove_entry(packed, refname->string) != -1)
-                       removed = 1;
-       if (!removed) {
                /*
-                * All packed entries disappeared while we were
-                * acquiring the lock.
+                * Add a reference creation for this reference to the
+                * packed-refs transaction:
                 */
-               rollback_packed_refs(refs);
-               return 0;
+               if (ref_transaction_update(transaction, iter->refname,
+                                          iter->oid, NULL,
+                                          REF_NO_DEREF, NULL, &err))
+                       die("failure preparing to create packed reference %s: %s",
+                           iter->refname, err.buf);
+
+               /* Schedule the loose reference for pruning if requested. */
+               if ((flags & PACK_REFS_PRUNE)) {
+                       struct ref_to_prune *n;
+                       FLEX_ALLOC_STR(n, name, iter->refname);
+                       oidcpy(&n->oid, iter->oid);
+                       n->next = refs_to_prune;
+                       refs_to_prune = n;
+               }
        }
+       if (ok != ITER_DONE)
+               die("error while iterating over references");
 
-       /* Write what remains */
-       ret = commit_packed_refs(refs);
-       if (ret)
-               strbuf_addf(err, "unable to overwrite old ref-pack file: %s",
-                           strerror(errno));
-       return ret;
-}
+       if (ref_transaction_commit(transaction, &err))
+               die("unable to write new packed-refs: %s", err.buf);
 
-static int delete_ref_loose(struct ref_lock *lock, int flag, struct strbuf *err)
-{
-       assert(err);
+       ref_transaction_free(transaction);
 
-       if (!(flag & REF_ISPACKED) || flag & REF_ISSYMREF) {
-               /*
-                * loose.  The loose file name is the same as the
-                * lockfile name, minus ".lock":
-                */
-               char *loose_filename = get_locked_file_path(lock->lk);
-               int res = unlink_or_msg(loose_filename, err);
-               free(loose_filename);
-               if (res)
-                       return 1;
-       }
+       packed_refs_unlock(refs->packed_ref_store);
+
+       prune_refs(refs, &refs_to_prune);
+       strbuf_release(&err);
        return 0;
 }
 
-static int files_delete_refs(struct ref_store *ref_store,
+static int files_delete_refs(struct ref_store *ref_store, const char *msg,
                             struct string_list *refnames, unsigned int flags)
 {
        struct files_ref_store *refs =
-               files_downcast(ref_store, 0, "delete_refs");
+               files_downcast(ref_store, REF_STORE_WRITE, "delete_refs");
        struct strbuf err = STRBUF_INIT;
        int i, result = 0;
 
        if (!refnames->nr)
                return 0;
 
-       result = repack_without_refs(refs, refnames, &err);
-       if (result) {
-               /*
-                * If we failed to rewrite the packed-refs file, then
-                * it is unsafe to try to remove loose refs, because
-                * doing so might expose an obsolete packed value for
-                * a reference that might even point at an object that
-                * has been garbage collected.
-                */
-               if (refnames->nr == 1)
-                       error(_("could not delete reference %s: %s"),
-                             refnames->items[0].string, err.buf);
-               else
-                       error(_("could not delete references: %s"), err.buf);
+       if (packed_refs_lock(refs->packed_ref_store, 0, &err))
+               goto error;
 
-               goto out;
+       if (refs_delete_refs(refs->packed_ref_store, msg, refnames, flags)) {
+               packed_refs_unlock(refs->packed_ref_store);
+               goto error;
        }
 
+       packed_refs_unlock(refs->packed_ref_store);
+
        for (i = 0; i < refnames->nr; i++) {
                const char *refname = refnames->items[i].string;
 
-               if (delete_ref(refname, NULL, flags))
+               if (refs_delete_ref(&refs->base, msg, refname, NULL, flags))
                        result |= error(_("could not remove reference %s"), refname);
        }
 
-out:
        strbuf_release(&err);
        return result;
+
+error:
+       /*
+        * If we failed to rewrite the packed-refs file, then it is
+        * unsafe to try to remove loose refs, because doing so might
+        * expose an obsolete packed value for a reference that might
+        * even point at an object that has been garbage collected.
+        */
+       if (refnames->nr == 1)
+               error(_("could not delete reference %s: %s"),
+                     refnames->items[0].string, err.buf);
+       else
+               error(_("could not delete references: %s"), err.buf);
+
+       strbuf_release(&err);
+       return -1;
 }
 
 /*
@@ -2505,137 +1218,148 @@ out:
  * IOW, to avoid cross device rename errors, the temporary renamed log must
  * live into logs/refs.
  */
-#define TMP_RENAMED_LOG  "logs/refs/.tmp-renamed-log"
+#define TMP_RENAMED_LOG  "refs/.tmp-renamed-log"
 
-static int rename_tmp_log(const char *newrefname)
-{
-       int attempts_remaining = 4;
-       struct strbuf path = STRBUF_INIT;
-       int ret = -1;
+struct rename_cb {
+       const char *tmp_renamed_log;
+       int true_errno;
+};
 
- retry:
-       strbuf_reset(&path);
-       strbuf_git_path(&path, "logs/%s", newrefname);
-       switch (safe_create_leading_directories_const(path.buf)) {
-       case SCLD_OK:
-               break; /* success */
-       case SCLD_VANISHED:
-               if (--attempts_remaining > 0)
-                       goto retry;
-               /* fall through */
-       default:
-               error("unable to create directory for %s", newrefname);
-               goto out;
-       }
+static int rename_tmp_log_callback(const char *path, void *cb_data)
+{
+       struct rename_cb *cb = cb_data;
 
-       if (rename(git_path(TMP_RENAMED_LOG), path.buf)) {
-               if ((errno==EISDIR || errno==ENOTDIR) && --attempts_remaining > 0) {
-                       /*
-                        * rename(a, b) when b is an existing
-                        * directory ought to result in ISDIR, but
-                        * Solaris 5.8 gives ENOTDIR.  Sheesh.
-                        */
-                       if (remove_empty_directories(&path)) {
-                               error("Directory not empty: logs/%s", newrefname);
-                               goto out;
-                       }
-                       goto retry;
-               } else if (errno == ENOENT && --attempts_remaining > 0) {
-                       /*
-                        * Maybe another process just deleted one of
-                        * the directories in the path to newrefname.
-                        * Try again from the beginning.
-                        */
-                       goto retry;
-               } else {
-                       error("unable to move logfile "TMP_RENAMED_LOG" to logs/%s: %s",
-                               newrefname, strerror(errno));
-                       goto out;
-               }
+       if (rename(cb->tmp_renamed_log, path)) {
+               /*
+                * rename(a, b) when b is an existing directory ought
+                * to result in ISDIR, but Solaris 5.8 gives ENOTDIR.
+                * Sheesh. Record the true errno for error reporting,
+                * but report EISDIR to raceproof_create_file() so
+                * that it knows to retry.
+                */
+               cb->true_errno = errno;
+               if (errno == ENOTDIR)
+                       errno = EISDIR;
+               return -1;
+       } else {
+               return 0;
        }
-       ret = 0;
-out:
-       strbuf_release(&path);
-       return ret;
 }
 
-static int files_verify_refname_available(struct ref_store *ref_store,
-                                         const char *newname,
-                                         const struct string_list *extras,
-                                         const struct string_list *skip,
-                                         struct strbuf *err)
+static int rename_tmp_log(struct files_ref_store *refs, const char *newrefname)
 {
-       struct files_ref_store *refs =
-               files_downcast(ref_store, 1, "verify_refname_available");
-       struct ref_dir *packed_refs = get_packed_refs(refs);
-       struct ref_dir *loose_refs = get_loose_refs(refs);
-
-       if (verify_refname_available_dir(newname, extras, skip,
-                                        packed_refs, err) ||
-           verify_refname_available_dir(newname, extras, skip,
-                                        loose_refs, err))
-               return -1;
+       struct strbuf path = STRBUF_INIT;
+       struct strbuf tmp = STRBUF_INIT;
+       struct rename_cb cb;
+       int ret;
 
-       return 0;
+       files_reflog_path(refs, &path, newrefname);
+       files_reflog_path(refs, &tmp, TMP_RENAMED_LOG);
+       cb.tmp_renamed_log = tmp.buf;
+       ret = raceproof_create_file(path.buf, rename_tmp_log_callback, &cb);
+       if (ret) {
+               if (errno == EISDIR)
+                       error("directory not empty: %s", path.buf);
+               else
+                       error("unable to move logfile %s to %s: %s",
+                             tmp.buf, path.buf,
+                             strerror(cb.true_errno));
+       }
+
+       strbuf_release(&path);
+       strbuf_release(&tmp);
+       return ret;
 }
 
 static int write_ref_to_lockfile(struct ref_lock *lock,
-                                const unsigned char *sha1, struct strbuf *err);
+                                const struct object_id *oid, struct strbuf *err);
 static int commit_ref_update(struct files_ref_store *refs,
                             struct ref_lock *lock,
-                            const unsigned char *sha1, const char *logmsg,
+                            const struct object_id *oid, const char *logmsg,
                             struct strbuf *err);
 
-static int files_rename_ref(struct ref_store *ref_store,
+static int files_copy_or_rename_ref(struct ref_store *ref_store,
                            const char *oldrefname, const char *newrefname,
-                           const char *logmsg)
+                           const char *logmsg, int copy)
 {
        struct files_ref_store *refs =
-               files_downcast(ref_store, 0, "rename_ref");
-       unsigned char sha1[20], orig_sha1[20];
+               files_downcast(ref_store, REF_STORE_WRITE, "rename_ref");
+       struct object_id oid, orig_oid;
        int flag = 0, logmoved = 0;
        struct ref_lock *lock;
        struct stat loginfo;
-       int log = !lstat(git_path("logs/%s", oldrefname), &loginfo);
+       struct strbuf sb_oldref = STRBUF_INIT;
+       struct strbuf sb_newref = STRBUF_INIT;
+       struct strbuf tmp_renamed_log = STRBUF_INIT;
+       int log, ret;
        struct strbuf err = STRBUF_INIT;
 
-       if (log && S_ISLNK(loginfo.st_mode))
-               return error("reflog for %s is a symlink", oldrefname);
+       files_reflog_path(refs, &sb_oldref, oldrefname);
+       files_reflog_path(refs, &sb_newref, newrefname);
+       files_reflog_path(refs, &tmp_renamed_log, TMP_RENAMED_LOG);
+
+       log = !lstat(sb_oldref.buf, &loginfo);
+       if (log && S_ISLNK(loginfo.st_mode)) {
+               ret = error("reflog for %s is a symlink", oldrefname);
+               goto out;
+       }
+
+       if (!refs_resolve_ref_unsafe(&refs->base, oldrefname,
+                                    RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
+                               &orig_oid, &flag)) {
+               ret = error("refname %s not found", oldrefname);
+               goto out;
+       }
 
-       if (!resolve_ref_unsafe(oldrefname, RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
-                               orig_sha1, &flag))
-               return error("refname %s not found", oldrefname);
+       if (flag & REF_ISSYMREF) {
+               if (copy)
+                       ret = error("refname %s is a symbolic ref, copying it is not supported",
+                                   oldrefname);
+               else
+                       ret = error("refname %s is a symbolic ref, renaming it is not supported",
+                                   oldrefname);
+               goto out;
+       }
+       if (!refs_rename_ref_available(&refs->base, oldrefname, newrefname)) {
+               ret = 1;
+               goto out;
+       }
 
-       if (flag & REF_ISSYMREF)
-               return error("refname %s is a symbolic ref, renaming it is not supported",
-                       oldrefname);
-       if (!rename_ref_available(oldrefname, newrefname))
-               return 1;
+       if (!copy && log && rename(sb_oldref.buf, tmp_renamed_log.buf)) {
+               ret = error("unable to move logfile logs/%s to logs/"TMP_RENAMED_LOG": %s",
+                           oldrefname, strerror(errno));
+               goto out;
+       }
 
-       if (log && rename(git_path("logs/%s", oldrefname), git_path(TMP_RENAMED_LOG)))
-               return error("unable to move logfile logs/%s to "TMP_RENAMED_LOG": %s",
-                       oldrefname, strerror(errno));
+       if (copy && log && copy_file(tmp_renamed_log.buf, sb_oldref.buf, 0644)) {
+               ret = error("unable to copy logfile logs/%s to logs/"TMP_RENAMED_LOG": %s",
+                           oldrefname, strerror(errno));
+               goto out;
+       }
 
-       if (delete_ref(oldrefname, orig_sha1, REF_NODEREF)) {
+       if (!copy && refs_delete_ref(&refs->base, logmsg, oldrefname,
+                           &orig_oid, REF_NO_DEREF)) {
                error("unable to delete old %s", oldrefname);
                goto rollback;
        }
 
        /*
-        * Since we are doing a shallow lookup, sha1 is not the
-        * correct value to pass to delete_ref as old_sha1. But that
-        * doesn't matter, because an old_sha1 check wouldn't add to
+        * Since we are doing a shallow lookup, oid is not the
+        * correct value to pass to delete_ref as old_oid. But that
+        * doesn't matter, because an old_oid check wouldn't add to
         * the safety anyway; we want to delete the reference whatever
         * its current value.
         */
-       if (!read_ref_full(newrefname, RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
-                          sha1, NULL) &&
-           delete_ref(newrefname, NULL, REF_NODEREF)) {
-               if (errno==EISDIR) {
+       if (!copy && !refs_read_ref_full(&refs->base, newrefname,
+                               RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
+                               &oid, NULL) &&
+           refs_delete_ref(&refs->base, NULL, newrefname,
+                           NULL, REF_NO_DEREF)) {
+               if (errno == EISDIR) {
                        struct strbuf path = STRBUF_INIT;
                        int result;
 
-                       strbuf_git_path(&path, "%s", newrefname);
+                       files_ref_path(refs, &path, newrefname);
                        result = remove_empty_directories(&path);
                        strbuf_release(&path);
 
@@ -2649,32 +1373,36 @@ static int files_rename_ref(struct ref_store *ref_store,
                }
        }
 
-       if (log && rename_tmp_log(newrefname))
+       if (log && rename_tmp_log(refs, newrefname))
                goto rollback;
 
        logmoved = log;
 
-       lock = lock_ref_sha1_basic(refs, newrefname, NULL, NULL, NULL,
-                                  REF_NODEREF, NULL, &err);
+       lock = lock_ref_oid_basic(refs, newrefname, NULL, NULL, NULL,
+                                 REF_NO_DEREF, NULL, &err);
        if (!lock) {
-               error("unable to rename '%s' to '%s': %s", oldrefname, newrefname, err.buf);
+               if (copy)
+                       error("unable to copy '%s' to '%s': %s", oldrefname, newrefname, err.buf);
+               else
+                       error("unable to rename '%s' to '%s': %s", oldrefname, newrefname, err.buf);
                strbuf_release(&err);
                goto rollback;
        }
-       hashcpy(lock->old_oid.hash, orig_sha1);
+       oidcpy(&lock->old_oid, &orig_oid);
 
-       if (write_ref_to_lockfile(lock, orig_sha1, &err) ||
-           commit_ref_update(refs, lock, orig_sha1, logmsg, &err)) {
+       if (write_ref_to_lockfile(lock, &orig_oid, &err) ||
+           commit_ref_update(refs, lock, &orig_oid, logmsg, &err)) {
                error("unable to write current sha1 into %s: %s", newrefname, err.buf);
                strbuf_release(&err);
                goto rollback;
        }
 
-       return 0;
+       ret = 0;
+       goto out;
 
  rollback:
-       lock = lock_ref_sha1_basic(refs, oldrefname, NULL, NULL, NULL,
-                                  REF_NODEREF, NULL, &err);
+       lock = lock_ref_oid_basic(refs, oldrefname, NULL, NULL, NULL,
+                                 REF_NO_DEREF, NULL, &err);
        if (!lock) {
                error("unable to lock %s for rollback: %s", oldrefname, err.buf);
                strbuf_release(&err);
@@ -2683,35 +1411,56 @@ static int files_rename_ref(struct ref_store *ref_store,
 
        flag = log_all_ref_updates;
        log_all_ref_updates = LOG_REFS_NONE;
-       if (write_ref_to_lockfile(lock, orig_sha1, &err) ||
-           commit_ref_update(refs, lock, orig_sha1, NULL, &err)) {
+       if (write_ref_to_lockfile(lock, &orig_oid, &err) ||
+           commit_ref_update(refs, lock, &orig_oid, NULL, &err)) {
                error("unable to write current sha1 into %s: %s", oldrefname, err.buf);
                strbuf_release(&err);
        }
        log_all_ref_updates = flag;
 
  rollbacklog:
-       if (logmoved && rename(git_path("logs/%s", newrefname), git_path("logs/%s", oldrefname)))
+       if (logmoved && rename(sb_newref.buf, sb_oldref.buf))
                error("unable to restore logfile %s from %s: %s",
                        oldrefname, newrefname, strerror(errno));
        if (!logmoved && log &&
-           rename(git_path(TMP_RENAMED_LOG), git_path("logs/%s", oldrefname)))
-               error("unable to restore logfile %s from "TMP_RENAMED_LOG": %s",
+           rename(tmp_renamed_log.buf, sb_oldref.buf))
+               error("unable to restore logfile %s from logs/"TMP_RENAMED_LOG": %s",
                        oldrefname, strerror(errno));
+       ret = 1;
+ out:
+       strbuf_release(&sb_newref);
+       strbuf_release(&sb_oldref);
+       strbuf_release(&tmp_renamed_log);
 
-       return 1;
+       return ret;
+}
+
+static int files_rename_ref(struct ref_store *ref_store,
+                           const char *oldrefname, const char *newrefname,
+                           const char *logmsg)
+{
+       return files_copy_or_rename_ref(ref_store, oldrefname,
+                                newrefname, logmsg, 0);
+}
+
+static int files_copy_ref(struct ref_store *ref_store,
+                           const char *oldrefname, const char *newrefname,
+                           const char *logmsg)
+{
+       return files_copy_or_rename_ref(ref_store, oldrefname,
+                                newrefname, logmsg, 1);
 }
 
-static int close_ref(struct ref_lock *lock)
+static int close_ref_gently(struct ref_lock *lock)
 {
-       if (close_lock_file(lock->lk))
+       if (close_lock_file_gently(&lock->lk))
                return -1;
        return 0;
 }
 
 static int commit_ref(struct ref_lock *lock)
 {
-       char *path = get_locked_file_path(lock->lk);
+       char *path = get_locked_file_path(&lock->lk);
        struct stat st;
 
        if (!lstat(path, &st) && S_ISDIR(st.st_mode)) {
@@ -2735,75 +1484,102 @@ static int commit_ref(struct ref_lock *lock)
                free(path);
        }
 
-       if (commit_lock_file(lock->lk))
+       if (commit_lock_file(&lock->lk))
                return -1;
        return 0;
 }
 
+static int open_or_create_logfile(const char *path, void *cb)
+{
+       int *fd = cb;
+
+       *fd = open(path, O_APPEND | O_WRONLY | O_CREAT, 0666);
+       return (*fd < 0) ? -1 : 0;
+}
+
 /*
- * Create a reflog for a ref.  If force_create = 0, the reflog will
- * only be created for certain refs (those for which
- * should_autocreate_reflog returns non-zero.  Otherwise, create it
- * regardless of the ref name.  Fill in *err and return -1 on failure.
+ * Create a reflog for a ref. If force_create = 0, only create the
+ * reflog for certain refs (those for which should_autocreate_reflog
+ * returns non-zero). Otherwise, create it regardless of the reference
+ * name. If the logfile already existed or was created, return 0 and
+ * set *logfd to the file descriptor opened for appending to the file.
+ * If no logfile exists and we decided not to create one, return 0 and
+ * set *logfd to -1. On failure, fill in *err, set *logfd to -1, and
+ * return -1.
  */
-static int log_ref_setup(const char *refname, struct strbuf *logfile, struct strbuf *err, int force_create)
+static int log_ref_setup(struct files_ref_store *refs,
+                        const char *refname, int force_create,
+                        int *logfd, struct strbuf *err)
 {
-       int logfd, oflags = O_APPEND | O_WRONLY;
-
-       strbuf_git_path(logfile, "logs/%s", refname);
-       if (force_create || should_autocreate_reflog(refname)) {
-               if (safe_create_leading_directories(logfile->buf) < 0) {
-                       strbuf_addf(err, "unable to create directory for '%s': "
-                                   "%s", logfile->buf, strerror(errno));
-                       return -1;
-               }
-               oflags |= O_CREAT;
-       }
+       struct strbuf logfile_sb = STRBUF_INIT;
+       char *logfile;
 
-       logfd = open(logfile->buf, oflags, 0666);
-       if (logfd < 0) {
-               if (!(oflags & O_CREAT) && (errno == ENOENT || errno == EISDIR))
-                       return 0;
+       files_reflog_path(refs, &logfile_sb, refname);
+       logfile = strbuf_detach(&logfile_sb, NULL);
 
-               if (errno == EISDIR) {
-                       if (remove_empty_directories(logfile)) {
-                               strbuf_addf(err, "there are still logs under "
-                                           "'%s'", logfile->buf);
-                               return -1;
-                       }
-                       logfd = open(logfile->buf, oflags, 0666);
-               }
+       if (force_create || should_autocreate_reflog(refname)) {
+               if (raceproof_create_file(logfile, open_or_create_logfile, logfd)) {
+                       if (errno == ENOENT)
+                               strbuf_addf(err, "unable to create directory for '%s': "
+                                           "%s", logfile, strerror(errno));
+                       else if (errno == EISDIR)
+                               strbuf_addf(err, "there are still logs under '%s'",
+                                           logfile);
+                       else
+                               strbuf_addf(err, "unable to append to '%s': %s",
+                                           logfile, strerror(errno));
 
-               if (logfd < 0) {
-                       strbuf_addf(err, "unable to append to '%s': %s",
-                                   logfile->buf, strerror(errno));
-                       return -1;
+                       goto error;
+               }
+       } else {
+               *logfd = open(logfile, O_APPEND | O_WRONLY, 0666);
+               if (*logfd < 0) {
+                       if (errno == ENOENT || errno == EISDIR) {
+                               /*
+                                * The logfile doesn't already exist,
+                                * but that is not an error; it only
+                                * means that we won't write log
+                                * entries to it.
+                                */
+                               ;
+                       } else {
+                               strbuf_addf(err, "unable to append to '%s': %s",
+                                           logfile, strerror(errno));
+                               goto error;
+                       }
                }
        }
 
-       adjust_shared_perm(logfile->buf);
-       close(logfd);
+       if (*logfd >= 0)
+               adjust_shared_perm(logfile);
+
+       free(logfile);
        return 0;
-}
 
+error:
+       free(logfile);
+       return -1;
+}
 
 static int files_create_reflog(struct ref_store *ref_store,
                               const char *refname, int force_create,
                               struct strbuf *err)
 {
-       int ret;
-       struct strbuf sb = STRBUF_INIT;
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE, "create_reflog");
+       int fd;
 
-       /* Check validity (but we don't need the result): */
-       files_downcast(ref_store, 0, "create_reflog");
+       if (log_ref_setup(refs, refname, force_create, &fd, err))
+               return -1;
 
-       ret = log_ref_setup(refname, &sb, err, force_create);
-       strbuf_release(&sb);
-       return ret;
+       if (fd >= 0)
+               close(fd);
+
+       return 0;
 }
 
-static int log_ref_write_fd(int fd, const unsigned char *old_sha1,
-                           const unsigned char *new_sha1,
+static int log_ref_write_fd(int fd, const struct object_id *old_oid,
+                           const struct object_id *new_oid,
                            const char *committer, const char *msg)
 {
        int msglen, written;
@@ -2814,106 +1590,97 @@ static int log_ref_write_fd(int fd, const unsigned char *old_sha1,
        maxlen = strlen(committer) + msglen + 100;
        logrec = xmalloc(maxlen);
        len = xsnprintf(logrec, maxlen, "%s %s %s\n",
-                       sha1_to_hex(old_sha1),
-                       sha1_to_hex(new_sha1),
+                       oid_to_hex(old_oid),
+                       oid_to_hex(new_oid),
                        committer);
        if (msglen)
                len += copy_reflog_msg(logrec + len - 1, msg) - 1;
 
        written = len <= maxlen ? write_in_full(fd, logrec, len) : -1;
        free(logrec);
-       if (written != len)
+       if (written < 0)
                return -1;
 
        return 0;
 }
 
-static int log_ref_write_1(const char *refname, const unsigned char *old_sha1,
-                          const unsigned char *new_sha1, const char *msg,
-                          struct strbuf *logfile, int flags,
-                          struct strbuf *err)
+static int files_log_ref_write(struct files_ref_store *refs,
+                              const char *refname, const struct object_id *old_oid,
+                              const struct object_id *new_oid, const char *msg,
+                              int flags, struct strbuf *err)
 {
-       int logfd, result, oflags = O_APPEND | O_WRONLY;
+       int logfd, result;
 
        if (log_all_ref_updates == LOG_REFS_UNSET)
                log_all_ref_updates = is_bare_repository() ? LOG_REFS_NONE : LOG_REFS_NORMAL;
 
-       result = log_ref_setup(refname, logfile, err, flags & REF_FORCE_CREATE_REFLOG);
+       result = log_ref_setup(refs, refname,
+                              flags & REF_FORCE_CREATE_REFLOG,
+                              &logfd, err);
 
        if (result)
                return result;
 
-       logfd = open(logfile->buf, oflags);
        if (logfd < 0)
                return 0;
-       result = log_ref_write_fd(logfd, old_sha1, new_sha1,
+       result = log_ref_write_fd(logfd, old_oid, new_oid,
                                  git_committer_info(0), msg);
        if (result) {
-               strbuf_addf(err, "unable to append to '%s': %s", logfile->buf,
-                           strerror(errno));
+               struct strbuf sb = STRBUF_INIT;
+               int save_errno = errno;
+
+               files_reflog_path(refs, &sb, refname);
+               strbuf_addf(err, "unable to append to '%s': %s",
+                           sb.buf, strerror(save_errno));
+               strbuf_release(&sb);
                close(logfd);
                return -1;
        }
        if (close(logfd)) {
-               strbuf_addf(err, "unable to append to '%s': %s", logfile->buf,
-                           strerror(errno));
+               struct strbuf sb = STRBUF_INIT;
+               int save_errno = errno;
+
+               files_reflog_path(refs, &sb, refname);
+               strbuf_addf(err, "unable to append to '%s': %s",
+                           sb.buf, strerror(save_errno));
+               strbuf_release(&sb);
                return -1;
        }
        return 0;
 }
 
-static int log_ref_write(const char *refname, const unsigned char *old_sha1,
-                        const unsigned char *new_sha1, const char *msg,
-                        int flags, struct strbuf *err)
-{
-       return files_log_ref_write(refname, old_sha1, new_sha1, msg, flags,
-                                  err);
-}
-
-int files_log_ref_write(const char *refname, const unsigned char *old_sha1,
-                       const unsigned char *new_sha1, const char *msg,
-                       int flags, struct strbuf *err)
-{
-       struct strbuf sb = STRBUF_INIT;
-       int ret = log_ref_write_1(refname, old_sha1, new_sha1, msg, &sb, flags,
-                                 err);
-       strbuf_release(&sb);
-       return ret;
-}
-
 /*
- * Write sha1 into the open lockfile, then close the lockfile. On
- * errors, rollback the lockfile, fill in *err and
- * return -1.
+ * Write oid into the open lockfile, then close the lockfile. On
+ * errors, rollback the lockfile, fill in *err and return -1.
  */
 static int write_ref_to_lockfile(struct ref_lock *lock,
-                                const unsigned char *sha1, struct strbuf *err)
+                                const struct object_id *oid, struct strbuf *err)
 {
        static char term = '\n';
        struct object *o;
        int fd;
 
-       o = parse_object(sha1);
+       o = parse_object(oid);
        if (!o) {
                strbuf_addf(err,
                            "trying to write ref '%s' with nonexistent object %s",
-                           lock->ref_name, sha1_to_hex(sha1));
+                           lock->ref_name, oid_to_hex(oid));
                unlock_ref(lock);
                return -1;
        }
        if (o->type != OBJ_COMMIT && is_branch(lock->ref_name)) {
                strbuf_addf(err,
                            "trying to write non-commit object %s to branch '%s'",
-                           sha1_to_hex(sha1), lock->ref_name);
+                           oid_to_hex(oid), lock->ref_name);
                unlock_ref(lock);
                return -1;
        }
-       fd = get_lock_file_fd(lock->lk);
-       if (write_in_full(fd, sha1_to_hex(sha1), 40) != 40 ||
-           write_in_full(fd, &term, 1) != 1 ||
-           close_ref(lock) < 0) {
+       fd = get_lock_file_fd(&lock->lk);
+       if (write_in_full(fd, oid_to_hex(oid), GIT_SHA1_HEXSZ) < 0 ||
+           write_in_full(fd, &term, 1) < 0 ||
+           close_ref_gently(lock) < 0) {
                strbuf_addf(err,
-                           "couldn't write '%s'", get_lock_file_path(lock->lk));
+                           "couldn't write '%s'", get_lock_file_path(&lock->lk));
                unlock_ref(lock);
                return -1;
        }
@@ -2927,13 +1694,15 @@ static int write_ref_to_lockfile(struct ref_lock *lock,
  */
 static int commit_ref_update(struct files_ref_store *refs,
                             struct ref_lock *lock,
-                            const unsigned char *sha1, const char *logmsg,
+                            const struct object_id *oid, const char *logmsg,
                             struct strbuf *err)
 {
-       assert_main_repository(&refs->base, "commit_ref_update");
+       files_assert_main_repository(refs, "commit_ref_update");
 
        clear_loose_ref_cache(refs);
-       if (log_ref_write(lock->ref_name, lock->old_oid.hash, sha1, logmsg, 0, err)) {
+       if (files_log_ref_write(refs, lock->ref_name,
+                               &lock->old_oid, oid,
+                               logmsg, 0, err)) {
                char *old_msg = strbuf_detach(err, NULL);
                strbuf_addf(err, "cannot update the ref '%s': %s",
                            lock->ref_name, old_msg);
@@ -2955,17 +1724,18 @@ static int commit_ref_update(struct files_ref_store *refs,
                 * check with HEAD only which should cover 99% of all usage
                 * scenarios (even 100% of the default ones).
                 */
-               unsigned char head_sha1[20];
                int head_flag;
                const char *head_ref;
 
-               head_ref = resolve_ref_unsafe("HEAD", RESOLVE_REF_READING,
-                                             head_sha1, &head_flag);
+               head_ref = refs_resolve_ref_unsafe(&refs->base, "HEAD",
+                                                  RESOLVE_REF_READING,
+                                                  NULL, &head_flag);
                if (head_ref && (head_flag & REF_ISSYMREF) &&
                    !strcmp(head_ref, lock->ref_name)) {
                        struct strbuf log_err = STRBUF_INIT;
-                       if (log_ref_write("HEAD", lock->old_oid.hash, sha1,
-                                         logmsg, 0, &log_err)) {
+                       if (files_log_ref_write(refs, "HEAD",
+                                               &lock->old_oid, oid,
+                                               logmsg, 0, &log_err)) {
                                error("%s", log_err.buf);
                                strbuf_release(&log_err);
                        }
@@ -2986,7 +1756,7 @@ static int create_ref_symlink(struct ref_lock *lock, const char *target)
 {
        int ret = -1;
 #ifndef NO_SYMLINK_HEAD
-       char *ref_path = get_locked_file_path(lock->lk);
+       char *ref_path = get_locked_file_path(&lock->lk);
        unlink(ref_path);
        ret = symlink(target, ref_path);
        free(ref_path);
@@ -2997,34 +1767,39 @@ static int create_ref_symlink(struct ref_lock *lock, const char *target)
        return ret;
 }
 
-static void update_symref_reflog(struct ref_lock *lock, const char *refname,
+static void update_symref_reflog(struct files_ref_store *refs,
+                                struct ref_lock *lock, const char *refname,
                                 const char *target, const char *logmsg)
 {
        struct strbuf err = STRBUF_INIT;
-       unsigned char new_sha1[20];
-       if (logmsg && !read_ref(target, new_sha1) &&
-           log_ref_write(refname, lock->old_oid.hash, new_sha1, logmsg, 0, &err)) {
+       struct object_id new_oid;
+       if (logmsg &&
+           !refs_read_ref_full(&refs->base, target,
+                               RESOLVE_REF_READING, &new_oid, NULL) &&
+           files_log_ref_write(refs, refname, &lock->old_oid,
+                               &new_oid, logmsg, 0, &err)) {
                error("%s", err.buf);
                strbuf_release(&err);
        }
 }
 
-static int create_symref_locked(struct ref_lock *lock, const char *refname,
+static int create_symref_locked(struct files_ref_store *refs,
+                               struct ref_lock *lock, const char *refname,
                                const char *target, const char *logmsg)
 {
        if (prefer_symlink_refs && !create_ref_symlink(lock, target)) {
-               update_symref_reflog(lock, refname, target, logmsg);
+               update_symref_reflog(refs, lock, refname, target, logmsg);
                return 0;
        }
 
-       if (!fdopen_lock_file(lock->lk, "w"))
+       if (!fdopen_lock_file(&lock->lk, "w"))
                return error("unable to fdopen %s: %s",
-                            lock->lk->tempfile.filename.buf, strerror(errno));
+                            lock->lk.tempfile->filename.buf, strerror(errno));
 
-       update_symref_reflog(lock, refname, target, logmsg);
+       update_symref_reflog(refs, lock, refname, target, logmsg);
 
        /* no error check; commit_ref will check ferror */
-       fprintf(lock->lk->tempfile.fp, "ref: %s\n", target);
+       fprintf(lock->lk.tempfile->fp, "ref: %s\n", target);
        if (commit_ref(lock) < 0)
                return error("unable to write symref for %s: %s", refname,
                             strerror(errno));
@@ -3036,95 +1811,69 @@ static int files_create_symref(struct ref_store *ref_store,
                               const char *logmsg)
 {
        struct files_ref_store *refs =
-               files_downcast(ref_store, 0, "create_symref");
+               files_downcast(ref_store, REF_STORE_WRITE, "create_symref");
        struct strbuf err = STRBUF_INIT;
        struct ref_lock *lock;
        int ret;
 
-       lock = lock_ref_sha1_basic(refs, refname, NULL,
-                                  NULL, NULL, REF_NODEREF, NULL,
-                                  &err);
+       lock = lock_ref_oid_basic(refs, refname, NULL,
+                                 NULL, NULL, REF_NO_DEREF, NULL,
+                                 &err);
        if (!lock) {
                error("%s", err.buf);
                strbuf_release(&err);
                return -1;
        }
 
-       ret = create_symref_locked(lock, refname, target, logmsg);
+       ret = create_symref_locked(refs, lock, refname, target, logmsg);
        unlock_ref(lock);
        return ret;
 }
 
-int set_worktree_head_symref(const char *gitdir, const char *target)
-{
-       static struct lock_file head_lock;
-       struct ref_lock *lock;
-       struct strbuf head_path = STRBUF_INIT;
-       const char *head_rel;
-       int ret;
-
-       strbuf_addf(&head_path, "%s/HEAD", absolute_path(gitdir));
-       if (hold_lock_file_for_update(&head_lock, head_path.buf,
-                                     LOCK_NO_DEREF) < 0) {
-               struct strbuf err = STRBUF_INIT;
-               unable_to_lock_message(head_path.buf, errno, &err);
-               error("%s", err.buf);
-               strbuf_release(&err);
-               strbuf_release(&head_path);
-               return -1;
-       }
-
-       /* head_rel will be "HEAD" for the main tree, "worktrees/wt/HEAD" for
-          linked trees */
-       head_rel = remove_leading_path(head_path.buf,
-                                      absolute_path(get_git_common_dir()));
-       /* to make use of create_symref_locked(), initialize ref_lock */
-       lock = xcalloc(1, sizeof(struct ref_lock));
-       lock->lk = &head_lock;
-       lock->ref_name = xstrdup(head_rel);
-
-       ret = create_symref_locked(lock, head_rel, target, NULL);
-
-       unlock_ref(lock); /* will free lock */
-       strbuf_release(&head_path);
-       return ret;
-}
-
 static int files_reflog_exists(struct ref_store *ref_store,
                               const char *refname)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ, "reflog_exists");
+       struct strbuf sb = STRBUF_INIT;
        struct stat st;
+       int ret;
 
-       /* Check validity (but we don't need the result): */
-       files_downcast(ref_store, 0, "reflog_exists");
-
-       return !lstat(git_path("logs/%s", refname), &st) &&
-               S_ISREG(st.st_mode);
+       files_reflog_path(refs, &sb, refname);
+       ret = !lstat(sb.buf, &st) && S_ISREG(st.st_mode);
+       strbuf_release(&sb);
+       return ret;
 }
 
 static int files_delete_reflog(struct ref_store *ref_store,
                               const char *refname)
 {
-       /* Check validity (but we don't need the result): */
-       files_downcast(ref_store, 0, "delete_reflog");
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE, "delete_reflog");
+       struct strbuf sb = STRBUF_INIT;
+       int ret;
 
-       return remove_path(git_path("logs/%s", refname));
+       files_reflog_path(refs, &sb, refname);
+       ret = remove_path(sb.buf);
+       strbuf_release(&sb);
+       return ret;
 }
 
 static int show_one_reflog_ent(struct strbuf *sb, each_reflog_ent_fn fn, void *cb_data)
 {
-       unsigned char osha1[20], nsha1[20];
+       struct object_id ooid, noid;
        char *email_end, *message;
-       unsigned long timestamp;
+       timestamp_t timestamp;
        int tz;
+       const char *p = sb->buf;
 
        /* old SP new SP name <email> SP time TAB msg LF */
-       if (sb->len < 83 || sb->buf[sb->len - 1] != '\n' ||
-           get_sha1_hex(sb->buf, osha1) || sb->buf[40] != ' ' ||
-           get_sha1_hex(sb->buf + 41, nsha1) || sb->buf[81] != ' ' ||
-           !(email_end = strchr(sb->buf + 82, '>')) ||
+       if (!sb->len || sb->buf[sb->len - 1] != '\n' ||
+           parse_oid_hex(p, &ooid, &p) || *p++ != ' ' ||
+           parse_oid_hex(p, &noid, &p) || *p++ != ' ' ||
+           !(email_end = strchr(p, '>')) ||
            email_end[1] != ' ' ||
-           !(timestamp = strtoul(email_end + 2, &message, 10)) ||
+           !(timestamp = parse_timestamp(email_end + 2, &message, 10)) ||
            !message || message[0] != ' ' ||
            (message[1] != '+' && message[1] != '-') ||
            !isdigit(message[2]) || !isdigit(message[3]) ||
@@ -3136,7 +1885,7 @@ static int show_one_reflog_ent(struct strbuf *sb, each_reflog_ent_fn fn, void *c
                message += 6;
        else
                message += 7;
-       return fn(osha1, nsha1, sb->buf + 82, timestamp, tz, message, cb_data);
+       return fn(&ooid, &noid, p, timestamp, tz, message, cb_data);
 }
 
 static char *find_beginning_of_line(char *bob, char *scan)
@@ -3155,22 +1904,24 @@ static int files_for_each_reflog_ent_reverse(struct ref_store *ref_store,
                                             each_reflog_ent_fn fn,
                                             void *cb_data)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ,
+                              "for_each_reflog_ent_reverse");
        struct strbuf sb = STRBUF_INIT;
        FILE *logfp;
        long pos;
        int ret = 0, at_tail = 1;
 
-       /* Check validity (but we don't need the result): */
-       files_downcast(ref_store, 0, "for_each_reflog_ent_reverse");
-
-       logfp = fopen(git_path("logs/%s", refname), "r");
+       files_reflog_path(refs, &sb, refname);
+       logfp = fopen(sb.buf, "r");
+       strbuf_release(&sb);
        if (!logfp)
                return -1;
 
        /* Jump to the end */
        if (fseek(logfp, 0, SEEK_END) < 0)
-               return error("cannot seek back reflog for %s: %s",
-                            refname, strerror(errno));
+               ret = error("cannot seek back reflog for %s: %s",
+                           refname, strerror(errno));
        pos = ftell(logfp);
        while (!ret && 0 < pos) {
                int cnt;
@@ -3180,13 +1931,17 @@ static int files_for_each_reflog_ent_reverse(struct ref_store *ref_store,
 
                /* Fill next block from the end */
                cnt = (sizeof(buf) < pos) ? sizeof(buf) : pos;
-               if (fseek(logfp, pos - cnt, SEEK_SET))
-                       return error("cannot seek back reflog for %s: %s",
-                                    refname, strerror(errno));
+               if (fseek(logfp, pos - cnt, SEEK_SET)) {
+                       ret = error("cannot seek back reflog for %s: %s",
+                                   refname, strerror(errno));
+                       break;
+               }
                nread = fread(buf, cnt, 1, logfp);
-               if (nread != 1)
-                       return error("cannot read %d bytes from reflog for %s: %s",
-                                    cnt, refname, strerror(errno));
+               if (nread != 1) {
+                       ret = error("cannot read %d bytes from reflog for %s: %s",
+                                   cnt, refname, strerror(errno));
+                       break;
+               }
                pos -= cnt;
 
                scanp = endp = buf + cnt;
@@ -3251,7 +2006,7 @@ static int files_for_each_reflog_ent_reverse(struct ref_store *ref_store,
 
        }
        if (!ret && sb.len)
-               die("BUG: reverse reflog parser had leftover data");
+               BUG("reverse reflog parser had leftover data");
 
        fclose(logfp);
        strbuf_release(&sb);
@@ -3262,14 +2017,16 @@ static int files_for_each_reflog_ent(struct ref_store *ref_store,
                                     const char *refname,
                                     each_reflog_ent_fn fn, void *cb_data)
 {
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ,
+                              "for_each_reflog_ent");
        FILE *logfp;
        struct strbuf sb = STRBUF_INIT;
        int ret = 0;
 
-       /* Check validity (but we don't need the result): */
-       files_downcast(ref_store, 0, "for_each_reflog_ent");
-
-       logfp = fopen(git_path("logs/%s", refname), "r");
+       files_reflog_path(refs, &sb, refname);
+       logfp = fopen(sb.buf, "r");
+       strbuf_release(&sb);
        if (!logfp)
                return -1;
 
@@ -3283,6 +2040,7 @@ static int files_for_each_reflog_ent(struct ref_store *ref_store,
 struct files_reflog_iterator {
        struct ref_iterator base;
 
+       struct ref_store *ref_store;
        struct dir_iterator *dir_iterator;
        struct object_id oid;
 };
@@ -3304,8 +2062,9 @@ static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
                if (ends_with(diter->basename, ".lock"))
                        continue;
 
-               if (read_ref_full(diter->relative_path, 0,
-                                 iter->oid.hash, &flags)) {
+               if (refs_read_ref_full(iter->ref_store,
+                                      diter->relative_path, 0,
+                                      &iter->oid, &flags)) {
                        error("bad ref for %s", diter->path.buf);
                        continue;
                }
@@ -3325,7 +2084,7 @@ static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
 static int files_reflog_iterator_peel(struct ref_iterator *ref_iterator,
                                   struct object_id *peeled)
 {
-       die("BUG: ref_iterator_peel() called for reflog_iterator");
+       BUG("ref_iterator_peel() called for reflog_iterator");
 }
 
 static int files_reflog_iterator_abort(struct ref_iterator *ref_iterator)
@@ -3347,34 +2106,62 @@ static struct ref_iterator_vtable files_reflog_iterator_vtable = {
        files_reflog_iterator_abort
 };
 
-static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_store)
+static struct ref_iterator *reflog_iterator_begin(struct ref_store *ref_store,
+                                                 const char *gitdir)
 {
        struct files_reflog_iterator *iter = xcalloc(1, sizeof(*iter));
        struct ref_iterator *ref_iterator = &iter->base;
+       struct strbuf sb = STRBUF_INIT;
 
-       /* Check validity (but we don't need the result): */
-       files_downcast(ref_store, 0, "reflog_iterator_begin");
+       base_ref_iterator_init(ref_iterator, &files_reflog_iterator_vtable, 0);
+       strbuf_addf(&sb, "%s/logs", gitdir);
+       iter->dir_iterator = dir_iterator_begin(sb.buf);
+       iter->ref_store = ref_store;
+       strbuf_release(&sb);
 
-       base_ref_iterator_init(ref_iterator, &files_reflog_iterator_vtable);
-       iter->dir_iterator = dir_iterator_begin(git_path("logs"));
        return ref_iterator;
 }
 
-static int ref_update_reject_duplicates(struct string_list *refnames,
-                                       struct strbuf *err)
+static enum iterator_selection reflog_iterator_select(
+       struct ref_iterator *iter_worktree,
+       struct ref_iterator *iter_common,
+       void *cb_data)
 {
-       int i, n = refnames->nr;
+       if (iter_worktree) {
+               /*
+                * We're a bit loose here. We probably should ignore
+                * common refs if they are accidentally added as
+                * per-worktree refs.
+                */
+               return ITER_SELECT_0;
+       } else if (iter_common) {
+               if (ref_type(iter_common->refname) == REF_TYPE_NORMAL)
+                       return ITER_SELECT_1;
 
-       assert(err);
+               /*
+                * The main ref store may contain main worktree's
+                * per-worktree refs, which should be ignored
+                */
+               return ITER_SKIP_1;
+       } else
+               return ITER_DONE;
+}
 
-       for (i = 1; i < n; i++)
-               if (!strcmp(refnames->items[i - 1].string, refnames->items[i].string)) {
-                       strbuf_addf(err,
-                                   "multiple updates for ref '%s' not allowed.",
-                                   refnames->items[i].string);
-                       return 1;
-               }
-       return 0;
+static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_store)
+{
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_READ,
+                              "reflog_iterator_begin");
+
+       if (!strcmp(refs->gitdir, refs->gitcommondir)) {
+               return reflog_iterator_begin(ref_store, refs->gitcommondir);
+       } else {
+               return merge_ref_iterator_begin(
+                       0,
+                       reflog_iterator_begin(ref_store, refs->gitdir),
+                       reflog_iterator_begin(ref_store, refs->gitcommondir),
+                       reflog_iterator_select, refs);
+       }
 }
 
 /*
@@ -3391,7 +2178,7 @@ static int split_head_update(struct ref_update *update,
        struct ref_update *new_update;
 
        if ((update->flags & REF_LOG_ONLY) ||
-           (update->flags & REF_ISPRUNING) ||
+           (update->flags & REF_IS_PRUNING) ||
            (update->flags & REF_UPDATE_VIA_HEAD))
                return 0;
 
@@ -3400,11 +2187,10 @@ static int split_head_update(struct ref_update *update,
 
        /*
         * First make sure that HEAD is not already in the
-        * transaction. This insertion is O(N) in the transaction
+        * transaction. This check is O(lg N) in the transaction
         * size, but it happens at most once per transaction.
         */
-       item = string_list_insert(affected_refnames, "HEAD");
-       if (item->util) {
+       if (string_list_has_string(affected_refnames, "HEAD")) {
                /* An entry already existed */
                strbuf_addf(err,
                            "multiple updates for 'HEAD' (including one "
@@ -3415,10 +2201,18 @@ static int split_head_update(struct ref_update *update,
 
        new_update = ref_transaction_add_update(
                        transaction, "HEAD",
-                       update->flags | REF_LOG_ONLY | REF_NODEREF,
-                       update->new_sha1, update->old_sha1,
+                       update->flags | REF_LOG_ONLY | REF_NO_DEREF,
+                       &update->new_oid, &update->old_oid,
                        update->msg);
 
+       /*
+        * Add "HEAD". This insertion is O(N) in the transaction
+        * size, but it happens at most once per transaction.
+        * Add new_update->refname instead of a literal "HEAD".
+        */
+       if (strcmp(new_update->refname, "HEAD"))
+               BUG("%s unexpectedly not 'HEAD'", new_update->refname);
+       item = string_list_insert(affected_refnames, new_update->refname);
        item->util = new_update;
 
        return 0;
@@ -3426,8 +2220,8 @@ static int split_head_update(struct ref_update *update,
 
 /*
  * update is for a symref that points at referent and doesn't have
- * REF_NODEREF set. Split it into two updates:
- * - The original update, but with REF_LOG_ONLY and REF_NODEREF set
+ * REF_NO_DEREF set. Split it into two updates:
+ * - The original update, but with REF_LOG_ONLY and REF_NO_DEREF set
  * - A new, separate update for the referent reference
  * Note that the new update will itself be subject to splitting when
  * the iteration gets to it.
@@ -3445,13 +2239,12 @@ static int split_symref_update(struct files_ref_store *refs,
 
        /*
         * First make sure that referent is not already in the
-        * transaction. This insertion is O(N) in the transaction
+        * transaction. This check is O(lg N) in the transaction
         * size, but it happens at most once per symref in a
         * transaction.
         */
-       item = string_list_insert(affected_refnames, referent);
-       if (item->util) {
-               /* An entry already existed */
+       if (string_list_has_string(affected_refnames, referent)) {
+               /* An entry already exists */
                strbuf_addf(err,
                            "multiple updates for '%s' (including one "
                            "via symref '%s') are not allowed",
@@ -3473,19 +2266,30 @@ static int split_symref_update(struct files_ref_store *refs,
 
        new_update = ref_transaction_add_update(
                        transaction, referent, new_flags,
-                       update->new_sha1, update->old_sha1,
+                       &update->new_oid, &update->old_oid,
                        update->msg);
 
        new_update->parent_update = update;
 
        /*
         * Change the symbolic ref update to log only. Also, it
-        * doesn't need to check its old SHA-1 value, as that will be
+        * doesn't need to check its old OID value, as that will be
         * done when new_update is processed.
         */
-       update->flags |= REF_LOG_ONLY | REF_NODEREF;
+       update->flags |= REF_LOG_ONLY | REF_NO_DEREF;
        update->flags &= ~REF_HAVE_OLD;
 
+       /*
+        * Add the referent. This insertion is O(N) in the transaction
+        * size, but it happens at most once per symref in a
+        * transaction. Make sure to add new_update->refname, which will
+        * be valid as long as affected_refnames is in use, and NOT
+        * referent, which might soon be freed by our caller.
+        */
+       item = string_list_insert(affected_refnames, new_update->refname);
+       if (item->util)
+               BUG("%s unexpectedly found in affected_refnames",
+                   new_update->refname);
        item->util = new_update;
 
        return 0;
@@ -3512,10 +2316,10 @@ static int check_old_oid(struct ref_update *update, struct object_id *oid,
                         struct strbuf *err)
 {
        if (!(update->flags & REF_HAVE_OLD) ||
-                  !hashcmp(oid->hash, update->old_sha1))
+                  !oidcmp(oid, &update->old_oid))
                return 0;
 
-       if (is_null_sha1(update->old_sha1))
+       if (is_null_oid(&update->old_oid))
                strbuf_addf(err, "cannot lock ref '%s': "
                            "reference already exists",
                            original_update_refname(update));
@@ -3523,13 +2327,13 @@ static int check_old_oid(struct ref_update *update, struct object_id *oid,
                strbuf_addf(err, "cannot lock ref '%s': "
                            "reference is missing but expected %s",
                            original_update_refname(update),
-                           sha1_to_hex(update->old_sha1));
+                           oid_to_hex(&update->old_oid));
        else
                strbuf_addf(err, "cannot lock ref '%s': "
                            "is at %s but expected %s",
                            original_update_refname(update),
                            oid_to_hex(oid),
-                           sha1_to_hex(update->old_sha1));
+                           oid_to_hex(&update->old_oid));
 
        return -1;
 }
@@ -3538,10 +2342,10 @@ static int check_old_oid(struct ref_update *update, struct object_id *oid,
  * Prepare for carrying out update:
  * - Lock the reference referred to by update.
  * - Read the reference under lock.
- * - Check that its old SHA-1 value (if specified) is correct, and in
+ * - Check that its old OID value (if specified) is correct, and in
  *   any case record it in update->lock->old_oid for later use when
  *   writing the reflog.
- * - If it is a symref update without REF_NODEREF, split it up into a
+ * - If it is a symref update without REF_NO_DEREF, split it up into a
  *   REF_LOG_ONLY update of the symref and add a separate update for
  *   the referent to transaction.
  * - If it is an update of head_ref, add a corresponding REF_LOG_ONLY
@@ -3556,20 +2360,20 @@ static int lock_ref_for_update(struct files_ref_store *refs,
 {
        struct strbuf referent = STRBUF_INIT;
        int mustexist = (update->flags & REF_HAVE_OLD) &&
-               !is_null_sha1(update->old_sha1);
-       int ret;
+               !is_null_oid(&update->old_oid);
+       int ret = 0;
        struct ref_lock *lock;
 
-       assert_main_repository(&refs->base, "lock_ref_for_update");
+       files_assert_main_repository(refs, "lock_ref_for_update");
 
-       if ((update->flags & REF_HAVE_NEW) && is_null_sha1(update->new_sha1))
+       if ((update->flags & REF_HAVE_NEW) && is_null_oid(&update->new_oid))
                update->flags |= REF_DELETING;
 
        if (head_ref) {
                ret = split_head_update(update, transaction, head_ref,
                                        affected_refnames, err);
                if (ret)
-                       return ret;
+                       goto out;
        }
 
        ret = lock_raw_ref(refs, update->refname, mustexist,
@@ -3583,34 +2387,37 @@ static int lock_ref_for_update(struct files_ref_store *refs,
                strbuf_addf(err, "cannot lock ref '%s': %s",
                            original_update_refname(update), reason);
                free(reason);
-               return ret;
+               goto out;
        }
 
        update->backend_data = lock;
 
        if (update->type & REF_ISSYMREF) {
-               if (update->flags & REF_NODEREF) {
+               if (update->flags & REF_NO_DEREF) {
                        /*
                         * We won't be reading the referent as part of
                         * the transaction, so we have to read it here
-                        * to record and possibly check old_sha1:
+                        * to record and possibly check old_oid:
                         */
-                       if (read_ref_full(referent.buf, 0,
-                                         lock->old_oid.hash, NULL)) {
+                       if (refs_read_ref_full(&refs->base,
+                                              referent.buf, 0,
+                                              &lock->old_oid, NULL)) {
                                if (update->flags & REF_HAVE_OLD) {
                                        strbuf_addf(err, "cannot lock ref '%s': "
                                                    "error reading reference",
                                                    original_update_refname(update));
-                                       return -1;
+                                       ret = TRANSACTION_GENERIC_ERROR;
+                                       goto out;
                                }
                        } else if (check_old_oid(update, &lock->old_oid, err)) {
-                               return TRANSACTION_GENERIC_ERROR;
+                               ret = TRANSACTION_GENERIC_ERROR;
+                               goto out;
                        }
                } else {
                        /*
                         * Create a new update for the reference this
                         * symref is pointing at. Also, we will record
-                        * and verify old_sha1 for this update as part
+                        * and verify old_oid for this update as part
                         * of processing the split-off update, so we
                         * don't have to do it here.
                         */
@@ -3618,17 +2425,19 @@ static int lock_ref_for_update(struct files_ref_store *refs,
                                                  referent.buf, transaction,
                                                  affected_refnames, err);
                        if (ret)
-                               return ret;
+                               goto out;
                }
        } else {
                struct ref_update *parent_update;
 
-               if (check_old_oid(update, &lock->old_oid, err))
-                       return TRANSACTION_GENERIC_ERROR;
+               if (check_old_oid(update, &lock->old_oid, err)) {
+                       ret = TRANSACTION_GENERIC_ERROR;
+                       goto out;
+               }
 
                /*
                 * If this update is happening indirectly because of a
-                * symref update, record the old SHA-1 in the parent
+                * symref update, record the old OID in the parent
                 * update:
                 */
                for (parent_update = update->parent_update;
@@ -3643,12 +2452,12 @@ static int lock_ref_for_update(struct files_ref_store *refs,
            !(update->flags & REF_DELETING) &&
            !(update->flags & REF_LOG_ONLY)) {
                if (!(update->type & REF_ISSYMREF) &&
-                   !hashcmp(lock->old_oid.hash, update->new_sha1)) {
+                   !oidcmp(&lock->old_oid, &update->new_oid)) {
                        /*
                         * The reference already has the desired
                         * value, so we don't need to write it.
                         */
-               } else if (write_ref_to_lockfile(lock, update->new_sha1,
+               } else if (write_ref_to_lockfile(lock, &update->new_oid,
                                                 err)) {
                        char *write_err = strbuf_detach(err, NULL);
 
@@ -3661,7 +2470,8 @@ static int lock_ref_for_update(struct files_ref_store *refs,
                                    "cannot update ref '%s': %s",
                                    update->refname, write_err);
                        free(write_err);
-                       return TRANSACTION_GENERIC_ERROR;
+                       ret = TRANSACTION_GENERIC_ERROR;
+                       goto out;
                } else {
                        update->flags |= REF_NEEDS_COMMIT;
                }
@@ -3672,51 +2482,100 @@ static int lock_ref_for_update(struct files_ref_store *refs,
                 * the lockfile is still open. Close it to
                 * free up the file descriptor:
                 */
-               if (close_ref(lock)) {
+               if (close_ref_gently(lock)) {
                        strbuf_addf(err, "couldn't close '%s.lock'",
                                    update->refname);
-                       return TRANSACTION_GENERIC_ERROR;
+                       ret = TRANSACTION_GENERIC_ERROR;
+                       goto out;
                }
        }
-       return 0;
+
+out:
+       strbuf_release(&referent);
+       return ret;
 }
 
-static int files_transaction_commit(struct ref_store *ref_store,
-                                   struct ref_transaction *transaction,
-                                   struct strbuf *err)
+struct files_transaction_backend_data {
+       struct ref_transaction *packed_transaction;
+       int packed_refs_locked;
+};
+
+/*
+ * Unlock any references in `transaction` that are still locked, and
+ * mark the transaction closed.
+ */
+static void files_transaction_cleanup(struct files_ref_store *refs,
+                                     struct ref_transaction *transaction)
+{
+       size_t i;
+       struct files_transaction_backend_data *backend_data =
+               transaction->backend_data;
+       struct strbuf err = STRBUF_INIT;
+
+       for (i = 0; i < transaction->nr; i++) {
+               struct ref_update *update = transaction->updates[i];
+               struct ref_lock *lock = update->backend_data;
+
+               if (lock) {
+                       unlock_ref(lock);
+                       update->backend_data = NULL;
+               }
+       }
+
+       if (backend_data->packed_transaction &&
+           ref_transaction_abort(backend_data->packed_transaction, &err)) {
+               error("error aborting transaction: %s", err.buf);
+               strbuf_release(&err);
+       }
+
+       if (backend_data->packed_refs_locked)
+               packed_refs_unlock(refs->packed_ref_store);
+
+       free(backend_data);
+
+       transaction->state = REF_TRANSACTION_CLOSED;
+}
+
+static int files_transaction_prepare(struct ref_store *ref_store,
+                                    struct ref_transaction *transaction,
+                                    struct strbuf *err)
 {
        struct files_ref_store *refs =
-               files_downcast(ref_store, 0, "ref_transaction_commit");
-       int ret = 0, i;
-       struct string_list refs_to_delete = STRING_LIST_INIT_NODUP;
-       struct string_list_item *ref_to_delete;
+               files_downcast(ref_store, REF_STORE_WRITE,
+                              "ref_transaction_prepare");
+       size_t i;
+       int ret = 0;
        struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
        char *head_ref = NULL;
        int head_type;
-       struct object_id head_oid;
+       struct files_transaction_backend_data *backend_data;
+       struct ref_transaction *packed_transaction = NULL;
 
        assert(err);
 
-       if (transaction->state != REF_TRANSACTION_OPEN)
-               die("BUG: commit called for transaction that is not open");
+       if (!transaction->nr)
+               goto cleanup;
 
-       if (!transaction->nr) {
-               transaction->state = REF_TRANSACTION_CLOSED;
-               return 0;
-       }
+       backend_data = xcalloc(1, sizeof(*backend_data));
+       transaction->backend_data = backend_data;
 
        /*
         * Fail if a refname appears more than once in the
         * transaction. (If we end up splitting up any updates using
         * split_symref_update() or split_head_update(), those
         * functions will check that the new updates don't have the
-        * same refname as any existing ones.)
+        * same refname as any existing ones.) Also fail if any of the
+        * updates use REF_IS_PRUNING without REF_NO_DEREF.
         */
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];
                struct string_list_item *item =
                        string_list_append(&affected_refnames, update->refname);
 
+               if ((update->flags & REF_IS_PRUNING) &&
+                   !(update->flags & REF_NO_DEREF))
+                       BUG("REF_IS_PRUNING set without REF_NO_DEREF");
+
                /*
                 * We store a pointer to update in item->util, but at
                 * the moment we never use the value of this field
@@ -3748,12 +2607,12 @@ static int files_transaction_commit(struct ref_store *ref_store,
         * head_ref within the transaction, then split_head_update()
         * arranges for the reflog of HEAD to be updated, too.
         */
-       head_ref = resolve_refdup("HEAD", RESOLVE_REF_NO_RECURSE,
-                                 head_oid.hash, &head_type);
+       head_ref = refs_resolve_refdup(ref_store, "HEAD",
+                                      RESOLVE_REF_NO_RECURSE,
+                                      NULL, &head_type);
 
        if (head_ref && !(head_type & REF_ISSYMREF)) {
-               free(head_ref);
-               head_ref = NULL;
+               FREE_AND_NULL(head_ref);
        }
 
        /*
@@ -3761,6 +2620,8 @@ static int files_transaction_commit(struct ref_store *ref_store,
         * that new values are valid, and write new values to the
         * lockfiles, ready to be activated. Only keep one lockfile
         * open at a time to avoid running out of file descriptors.
+        * Note that lock_ref_for_update() might append more updates
+        * to the transaction.
         */
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];
@@ -3769,8 +2630,94 @@ static int files_transaction_commit(struct ref_store *ref_store,
                                          head_ref, &affected_refnames, err);
                if (ret)
                        goto cleanup;
+
+               if (update->flags & REF_DELETING &&
+                   !(update->flags & REF_LOG_ONLY) &&
+                   !(update->flags & REF_IS_PRUNING)) {
+                       /*
+                        * This reference has to be deleted from
+                        * packed-refs if it exists there.
+                        */
+                       if (!packed_transaction) {
+                               packed_transaction = ref_store_transaction_begin(
+                                               refs->packed_ref_store, err);
+                               if (!packed_transaction) {
+                                       ret = TRANSACTION_GENERIC_ERROR;
+                                       goto cleanup;
+                               }
+
+                               backend_data->packed_transaction =
+                                       packed_transaction;
+                       }
+
+                       ref_transaction_add_update(
+                                       packed_transaction, update->refname,
+                                       REF_HAVE_NEW | REF_NO_DEREF,
+                                       &update->new_oid, NULL,
+                                       NULL);
+               }
+       }
+
+       if (packed_transaction) {
+               if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
+                       ret = TRANSACTION_GENERIC_ERROR;
+                       goto cleanup;
+               }
+               backend_data->packed_refs_locked = 1;
+
+               if (is_packed_transaction_needed(refs->packed_ref_store,
+                                                packed_transaction)) {
+                       ret = ref_transaction_prepare(packed_transaction, err);
+               } else {
+                       /*
+                        * We can skip rewriting the `packed-refs`
+                        * file. But we do need to leave it locked, so
+                        * that somebody else doesn't pack a reference
+                        * that we are trying to delete.
+                        */
+                       if (ref_transaction_abort(packed_transaction, err)) {
+                               ret = TRANSACTION_GENERIC_ERROR;
+                               goto cleanup;
+                       }
+                       backend_data->packed_transaction = NULL;
+               }
+       }
+
+cleanup:
+       free(head_ref);
+       string_list_clear(&affected_refnames, 0);
+
+       if (ret)
+               files_transaction_cleanup(refs, transaction);
+       else
+               transaction->state = REF_TRANSACTION_PREPARED;
+
+       return ret;
+}
+
+static int files_transaction_finish(struct ref_store *ref_store,
+                                   struct ref_transaction *transaction,
+                                   struct strbuf *err)
+{
+       struct files_ref_store *refs =
+               files_downcast(ref_store, 0, "ref_transaction_finish");
+       size_t i;
+       int ret = 0;
+       struct strbuf sb = STRBUF_INIT;
+       struct files_transaction_backend_data *backend_data;
+       struct ref_transaction *packed_transaction;
+
+
+       assert(err);
+
+       if (!transaction->nr) {
+               transaction->state = REF_TRANSACTION_CLOSED;
+               return 0;
        }
 
+       backend_data = transaction->backend_data;
+       packed_transaction = backend_data->packed_transaction;
+
        /* Perform updates first so live commits remain referenced */
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];
@@ -3778,9 +2725,12 @@ static int files_transaction_commit(struct ref_store *ref_store,
 
                if (update->flags & REF_NEEDS_COMMIT ||
                    update->flags & REF_LOG_ONLY) {
-                       if (log_ref_write(lock->ref_name, lock->old_oid.hash,
-                                         update->new_sha1,
-                                         update->msg, update->flags, err)) {
+                       if (files_log_ref_write(refs,
+                                               lock->ref_name,
+                                               &lock->old_oid,
+                                               &update->new_oid,
+                                               update->msg, update->flags,
+                                               err)) {
                                char *old_msg = strbuf_detach(err, NULL);
 
                                strbuf_addf(err, "cannot update the ref '%s': %s",
@@ -3803,45 +2753,99 @@ static int files_transaction_commit(struct ref_store *ref_store,
                        }
                }
        }
-       /* Perform deletes now that updates are safely completed */
+
+       /*
+        * Now that updates are safely completed, we can perform
+        * deletes. First delete the reflogs of any references that
+        * will be deleted, since (in the unexpected event of an
+        * error) leaving a reference without a reflog is less bad
+        * than leaving a reflog without a reference (the latter is a
+        * mildly invalid repository state):
+        */
+       for (i = 0; i < transaction->nr; i++) {
+               struct ref_update *update = transaction->updates[i];
+               if (update->flags & REF_DELETING &&
+                   !(update->flags & REF_LOG_ONLY) &&
+                   !(update->flags & REF_IS_PRUNING)) {
+                       strbuf_reset(&sb);
+                       files_reflog_path(refs, &sb, update->refname);
+                       if (!unlink_or_warn(sb.buf))
+                               try_remove_empty_parents(refs, update->refname,
+                                                        REMOVE_EMPTY_PARENTS_REFLOG);
+               }
+       }
+
+       /*
+        * Perform deletes now that updates are safely completed.
+        *
+        * First delete any packed versions of the references, while
+        * retaining the packed-refs lock:
+        */
+       if (packed_transaction) {
+               ret = ref_transaction_commit(packed_transaction, err);
+               ref_transaction_free(packed_transaction);
+               packed_transaction = NULL;
+               backend_data->packed_transaction = NULL;
+               if (ret)
+                       goto cleanup;
+       }
+
+       /* Now delete the loose versions of the references: */
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];
                struct ref_lock *lock = update->backend_data;
 
                if (update->flags & REF_DELETING &&
                    !(update->flags & REF_LOG_ONLY)) {
-                       if (delete_ref_loose(lock, update->type, err)) {
-                               ret = TRANSACTION_GENERIC_ERROR;
-                               goto cleanup;
+                       if (!(update->type & REF_ISPACKED) ||
+                           update->type & REF_ISSYMREF) {
+                               /* It is a loose reference. */
+                               strbuf_reset(&sb);
+                               files_ref_path(refs, &sb, lock->ref_name);
+                               if (unlink_or_msg(sb.buf, err)) {
+                                       ret = TRANSACTION_GENERIC_ERROR;
+                                       goto cleanup;
+                               }
+                               update->flags |= REF_DELETED_LOOSE;
                        }
-
-                       if (!(update->flags & REF_ISPRUNING))
-                               string_list_append(&refs_to_delete,
-                                                  lock->ref_name);
                }
        }
 
-       if (repack_without_refs(refs, &refs_to_delete, err)) {
-               ret = TRANSACTION_GENERIC_ERROR;
-               goto cleanup;
-       }
-       for_each_string_list_item(ref_to_delete, &refs_to_delete)
-               unlink_or_warn(git_path("logs/%s", ref_to_delete->string));
        clear_loose_ref_cache(refs);
 
 cleanup:
-       transaction->state = REF_TRANSACTION_CLOSED;
+       files_transaction_cleanup(refs, transaction);
 
-       for (i = 0; i < transaction->nr; i++)
-               if (transaction->updates[i]->backend_data)
-                       unlock_ref(transaction->updates[i]->backend_data);
-       string_list_clear(&refs_to_delete, 0);
-       free(head_ref);
-       string_list_clear(&affected_refnames, 0);
+       for (i = 0; i < transaction->nr; i++) {
+               struct ref_update *update = transaction->updates[i];
+
+               if (update->flags & REF_DELETED_LOOSE) {
+                       /*
+                        * The loose reference was deleted. Delete any
+                        * empty parent directories. (Note that this
+                        * can only work because we have already
+                        * removed the lockfile.)
+                        */
+                       try_remove_empty_parents(refs, update->refname,
+                                                REMOVE_EMPTY_PARENTS_REF);
+               }
+       }
 
+       strbuf_release(&sb);
        return ret;
 }
 
+static int files_transaction_abort(struct ref_store *ref_store,
+                                  struct ref_transaction *transaction,
+                                  struct strbuf *err)
+{
+       struct files_ref_store *refs =
+               files_downcast(ref_store, 0, "ref_transaction_abort");
+
+       files_transaction_cleanup(refs, transaction);
+       return 0;
+}
+
 static int ref_present(const char *refname,
                       const struct object_id *oid, int flags, void *cb_data)
 {
@@ -3855,14 +2859,17 @@ static int files_initial_transaction_commit(struct ref_store *ref_store,
                                            struct strbuf *err)
 {
        struct files_ref_store *refs =
-               files_downcast(ref_store, 0, "initial_ref_transaction_commit");
-       int ret = 0, i;
+               files_downcast(ref_store, REF_STORE_WRITE,
+                              "initial_ref_transaction_commit");
+       size_t i;
+       int ret = 0;
        struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
+       struct ref_transaction *packed_transaction = NULL;
 
        assert(err);
 
        if (transaction->state != REF_TRANSACTION_OPEN)
-               die("BUG: commit called for transaction that is not open");
+               BUG("commit called for transaction that is not open");
 
        /* Fail if a refname appears more than once in the transaction: */
        for (i = 0; i < transaction->nr; i++)
@@ -3886,46 +2893,52 @@ static int files_initial_transaction_commit(struct ref_store *ref_store,
         * so here we really only check that none of the references
         * that we are creating already exists.
         */
-       if (for_each_rawref(ref_present, &affected_refnames))
-               die("BUG: initial ref transaction called with existing refs");
+       if (refs_for_each_rawref(&refs->base, ref_present,
+                                &affected_refnames))
+               BUG("initial ref transaction called with existing refs");
+
+       packed_transaction = ref_store_transaction_begin(refs->packed_ref_store, err);
+       if (!packed_transaction) {
+               ret = TRANSACTION_GENERIC_ERROR;
+               goto cleanup;
+       }
 
        for (i = 0; i < transaction->nr; i++) {
                struct ref_update *update = transaction->updates[i];
 
                if ((update->flags & REF_HAVE_OLD) &&
-                   !is_null_sha1(update->old_sha1))
-                       die("BUG: initial ref transaction with old_sha1 set");
-               if (verify_refname_available(update->refname,
-                                            &affected_refnames, NULL,
-                                            err)) {
+                   !is_null_oid(&update->old_oid))
+                       BUG("initial ref transaction with old_sha1 set");
+               if (refs_verify_refname_available(&refs->base, update->refname,
+                                                 &affected_refnames, NULL,
+                                                 err)) {
                        ret = TRANSACTION_NAME_CONFLICT;
                        goto cleanup;
                }
+
+               /*
+                * Add a reference creation for this reference to the
+                * packed-refs transaction:
+                */
+               ref_transaction_add_update(packed_transaction, update->refname,
+                                          update->flags & ~REF_HAVE_OLD,
+                                          &update->new_oid, &update->old_oid,
+                                          NULL);
        }
 
-       if (lock_packed_refs(refs, 0)) {
-               strbuf_addf(err, "unable to lock packed-refs file: %s",
-                           strerror(errno));
+       if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
                ret = TRANSACTION_GENERIC_ERROR;
                goto cleanup;
        }
 
-       for (i = 0; i < transaction->nr; i++) {
-               struct ref_update *update = transaction->updates[i];
-
-               if ((update->flags & REF_HAVE_NEW) &&
-                   !is_null_sha1(update->new_sha1))
-                       add_packed_ref(refs, update->refname, update->new_sha1);
-       }
-
-       if (commit_packed_refs(refs)) {
-               strbuf_addf(err, "unable to commit packed-refs file: %s",
-                           strerror(errno));
+       if (initial_ref_transaction_commit(packed_transaction, err)) {
                ret = TRANSACTION_GENERIC_ERROR;
-               goto cleanup;
        }
 
+       packed_refs_unlock(refs->packed_ref_store);
 cleanup:
+       if (packed_transaction)
+               ref_transaction_free(packed_transaction);
        transaction->state = REF_TRANSACTION_CLOSED;
        string_list_clear(&affected_refnames, 0);
        return ret;
@@ -3936,20 +2949,20 @@ struct expire_reflog_cb {
        reflog_expiry_should_prune_fn *should_prune_fn;
        void *policy_cb;
        FILE *newlog;
-       unsigned char last_kept_sha1[20];
+       struct object_id last_kept_oid;
 };
 
-static int expire_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
-                            const char *email, unsigned long timestamp, int tz,
+static int expire_reflog_ent(struct object_id *ooid, struct object_id *noid,
+                            const char *email, timestamp_t timestamp, int tz,
                             const char *message, void *cb_data)
 {
        struct expire_reflog_cb *cb = cb_data;
        struct expire_reflog_policy_cb *policy_cb = cb->policy_cb;
 
        if (cb->flags & EXPIRE_REFLOGS_REWRITE)
-               osha1 = cb->last_kept_sha1;
+               ooid = &cb->last_kept_oid;
 
-       if ((*cb->should_prune_fn)(osha1, nsha1, email, timestamp, tz,
+       if ((*cb->should_prune_fn)(ooid, noid, email, timestamp, tz,
                                   message, policy_cb)) {
                if (!cb->newlog)
                        printf("would prune %s", message);
@@ -3957,10 +2970,10 @@ static int expire_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
                        printf("prune %s", message);
        } else {
                if (cb->newlog) {
-                       fprintf(cb->newlog, "%s %s %s %lu %+05d\t%s",
-                               sha1_to_hex(osha1), sha1_to_hex(nsha1),
+                       fprintf(cb->newlog, "%s %s %s %"PRItime" %+05d\t%s",
+                               oid_to_hex(ooid), oid_to_hex(noid),
                                email, timestamp, tz, message);
-                       hashcpy(cb->last_kept_sha1, nsha1);
+                       oidcpy(&cb->last_kept_oid, noid);
                }
                if (cb->flags & EXPIRE_REFLOGS_VERBOSE)
                        printf("keep %s", message);
@@ -3969,7 +2982,7 @@ static int expire_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
 }
 
 static int files_reflog_expire(struct ref_store *ref_store,
-                              const char *refname, const unsigned char *sha1,
+                              const char *refname, const struct object_id *oid,
                               unsigned int flags,
                               reflog_expiry_prepare_fn prepare_fn,
                               reflog_expiry_should_prune_fn should_prune_fn,
@@ -3977,10 +2990,11 @@ static int files_reflog_expire(struct ref_store *ref_store,
                               void *policy_cb_data)
 {
        struct files_ref_store *refs =
-               files_downcast(ref_store, 0, "reflog_expire");
-       static struct lock_file reflog_lock;
+               files_downcast(ref_store, REF_STORE_WRITE, "reflog_expire");
+       struct lock_file reflog_lock = LOCK_INIT;
        struct expire_reflog_cb cb;
        struct ref_lock *lock;
+       struct strbuf log_file_sb = STRBUF_INIT;
        char *log_file;
        int status = 0;
        int type;
@@ -3996,20 +3010,21 @@ static int files_reflog_expire(struct ref_store *ref_store,
         * reference itself, plus we might need to update the
         * reference if --updateref was specified:
         */
-       lock = lock_ref_sha1_basic(refs, refname, sha1,
-                                  NULL, NULL, REF_NODEREF,
-                                  &type, &err);
+       lock = lock_ref_oid_basic(refs, refname, oid,
+                                 NULL, NULL, REF_NO_DEREF,
+                                 &type, &err);
        if (!lock) {
                error("cannot lock ref '%s': %s", refname, err.buf);
                strbuf_release(&err);
                return -1;
        }
-       if (!reflog_exists(refname)) {
+       if (!refs_reflog_exists(ref_store, refname)) {
                unlock_ref(lock);
                return 0;
        }
 
-       log_file = git_pathdup("logs/%s", refname);
+       files_reflog_path(refs, &log_file_sb, refname);
+       log_file = strbuf_detach(&log_file_sb, NULL);
        if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
                /*
                 * Even though holding $GIT_DIR/logs/$reflog.lock has
@@ -4033,8 +3048,8 @@ static int files_reflog_expire(struct ref_store *ref_store,
                }
        }
 
-       (*prepare_fn)(refname, sha1, cb.policy_cb);
-       for_each_reflog_ent(refname, expire_reflog_ent, &cb);
+       (*prepare_fn)(refname, oid, cb.policy_cb);
+       refs_for_each_reflog_ent(ref_store, refname, expire_reflog_ent, &cb);
        (*cleanup_fn)(cb.policy_cb);
 
        if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
@@ -4047,18 +3062,19 @@ static int files_reflog_expire(struct ref_store *ref_store,
                 */
                int update = (flags & EXPIRE_REFLOGS_UPDATE_REF) &&
                        !(type & REF_ISSYMREF) &&
-                       !is_null_sha1(cb.last_kept_sha1);
+                       !is_null_oid(&cb.last_kept_oid);
 
-               if (close_lock_file(&reflog_lock)) {
+               if (close_lock_file_gently(&reflog_lock)) {
                        status |= error("couldn't write %s: %s", log_file,
                                        strerror(errno));
+                       rollback_lock_file(&reflog_lock);
                } else if (update &&
-                          (write_in_full(get_lock_file_fd(lock->lk),
-                               sha1_to_hex(cb.last_kept_sha1), 40) != 40 ||
-                           write_str_in_full(get_lock_file_fd(lock->lk), "\n") != 1 ||
-                           close_ref(lock) < 0)) {
+                          (write_in_full(get_lock_file_fd(&lock->lk),
+                               oid_to_hex(&cb.last_kept_oid), GIT_SHA1_HEXSZ) < 0 ||
+                           write_str_in_full(get_lock_file_fd(&lock->lk), "\n") < 0 ||
+                           close_ref_gently(lock) < 0)) {
                        status |= error("couldn't write %s",
-                                       get_lock_file_path(lock->lk));
+                                       get_lock_file_path(&lock->lk));
                        rollback_lock_file(&reflog_lock);
                } else if (commit_lock_file(&reflog_lock)) {
                        status |= error("unable to write reflog '%s' (%s)",
@@ -4080,18 +3096,21 @@ static int files_reflog_expire(struct ref_store *ref_store,
 
 static int files_init_db(struct ref_store *ref_store, struct strbuf *err)
 {
-       /* Check validity (but we don't need the result): */
-       files_downcast(ref_store, 0, "init_db");
+       struct files_ref_store *refs =
+               files_downcast(ref_store, REF_STORE_WRITE, "init_db");
+       struct strbuf sb = STRBUF_INIT;
 
        /*
         * Create .git/refs/{heads,tags}
         */
-       safe_create_dir(git_path("refs/heads"), 1);
-       safe_create_dir(git_path("refs/tags"), 1);
-       if (get_shared_repository()) {
-               adjust_shared_perm(git_path("refs/heads"));
-               adjust_shared_perm(git_path("refs/tags"));
-       }
+       files_ref_path(refs, &sb, "refs/heads");
+       safe_create_dir(sb.buf, 1);
+
+       strbuf_reset(&sb);
+       files_ref_path(refs, &sb, "refs/tags");
+       safe_create_dir(sb.buf, 1);
+
+       strbuf_release(&sb);
        return 0;
 }
 
@@ -4100,18 +3119,19 @@ struct ref_storage_be refs_be_files = {
        "files",
        files_ref_store_create,
        files_init_db,
-       files_transaction_commit,
+       files_transaction_prepare,
+       files_transaction_finish,
+       files_transaction_abort,
        files_initial_transaction_commit,
 
        files_pack_refs,
-       files_peel_ref,
        files_create_symref,
        files_delete_refs,
        files_rename_ref,
+       files_copy_ref,
 
        files_ref_iterator_begin,
        files_read_raw_ref,
-       files_verify_refname_available,
 
        files_reflog_iterator_begin,
        files_for_each_reflog_ent,