refs/files-backend.c

   1 #include "../cache.h"
   2 #include "../config.h"
   3 #include "../refs.h"
   4 #include "refs-internal.h"
   5 #include "ref-cache.h"
   6 #include "../iterator.h"
   7 #include "../dir-iterator.h"
   8 #include "../lockfile.h"
   9 #include "../object.h"
  10 #include "../dir.h"
  11
  12 struct ref_lock {
  13         char *ref_name;
  14         struct lock_file *lk;
  15         struct object_id old_oid;
  16 };
  17
  18 /*
  19  * Return true if refname, which has the specified oid and flags, can
  20  * be resolved to an object in the database. If the referred-to object
  21  * does not exist, emit a warning and return false.
  22  */
  23 static int ref_resolves_to_object(const char *refname,
  24                                   const struct object_id *oid,
  25                                   unsigned int flags)
  26 {
  27         if (flags & REF_ISBROKEN)
  28                 return 0;
  29         if (!has_sha1_file(oid->hash)) {
  30                 error("%s does not point to a valid object!", refname);
  31                 return 0;
  32         }
  33         return 1;
  34 }
  35
  36 struct packed_ref_cache {
  37         struct ref_cache *cache;
  38
  39         /*
  40          * Count of references to the data structure in this instance,
  41          * including the pointer from files_ref_store::packed if any.
  42          * The data will not be freed as long as the reference count
  43          * is nonzero.
  44          */
  45         unsigned int referrers;
  46
  47         /* The metadata from when this packed-refs cache was read */
  48         struct stat_validity validity;
  49 };
  50
  51 /*
  52  * Future: need to be in "struct repository"
  53  * when doing a full libification.
  54  */
  55 struct files_ref_store {
  56         struct ref_store base;
  57         unsigned int store_flags;
  58
  59         char *gitdir;
  60         char *gitcommondir;
  61         char *packed_refs_path;
  62
  63         struct ref_cache *loose;
  64         struct packed_ref_cache *packed;
  65
  66         /*
  67          * Lock used for the "packed-refs" file. Note that this (and
  68          * thus the enclosing `files_ref_store`) must not be freed.
  69          */
  70         struct lock_file packed_refs_lock;
  71 };
  72
  73 /*
  74  * Increment the reference count of *packed_refs.
  75  */
  76 static void acquire_packed_ref_cache(struct packed_ref_cache *packed_refs)
  77 {
  78         packed_refs->referrers++;
  79 }
  80
  81 /*
  82  * Decrease the reference count of *packed_refs.  If it goes to zero,
  83  * free *packed_refs and return true; otherwise return false.
  84  */
  85 static int release_packed_ref_cache(struct packed_ref_cache *packed_refs)
  86 {
  87         if (!--packed_refs->referrers) {
  88                 free_ref_cache(packed_refs->cache);
  89                 stat_validity_clear(&packed_refs->validity);
  90                 free(packed_refs);
  91                 return 1;
  92         } else {
  93                 return 0;
  94         }
  95 }
  96
  97 static void clear_packed_ref_cache(struct files_ref_store *refs)
  98 {
  99         if (refs->packed) {
 100                 struct packed_ref_cache *packed_refs = refs->packed;
 101
 102                 if (is_lock_file_locked(&refs->packed_refs_lock))
 103                         die("BUG: packed-ref cache cleared while locked");
 104                 refs->packed = NULL;
 105                 release_packed_ref_cache(packed_refs);
 106         }
 107 }
 108
 109 static void clear_loose_ref_cache(struct files_ref_store *refs)
 110 {
 111         if (refs->loose) {
 112                 free_ref_cache(refs->loose);
 113                 refs->loose = NULL;
 114         }
 115 }
 116
 117 /*
 118  * Create a new submodule ref cache and add it to the internal
 119  * set of caches.
 120  */
 121 static struct ref_store *files_ref_store_create(const char *gitdir,
 122                                                 unsigned int flags)
 123 {
 124         struct files_ref_store *refs = xcalloc(1, sizeof(*refs));
 125         struct ref_store *ref_store = (struct ref_store *)refs;
 126         struct strbuf sb = STRBUF_INIT;
 127
 128         base_ref_store_init(ref_store, &refs_be_files);
 129         refs->store_flags = flags;
 130
 131         refs->gitdir = xstrdup(gitdir);
 132         get_common_dir_noenv(&sb, gitdir);
 133         refs->gitcommondir = strbuf_detach(&sb, NULL);
 134         strbuf_addf(&sb, "%s/packed-refs", refs->gitcommondir);
 135         refs->packed_refs_path = strbuf_detach(&sb, NULL);
 136
 137         return ref_store;
 138 }
 139
 140 /*
 141  * Die if refs is not the main ref store. caller is used in any
 142  * necessary error messages.
 143  */
 144 static void files_assert_main_repository(struct files_ref_store *refs,
 145                                          const char *caller)
 146 {
 147         if (refs->store_flags & REF_STORE_MAIN)
 148                 return;
 149
 150         die("BUG: operation %s only allowed for main ref store", caller);
 151 }
 152
 153 /*
 154  * Downcast ref_store to files_ref_store. Die if ref_store is not a
 155  * files_ref_store. required_flags is compared with ref_store's
 156  * store_flags to ensure the ref_store has all required capabilities.
 157  * "caller" is used in any necessary error messages.
 158  */
 159 static struct files_ref_store *files_downcast(struct ref_store *ref_store,
 160                                               unsigned int required_flags,
 161                                               const char *caller)
 162 {
 163         struct files_ref_store *refs;
 164
 165         if (ref_store->be != &refs_be_files)
 166                 die("BUG: ref_store is type \"%s\" not \"files\" in %s",
 167                     ref_store->be->name, caller);
 168
 169         refs = (struct files_ref_store *)ref_store;
 170
 171         if ((refs->store_flags & required_flags) != required_flags)
 172                 die("BUG: operation %s requires abilities 0x%x, but only have 0x%x",
 173                     caller, required_flags, refs->store_flags);
 174
 175         return refs;
 176 }
 177
 178 /* The length of a peeled reference line in packed-refs, including EOL: */
 179 #define PEELED_LINE_LENGTH 42
 180
 181 /*
 182  * The packed-refs header line that we write out.  Perhaps other
 183  * traits will be added later.  The trailing space is required.
 184  */
 185 static const char PACKED_REFS_HEADER[] =
 186         "# pack-refs with: peeled fully-peeled \n";
 187
 188 /*
 189  * Parse one line from a packed-refs file.  Write the SHA1 to sha1.
 190  * Return a pointer to the refname within the line (null-terminated),
 191  * or NULL if there was a problem.
 192  */
 193 static const char *parse_ref_line(struct strbuf *line, struct object_id *oid)
 194 {
 195         const char *ref;
 196
 197         if (parse_oid_hex(line->buf, oid, &ref) < 0)
 198                 return NULL;
 199         if (!isspace(*ref++))
 200                 return NULL;
 201
 202         if (isspace(*ref))
 203                 return NULL;
 204
 205         if (line->buf[line->len - 1] != '\n')
 206                 return NULL;
 207         line->buf[--line->len] = 0;
 208
 209         return ref;
 210 }
 211
 212 /*
 213  * Read from `packed_refs_file` into a newly-allocated
 214  * `packed_ref_cache` and return it. The return value will already
 215  * have its reference count incremented.
 216  *
 217  * A comment line of the form "# pack-refs with: " may contain zero or
 218  * more traits. We interpret the traits as follows:
 219  *
 220  *   No traits:
 221  *
 222  *      Probably no references are peeled. But if the file contains a
 223  *      peeled value for a reference, we will use it.
 224  *
 225  *   peeled:
 226  *
 227  *      References under "refs/tags/", if they *can* be peeled, *are*
 228  *      peeled in this file. References outside of "refs/tags/" are
 229  *      probably not peeled even if they could have been, but if we find
 230  *      a peeled value for such a reference we will use it.
 231  *
 232  *   fully-peeled:
 233  *
 234  *      All references in the file that can be peeled are peeled.
 235  *      Inversely (and this is more important), any references in the
 236  *      file for which no peeled value is recorded is not peelable. This
 237  *      trait should typically be written alongside "peeled" for
 238  *      compatibility with older clients, but we do not require it
 239  *      (i.e., "peeled" is a no-op if "fully-peeled" is set).
 240  */
 241 static struct packed_ref_cache *read_packed_refs(const char *packed_refs_file)
 242 {
 243         FILE *f;
 244         struct packed_ref_cache *packed_refs = xcalloc(1, sizeof(*packed_refs));
 245         struct ref_entry *last = NULL;
 246         struct strbuf line = STRBUF_INIT;
 247         enum { PEELED_NONE, PEELED_TAGS, PEELED_FULLY } peeled = PEELED_NONE;
 248         struct ref_dir *dir;
 249
 250         acquire_packed_ref_cache(packed_refs);
 251         packed_refs->cache = create_ref_cache(NULL, NULL);
 252         packed_refs->cache->root->flag &= ~REF_INCOMPLETE;
 253
 254         f = fopen(packed_refs_file, "r");
 255         if (!f) {
 256                 if (errno == ENOENT) {
 257                         /*
 258                          * This is OK; it just means that no
 259                          * "packed-refs" file has been written yet,
 260                          * which is equivalent to it being empty.
 261                          */
 262                         return packed_refs;
 263                 } else {
 264                         die_errno("couldn't read %s", packed_refs_file);
 265                 }
 266         }
 267
 268         stat_validity_update(&packed_refs->validity, fileno(f));
 269
 270         dir = get_ref_dir(packed_refs->cache->root);
 271         while (strbuf_getwholeline(&line, f, '\n') != EOF) {
 272                 struct object_id oid;
 273                 const char *refname;
 274                 const char *traits;
 275
 276                 if (skip_prefix(line.buf, "# pack-refs with:", &traits)) {
 277                         if (strstr(traits, " fully-peeled "))
 278                                 peeled = PEELED_FULLY;
 279                         else if (strstr(traits, " peeled "))
 280                                 peeled = PEELED_TAGS;
 281                         /* perhaps other traits later as well */
 282                         continue;
 283                 }
 284
 285                 refname = parse_ref_line(&line, &oid);
 286                 if (refname) {
 287                         int flag = REF_ISPACKED;
 288
 289                         if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
 290                                 if (!refname_is_safe(refname))
 291                                         die("packed refname is dangerous: %s", refname);
 292                                 oidclr(&oid);
 293                                 flag |= REF_BAD_NAME | REF_ISBROKEN;
 294                         }
 295                         last = create_ref_entry(refname, &oid, flag);
 296                         if (peeled == PEELED_FULLY ||
 297                             (peeled == PEELED_TAGS && starts_with(refname, "refs/tags/")))
 298                                 last->flag |= REF_KNOWS_PEELED;
 299                         add_ref_entry(dir, last);
 300                         continue;
 301                 }
 302                 if (last &&
 303                     line.buf[0] == '^' &&
 304                     line.len == PEELED_LINE_LENGTH &&
 305                     line.buf[PEELED_LINE_LENGTH - 1] == '\n' &&
 306                     !get_oid_hex(line.buf + 1, &oid)) {
 307                         oidcpy(&last->u.value.peeled, &oid);
 308                         /*
 309                          * Regardless of what the file header said,
 310                          * we definitely know the value of *this*
 311                          * reference:
 312                          */
 313                         last->flag |= REF_KNOWS_PEELED;
 314                 }
 315         }
 316
 317         fclose(f);
 318         strbuf_release(&line);
 319
 320         return packed_refs;
 321 }
 322
 323 static const char *files_packed_refs_path(struct files_ref_store *refs)
 324 {
 325         return refs->packed_refs_path;
 326 }
 327
 328 static void files_reflog_path(struct files_ref_store *refs,
 329                               struct strbuf *sb,
 330                               const char *refname)
 331 {
 332         if (!refname) {
 333                 /*
 334                  * FIXME: of course this is wrong in multi worktree
 335                  * setting. To be fixed real soon.
 336                  */
 337                 strbuf_addf(sb, "%s/logs", refs->gitcommondir);
 338                 return;
 339         }
 340
 341         switch (ref_type(refname)) {
 342         case REF_TYPE_PER_WORKTREE:
 343         case REF_TYPE_PSEUDOREF:
 344                 strbuf_addf(sb, "%s/logs/%s", refs->gitdir, refname);
 345                 break;
 346         case REF_TYPE_NORMAL:
 347                 strbuf_addf(sb, "%s/logs/%s", refs->gitcommondir, refname);
 348                 break;
 349         default:
 350                 die("BUG: unknown ref type %d of ref %s",
 351                     ref_type(refname), refname);
 352         }
 353 }
 354
 355 static void files_ref_path(struct files_ref_store *refs,
 356                            struct strbuf *sb,
 357                            const char *refname)
 358 {
 359         switch (ref_type(refname)) {
 360         case REF_TYPE_PER_WORKTREE:
 361         case REF_TYPE_PSEUDOREF:
 362                 strbuf_addf(sb, "%s/%s", refs->gitdir, refname);
 363                 break;
 364         case REF_TYPE_NORMAL:
 365                 strbuf_addf(sb, "%s/%s", refs->gitcommondir, refname);
 366                 break;
 367         default:
 368                 die("BUG: unknown ref type %d of ref %s",
 369                     ref_type(refname), refname);
 370         }
 371 }
 372
 373 /*
 374  * Check that the packed refs cache (if any) still reflects the
 375  * contents of the file. If not, clear the cache.
 376  */
 377 static void validate_packed_ref_cache(struct files_ref_store *refs)
 378 {
 379         if (refs->packed &&
 380             !stat_validity_check(&refs->packed->validity,
 381                                  files_packed_refs_path(refs)))
 382                 clear_packed_ref_cache(refs);
 383 }
 384
 385 /*
 386  * Get the packed_ref_cache for the specified files_ref_store,
 387  * creating and populating it if it hasn't been read before or if the
 388  * file has been changed (according to its `validity` field) since it
 389  * was last read. On the other hand, if we hold the lock, then assume
 390  * that the file hasn't been changed out from under us, so skip the
 391  * extra `stat()` call in `stat_validity_check()`.
 392  */
 393 static struct packed_ref_cache *get_packed_ref_cache(struct files_ref_store *refs)
 394 {
 395         const char *packed_refs_file = files_packed_refs_path(refs);
 396
 397         if (!is_lock_file_locked(&refs->packed_refs_lock))
 398                 validate_packed_ref_cache(refs);
 399
 400         if (!refs->packed)
 401                 refs->packed = read_packed_refs(packed_refs_file);
 402
 403         return refs->packed;
 404 }
 405
 406 static struct ref_dir *get_packed_ref_dir(struct packed_ref_cache *packed_ref_cache)
 407 {
 408         return get_ref_dir(packed_ref_cache->cache->root);
 409 }
 410
 411 static struct ref_dir *get_packed_refs(struct files_ref_store *refs)
 412 {
 413         return get_packed_ref_dir(get_packed_ref_cache(refs));
 414 }
 415
 416 /*
 417  * Add a reference to the in-memory packed reference cache.  This may
 418  * only be called while the packed-refs file is locked (see
 419  * lock_packed_refs()).  To actually write the packed-refs file, call
 420  * commit_packed_refs().
 421  */
 422 static void add_packed_ref(struct files_ref_store *refs,
 423                            const char *refname, const struct object_id *oid)
 424 {
 425         struct packed_ref_cache *packed_ref_cache = get_packed_ref_cache(refs);
 426
 427         if (!is_lock_file_locked(&refs->packed_refs_lock))
 428                 die("BUG: packed refs not locked");
 429
 430         if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
 431                 die("Reference has invalid format: '%s'", refname);
 432
 433         add_ref_entry(get_packed_ref_dir(packed_ref_cache),
 434                       create_ref_entry(refname, oid, REF_ISPACKED));
 435 }
 436
 437 /*
 438  * Read the loose references from the namespace dirname into dir
 439  * (without recursing).  dirname must end with '/'.  dir must be the
 440  * directory entry corresponding to dirname.
 441  */
 442 static void loose_fill_ref_dir(struct ref_store *ref_store,
 443                                struct ref_dir *dir, const char *dirname)
 444 {
 445         struct files_ref_store *refs =
 446                 files_downcast(ref_store, REF_STORE_READ, "fill_ref_dir");
 447         DIR *d;
 448         struct dirent *de;
 449         int dirnamelen = strlen(dirname);
 450         struct strbuf refname;
 451         struct strbuf path = STRBUF_INIT;
 452         size_t path_baselen;
 453
 454         files_ref_path(refs, &path, dirname);
 455         path_baselen = path.len;
 456
 457         d = opendir(path.buf);
 458         if (!d) {
 459                 strbuf_release(&path);
 460                 return;
 461         }
 462
 463         strbuf_init(&refname, dirnamelen + 257);
 464         strbuf_add(&refname, dirname, dirnamelen);
 465
 466         while ((de = readdir(d)) != NULL) {
 467                 struct object_id oid;
 468                 struct stat st;
 469                 int flag;
 470
 471                 if (de->d_name[0] == '.')
 472                         continue;
 473                 if (ends_with(de->d_name, ".lock"))
 474                         continue;
 475                 strbuf_addstr(&refname, de->d_name);
 476                 strbuf_addstr(&path, de->d_name);
 477                 if (stat(path.buf, &st) < 0) {
 478                         ; /* silently ignore */
 479                 } else if (S_ISDIR(st.st_mode)) {
 480                         strbuf_addch(&refname, '/');
 481                         add_entry_to_dir(dir,
 482                                          create_dir_entry(dir->cache, refname.buf,
 483                                                           refname.len, 1));
 484                 } else {
 485                         if (!refs_resolve_ref_unsafe(&refs->base,
 486                                                      refname.buf,
 487                                                      RESOLVE_REF_READING,
 488                                                      oid.hash, &flag)) {
 489                                 oidclr(&oid);
 490                                 flag |= REF_ISBROKEN;
 491                         } else if (is_null_oid(&oid)) {
 492                                 /*
 493                                  * It is so astronomically unlikely
 494                                  * that NULL_SHA1 is the SHA-1 of an
 495                                  * actual object that we consider its
 496                                  * appearance in a loose reference
 497                                  * file to be repo corruption
 498                                  * (probably due to a software bug).
 499                                  */
 500                                 flag |= REF_ISBROKEN;
 501                         }
 502
 503                         if (check_refname_format(refname.buf,
 504                                                  REFNAME_ALLOW_ONELEVEL)) {
 505                                 if (!refname_is_safe(refname.buf))
 506                                         die("loose refname is dangerous: %s", refname.buf);
 507                                 oidclr(&oid);
 508                                 flag |= REF_BAD_NAME | REF_ISBROKEN;
 509                         }
 510                         add_entry_to_dir(dir,
 511                                          create_ref_entry(refname.buf, &oid, flag));
 512                 }
 513                 strbuf_setlen(&refname, dirnamelen);
 514                 strbuf_setlen(&path, path_baselen);
 515         }
 516         strbuf_release(&refname);
 517         strbuf_release(&path);
 518         closedir(d);
 519
 520         /*
 521          * Manually add refs/bisect, which, being per-worktree, might
 522          * not appear in the directory listing for refs/ in the main
 523          * repo.
 524          */
 525         if (!strcmp(dirname, "refs/")) {
 526                 int pos = search_ref_dir(dir, "refs/bisect/", 12);
 527
 528                 if (pos < 0) {
 529                         struct ref_entry *child_entry = create_dir_entry(
 530                                         dir->cache, "refs/bisect/", 12, 1);
 531                         add_entry_to_dir(dir, child_entry);
 532                 }
 533         }
 534 }
 535
 536 static struct ref_cache *get_loose_ref_cache(struct files_ref_store *refs)
 537 {
 538         if (!refs->loose) {
 539                 /*
 540                  * Mark the top-level directory complete because we
 541                  * are about to read the only subdirectory that can
 542                  * hold references:
 543                  */
 544                 refs->loose = create_ref_cache(&refs->base, loose_fill_ref_dir);
 545
 546                 /* We're going to fill the top level ourselves: */
 547                 refs->loose->root->flag &= ~REF_INCOMPLETE;
 548
 549                 /*
 550                  * Add an incomplete entry for "refs/" (to be filled
 551                  * lazily):
 552                  */
 553                 add_entry_to_dir(get_ref_dir(refs->loose->root),
 554                                  create_dir_entry(refs->loose, "refs/", 5, 1));
 555         }
 556         return refs->loose;
 557 }
 558
 559 /*
 560  * Return the ref_entry for the given refname from the packed
 561  * references.  If it does not exist, return NULL.
 562  */
 563 static struct ref_entry *get_packed_ref(struct files_ref_store *refs,
 564                                         const char *refname)
 565 {
 566         return find_ref_entry(get_packed_refs(refs), refname);
 567 }
 568
 569 /*
 570  * A loose ref file doesn't exist; check for a packed ref.
 571  */
 572 static int resolve_packed_ref(struct files_ref_store *refs,
 573                               const char *refname,
 574                               unsigned char *sha1, unsigned int *flags)
 575 {
 576         struct ref_entry *entry;
 577
 578         /*
 579          * The loose reference file does not exist; check for a packed
 580          * reference.
 581          */
 582         entry = get_packed_ref(refs, refname);
 583         if (entry) {
 584                 hashcpy(sha1, entry->u.value.oid.hash);
 585                 *flags |= REF_ISPACKED;
 586                 return 0;
 587         }
 588         /* refname is not a packed reference. */
 589         return -1;
 590 }
 591
 592 static int files_read_raw_ref(struct ref_store *ref_store,
 593                               const char *refname, unsigned char *sha1,
 594                               struct strbuf *referent, unsigned int *type)
 595 {
 596         struct files_ref_store *refs =
 597                 files_downcast(ref_store, REF_STORE_READ, "read_raw_ref");
 598         struct strbuf sb_contents = STRBUF_INIT;
 599         struct strbuf sb_path = STRBUF_INIT;
 600         const char *path;
 601         const char *buf;
 602         struct stat st;
 603         int fd;
 604         int ret = -1;
 605         int save_errno;
 606         int remaining_retries = 3;
 607
 608         *type = 0;
 609         strbuf_reset(&sb_path);
 610
 611         files_ref_path(refs, &sb_path, refname);
 612
 613         path = sb_path.buf;
 614
 615 stat_ref:
 616         /*
 617          * We might have to loop back here to avoid a race
 618          * condition: first we lstat() the file, then we try
 619          * to read it as a link or as a file.  But if somebody
 620          * changes the type of the file (file <-> directory
 621          * <-> symlink) between the lstat() and reading, then
 622          * we don't want to report that as an error but rather
 623          * try again starting with the lstat().
 624          *
 625          * We'll keep a count of the retries, though, just to avoid
 626          * any confusing situation sending us into an infinite loop.
 627          */
 628
 629         if (remaining_retries-- <= 0)
 630                 goto out;
 631
 632         if (lstat(path, &st) < 0) {
 633                 if (errno != ENOENT)
 634                         goto out;
 635                 if (resolve_packed_ref(refs, refname, sha1, type)) {
 636                         errno = ENOENT;
 637                         goto out;
 638                 }
 639                 ret = 0;
 640                 goto out;
 641         }
 642
 643         /* Follow "normalized" - ie "refs/.." symlinks by hand */
 644         if (S_ISLNK(st.st_mode)) {
 645                 strbuf_reset(&sb_contents);
 646                 if (strbuf_readlink(&sb_contents, path, 0) < 0) {
 647                         if (errno == ENOENT || errno == EINVAL)
 648                                 /* inconsistent with lstat; retry */
 649                                 goto stat_ref;
 650                         else
 651                                 goto out;
 652                 }
 653                 if (starts_with(sb_contents.buf, "refs/") &&
 654                     !check_refname_format(sb_contents.buf, 0)) {
 655                         strbuf_swap(&sb_contents, referent);
 656                         *type |= REF_ISSYMREF;
 657                         ret = 0;
 658                         goto out;
 659                 }
 660                 /*
 661                  * It doesn't look like a refname; fall through to just
 662                  * treating it like a non-symlink, and reading whatever it
 663                  * points to.
 664                  */
 665         }
 666
 667         /* Is it a directory? */
 668         if (S_ISDIR(st.st_mode)) {
 669                 /*
 670                  * Even though there is a directory where the loose
 671                  * ref is supposed to be, there could still be a
 672                  * packed ref:
 673                  */
 674                 if (resolve_packed_ref(refs, refname, sha1, type)) {
 675                         errno = EISDIR;
 676                         goto out;
 677                 }
 678                 ret = 0;
 679                 goto out;
 680         }
 681
 682         /*
 683          * Anything else, just open it and try to use it as
 684          * a ref
 685          */
 686         fd = open(path, O_RDONLY);
 687         if (fd < 0) {
 688                 if (errno == ENOENT && !S_ISLNK(st.st_mode))
 689                         /* inconsistent with lstat; retry */
 690                         goto stat_ref;
 691                 else
 692                         goto out;
 693         }
 694         strbuf_reset(&sb_contents);
 695         if (strbuf_read(&sb_contents, fd, 256) < 0) {
 696                 int save_errno = errno;
 697                 close(fd);
 698                 errno = save_errno;
 699                 goto out;
 700         }
 701         close(fd);
 702         strbuf_rtrim(&sb_contents);
 703         buf = sb_contents.buf;
 704         if (starts_with(buf, "ref:")) {
 705                 buf += 4;
 706                 while (isspace(*buf))
 707                         buf++;
 708
 709                 strbuf_reset(referent);
 710                 strbuf_addstr(referent, buf);
 711                 *type |= REF_ISSYMREF;
 712                 ret = 0;
 713                 goto out;
 714         }
 715
 716         /*
 717          * Please note that FETCH_HEAD has additional
 718          * data after the sha.
 719          */
 720         if (get_sha1_hex(buf, sha1) ||
 721             (buf[40] != '\0' && !isspace(buf[40]))) {
 722                 *type |= REF_ISBROKEN;
 723                 errno = EINVAL;
 724                 goto out;
 725         }
 726
 727         ret = 0;
 728
 729 out:
 730         save_errno = errno;
 731         strbuf_release(&sb_path);
 732         strbuf_release(&sb_contents);
 733         errno = save_errno;
 734         return ret;
 735 }
 736
 737 static void unlock_ref(struct ref_lock *lock)
 738 {
 739         /* Do not free lock->lk -- atexit() still looks at them */
 740         if (lock->lk)
 741                 rollback_lock_file(lock->lk);
 742         free(lock->ref_name);
 743         free(lock);
 744 }
 745
 746 /*
 747  * Lock refname, without following symrefs, and set *lock_p to point
 748  * at a newly-allocated lock object. Fill in lock->old_oid, referent,
 749  * and type similarly to read_raw_ref().
 750  *
 751  * The caller must verify that refname is a "safe" reference name (in
 752  * the sense of refname_is_safe()) before calling this function.
 753  *
 754  * If the reference doesn't already exist, verify that refname doesn't
 755  * have a D/F conflict with any existing references. extras and skip
 756  * are passed to refs_verify_refname_available() for this check.
 757  *
 758  * If mustexist is not set and the reference is not found or is
 759  * broken, lock the reference anyway but clear sha1.
 760  *
 761  * Return 0 on success. On failure, write an error message to err and
 762  * return TRANSACTION_NAME_CONFLICT or TRANSACTION_GENERIC_ERROR.
 763  *
 764  * Implementation note: This function is basically
 765  *
 766  *     lock reference
 767  *     read_raw_ref()
 768  *
 769  * but it includes a lot more code to
 770  * - Deal with possible races with other processes
 771  * - Avoid calling refs_verify_refname_available() when it can be
 772  *   avoided, namely if we were successfully able to read the ref
 773  * - Generate informative error messages in the case of failure
 774  */
 775 static int lock_raw_ref(struct files_ref_store *refs,
 776                         const char *refname, int mustexist,
 777                         const struct string_list *extras,
 778                         const struct string_list *skip,
 779                         struct ref_lock **lock_p,
 780                         struct strbuf *referent,
 781                         unsigned int *type,
 782                         struct strbuf *err)
 783 {
 784         struct ref_lock *lock;
 785         struct strbuf ref_file = STRBUF_INIT;
 786         int attempts_remaining = 3;
 787         int ret = TRANSACTION_GENERIC_ERROR;
 788
 789         assert(err);
 790         files_assert_main_repository(refs, "lock_raw_ref");
 791
 792         *type = 0;
 793
 794         /* First lock the file so it can't change out from under us. */
 795
 796         *lock_p = lock = xcalloc(1, sizeof(*lock));
 797
 798         lock->ref_name = xstrdup(refname);
 799         files_ref_path(refs, &ref_file, refname);
 800
 801 retry:
 802         switch (safe_create_leading_directories(ref_file.buf)) {
 803         case SCLD_OK:
 804                 break; /* success */
 805         case SCLD_EXISTS:
 806                 /*
 807                  * Suppose refname is "refs/foo/bar". We just failed
 808                  * to create the containing directory, "refs/foo",
 809                  * because there was a non-directory in the way. This
 810                  * indicates a D/F conflict, probably because of
 811                  * another reference such as "refs/foo". There is no
 812                  * reason to expect this error to be transitory.
 813                  */
 814                 if (refs_verify_refname_available(&refs->base, refname,
 815                                                   extras, skip, err)) {
 816                         if (mustexist) {
 817                                 /*
 818                                  * To the user the relevant error is
 819                                  * that the "mustexist" reference is
 820                                  * missing:
 821                                  */
 822                                 strbuf_reset(err);
 823                                 strbuf_addf(err, "unable to resolve reference '%s'",
 824                                             refname);
 825                         } else {
 826                                 /*
 827                                  * The error message set by
 828                                  * refs_verify_refname_available() is
 829                                  * OK.
 830                                  */
 831                                 ret = TRANSACTION_NAME_CONFLICT;
 832                         }
 833                 } else {
 834                         /*
 835                          * The file that is in the way isn't a loose
 836                          * reference. Report it as a low-level
 837                          * failure.
 838                          */
 839                         strbuf_addf(err, "unable to create lock file %s.lock; "
 840                                     "non-directory in the way",
 841                                     ref_file.buf);
 842                 }
 843                 goto error_return;
 844         case SCLD_VANISHED:
 845                 /* Maybe another process was tidying up. Try again. */
 846                 if (--attempts_remaining > 0)
 847                         goto retry;
 848                 /* fall through */
 849         default:
 850                 strbuf_addf(err, "unable to create directory for %s",
 851                             ref_file.buf);
 852                 goto error_return;
 853         }
 854
 855         if (!lock->lk)
 856                 lock->lk = xcalloc(1, sizeof(struct lock_file));
 857
 858         if (hold_lock_file_for_update(lock->lk, ref_file.buf, LOCK_NO_DEREF) < 0) {
 859                 if (errno == ENOENT && --attempts_remaining > 0) {
 860                         /*
 861                          * Maybe somebody just deleted one of the
 862                          * directories leading to ref_file.  Try
 863                          * again:
 864                          */
 865                         goto retry;
 866                 } else {
 867                         unable_to_lock_message(ref_file.buf, errno, err);
 868                         goto error_return;
 869                 }
 870         }
 871
 872         /*
 873          * Now we hold the lock and can read the reference without
 874          * fear that its value will change.
 875          */
 876
 877         if (files_read_raw_ref(&refs->base, refname,
 878                                lock->old_oid.hash, referent, type)) {
 879                 if (errno == ENOENT) {
 880                         if (mustexist) {
 881                                 /* Garden variety missing reference. */
 882                                 strbuf_addf(err, "unable to resolve reference '%s'",
 883                                             refname);
 884                                 goto error_return;
 885                         } else {
 886                                 /*
 887                                  * Reference is missing, but that's OK. We
 888                                  * know that there is not a conflict with
 889                                  * another loose reference because
 890                                  * (supposing that we are trying to lock
 891                                  * reference "refs/foo/bar"):
 892                                  *
 893                                  * - We were successfully able to create
 894                                  *   the lockfile refs/foo/bar.lock, so we
 895                                  *   know there cannot be a loose reference
 896                                  *   named "refs/foo".
 897                                  *
 898                                  * - We got ENOENT and not EISDIR, so we
 899                                  *   know that there cannot be a loose
 900                                  *   reference named "refs/foo/bar/baz".
 901                                  */
 902                         }
 903                 } else if (errno == EISDIR) {
 904                         /*
 905                          * There is a directory in the way. It might have
 906                          * contained references that have been deleted. If
 907                          * we don't require that the reference already
 908                          * exists, try to remove the directory so that it
 909                          * doesn't cause trouble when we want to rename the
 910                          * lockfile into place later.
 911                          */
 912                         if (mustexist) {
 913                                 /* Garden variety missing reference. */
 914                                 strbuf_addf(err, "unable to resolve reference '%s'",
 915                                             refname);
 916                                 goto error_return;
 917                         } else if (remove_dir_recursively(&ref_file,
 918                                                           REMOVE_DIR_EMPTY_ONLY)) {
 919                                 if (refs_verify_refname_available(
 920                                                     &refs->base, refname,
 921                                                     extras, skip, err)) {
 922                                         /*
 923                                          * The error message set by
 924                                          * verify_refname_available() is OK.
 925                                          */
 926                                         ret = TRANSACTION_NAME_CONFLICT;
 927                                         goto error_return;
 928                                 } else {
 929                                         /*
 930                                          * We can't delete the directory,
 931                                          * but we also don't know of any
 932                                          * references that it should
 933                                          * contain.
 934                                          */
 935                                         strbuf_addf(err, "there is a non-empty directory '%s' "
 936                                                     "blocking reference '%s'",
 937                                                     ref_file.buf, refname);
 938                                         goto error_return;
 939                                 }
 940                         }
 941                 } else if (errno == EINVAL && (*type & REF_ISBROKEN)) {
 942                         strbuf_addf(err, "unable to resolve reference '%s': "
 943                                     "reference broken", refname);
 944                         goto error_return;
 945                 } else {
 946                         strbuf_addf(err, "unable to resolve reference '%s': %s",
 947                                     refname, strerror(errno));
 948                         goto error_return;
 949                 }
 950
 951                 /*
 952                  * If the ref did not exist and we are creating it,
 953                  * make sure there is no existing ref that conflicts
 954                  * with refname:
 955                  */
 956                 if (refs_verify_refname_available(
 957                                     &refs->base, refname,
 958                                     extras, skip, err))
 959                         goto error_return;
 960         }
 961
 962         ret = 0;
 963         goto out;
 964
 965 error_return:
 966         unlock_ref(lock);
 967         *lock_p = NULL;
 968
 969 out:
 970         strbuf_release(&ref_file);
 971         return ret;
 972 }
 973
 974 static int files_peel_ref(struct ref_store *ref_store,
 975                           const char *refname, unsigned char *sha1)
 976 {
 977         struct files_ref_store *refs =
 978                 files_downcast(ref_store, REF_STORE_READ | REF_STORE_ODB,
 979                                "peel_ref");
 980         int flag;
 981         unsigned char base[20];
 982
 983         if (current_ref_iter && current_ref_iter->refname == refname) {
 984                 struct object_id peeled;
 985
 986                 if (ref_iterator_peel(current_ref_iter, &peeled))
 987                         return -1;
 988                 hashcpy(sha1, peeled.hash);
 989                 return 0;
 990         }
 991
 992         if (refs_read_ref_full(ref_store, refname,
 993                                RESOLVE_REF_READING, base, &flag))
 994                 return -1;
 995
 996         /*
 997          * If the reference is packed, read its ref_entry from the
 998          * cache in the hope that we already know its peeled value.
 999          * We only try this optimization on packed references because
1000          * (a) forcing the filling of the loose reference cache could
1001          * be expensive and (b) loose references anyway usually do not
1002          * have REF_KNOWS_PEELED.
1003          */
1004         if (flag & REF_ISPACKED) {
1005                 struct ref_entry *r = get_packed_ref(refs, refname);
1006                 if (r) {
1007                         if (peel_entry(r, 0))
1008                                 return -1;
1009                         hashcpy(sha1, r->u.value.peeled.hash);
1010                         return 0;
1011                 }
1012         }
1013
1014         return peel_object(base, sha1);
1015 }
1016
1017 struct files_ref_iterator {
1018         struct ref_iterator base;
1019
1020         struct packed_ref_cache *packed_ref_cache;
1021         struct ref_iterator *iter0;
1022         unsigned int flags;
1023 };
1024
1025 static int files_ref_iterator_advance(struct ref_iterator *ref_iterator)
1026 {
1027         struct files_ref_iterator *iter =
1028                 (struct files_ref_iterator *)ref_iterator;
1029         int ok;
1030
1031         while ((ok = ref_iterator_advance(iter->iter0)) == ITER_OK) {
1032                 if (iter->flags & DO_FOR_EACH_PER_WORKTREE_ONLY &&
1033                     ref_type(iter->iter0->refname) != REF_TYPE_PER_WORKTREE)
1034                         continue;
1035
1036                 if (!(iter->flags & DO_FOR_EACH_INCLUDE_BROKEN) &&
1037                     !ref_resolves_to_object(iter->iter0->refname,
1038                                             iter->iter0->oid,
1039                                             iter->iter0->flags))
1040                         continue;
1041
1042                 iter->base.refname = iter->iter0->refname;
1043                 iter->base.oid = iter->iter0->oid;
1044                 iter->base.flags = iter->iter0->flags;
1045                 return ITER_OK;
1046         }
1047
1048         iter->iter0 = NULL;
1049         if (ref_iterator_abort(ref_iterator) != ITER_DONE)
1050                 ok = ITER_ERROR;
1051
1052         return ok;
1053 }
1054
1055 static int files_ref_iterator_peel(struct ref_iterator *ref_iterator,
1056                                    struct object_id *peeled)
1057 {
1058         struct files_ref_iterator *iter =
1059                 (struct files_ref_iterator *)ref_iterator;
1060
1061         return ref_iterator_peel(iter->iter0, peeled);
1062 }
1063
1064 static int files_ref_iterator_abort(struct ref_iterator *ref_iterator)
1065 {
1066         struct files_ref_iterator *iter =
1067                 (struct files_ref_iterator *)ref_iterator;
1068         int ok = ITER_DONE;
1069
1070         if (iter->iter0)
1071                 ok = ref_iterator_abort(iter->iter0);
1072
1073         release_packed_ref_cache(iter->packed_ref_cache);
1074         base_ref_iterator_free(ref_iterator);
1075         return ok;
1076 }
1077
1078 static struct ref_iterator_vtable files_ref_iterator_vtable = {
1079         files_ref_iterator_advance,
1080         files_ref_iterator_peel,
1081         files_ref_iterator_abort
1082 };
1083
1084 static struct ref_iterator *files_ref_iterator_begin(
1085                 struct ref_store *ref_store,
1086                 const char *prefix, unsigned int flags)
1087 {
1088         struct files_ref_store *refs;
1089         struct ref_iterator *loose_iter, *packed_iter;
1090         struct files_ref_iterator *iter;
1091         struct ref_iterator *ref_iterator;
1092         unsigned int required_flags = REF_STORE_READ;
1093
1094         if (!(flags & DO_FOR_EACH_INCLUDE_BROKEN))
1095                 required_flags |= REF_STORE_ODB;
1096
1097         refs = files_downcast(ref_store, required_flags, "ref_iterator_begin");
1098
1099         iter = xcalloc(1, sizeof(*iter));
1100         ref_iterator = &iter->base;
1101         base_ref_iterator_init(ref_iterator, &files_ref_iterator_vtable);
1102
1103         /*
1104          * We must make sure that all loose refs are read before
1105          * accessing the packed-refs file; this avoids a race
1106          * condition if loose refs are migrated to the packed-refs
1107          * file by a simultaneous process, but our in-memory view is
1108          * from before the migration. We ensure this as follows:
1109          * First, we call start the loose refs iteration with its
1110          * `prime_ref` argument set to true. This causes the loose
1111          * references in the subtree to be pre-read into the cache.
1112          * (If they've already been read, that's OK; we only need to
1113          * guarantee that they're read before the packed refs, not
1114          * *how much* before.) After that, we call
1115          * get_packed_ref_cache(), which internally checks whether the
1116          * packed-ref cache is up to date with what is on disk, and
1117          * re-reads it if not.
1118          */
1119
1120         loose_iter = cache_ref_iterator_begin(get_loose_ref_cache(refs),
1121                                               prefix, 1);
1122
1123         iter->packed_ref_cache = get_packed_ref_cache(refs);
1124         acquire_packed_ref_cache(iter->packed_ref_cache);
1125         packed_iter = cache_ref_iterator_begin(iter->packed_ref_cache->cache,
1126                                                prefix, 0);
1127
1128         iter->iter0 = overlay_ref_iterator_begin(loose_iter, packed_iter);
1129         iter->flags = flags;
1130
1131         return ref_iterator;
1132 }
1133
1134 /*
1135  * Verify that the reference locked by lock has the value old_sha1.
1136  * Fail if the reference doesn't exist and mustexist is set. Return 0
1137  * on success. On error, write an error message to err, set errno, and
1138  * return a negative value.
1139  */
1140 static int verify_lock(struct ref_store *ref_store, struct ref_lock *lock,
1141                        const unsigned char *old_sha1, int mustexist,
1142                        struct strbuf *err)
1143 {
1144         assert(err);
1145
1146         if (refs_read_ref_full(ref_store, lock->ref_name,
1147                                mustexist ? RESOLVE_REF_READING : 0,
1148                                lock->old_oid.hash, NULL)) {
1149                 if (old_sha1) {
1150                         int save_errno = errno;
1151                         strbuf_addf(err, "can't verify ref '%s'", lock->ref_name);
1152                         errno = save_errno;
1153                         return -1;
1154                 } else {
1155                         oidclr(&lock->old_oid);
1156                         return 0;
1157                 }
1158         }
1159         if (old_sha1 && hashcmp(lock->old_oid.hash, old_sha1)) {
1160                 strbuf_addf(err, "ref '%s' is at %s but expected %s",
1161                             lock->ref_name,
1162                             oid_to_hex(&lock->old_oid),
1163                             sha1_to_hex(old_sha1));
1164                 errno = EBUSY;
1165                 return -1;
1166         }
1167         return 0;
1168 }
1169
1170 static int remove_empty_directories(struct strbuf *path)
1171 {
1172         /*
1173          * we want to create a file but there is a directory there;
1174          * if that is an empty directory (or a directory that contains
1175          * only empty directories), remove them.
1176          */
1177         return remove_dir_recursively(path, REMOVE_DIR_EMPTY_ONLY);
1178 }
1179
1180 static int create_reflock(const char *path, void *cb)
1181 {
1182         struct lock_file *lk = cb;
1183
1184         return hold_lock_file_for_update(lk, path, LOCK_NO_DEREF) < 0 ? -1 : 0;
1185 }
1186
1187 /*
1188  * Locks a ref returning the lock on success and NULL on failure.
1189  * On failure errno is set to something meaningful.
1190  */
1191 static struct ref_lock *lock_ref_sha1_basic(struct files_ref_store *refs,
1192                                             const char *refname,
1193                                             const unsigned char *old_sha1,
1194                                             const struct string_list *extras,
1195                                             const struct string_list *skip,
1196                                             unsigned int flags, int *type,
1197                                             struct strbuf *err)
1198 {
1199         struct strbuf ref_file = STRBUF_INIT;
1200         struct ref_lock *lock;
1201         int last_errno = 0;
1202         int mustexist = (old_sha1 && !is_null_sha1(old_sha1));
1203         int resolve_flags = RESOLVE_REF_NO_RECURSE;
1204         int resolved;
1205
1206         files_assert_main_repository(refs, "lock_ref_sha1_basic");
1207         assert(err);
1208
1209         lock = xcalloc(1, sizeof(struct ref_lock));
1210
1211         if (mustexist)
1212                 resolve_flags |= RESOLVE_REF_READING;
1213         if (flags & REF_DELETING)
1214                 resolve_flags |= RESOLVE_REF_ALLOW_BAD_NAME;
1215
1216         files_ref_path(refs, &ref_file, refname);
1217         resolved = !!refs_resolve_ref_unsafe(&refs->base,
1218                                              refname, resolve_flags,
1219                                              lock->old_oid.hash, type);
1220         if (!resolved && errno == EISDIR) {
1221                 /*
1222                  * we are trying to lock foo but we used to
1223                  * have foo/bar which now does not exist;
1224                  * it is normal for the empty directory 'foo'
1225                  * to remain.
1226                  */
1227                 if (remove_empty_directories(&ref_file)) {
1228                         last_errno = errno;
1229                         if (!refs_verify_refname_available(
1230                                             &refs->base,
1231                                             refname, extras, skip, err))
1232                                 strbuf_addf(err, "there are still refs under '%s'",
1233                                             refname);
1234                         goto error_return;
1235                 }
1236                 resolved = !!refs_resolve_ref_unsafe(&refs->base,
1237                                                      refname, resolve_flags,
1238                                                      lock->old_oid.hash, type);
1239         }
1240         if (!resolved) {
1241                 last_errno = errno;
1242                 if (last_errno != ENOTDIR ||
1243                     !refs_verify_refname_available(&refs->base, refname,
1244                                                    extras, skip, err))
1245                         strbuf_addf(err, "unable to resolve reference '%s': %s",
1246                                     refname, strerror(last_errno));
1247
1248                 goto error_return;
1249         }
1250
1251         /*
1252          * If the ref did not exist and we are creating it, make sure
1253          * there is no existing packed ref whose name begins with our
1254          * refname, nor a packed ref whose name is a proper prefix of
1255          * our refname.
1256          */
1257         if (is_null_oid(&lock->old_oid) &&
1258             refs_verify_refname_available(&refs->base, refname,
1259                                           extras, skip, err)) {
1260                 last_errno = ENOTDIR;
1261                 goto error_return;
1262         }
1263
1264         lock->lk = xcalloc(1, sizeof(struct lock_file));
1265
1266         lock->ref_name = xstrdup(refname);
1267
1268         if (raceproof_create_file(ref_file.buf, create_reflock, lock->lk)) {
1269                 last_errno = errno;
1270                 unable_to_lock_message(ref_file.buf, errno, err);
1271                 goto error_return;
1272         }
1273
1274         if (verify_lock(&refs->base, lock, old_sha1, mustexist, err)) {
1275                 last_errno = errno;
1276                 goto error_return;
1277         }
1278         goto out;
1279
1280  error_return:
1281         unlock_ref(lock);
1282         lock = NULL;
1283
1284  out:
1285         strbuf_release(&ref_file);
1286         errno = last_errno;
1287         return lock;
1288 }
1289
1290 /*
1291  * Write an entry to the packed-refs file for the specified refname.
1292  * If peeled is non-NULL, write it as the entry's peeled value.
1293  */
1294 static void write_packed_entry(FILE *fh, const char *refname,
1295                                const unsigned char *sha1,
1296                                const unsigned char *peeled)
1297 {
1298         fprintf_or_die(fh, "%s %s\n", sha1_to_hex(sha1), refname);
1299         if (peeled)
1300                 fprintf_or_die(fh, "^%s\n", sha1_to_hex(peeled));
1301 }
1302
1303 /*
1304  * Lock the packed-refs file for writing. Flags is passed to
1305  * hold_lock_file_for_update(). Return 0 on success. On errors, set
1306  * errno appropriately and return a nonzero value.
1307  */
1308 static int lock_packed_refs(struct files_ref_store *refs, int flags)
1309 {
1310         static int timeout_configured = 0;
1311         static int timeout_value = 1000;
1312         struct packed_ref_cache *packed_ref_cache;
1313
1314         files_assert_main_repository(refs, "lock_packed_refs");
1315
1316         if (!timeout_configured) {
1317                 git_config_get_int("core.packedrefstimeout", &timeout_value);
1318                 timeout_configured = 1;
1319         }
1320
1321         if (hold_lock_file_for_update_timeout(
1322                             &refs->packed_refs_lock, files_packed_refs_path(refs),
1323                             flags, timeout_value) < 0)
1324                 return -1;
1325
1326         /*
1327          * Now that we hold the `packed-refs` lock, make sure that our
1328          * cache matches the current version of the file. Normally
1329          * `get_packed_ref_cache()` does that for us, but that
1330          * function assumes that when the file is locked, any existing
1331          * cache is still valid. We've just locked the file, but it
1332          * might have changed the moment *before* we locked it.
1333          */
1334         validate_packed_ref_cache(refs);
1335
1336         packed_ref_cache = get_packed_ref_cache(refs);
1337         /* Increment the reference count to prevent it from being freed: */
1338         acquire_packed_ref_cache(packed_ref_cache);
1339         return 0;
1340 }
1341
1342 /*
1343  * Write the current version of the packed refs cache from memory to
1344  * disk. The packed-refs file must already be locked for writing (see
1345  * lock_packed_refs()). Return zero on success. On errors, set errno
1346  * and return a nonzero value
1347  */
1348 static int commit_packed_refs(struct files_ref_store *refs)
1349 {
1350         struct packed_ref_cache *packed_ref_cache =
1351                 get_packed_ref_cache(refs);
1352         int ok, error = 0;
1353         int save_errno = 0;
1354         FILE *out;
1355         struct ref_iterator *iter;
1356
1357         files_assert_main_repository(refs, "commit_packed_refs");
1358
1359         if (!is_lock_file_locked(&refs->packed_refs_lock))
1360                 die("BUG: packed-refs not locked");
1361
1362         out = fdopen_lock_file(&refs->packed_refs_lock, "w");
1363         if (!out)
1364                 die_errno("unable to fdopen packed-refs descriptor");
1365
1366         fprintf_or_die(out, "%s", PACKED_REFS_HEADER);
1367
1368         iter = cache_ref_iterator_begin(packed_ref_cache->cache, NULL, 0);
1369         while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
1370                 struct object_id peeled;
1371                 int peel_error = ref_iterator_peel(iter, &peeled);
1372
1373                 write_packed_entry(out, iter->refname, iter->oid->hash,
1374                                    peel_error ? NULL : peeled.hash);
1375         }
1376
1377         if (ok != ITER_DONE)
1378                 die("error while iterating over references");
1379
1380         if (commit_lock_file(&refs->packed_refs_lock)) {
1381                 save_errno = errno;
1382                 error = -1;
1383         }
1384         release_packed_ref_cache(packed_ref_cache);
1385         errno = save_errno;
1386         return error;
1387 }
1388
1389 /*
1390  * Rollback the lockfile for the packed-refs file, and discard the
1391  * in-memory packed reference cache.  (The packed-refs file will be
1392  * read anew if it is needed again after this function is called.)
1393  */
1394 static void rollback_packed_refs(struct files_ref_store *refs)
1395 {
1396         struct packed_ref_cache *packed_ref_cache =
1397                 get_packed_ref_cache(refs);
1398
1399         files_assert_main_repository(refs, "rollback_packed_refs");
1400
1401         if (!is_lock_file_locked(&refs->packed_refs_lock))
1402                 die("BUG: packed-refs not locked");
1403         rollback_lock_file(&refs->packed_refs_lock);
1404         release_packed_ref_cache(packed_ref_cache);
1405         clear_packed_ref_cache(refs);
1406 }
1407
1408 struct ref_to_prune {
1409         struct ref_to_prune *next;
1410         unsigned char sha1[20];
1411         char name[FLEX_ARRAY];
1412 };
1413
1414 enum {
1415         REMOVE_EMPTY_PARENTS_REF = 0x01,
1416         REMOVE_EMPTY_PARENTS_REFLOG = 0x02
1417 };
1418
1419 /*
1420  * Remove empty parent directories associated with the specified
1421  * reference and/or its reflog, but spare [logs/]refs/ and immediate
1422  * subdirs. flags is a combination of REMOVE_EMPTY_PARENTS_REF and/or
1423  * REMOVE_EMPTY_PARENTS_REFLOG.
1424  */
1425 static void try_remove_empty_parents(struct files_ref_store *refs,
1426                                      const char *refname,
1427                                      unsigned int flags)
1428 {
1429         struct strbuf buf = STRBUF_INIT;
1430         struct strbuf sb = STRBUF_INIT;
1431         char *p, *q;
1432         int i;
1433
1434         strbuf_addstr(&buf, refname);
1435         p = buf.buf;
1436         for (i = 0; i < 2; i++) { /* refs/{heads,tags,...}/ */
1437                 while (*p && *p != '/')
1438                         p++;
1439                 /* tolerate duplicate slashes; see check_refname_format() */
1440                 while (*p == '/')
1441                         p++;
1442         }
1443         q = buf.buf + buf.len;
1444         while (flags & (REMOVE_EMPTY_PARENTS_REF | REMOVE_EMPTY_PARENTS_REFLOG)) {
1445                 while (q > p && *q != '/')
1446                         q--;
1447                 while (q > p && *(q-1) == '/')
1448                         q--;
1449                 if (q == p)
1450                         break;
1451                 strbuf_setlen(&buf, q - buf.buf);
1452
1453                 strbuf_reset(&sb);
1454                 files_ref_path(refs, &sb, buf.buf);
1455                 if ((flags & REMOVE_EMPTY_PARENTS_REF) && rmdir(sb.buf))
1456                         flags &= ~REMOVE_EMPTY_PARENTS_REF;
1457
1458                 strbuf_reset(&sb);
1459                 files_reflog_path(refs, &sb, buf.buf);
1460                 if ((flags & REMOVE_EMPTY_PARENTS_REFLOG) && rmdir(sb.buf))
1461                         flags &= ~REMOVE_EMPTY_PARENTS_REFLOG;
1462         }
1463         strbuf_release(&buf);
1464         strbuf_release(&sb);
1465 }
1466
1467 /* make sure nobody touched the ref, and unlink */
1468 static void prune_ref(struct files_ref_store *refs, struct ref_to_prune *r)
1469 {
1470         struct ref_transaction *transaction;
1471         struct strbuf err = STRBUF_INIT;
1472
1473         if (check_refname_format(r->name, 0))
1474                 return;
1475
1476         transaction = ref_store_transaction_begin(&refs->base, &err);
1477         if (!transaction ||
1478             ref_transaction_delete(transaction, r->name, r->sha1,
1479                                    REF_ISPRUNING | REF_NODEREF, NULL, &err) ||
1480             ref_transaction_commit(transaction, &err)) {
1481                 ref_transaction_free(transaction);
1482                 error("%s", err.buf);
1483                 strbuf_release(&err);
1484                 return;
1485         }
1486         ref_transaction_free(transaction);
1487         strbuf_release(&err);
1488 }
1489
1490 static void prune_refs(struct files_ref_store *refs, struct ref_to_prune *r)
1491 {
1492         while (r) {
1493                 prune_ref(refs, r);
1494                 r = r->next;
1495         }
1496 }
1497
1498 /*
1499  * Return true if the specified reference should be packed.
1500  */
1501 static int should_pack_ref(const char *refname,
1502                            const struct object_id *oid, unsigned int ref_flags,
1503                            unsigned int pack_flags)
1504 {
1505         /* Do not pack per-worktree refs: */
1506         if (ref_type(refname) != REF_TYPE_NORMAL)
1507                 return 0;
1508
1509         /* Do not pack non-tags unless PACK_REFS_ALL is set: */
1510         if (!(pack_flags & PACK_REFS_ALL) && !starts_with(refname, "refs/tags/"))
1511                 return 0;
1512
1513         /* Do not pack symbolic refs: */
1514         if (ref_flags & REF_ISSYMREF)
1515                 return 0;
1516
1517         /* Do not pack broken refs: */
1518         if (!ref_resolves_to_object(refname, oid, ref_flags))
1519                 return 0;
1520
1521         return 1;
1522 }
1523
1524 static int files_pack_refs(struct ref_store *ref_store, unsigned int flags)
1525 {
1526         struct files_ref_store *refs =
1527                 files_downcast(ref_store, REF_STORE_WRITE | REF_STORE_ODB,
1528                                "pack_refs");
1529         struct ref_iterator *iter;
1530         struct ref_dir *packed_refs;
1531         int ok;
1532         struct ref_to_prune *refs_to_prune = NULL;
1533
1534         lock_packed_refs(refs, LOCK_DIE_ON_ERROR);
1535         packed_refs = get_packed_refs(refs);
1536
1537         iter = cache_ref_iterator_begin(get_loose_ref_cache(refs), NULL, 0);
1538         while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
1539                 /*
1540                  * If the loose reference can be packed, add an entry
1541                  * in the packed ref cache. If the reference should be
1542                  * pruned, also add it to refs_to_prune.
1543                  */
1544                 struct ref_entry *packed_entry;
1545
1546                 if (!should_pack_ref(iter->refname, iter->oid, iter->flags,
1547                                      flags))
1548                         continue;
1549
1550                 /*
1551                  * Create an entry in the packed-refs cache equivalent
1552                  * to the one from the loose ref cache, except that
1553                  * we don't copy the peeled status, because we want it
1554                  * to be re-peeled.
1555                  */
1556                 packed_entry = find_ref_entry(packed_refs, iter->refname);
1557                 if (packed_entry) {
1558                         /* Overwrite existing packed entry with info from loose entry */
1559                         packed_entry->flag = REF_ISPACKED;
1560                         oidcpy(&packed_entry->u.value.oid, iter->oid);
1561                 } else {
1562                         packed_entry = create_ref_entry(iter->refname, iter->oid,
1563                                                         REF_ISPACKED);
1564                         add_ref_entry(packed_refs, packed_entry);
1565                 }
1566                 oidclr(&packed_entry->u.value.peeled);
1567
1568                 /* Schedule the loose reference for pruning if requested. */
1569                 if ((flags & PACK_REFS_PRUNE)) {
1570                         struct ref_to_prune *n;
1571                         FLEX_ALLOC_STR(n, name, iter->refname);
1572                         hashcpy(n->sha1, iter->oid->hash);
1573                         n->next = refs_to_prune;
1574                         refs_to_prune = n;
1575                 }
1576         }
1577         if (ok != ITER_DONE)
1578                 die("error while iterating over references");
1579
1580         if (commit_packed_refs(refs))
1581                 die_errno("unable to overwrite old ref-pack file");
1582
1583         prune_refs(refs, refs_to_prune);
1584         return 0;
1585 }
1586
1587 /*
1588  * Rewrite the packed-refs file, omitting any refs listed in
1589  * 'refnames'. On error, leave packed-refs unchanged, write an error
1590  * message to 'err', and return a nonzero value.
1591  *
1592  * The refs in 'refnames' needn't be sorted. `err` must not be NULL.
1593  */
1594 static int repack_without_refs(struct files_ref_store *refs,
1595                                struct string_list *refnames, struct strbuf *err)
1596 {
1597         struct ref_dir *packed;
1598         struct string_list_item *refname;
1599         int ret, needs_repacking = 0, removed = 0;
1600
1601         files_assert_main_repository(refs, "repack_without_refs");
1602         assert(err);
1603
1604         /* Look for a packed ref */
1605         for_each_string_list_item(refname, refnames) {
1606                 if (get_packed_ref(refs, refname->string)) {
1607                         needs_repacking = 1;
1608                         break;
1609                 }
1610         }
1611
1612         /* Avoid locking if we have nothing to do */
1613         if (!needs_repacking)
1614                 return 0; /* no refname exists in packed refs */
1615
1616         if (lock_packed_refs(refs, 0)) {
1617                 unable_to_lock_message(files_packed_refs_path(refs), errno, err);
1618                 return -1;
1619         }
1620         packed = get_packed_refs(refs);
1621
1622         /* Remove refnames from the cache */
1623         for_each_string_list_item(refname, refnames)
1624                 if (remove_entry_from_dir(packed, refname->string) != -1)
1625                         removed = 1;
1626         if (!removed) {
1627                 /*
1628                  * All packed entries disappeared while we were
1629                  * acquiring the lock.
1630                  */
1631                 rollback_packed_refs(refs);
1632                 return 0;
1633         }
1634
1635         /* Write what remains */
1636         ret = commit_packed_refs(refs);
1637         if (ret)
1638                 strbuf_addf(err, "unable to overwrite old ref-pack file: %s",
1639                             strerror(errno));
1640         return ret;
1641 }
1642
1643 static int files_delete_refs(struct ref_store *ref_store, const char *msg,
1644                              struct string_list *refnames, unsigned int flags)
1645 {
1646         struct files_ref_store *refs =
1647                 files_downcast(ref_store, REF_STORE_WRITE, "delete_refs");
1648         struct strbuf err = STRBUF_INIT;
1649         int i, result = 0;
1650
1651         if (!refnames->nr)
1652                 return 0;
1653
1654         result = repack_without_refs(refs, refnames, &err);
1655         if (result) {
1656                 /*
1657                  * If we failed to rewrite the packed-refs file, then
1658                  * it is unsafe to try to remove loose refs, because
1659                  * doing so might expose an obsolete packed value for
1660                  * a reference that might even point at an object that
1661                  * has been garbage collected.
1662                  */
1663                 if (refnames->nr == 1)
1664                         error(_("could not delete reference %s: %s"),
1665                               refnames->items[0].string, err.buf);
1666                 else
1667                         error(_("could not delete references: %s"), err.buf);
1668
1669                 goto out;
1670         }
1671
1672         for (i = 0; i < refnames->nr; i++) {
1673                 const char *refname = refnames->items[i].string;
1674
1675                 if (refs_delete_ref(&refs->base, msg, refname, NULL, flags))
1676                         result |= error(_("could not remove reference %s"), refname);
1677         }
1678
1679 out:
1680         strbuf_release(&err);
1681         return result;
1682 }
1683
1684 /*
1685  * People using contrib's git-new-workdir have .git/logs/refs ->
1686  * /some/other/path/.git/logs/refs, and that may live on another device.
1687  *
1688  * IOW, to avoid cross device rename errors, the temporary renamed log must
1689  * live into logs/refs.
1690  */
1691 #define TMP_RENAMED_LOG  "refs/.tmp-renamed-log"
1692
1693 struct rename_cb {
1694         const char *tmp_renamed_log;
1695         int true_errno;
1696 };
1697
1698 static int rename_tmp_log_callback(const char *path, void *cb_data)
1699 {
1700         struct rename_cb *cb = cb_data;
1701
1702         if (rename(cb->tmp_renamed_log, path)) {
1703                 /*
1704                  * rename(a, b) when b is an existing directory ought
1705                  * to result in ISDIR, but Solaris 5.8 gives ENOTDIR.
1706                  * Sheesh. Record the true errno for error reporting,
1707                  * but report EISDIR to raceproof_create_file() so
1708                  * that it knows to retry.
1709                  */
1710                 cb->true_errno = errno;
1711                 if (errno == ENOTDIR)
1712                         errno = EISDIR;
1713                 return -1;
1714         } else {
1715                 return 0;
1716         }
1717 }
1718
1719 static int rename_tmp_log(struct files_ref_store *refs, const char *newrefname)
1720 {
1721         struct strbuf path = STRBUF_INIT;
1722         struct strbuf tmp = STRBUF_INIT;
1723         struct rename_cb cb;
1724         int ret;
1725
1726         files_reflog_path(refs, &path, newrefname);
1727         files_reflog_path(refs, &tmp, TMP_RENAMED_LOG);
1728         cb.tmp_renamed_log = tmp.buf;
1729         ret = raceproof_create_file(path.buf, rename_tmp_log_callback, &cb);
1730         if (ret) {
1731                 if (errno == EISDIR)
1732                         error("directory not empty: %s", path.buf);
1733                 else
1734                         error("unable to move logfile %s to %s: %s",
1735                               tmp.buf, path.buf,
1736                               strerror(cb.true_errno));
1737         }
1738
1739         strbuf_release(&path);
1740         strbuf_release(&tmp);
1741         return ret;
1742 }
1743
1744 static int write_ref_to_lockfile(struct ref_lock *lock,
1745                                  const struct object_id *oid, struct strbuf *err);
1746 static int commit_ref_update(struct files_ref_store *refs,
1747                              struct ref_lock *lock,
1748                              const struct object_id *oid, const char *logmsg,
1749                              struct strbuf *err);
1750
1751 static int files_rename_ref(struct ref_store *ref_store,
1752                             const char *oldrefname, const char *newrefname,
1753                             const char *logmsg)
1754 {
1755         struct files_ref_store *refs =
1756                 files_downcast(ref_store, REF_STORE_WRITE, "rename_ref");
1757         struct object_id oid, orig_oid;
1758         int flag = 0, logmoved = 0;
1759         struct ref_lock *lock;
1760         struct stat loginfo;
1761         struct strbuf sb_oldref = STRBUF_INIT;
1762         struct strbuf sb_newref = STRBUF_INIT;
1763         struct strbuf tmp_renamed_log = STRBUF_INIT;
1764         int log, ret;
1765         struct strbuf err = STRBUF_INIT;
1766
1767         files_reflog_path(refs, &sb_oldref, oldrefname);
1768         files_reflog_path(refs, &sb_newref, newrefname);
1769         files_reflog_path(refs, &tmp_renamed_log, TMP_RENAMED_LOG);
1770
1771         log = !lstat(sb_oldref.buf, &loginfo);
1772         if (log && S_ISLNK(loginfo.st_mode)) {
1773                 ret = error("reflog for %s is a symlink", oldrefname);
1774                 goto out;
1775         }
1776
1777         if (!refs_resolve_ref_unsafe(&refs->base, oldrefname,
1778                                      RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
1779                                 orig_oid.hash, &flag)) {
1780                 ret = error("refname %s not found", oldrefname);
1781                 goto out;
1782         }
1783
1784         if (flag & REF_ISSYMREF) {
1785                 ret = error("refname %s is a symbolic ref, renaming it is not supported",
1786                             oldrefname);
1787                 goto out;
1788         }
1789         if (!refs_rename_ref_available(&refs->base, oldrefname, newrefname)) {
1790                 ret = 1;
1791                 goto out;
1792         }
1793
1794         if (log && rename(sb_oldref.buf, tmp_renamed_log.buf)) {
1795                 ret = error("unable to move logfile logs/%s to logs/"TMP_RENAMED_LOG": %s",
1796                             oldrefname, strerror(errno));
1797                 goto out;
1798         }
1799
1800         if (refs_delete_ref(&refs->base, logmsg, oldrefname,
1801                             orig_oid.hash, REF_NODEREF)) {
1802                 error("unable to delete old %s", oldrefname);
1803                 goto rollback;
1804         }
1805
1806         /*
1807          * Since we are doing a shallow lookup, oid is not the
1808          * correct value to pass to delete_ref as old_oid. But that
1809          * doesn't matter, because an old_oid check wouldn't add to
1810          * the safety anyway; we want to delete the reference whatever
1811          * its current value.
1812          */
1813         if (!refs_read_ref_full(&refs->base, newrefname,
1814                                 RESOLVE_REF_READING | RESOLVE_REF_NO_RECURSE,
1815                                 oid.hash, NULL) &&
1816             refs_delete_ref(&refs->base, NULL, newrefname,
1817                             NULL, REF_NODEREF)) {
1818                 if (errno == EISDIR) {
1819                         struct strbuf path = STRBUF_INIT;
1820                         int result;
1821
1822                         files_ref_path(refs, &path, newrefname);
1823                         result = remove_empty_directories(&path);
1824                         strbuf_release(&path);
1825
1826                         if (result) {
1827                                 error("Directory not empty: %s", newrefname);
1828                                 goto rollback;
1829                         }
1830                 } else {
1831                         error("unable to delete existing %s", newrefname);
1832                         goto rollback;
1833                 }
1834         }
1835
1836         if (log && rename_tmp_log(refs, newrefname))
1837                 goto rollback;
1838
1839         logmoved = log;
1840
1841         lock = lock_ref_sha1_basic(refs, newrefname, NULL, NULL, NULL,
1842                                    REF_NODEREF, NULL, &err);
1843         if (!lock) {
1844                 error("unable to rename '%s' to '%s': %s", oldrefname, newrefname, err.buf);
1845                 strbuf_release(&err);
1846                 goto rollback;
1847         }
1848         oidcpy(&lock->old_oid, &orig_oid);
1849
1850         if (write_ref_to_lockfile(lock, &orig_oid, &err) ||
1851             commit_ref_update(refs, lock, &orig_oid, logmsg, &err)) {
1852                 error("unable to write current sha1 into %s: %s", newrefname, err.buf);
1853                 strbuf_release(&err);
1854                 goto rollback;
1855         }
1856
1857         ret = 0;
1858         goto out;
1859
1860  rollback:
1861         lock = lock_ref_sha1_basic(refs, oldrefname, NULL, NULL, NULL,
1862                                    REF_NODEREF, NULL, &err);
1863         if (!lock) {
1864                 error("unable to lock %s for rollback: %s", oldrefname, err.buf);
1865                 strbuf_release(&err);
1866                 goto rollbacklog;
1867         }
1868
1869         flag = log_all_ref_updates;
1870         log_all_ref_updates = LOG_REFS_NONE;
1871         if (write_ref_to_lockfile(lock, &orig_oid, &err) ||
1872             commit_ref_update(refs, lock, &orig_oid, NULL, &err)) {
1873                 error("unable to write current sha1 into %s: %s", oldrefname, err.buf);
1874                 strbuf_release(&err);
1875         }
1876         log_all_ref_updates = flag;
1877
1878  rollbacklog:
1879         if (logmoved && rename(sb_newref.buf, sb_oldref.buf))
1880                 error("unable to restore logfile %s from %s: %s",
1881                         oldrefname, newrefname, strerror(errno));
1882         if (!logmoved && log &&
1883             rename(tmp_renamed_log.buf, sb_oldref.buf))
1884                 error("unable to restore logfile %s from logs/"TMP_RENAMED_LOG": %s",
1885                         oldrefname, strerror(errno));
1886         ret = 1;
1887  out:
1888         strbuf_release(&sb_newref);
1889         strbuf_release(&sb_oldref);
1890         strbuf_release(&tmp_renamed_log);
1891
1892         return ret;
1893 }
1894
1895 static int close_ref(struct ref_lock *lock)
1896 {
1897         if (close_lock_file(lock->lk))
1898                 return -1;
1899         return 0;
1900 }
1901
1902 static int commit_ref(struct ref_lock *lock)
1903 {
1904         char *path = get_locked_file_path(lock->lk);
1905         struct stat st;
1906
1907         if (!lstat(path, &st) && S_ISDIR(st.st_mode)) {
1908                 /*
1909                  * There is a directory at the path we want to rename
1910                  * the lockfile to. Hopefully it is empty; try to
1911                  * delete it.
1912                  */
1913                 size_t len = strlen(path);
1914                 struct strbuf sb_path = STRBUF_INIT;
1915
1916                 strbuf_attach(&sb_path, path, len, len);
1917
1918                 /*
1919                  * If this fails, commit_lock_file() will also fail
1920                  * and will report the problem.
1921                  */
1922                 remove_empty_directories(&sb_path);
1923                 strbuf_release(&sb_path);
1924         } else {
1925                 free(path);
1926         }
1927
1928         if (commit_lock_file(lock->lk))
1929                 return -1;
1930         return 0;
1931 }
1932
1933 static int open_or_create_logfile(const char *path, void *cb)
1934 {
1935         int *fd = cb;
1936
1937         *fd = open(path, O_APPEND | O_WRONLY | O_CREAT, 0666);
1938         return (*fd < 0) ? -1 : 0;
1939 }
1940
1941 /*
1942  * Create a reflog for a ref. If force_create = 0, only create the
1943  * reflog for certain refs (those for which should_autocreate_reflog
1944  * returns non-zero). Otherwise, create it regardless of the reference
1945  * name. If the logfile already existed or was created, return 0 and
1946  * set *logfd to the file descriptor opened for appending to the file.
1947  * If no logfile exists and we decided not to create one, return 0 and
1948  * set *logfd to -1. On failure, fill in *err, set *logfd to -1, and
1949  * return -1.
1950  */
1951 static int log_ref_setup(struct files_ref_store *refs,
1952                          const char *refname, int force_create,
1953                          int *logfd, struct strbuf *err)
1954 {
1955         struct strbuf logfile_sb = STRBUF_INIT;
1956         char *logfile;
1957
1958         files_reflog_path(refs, &logfile_sb, refname);
1959         logfile = strbuf_detach(&logfile_sb, NULL);
1960
1961         if (force_create || should_autocreate_reflog(refname)) {
1962                 if (raceproof_create_file(logfile, open_or_create_logfile, logfd)) {
1963                         if (errno == ENOENT)
1964                                 strbuf_addf(err, "unable to create directory for '%s': "
1965                                             "%s", logfile, strerror(errno));
1966                         else if (errno == EISDIR)
1967                                 strbuf_addf(err, "there are still logs under '%s'",
1968                                             logfile);
1969                         else
1970                                 strbuf_addf(err, "unable to append to '%s': %s",
1971                                             logfile, strerror(errno));
1972
1973                         goto error;
1974                 }
1975         } else {
1976                 *logfd = open(logfile, O_APPEND | O_WRONLY, 0666);
1977                 if (*logfd < 0) {
1978                         if (errno == ENOENT || errno == EISDIR) {
1979                                 /*
1980                                  * The logfile doesn't already exist,
1981                                  * but that is not an error; it only
1982                                  * means that we won't write log
1983                                  * entries to it.
1984                                  */
1985                                 ;
1986                         } else {
1987                                 strbuf_addf(err, "unable to append to '%s': %s",
1988                                             logfile, strerror(errno));
1989                                 goto error;
1990                         }
1991                 }
1992         }
1993
1994         if (*logfd >= 0)
1995                 adjust_shared_perm(logfile);
1996
1997         free(logfile);
1998         return 0;
1999
2000 error:
2001         free(logfile);
2002         return -1;
2003 }
2004
2005 static int files_create_reflog(struct ref_store *ref_store,
2006                                const char *refname, int force_create,
2007                                struct strbuf *err)
2008 {
2009         struct files_ref_store *refs =
2010                 files_downcast(ref_store, REF_STORE_WRITE, "create_reflog");
2011         int fd;
2012
2013         if (log_ref_setup(refs, refname, force_create, &fd, err))
2014                 return -1;
2015
2016         if (fd >= 0)
2017                 close(fd);
2018
2019         return 0;
2020 }
2021
2022 static int log_ref_write_fd(int fd, const struct object_id *old_oid,
2023                             const struct object_id *new_oid,
2024                             const char *committer, const char *msg)
2025 {
2026         int msglen, written;
2027         unsigned maxlen, len;
2028         char *logrec;
2029
2030         msglen = msg ? strlen(msg) : 0;
2031         maxlen = strlen(committer) + msglen + 100;
2032         logrec = xmalloc(maxlen);
2033         len = xsnprintf(logrec, maxlen, "%s %s %s\n",
2034                         oid_to_hex(old_oid),
2035                         oid_to_hex(new_oid),
2036                         committer);
2037         if (msglen)
2038                 len += copy_reflog_msg(logrec + len - 1, msg) - 1;
2039
2040         written = len <= maxlen ? write_in_full(fd, logrec, len) : -1;
2041         free(logrec);
2042         if (written < 0)
2043                 return -1;
2044
2045         return 0;
2046 }
2047
2048 static int files_log_ref_write(struct files_ref_store *refs,
2049                                const char *refname, const struct object_id *old_oid,
2050                                const struct object_id *new_oid, const char *msg,
2051                                int flags, struct strbuf *err)
2052 {
2053         int logfd, result;
2054
2055         if (log_all_ref_updates == LOG_REFS_UNSET)
2056                 log_all_ref_updates = is_bare_repository() ? LOG_REFS_NONE : LOG_REFS_NORMAL;
2057
2058         result = log_ref_setup(refs, refname,
2059                                flags & REF_FORCE_CREATE_REFLOG,
2060                                &logfd, err);
2061
2062         if (result)
2063                 return result;
2064
2065         if (logfd < 0)
2066                 return 0;
2067         result = log_ref_write_fd(logfd, old_oid, new_oid,
2068                                   git_committer_info(0), msg);
2069         if (result) {
2070                 struct strbuf sb = STRBUF_INIT;
2071                 int save_errno = errno;
2072
2073                 files_reflog_path(refs, &sb, refname);
2074                 strbuf_addf(err, "unable to append to '%s': %s",
2075                             sb.buf, strerror(save_errno));
2076                 strbuf_release(&sb);
2077                 close(logfd);
2078                 return -1;
2079         }
2080         if (close(logfd)) {
2081                 struct strbuf sb = STRBUF_INIT;
2082                 int save_errno = errno;
2083
2084                 files_reflog_path(refs, &sb, refname);
2085                 strbuf_addf(err, "unable to append to '%s': %s",
2086                             sb.buf, strerror(save_errno));
2087                 strbuf_release(&sb);
2088                 return -1;
2089         }
2090         return 0;
2091 }
2092
2093 /*
2094  * Write sha1 into the open lockfile, then close the lockfile. On
2095  * errors, rollback the lockfile, fill in *err and
2096  * return -1.
2097  */
2098 static int write_ref_to_lockfile(struct ref_lock *lock,
2099                                  const struct object_id *oid, struct strbuf *err)
2100 {
2101         static char term = '\n';
2102         struct object *o;
2103         int fd;
2104
2105         o = parse_object(oid);
2106         if (!o) {
2107                 strbuf_addf(err,
2108                             "trying to write ref '%s' with nonexistent object %s",
2109                             lock->ref_name, oid_to_hex(oid));
2110                 unlock_ref(lock);
2111                 return -1;
2112         }
2113         if (o->type != OBJ_COMMIT && is_branch(lock->ref_name)) {
2114                 strbuf_addf(err,
2115                             "trying to write non-commit object %s to branch '%s'",
2116                             oid_to_hex(oid), lock->ref_name);
2117                 unlock_ref(lock);
2118                 return -1;
2119         }
2120         fd = get_lock_file_fd(lock->lk);
2121         if (write_in_full(fd, oid_to_hex(oid), GIT_SHA1_HEXSZ) < 0 ||
2122             write_in_full(fd, &term, 1) < 0 ||
2123             close_ref(lock) < 0) {
2124                 strbuf_addf(err,
2125                             "couldn't write '%s'", get_lock_file_path(lock->lk));
2126                 unlock_ref(lock);
2127                 return -1;
2128         }
2129         return 0;
2130 }
2131
2132 /*
2133  * Commit a change to a loose reference that has already been written
2134  * to the loose reference lockfile. Also update the reflogs if
2135  * necessary, using the specified lockmsg (which can be NULL).
2136  */
2137 static int commit_ref_update(struct files_ref_store *refs,
2138                              struct ref_lock *lock,
2139                              const struct object_id *oid, const char *logmsg,
2140                              struct strbuf *err)
2141 {
2142         files_assert_main_repository(refs, "commit_ref_update");
2143
2144         clear_loose_ref_cache(refs);
2145         if (files_log_ref_write(refs, lock->ref_name,
2146                                 &lock->old_oid, oid,
2147                                 logmsg, 0, err)) {
2148                 char *old_msg = strbuf_detach(err, NULL);
2149                 strbuf_addf(err, "cannot update the ref '%s': %s",
2150                             lock->ref_name, old_msg);
2151                 free(old_msg);
2152                 unlock_ref(lock);
2153                 return -1;
2154         }
2155
2156         if (strcmp(lock->ref_name, "HEAD") != 0) {
2157                 /*
2158                  * Special hack: If a branch is updated directly and HEAD
2159                  * points to it (may happen on the remote side of a push
2160                  * for example) then logically the HEAD reflog should be
2161                  * updated too.
2162                  * A generic solution implies reverse symref information,
2163                  * but finding all symrefs pointing to the given branch
2164                  * would be rather costly for this rare event (the direct
2165                  * update of a branch) to be worth it.  So let's cheat and
2166                  * check with HEAD only which should cover 99% of all usage
2167                  * scenarios (even 100% of the default ones).
2168                  */
2169                 struct object_id head_oid;
2170                 int head_flag;
2171                 const char *head_ref;
2172
2173                 head_ref = refs_resolve_ref_unsafe(&refs->base, "HEAD",
2174                                                    RESOLVE_REF_READING,
2175                                                    head_oid.hash, &head_flag);
2176                 if (head_ref && (head_flag & REF_ISSYMREF) &&
2177                     !strcmp(head_ref, lock->ref_name)) {
2178                         struct strbuf log_err = STRBUF_INIT;
2179                         if (files_log_ref_write(refs, "HEAD",
2180                                                 &lock->old_oid, oid,
2181                                                 logmsg, 0, &log_err)) {
2182                                 error("%s", log_err.buf);
2183                                 strbuf_release(&log_err);
2184                         }
2185                 }
2186         }
2187
2188         if (commit_ref(lock)) {
2189                 strbuf_addf(err, "couldn't set '%s'", lock->ref_name);
2190                 unlock_ref(lock);
2191                 return -1;
2192         }
2193
2194         unlock_ref(lock);
2195         return 0;
2196 }
2197
2198 static int create_ref_symlink(struct ref_lock *lock, const char *target)
2199 {
2200         int ret = -1;
2201 #ifndef NO_SYMLINK_HEAD
2202         char *ref_path = get_locked_file_path(lock->lk);
2203         unlink(ref_path);
2204         ret = symlink(target, ref_path);
2205         free(ref_path);
2206
2207         if (ret)
2208                 fprintf(stderr, "no symlink - falling back to symbolic ref\n");
2209 #endif
2210         return ret;
2211 }
2212
2213 static void update_symref_reflog(struct files_ref_store *refs,
2214                                  struct ref_lock *lock, const char *refname,
2215                                  const char *target, const char *logmsg)
2216 {
2217         struct strbuf err = STRBUF_INIT;
2218         struct object_id new_oid;
2219         if (logmsg &&
2220             !refs_read_ref_full(&refs->base, target,
2221                                 RESOLVE_REF_READING, new_oid.hash, NULL) &&
2222             files_log_ref_write(refs, refname, &lock->old_oid,
2223                                 &new_oid, logmsg, 0, &err)) {
2224                 error("%s", err.buf);
2225                 strbuf_release(&err);
2226         }
2227 }
2228
2229 static int create_symref_locked(struct files_ref_store *refs,
2230                                 struct ref_lock *lock, const char *refname,
2231                                 const char *target, const char *logmsg)
2232 {
2233         if (prefer_symlink_refs && !create_ref_symlink(lock, target)) {
2234                 update_symref_reflog(refs, lock, refname, target, logmsg);
2235                 return 0;
2236         }
2237
2238         if (!fdopen_lock_file(lock->lk, "w"))
2239                 return error("unable to fdopen %s: %s",
2240                              lock->lk->tempfile.filename.buf, strerror(errno));
2241
2242         update_symref_reflog(refs, lock, refname, target, logmsg);
2243
2244         /* no error check; commit_ref will check ferror */
2245         fprintf(lock->lk->tempfile.fp, "ref: %s\n", target);
2246         if (commit_ref(lock) < 0)
2247                 return error("unable to write symref for %s: %s", refname,
2248                              strerror(errno));
2249         return 0;
2250 }
2251
2252 static int files_create_symref(struct ref_store *ref_store,
2253                                const char *refname, const char *target,
2254                                const char *logmsg)
2255 {
2256         struct files_ref_store *refs =
2257                 files_downcast(ref_store, REF_STORE_WRITE, "create_symref");
2258         struct strbuf err = STRBUF_INIT;
2259         struct ref_lock *lock;
2260         int ret;
2261
2262         lock = lock_ref_sha1_basic(refs, refname, NULL,
2263                                    NULL, NULL, REF_NODEREF, NULL,
2264                                    &err);
2265         if (!lock) {
2266                 error("%s", err.buf);
2267                 strbuf_release(&err);
2268                 return -1;
2269         }
2270
2271         ret = create_symref_locked(refs, lock, refname, target, logmsg);
2272         unlock_ref(lock);
2273         return ret;
2274 }
2275
2276 static int files_reflog_exists(struct ref_store *ref_store,
2277                                const char *refname)
2278 {
2279         struct files_ref_store *refs =
2280                 files_downcast(ref_store, REF_STORE_READ, "reflog_exists");
2281         struct strbuf sb = STRBUF_INIT;
2282         struct stat st;
2283         int ret;
2284
2285         files_reflog_path(refs, &sb, refname);
2286         ret = !lstat(sb.buf, &st) && S_ISREG(st.st_mode);
2287         strbuf_release(&sb);
2288         return ret;
2289 }
2290
2291 static int files_delete_reflog(struct ref_store *ref_store,
2292                                const char *refname)
2293 {
2294         struct files_ref_store *refs =
2295                 files_downcast(ref_store, REF_STORE_WRITE, "delete_reflog");
2296         struct strbuf sb = STRBUF_INIT;
2297         int ret;
2298
2299         files_reflog_path(refs, &sb, refname);
2300         ret = remove_path(sb.buf);
2301         strbuf_release(&sb);
2302         return ret;
2303 }
2304
2305 static int show_one_reflog_ent(struct strbuf *sb, each_reflog_ent_fn fn, void *cb_data)
2306 {
2307         struct object_id ooid, noid;
2308         char *email_end, *message;
2309         timestamp_t timestamp;
2310         int tz;
2311         const char *p = sb->buf;
2312
2313         /* old SP new SP name <email> SP time TAB msg LF */
2314         if (!sb->len || sb->buf[sb->len - 1] != '\n' ||
2315             parse_oid_hex(p, &ooid, &p) || *p++ != ' ' ||
2316             parse_oid_hex(p, &noid, &p) || *p++ != ' ' ||
2317             !(email_end = strchr(p, '>')) ||
2318             email_end[1] != ' ' ||
2319             !(timestamp = parse_timestamp(email_end + 2, &message, 10)) ||
2320             !message || message[0] != ' ' ||
2321             (message[1] != '+' && message[1] != '-') ||
2322             !isdigit(message[2]) || !isdigit(message[3]) ||
2323             !isdigit(message[4]) || !isdigit(message[5]))
2324                 return 0; /* corrupt? */
2325         email_end[1] = '\0';
2326         tz = strtol(message + 1, NULL, 10);
2327         if (message[6] != '\t')
2328                 message += 6;
2329         else
2330                 message += 7;
2331         return fn(&ooid, &noid, p, timestamp, tz, message, cb_data);
2332 }
2333
2334 static char *find_beginning_of_line(char *bob, char *scan)
2335 {
2336         while (bob < scan && *(--scan) != '\n')
2337                 ; /* keep scanning backwards */
2338         /*
2339          * Return either beginning of the buffer, or LF at the end of
2340          * the previous line.
2341          */
2342         return scan;
2343 }
2344
2345 static int files_for_each_reflog_ent_reverse(struct ref_store *ref_store,
2346                                              const char *refname,
2347                                              each_reflog_ent_fn fn,
2348                                              void *cb_data)
2349 {
2350         struct files_ref_store *refs =
2351                 files_downcast(ref_store, REF_STORE_READ,
2352                                "for_each_reflog_ent_reverse");
2353         struct strbuf sb = STRBUF_INIT;
2354         FILE *logfp;
2355         long pos;
2356         int ret = 0, at_tail = 1;
2357
2358         files_reflog_path(refs, &sb, refname);
2359         logfp = fopen(sb.buf, "r");
2360         strbuf_release(&sb);
2361         if (!logfp)
2362                 return -1;
2363
2364         /* Jump to the end */
2365         if (fseek(logfp, 0, SEEK_END) < 0)
2366                 ret = error("cannot seek back reflog for %s: %s",
2367                             refname, strerror(errno));
2368         pos = ftell(logfp);
2369         while (!ret && 0 < pos) {
2370                 int cnt;
2371                 size_t nread;
2372                 char buf[BUFSIZ];
2373                 char *endp, *scanp;
2374
2375                 /* Fill next block from the end */
2376                 cnt = (sizeof(buf) < pos) ? sizeof(buf) : pos;
2377                 if (fseek(logfp, pos - cnt, SEEK_SET)) {
2378                         ret = error("cannot seek back reflog for %s: %s",
2379                                     refname, strerror(errno));
2380                         break;
2381                 }
2382                 nread = fread(buf, cnt, 1, logfp);
2383                 if (nread != 1) {
2384                         ret = error("cannot read %d bytes from reflog for %s: %s",
2385                                     cnt, refname, strerror(errno));
2386                         break;
2387                 }
2388                 pos -= cnt;
2389
2390                 scanp = endp = buf + cnt;
2391                 if (at_tail && scanp[-1] == '\n')
2392                         /* Looking at the final LF at the end of the file */
2393                         scanp--;
2394                 at_tail = 0;
2395
2396                 while (buf < scanp) {
2397                         /*
2398                          * terminating LF of the previous line, or the beginning
2399                          * of the buffer.
2400                          */
2401                         char *bp;
2402
2403                         bp = find_beginning_of_line(buf, scanp);
2404
2405                         if (*bp == '\n') {
2406                                 /*
2407                                  * The newline is the end of the previous line,
2408                                  * so we know we have complete line starting
2409                                  * at (bp + 1). Prefix it onto any prior data
2410                                  * we collected for the line and process it.
2411                                  */
2412                                 strbuf_splice(&sb, 0, 0, bp + 1, endp - (bp + 1));
2413                                 scanp = bp;
2414                                 endp = bp + 1;
2415                                 ret = show_one_reflog_ent(&sb, fn, cb_data);
2416                                 strbuf_reset(&sb);
2417                                 if (ret)
2418                                         break;
2419                         } else if (!pos) {
2420                                 /*
2421                                  * We are at the start of the buffer, and the
2422                                  * start of the file; there is no previous
2423                                  * line, and we have everything for this one.
2424                                  * Process it, and we can end the loop.
2425                                  */
2426                                 strbuf_splice(&sb, 0, 0, buf, endp - buf);
2427                                 ret = show_one_reflog_ent(&sb, fn, cb_data);
2428                                 strbuf_reset(&sb);
2429                                 break;
2430                         }
2431
2432                         if (bp == buf) {
2433                                 /*
2434                                  * We are at the start of the buffer, and there
2435                                  * is more file to read backwards. Which means
2436                                  * we are in the middle of a line. Note that we
2437                                  * may get here even if *bp was a newline; that
2438                                  * just means we are at the exact end of the
2439                                  * previous line, rather than some spot in the
2440                                  * middle.
2441                                  *
2442                                  * Save away what we have to be combined with
2443                                  * the data from the next read.
2444                                  */
2445                                 strbuf_splice(&sb, 0, 0, buf, endp - buf);
2446                                 break;
2447                         }
2448                 }
2449
2450         }
2451         if (!ret && sb.len)
2452                 die("BUG: reverse reflog parser had leftover data");
2453
2454         fclose(logfp);
2455         strbuf_release(&sb);
2456         return ret;
2457 }
2458
2459 static int files_for_each_reflog_ent(struct ref_store *ref_store,
2460                                      const char *refname,
2461                                      each_reflog_ent_fn fn, void *cb_data)
2462 {
2463         struct files_ref_store *refs =
2464                 files_downcast(ref_store, REF_STORE_READ,
2465                                "for_each_reflog_ent");
2466         FILE *logfp;
2467         struct strbuf sb = STRBUF_INIT;
2468         int ret = 0;
2469
2470         files_reflog_path(refs, &sb, refname);
2471         logfp = fopen(sb.buf, "r");
2472         strbuf_release(&sb);
2473         if (!logfp)
2474                 return -1;
2475
2476         while (!ret && !strbuf_getwholeline(&sb, logfp, '\n'))
2477                 ret = show_one_reflog_ent(&sb, fn, cb_data);
2478         fclose(logfp);
2479         strbuf_release(&sb);
2480         return ret;
2481 }
2482
2483 struct files_reflog_iterator {
2484         struct ref_iterator base;
2485
2486         struct ref_store *ref_store;
2487         struct dir_iterator *dir_iterator;
2488         struct object_id oid;
2489 };
2490
2491 static int files_reflog_iterator_advance(struct ref_iterator *ref_iterator)
2492 {
2493         struct files_reflog_iterator *iter =
2494                 (struct files_reflog_iterator *)ref_iterator;
2495         struct dir_iterator *diter = iter->dir_iterator;
2496         int ok;
2497
2498         while ((ok = dir_iterator_advance(diter)) == ITER_OK) {
2499                 int flags;
2500
2501                 if (!S_ISREG(diter->st.st_mode))
2502                         continue;
2503                 if (diter->basename[0] == '.')
2504                         continue;
2505                 if (ends_with(diter->basename, ".lock"))
2506                         continue;
2507
2508                 if (refs_read_ref_full(iter->ref_store,
2509                                        diter->relative_path, 0,
2510                                        iter->oid.hash, &flags)) {
2511                         error("bad ref for %s", diter->path.buf);
2512                         continue;
2513                 }
2514
2515                 iter->base.refname = diter->relative_path;
2516                 iter->base.oid = &iter->oid;
2517                 iter->base.flags = flags;
2518                 return ITER_OK;
2519         }
2520
2521         iter->dir_iterator = NULL;
2522         if (ref_iterator_abort(ref_iterator) == ITER_ERROR)
2523                 ok = ITER_ERROR;
2524         return ok;
2525 }
2526
2527 static int files_reflog_iterator_peel(struct ref_iterator *ref_iterator,
2528                                    struct object_id *peeled)
2529 {
2530         die("BUG: ref_iterator_peel() called for reflog_iterator");
2531 }
2532
2533 static int files_reflog_iterator_abort(struct ref_iterator *ref_iterator)
2534 {
2535         struct files_reflog_iterator *iter =
2536                 (struct files_reflog_iterator *)ref_iterator;
2537         int ok = ITER_DONE;
2538
2539         if (iter->dir_iterator)
2540                 ok = dir_iterator_abort(iter->dir_iterator);
2541
2542         base_ref_iterator_free(ref_iterator);
2543         return ok;
2544 }
2545
2546 static struct ref_iterator_vtable files_reflog_iterator_vtable = {
2547         files_reflog_iterator_advance,
2548         files_reflog_iterator_peel,
2549         files_reflog_iterator_abort
2550 };
2551
2552 static struct ref_iterator *files_reflog_iterator_begin(struct ref_store *ref_store)
2553 {
2554         struct files_ref_store *refs =
2555                 files_downcast(ref_store, REF_STORE_READ,
2556                                "reflog_iterator_begin");
2557         struct files_reflog_iterator *iter = xcalloc(1, sizeof(*iter));
2558         struct ref_iterator *ref_iterator = &iter->base;
2559         struct strbuf sb = STRBUF_INIT;
2560
2561         base_ref_iterator_init(ref_iterator, &files_reflog_iterator_vtable);
2562         files_reflog_path(refs, &sb, NULL);
2563         iter->dir_iterator = dir_iterator_begin(sb.buf);
2564         iter->ref_store = ref_store;
2565         strbuf_release(&sb);
2566         return ref_iterator;
2567 }
2568
2569 /*
2570  * If update is a direct update of head_ref (the reference pointed to
2571  * by HEAD), then add an extra REF_LOG_ONLY update for HEAD.
2572  */
2573 static int split_head_update(struct ref_update *update,
2574                              struct ref_transaction *transaction,
2575                              const char *head_ref,
2576                              struct string_list *affected_refnames,
2577                              struct strbuf *err)
2578 {
2579         struct string_list_item *item;
2580         struct ref_update *new_update;
2581
2582         if ((update->flags & REF_LOG_ONLY) ||
2583             (update->flags & REF_ISPRUNING) ||
2584             (update->flags & REF_UPDATE_VIA_HEAD))
2585                 return 0;
2586
2587         if (strcmp(update->refname, head_ref))
2588                 return 0;
2589
2590         /*
2591          * First make sure that HEAD is not already in the
2592          * transaction. This insertion is O(N) in the transaction
2593          * size, but it happens at most once per transaction.
2594          */
2595         item = string_list_insert(affected_refnames, "HEAD");
2596         if (item->util) {
2597                 /* An entry already existed */
2598                 strbuf_addf(err,
2599                             "multiple updates for 'HEAD' (including one "
2600                             "via its referent '%s') are not allowed",
2601                             update->refname);
2602                 return TRANSACTION_NAME_CONFLICT;
2603         }
2604
2605         new_update = ref_transaction_add_update(
2606                         transaction, "HEAD",
2607                         update->flags | REF_LOG_ONLY | REF_NODEREF,
2608                         update->new_oid.hash, update->old_oid.hash,
2609                         update->msg);
2610
2611         item->util = new_update;
2612
2613         return 0;
2614 }
2615
2616 /*
2617  * update is for a symref that points at referent and doesn't have
2618  * REF_NODEREF set. Split it into two updates:
2619  * - The original update, but with REF_LOG_ONLY and REF_NODEREF set
2620  * - A new, separate update for the referent reference
2621  * Note that the new update will itself be subject to splitting when
2622  * the iteration gets to it.
2623  */
2624 static int split_symref_update(struct files_ref_store *refs,
2625                                struct ref_update *update,
2626                                const char *referent,
2627                                struct ref_transaction *transaction,
2628                                struct string_list *affected_refnames,
2629                                struct strbuf *err)
2630 {
2631         struct string_list_item *item;
2632         struct ref_update *new_update;
2633         unsigned int new_flags;
2634
2635         /*
2636          * First make sure that referent is not already in the
2637          * transaction. This insertion is O(N) in the transaction
2638          * size, but it happens at most once per symref in a
2639          * transaction.
2640          */
2641         item = string_list_insert(affected_refnames, referent);
2642         if (item->util) {
2643                 /* An entry already existed */
2644                 strbuf_addf(err,
2645                             "multiple updates for '%s' (including one "
2646                             "via symref '%s') are not allowed",
2647                             referent, update->refname);
2648                 return TRANSACTION_NAME_CONFLICT;
2649         }
2650
2651         new_flags = update->flags;
2652         if (!strcmp(update->refname, "HEAD")) {
2653                 /*
2654                  * Record that the new update came via HEAD, so that
2655                  * when we process it, split_head_update() doesn't try
2656                  * to add another reflog update for HEAD. Note that
2657                  * this bit will be propagated if the new_update
2658                  * itself needs to be split.
2659                  */
2660                 new_flags |= REF_UPDATE_VIA_HEAD;
2661         }
2662
2663         new_update = ref_transaction_add_update(
2664                         transaction, referent, new_flags,
2665                         update->new_oid.hash, update->old_oid.hash,
2666                         update->msg);
2667
2668         new_update->parent_update = update;
2669
2670         /*
2671          * Change the symbolic ref update to log only. Also, it
2672          * doesn't need to check its old SHA-1 value, as that will be
2673          * done when new_update is processed.
2674          */
2675         update->flags |= REF_LOG_ONLY | REF_NODEREF;
2676         update->flags &= ~REF_HAVE_OLD;
2677
2678         item->util = new_update;
2679
2680         return 0;
2681 }
2682
2683 /*
2684  * Return the refname under which update was originally requested.
2685  */
2686 static const char *original_update_refname(struct ref_update *update)
2687 {
2688         while (update->parent_update)
2689                 update = update->parent_update;
2690
2691         return update->refname;
2692 }
2693
2694 /*
2695  * Check whether the REF_HAVE_OLD and old_oid values stored in update
2696  * are consistent with oid, which is the reference's current value. If
2697  * everything is OK, return 0; otherwise, write an error message to
2698  * err and return -1.
2699  */
2700 static int check_old_oid(struct ref_update *update, struct object_id *oid,
2701                          struct strbuf *err)
2702 {
2703         if (!(update->flags & REF_HAVE_OLD) ||
2704                    !oidcmp(oid, &update->old_oid))
2705                 return 0;
2706
2707         if (is_null_oid(&update->old_oid))
2708                 strbuf_addf(err, "cannot lock ref '%s': "
2709                             "reference already exists",
2710                             original_update_refname(update));
2711         else if (is_null_oid(oid))
2712                 strbuf_addf(err, "cannot lock ref '%s': "
2713                             "reference is missing but expected %s",
2714                             original_update_refname(update),
2715                             oid_to_hex(&update->old_oid));
2716         else
2717                 strbuf_addf(err, "cannot lock ref '%s': "
2718                             "is at %s but expected %s",
2719                             original_update_refname(update),
2720                             oid_to_hex(oid),
2721                             oid_to_hex(&update->old_oid));
2722
2723         return -1;
2724 }
2725
2726 /*
2727  * Prepare for carrying out update:
2728  * - Lock the reference referred to by update.
2729  * - Read the reference under lock.
2730  * - Check that its old SHA-1 value (if specified) is correct, and in
2731  *   any case record it in update->lock->old_oid for later use when
2732  *   writing the reflog.
2733  * - If it is a symref update without REF_NODEREF, split it up into a
2734  *   REF_LOG_ONLY update of the symref and add a separate update for
2735  *   the referent to transaction.
2736  * - If it is an update of head_ref, add a corresponding REF_LOG_ONLY
2737  *   update of HEAD.
2738  */
2739 static int lock_ref_for_update(struct files_ref_store *refs,
2740                                struct ref_update *update,
2741                                struct ref_transaction *transaction,
2742                                const char *head_ref,
2743                                struct string_list *affected_refnames,
2744                                struct strbuf *err)
2745 {
2746         struct strbuf referent = STRBUF_INIT;
2747         int mustexist = (update->flags & REF_HAVE_OLD) &&
2748                 !is_null_oid(&update->old_oid);
2749         int ret;
2750         struct ref_lock *lock;
2751
2752         files_assert_main_repository(refs, "lock_ref_for_update");
2753
2754         if ((update->flags & REF_HAVE_NEW) && is_null_oid(&update->new_oid))
2755                 update->flags |= REF_DELETING;
2756
2757         if (head_ref) {
2758                 ret = split_head_update(update, transaction, head_ref,
2759                                         affected_refnames, err);
2760                 if (ret)
2761                         return ret;
2762         }
2763
2764         ret = lock_raw_ref(refs, update->refname, mustexist,
2765                            affected_refnames, NULL,
2766                            &lock, &referent,
2767                            &update->type, err);
2768         if (ret) {
2769                 char *reason;
2770
2771                 reason = strbuf_detach(err, NULL);
2772                 strbuf_addf(err, "cannot lock ref '%s': %s",
2773                             original_update_refname(update), reason);
2774                 free(reason);
2775                 return ret;
2776         }
2777
2778         update->backend_data = lock;
2779
2780         if (update->type & REF_ISSYMREF) {
2781                 if (update->flags & REF_NODEREF) {
2782                         /*
2783                          * We won't be reading the referent as part of
2784                          * the transaction, so we have to read it here
2785                          * to record and possibly check old_sha1:
2786                          */
2787                         if (refs_read_ref_full(&refs->base,
2788                                                referent.buf, 0,
2789                                                lock->old_oid.hash, NULL)) {
2790                                 if (update->flags & REF_HAVE_OLD) {
2791                                         strbuf_addf(err, "cannot lock ref '%s': "
2792                                                     "error reading reference",
2793                                                     original_update_refname(update));
2794                                         return -1;
2795                                 }
2796                         } else if (check_old_oid(update, &lock->old_oid, err)) {
2797                                 return TRANSACTION_GENERIC_ERROR;
2798                         }
2799                 } else {
2800                         /*
2801                          * Create a new update for the reference this
2802                          * symref is pointing at. Also, we will record
2803                          * and verify old_sha1 for this update as part
2804                          * of processing the split-off update, so we
2805                          * don't have to do it here.
2806                          */
2807                         ret = split_symref_update(refs, update,
2808                                                   referent.buf, transaction,
2809                                                   affected_refnames, err);
2810                         if (ret)
2811                                 return ret;
2812                 }
2813         } else {
2814                 struct ref_update *parent_update;
2815
2816                 if (check_old_oid(update, &lock->old_oid, err))
2817                         return TRANSACTION_GENERIC_ERROR;
2818
2819                 /*
2820                  * If this update is happening indirectly because of a
2821                  * symref update, record the old SHA-1 in the parent
2822                  * update:
2823                  */
2824                 for (parent_update = update->parent_update;
2825                      parent_update;
2826                      parent_update = parent_update->parent_update) {
2827                         struct ref_lock *parent_lock = parent_update->backend_data;
2828                         oidcpy(&parent_lock->old_oid, &lock->old_oid);
2829                 }
2830         }
2831
2832         if ((update->flags & REF_HAVE_NEW) &&
2833             !(update->flags & REF_DELETING) &&
2834             !(update->flags & REF_LOG_ONLY)) {
2835                 if (!(update->type & REF_ISSYMREF) &&
2836                     !oidcmp(&lock->old_oid, &update->new_oid)) {
2837                         /*
2838                          * The reference already has the desired
2839                          * value, so we don't need to write it.
2840                          */
2841                 } else if (write_ref_to_lockfile(lock, &update->new_oid,
2842                                                  err)) {
2843                         char *write_err = strbuf_detach(err, NULL);
2844
2845                         /*
2846                          * The lock was freed upon failure of
2847                          * write_ref_to_lockfile():
2848                          */
2849                         update->backend_data = NULL;
2850                         strbuf_addf(err,
2851                                     "cannot update ref '%s': %s",
2852                                     update->refname, write_err);
2853                         free(write_err);
2854                         return TRANSACTION_GENERIC_ERROR;
2855                 } else {
2856                         update->flags |= REF_NEEDS_COMMIT;
2857                 }
2858         }
2859         if (!(update->flags & REF_NEEDS_COMMIT)) {
2860                 /*
2861                  * We didn't call write_ref_to_lockfile(), so
2862                  * the lockfile is still open. Close it to
2863                  * free up the file descriptor:
2864                  */
2865                 if (close_ref(lock)) {
2866                         strbuf_addf(err, "couldn't close '%s.lock'",
2867                                     update->refname);
2868                         return TRANSACTION_GENERIC_ERROR;
2869                 }
2870         }
2871         return 0;
2872 }
2873
2874 /*
2875  * Unlock any references in `transaction` that are still locked, and
2876  * mark the transaction closed.
2877  */
2878 static void files_transaction_cleanup(struct ref_transaction *transaction)
2879 {
2880         size_t i;
2881
2882         for (i = 0; i < transaction->nr; i++) {
2883                 struct ref_update *update = transaction->updates[i];
2884                 struct ref_lock *lock = update->backend_data;
2885
2886                 if (lock) {
2887                         unlock_ref(lock);
2888                         update->backend_data = NULL;
2889                 }
2890         }
2891
2892         transaction->state = REF_TRANSACTION_CLOSED;
2893 }
2894
2895 static int files_transaction_prepare(struct ref_store *ref_store,
2896                                      struct ref_transaction *transaction,
2897                                      struct strbuf *err)
2898 {
2899         struct files_ref_store *refs =
2900                 files_downcast(ref_store, REF_STORE_WRITE,
2901                                "ref_transaction_prepare");
2902         size_t i;
2903         int ret = 0;
2904         struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
2905         char *head_ref = NULL;
2906         int head_type;
2907         struct object_id head_oid;
2908
2909         assert(err);
2910
2911         if (!transaction->nr)
2912                 goto cleanup;
2913
2914         /*
2915          * Fail if a refname appears more than once in the
2916          * transaction. (If we end up splitting up any updates using
2917          * split_symref_update() or split_head_update(), those
2918          * functions will check that the new updates don't have the
2919          * same refname as any existing ones.)
2920          */
2921         for (i = 0; i < transaction->nr; i++) {
2922                 struct ref_update *update = transaction->updates[i];
2923                 struct string_list_item *item =
2924                         string_list_append(&affected_refnames, update->refname);
2925
2926                 /*
2927                  * We store a pointer to update in item->util, but at
2928                  * the moment we never use the value of this field
2929                  * except to check whether it is non-NULL.
2930                  */
2931                 item->util = update;
2932         }
2933         string_list_sort(&affected_refnames);
2934         if (ref_update_reject_duplicates(&affected_refnames, err)) {
2935                 ret = TRANSACTION_GENERIC_ERROR;
2936                 goto cleanup;
2937         }
2938
2939         /*
2940          * Special hack: If a branch is updated directly and HEAD
2941          * points to it (may happen on the remote side of a push
2942          * for example) then logically the HEAD reflog should be
2943          * updated too.
2944          *
2945          * A generic solution would require reverse symref lookups,
2946          * but finding all symrefs pointing to a given branch would be
2947          * rather costly for this rare event (the direct update of a
2948          * branch) to be worth it. So let's cheat and check with HEAD
2949          * only, which should cover 99% of all usage scenarios (even
2950          * 100% of the default ones).
2951          *
2952          * So if HEAD is a symbolic reference, then record the name of
2953          * the reference that it points to. If we see an update of
2954          * head_ref within the transaction, then split_head_update()
2955          * arranges for the reflog of HEAD to be updated, too.
2956          */
2957         head_ref = refs_resolve_refdup(ref_store, "HEAD",
2958                                        RESOLVE_REF_NO_RECURSE,
2959                                        head_oid.hash, &head_type);
2960
2961         if (head_ref && !(head_type & REF_ISSYMREF)) {
2962                 FREE_AND_NULL(head_ref);
2963         }
2964
2965         /*
2966          * Acquire all locks, verify old values if provided, check
2967          * that new values are valid, and write new values to the
2968          * lockfiles, ready to be activated. Only keep one lockfile
2969          * open at a time to avoid running out of file descriptors.
2970          * Note that lock_ref_for_update() might append more updates
2971          * to the transaction.
2972          */
2973         for (i = 0; i < transaction->nr; i++) {
2974                 struct ref_update *update = transaction->updates[i];
2975
2976                 ret = lock_ref_for_update(refs, update, transaction,
2977                                           head_ref, &affected_refnames, err);
2978                 if (ret)
2979                         break;
2980         }
2981
2982 cleanup:
2983         free(head_ref);
2984         string_list_clear(&affected_refnames, 0);
2985
2986         if (ret)
2987                 files_transaction_cleanup(transaction);
2988         else
2989                 transaction->state = REF_TRANSACTION_PREPARED;
2990
2991         return ret;
2992 }
2993
2994 static int files_transaction_finish(struct ref_store *ref_store,
2995                                     struct ref_transaction *transaction,
2996                                     struct strbuf *err)
2997 {
2998         struct files_ref_store *refs =
2999                 files_downcast(ref_store, 0, "ref_transaction_finish");
3000         size_t i;
3001         int ret = 0;
3002         struct string_list refs_to_delete = STRING_LIST_INIT_NODUP;
3003         struct string_list_item *ref_to_delete;
3004         struct strbuf sb = STRBUF_INIT;
3005
3006         assert(err);
3007
3008         if (!transaction->nr) {
3009                 transaction->state = REF_TRANSACTION_CLOSED;
3010                 return 0;
3011         }
3012
3013         /* Perform updates first so live commits remain referenced */
3014         for (i = 0; i < transaction->nr; i++) {
3015                 struct ref_update *update = transaction->updates[i];
3016                 struct ref_lock *lock = update->backend_data;
3017
3018                 if (update->flags & REF_NEEDS_COMMIT ||
3019                     update->flags & REF_LOG_ONLY) {
3020                         if (files_log_ref_write(refs,
3021                                                 lock->ref_name,
3022                                                 &lock->old_oid,
3023                                                 &update->new_oid,
3024                                                 update->msg, update->flags,
3025                                                 err)) {
3026                                 char *old_msg = strbuf_detach(err, NULL);
3027
3028                                 strbuf_addf(err, "cannot update the ref '%s': %s",
3029                                             lock->ref_name, old_msg);
3030                                 free(old_msg);
3031                                 unlock_ref(lock);
3032                                 update->backend_data = NULL;
3033                                 ret = TRANSACTION_GENERIC_ERROR;
3034                                 goto cleanup;
3035                         }
3036                 }
3037                 if (update->flags & REF_NEEDS_COMMIT) {
3038                         clear_loose_ref_cache(refs);
3039                         if (commit_ref(lock)) {
3040                                 strbuf_addf(err, "couldn't set '%s'", lock->ref_name);
3041                                 unlock_ref(lock);
3042                                 update->backend_data = NULL;
3043                                 ret = TRANSACTION_GENERIC_ERROR;
3044                                 goto cleanup;
3045                         }
3046                 }
3047         }
3048         /* Perform deletes now that updates are safely completed */
3049         for (i = 0; i < transaction->nr; i++) {
3050                 struct ref_update *update = transaction->updates[i];
3051                 struct ref_lock *lock = update->backend_data;
3052
3053                 if (update->flags & REF_DELETING &&
3054                     !(update->flags & REF_LOG_ONLY)) {
3055                         if (!(update->type & REF_ISPACKED) ||
3056                             update->type & REF_ISSYMREF) {
3057                                 /* It is a loose reference. */
3058                                 strbuf_reset(&sb);
3059                                 files_ref_path(refs, &sb, lock->ref_name);
3060                                 if (unlink_or_msg(sb.buf, err)) {
3061                                         ret = TRANSACTION_GENERIC_ERROR;
3062                                         goto cleanup;
3063                                 }
3064                                 update->flags |= REF_DELETED_LOOSE;
3065                         }
3066
3067                         if (!(update->flags & REF_ISPRUNING))
3068                                 string_list_append(&refs_to_delete,
3069                                                    lock->ref_name);
3070                 }
3071         }
3072
3073         if (repack_without_refs(refs, &refs_to_delete, err)) {
3074                 ret = TRANSACTION_GENERIC_ERROR;
3075                 goto cleanup;
3076         }
3077
3078         /* Delete the reflogs of any references that were deleted: */
3079         for_each_string_list_item(ref_to_delete, &refs_to_delete) {
3080                 strbuf_reset(&sb);
3081                 files_reflog_path(refs, &sb, ref_to_delete->string);
3082                 if (!unlink_or_warn(sb.buf))
3083                         try_remove_empty_parents(refs, ref_to_delete->string,
3084                                                  REMOVE_EMPTY_PARENTS_REFLOG);
3085         }
3086
3087         clear_loose_ref_cache(refs);
3088
3089 cleanup:
3090         files_transaction_cleanup(transaction);
3091
3092         for (i = 0; i < transaction->nr; i++) {
3093                 struct ref_update *update = transaction->updates[i];
3094
3095                 if (update->flags & REF_DELETED_LOOSE) {
3096                         /*
3097                          * The loose reference was deleted. Delete any
3098                          * empty parent directories. (Note that this
3099                          * can only work because we have already
3100                          * removed the lockfile.)
3101                          */
3102                         try_remove_empty_parents(refs, update->refname,
3103                                                  REMOVE_EMPTY_PARENTS_REF);
3104                 }
3105         }
3106
3107         strbuf_release(&sb);
3108         string_list_clear(&refs_to_delete, 0);
3109         return ret;
3110 }
3111
3112 static int files_transaction_abort(struct ref_store *ref_store,
3113                                    struct ref_transaction *transaction,
3114                                    struct strbuf *err)
3115 {
3116         files_transaction_cleanup(transaction);
3117         return 0;
3118 }
3119
3120 static int ref_present(const char *refname,
3121                        const struct object_id *oid, int flags, void *cb_data)
3122 {
3123         struct string_list *affected_refnames = cb_data;
3124
3125         return string_list_has_string(affected_refnames, refname);
3126 }
3127
3128 static int files_initial_transaction_commit(struct ref_store *ref_store,
3129                                             struct ref_transaction *transaction,
3130                                             struct strbuf *err)
3131 {
3132         struct files_ref_store *refs =
3133                 files_downcast(ref_store, REF_STORE_WRITE,
3134                                "initial_ref_transaction_commit");
3135         size_t i;
3136         int ret = 0;
3137         struct string_list affected_refnames = STRING_LIST_INIT_NODUP;
3138
3139         assert(err);
3140
3141         if (transaction->state != REF_TRANSACTION_OPEN)
3142                 die("BUG: commit called for transaction that is not open");
3143
3144         /* Fail if a refname appears more than once in the transaction: */
3145         for (i = 0; i < transaction->nr; i++)
3146                 string_list_append(&affected_refnames,
3147                                    transaction->updates[i]->refname);
3148         string_list_sort(&affected_refnames);
3149         if (ref_update_reject_duplicates(&affected_refnames, err)) {
3150                 ret = TRANSACTION_GENERIC_ERROR;
3151                 goto cleanup;
3152         }
3153
3154         /*
3155          * It's really undefined to call this function in an active
3156          * repository or when there are existing references: we are
3157          * only locking and changing packed-refs, so (1) any
3158          * simultaneous processes might try to change a reference at
3159          * the same time we do, and (2) any existing loose versions of
3160          * the references that we are setting would have precedence
3161          * over our values. But some remote helpers create the remote
3162          * "HEAD" and "master" branches before calling this function,
3163          * so here we really only check that none of the references
3164          * that we are creating already exists.
3165          */
3166         if (refs_for_each_rawref(&refs->base, ref_present,
3167                                  &affected_refnames))
3168                 die("BUG: initial ref transaction called with existing refs");
3169
3170         for (i = 0; i < transaction->nr; i++) {
3171                 struct ref_update *update = transaction->updates[i];
3172
3173                 if ((update->flags & REF_HAVE_OLD) &&
3174                     !is_null_oid(&update->old_oid))
3175                         die("BUG: initial ref transaction with old_sha1 set");
3176                 if (refs_verify_refname_available(&refs->base, update->refname,
3177                                                   &affected_refnames, NULL,
3178                                                   err)) {
3179                         ret = TRANSACTION_NAME_CONFLICT;
3180                         goto cleanup;
3181                 }
3182         }
3183
3184         if (lock_packed_refs(refs, 0)) {
3185                 strbuf_addf(err, "unable to lock packed-refs file: %s",
3186                             strerror(errno));
3187                 ret = TRANSACTION_GENERIC_ERROR;
3188                 goto cleanup;
3189         }
3190
3191         for (i = 0; i < transaction->nr; i++) {
3192                 struct ref_update *update = transaction->updates[i];
3193
3194                 if ((update->flags & REF_HAVE_NEW) &&
3195                     !is_null_oid(&update->new_oid))
3196                         add_packed_ref(refs, update->refname,
3197                                        &update->new_oid);
3198         }
3199
3200         if (commit_packed_refs(refs)) {
3201                 strbuf_addf(err, "unable to commit packed-refs file: %s",
3202                             strerror(errno));
3203                 ret = TRANSACTION_GENERIC_ERROR;
3204                 goto cleanup;
3205         }
3206
3207 cleanup:
3208         transaction->state = REF_TRANSACTION_CLOSED;
3209         string_list_clear(&affected_refnames, 0);
3210         return ret;
3211 }
3212
3213 struct expire_reflog_cb {
3214         unsigned int flags;
3215         reflog_expiry_should_prune_fn *should_prune_fn;
3216         void *policy_cb;
3217         FILE *newlog;
3218         struct object_id last_kept_oid;
3219 };
3220
3221 static int expire_reflog_ent(struct object_id *ooid, struct object_id *noid,
3222                              const char *email, timestamp_t timestamp, int tz,
3223                              const char *message, void *cb_data)
3224 {
3225         struct expire_reflog_cb *cb = cb_data;
3226         struct expire_reflog_policy_cb *policy_cb = cb->policy_cb;
3227
3228         if (cb->flags & EXPIRE_REFLOGS_REWRITE)
3229                 ooid = &cb->last_kept_oid;
3230
3231         if ((*cb->should_prune_fn)(ooid, noid, email, timestamp, tz,
3232                                    message, policy_cb)) {
3233                 if (!cb->newlog)
3234                         printf("would prune %s", message);
3235                 else if (cb->flags & EXPIRE_REFLOGS_VERBOSE)
3236                         printf("prune %s", message);
3237         } else {
3238                 if (cb->newlog) {
3239                         fprintf(cb->newlog, "%s %s %s %"PRItime" %+05d\t%s",
3240                                 oid_to_hex(ooid), oid_to_hex(noid),
3241                                 email, timestamp, tz, message);
3242                         oidcpy(&cb->last_kept_oid, noid);
3243                 }
3244                 if (cb->flags & EXPIRE_REFLOGS_VERBOSE)
3245                         printf("keep %s", message);
3246         }
3247         return 0;
3248 }
3249
3250 static int files_reflog_expire(struct ref_store *ref_store,
3251                                const char *refname, const unsigned char *sha1,
3252                                unsigned int flags,
3253                                reflog_expiry_prepare_fn prepare_fn,
3254                                reflog_expiry_should_prune_fn should_prune_fn,
3255                                reflog_expiry_cleanup_fn cleanup_fn,
3256                                void *policy_cb_data)
3257 {
3258         struct files_ref_store *refs =
3259                 files_downcast(ref_store, REF_STORE_WRITE, "reflog_expire");
3260         static struct lock_file reflog_lock;
3261         struct expire_reflog_cb cb;
3262         struct ref_lock *lock;
3263         struct strbuf log_file_sb = STRBUF_INIT;
3264         char *log_file;
3265         int status = 0;
3266         int type;
3267         struct strbuf err = STRBUF_INIT;
3268         struct object_id oid;
3269
3270         memset(&cb, 0, sizeof(cb));
3271         cb.flags = flags;
3272         cb.policy_cb = policy_cb_data;
3273         cb.should_prune_fn = should_prune_fn;
3274
3275         /*
3276          * The reflog file is locked by holding the lock on the
3277          * reference itself, plus we might need to update the
3278          * reference if --updateref was specified:
3279          */
3280         lock = lock_ref_sha1_basic(refs, refname, sha1,
3281                                    NULL, NULL, REF_NODEREF,
3282                                    &type, &err);
3283         if (!lock) {
3284                 error("cannot lock ref '%s': %s", refname, err.buf);
3285                 strbuf_release(&err);
3286                 return -1;
3287         }
3288         if (!refs_reflog_exists(ref_store, refname)) {
3289                 unlock_ref(lock);
3290                 return 0;
3291         }
3292
3293         files_reflog_path(refs, &log_file_sb, refname);
3294         log_file = strbuf_detach(&log_file_sb, NULL);
3295         if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
3296                 /*
3297                  * Even though holding $GIT_DIR/logs/$reflog.lock has
3298                  * no locking implications, we use the lock_file
3299                  * machinery here anyway because it does a lot of the
3300                  * work we need, including cleaning up if the program
3301                  * exits unexpectedly.
3302                  */
3303                 if (hold_lock_file_for_update(&reflog_lock, log_file, 0) < 0) {
3304                         struct strbuf err = STRBUF_INIT;
3305                         unable_to_lock_message(log_file, errno, &err);
3306                         error("%s", err.buf);
3307                         strbuf_release(&err);
3308                         goto failure;
3309                 }
3310                 cb.newlog = fdopen_lock_file(&reflog_lock, "w");
3311                 if (!cb.newlog) {
3312                         error("cannot fdopen %s (%s)",
3313                               get_lock_file_path(&reflog_lock), strerror(errno));
3314                         goto failure;
3315                 }
3316         }
3317
3318         hashcpy(oid.hash, sha1);
3319
3320         (*prepare_fn)(refname, &oid, cb.policy_cb);
3321         refs_for_each_reflog_ent(ref_store, refname, expire_reflog_ent, &cb);
3322         (*cleanup_fn)(cb.policy_cb);
3323
3324         if (!(flags & EXPIRE_REFLOGS_DRY_RUN)) {
3325                 /*
3326                  * It doesn't make sense to adjust a reference pointed
3327                  * to by a symbolic ref based on expiring entries in
3328                  * the symbolic reference's reflog. Nor can we update
3329                  * a reference if there are no remaining reflog
3330                  * entries.
3331                  */
3332                 int update = (flags & EXPIRE_REFLOGS_UPDATE_REF) &&
3333                         !(type & REF_ISSYMREF) &&
3334                         !is_null_oid(&cb.last_kept_oid);
3335
3336                 if (close_lock_file(&reflog_lock)) {
3337                         status |= error("couldn't write %s: %s", log_file,
3338                                         strerror(errno));
3339                 } else if (update &&
3340                            (write_in_full(get_lock_file_fd(lock->lk),
3341                                 oid_to_hex(&cb.last_kept_oid), GIT_SHA1_HEXSZ) < 0 ||
3342                             write_str_in_full(get_lock_file_fd(lock->lk), "\n") < 0 ||
3343                             close_ref(lock) < 0)) {
3344                         status |= error("couldn't write %s",
3345                                         get_lock_file_path(lock->lk));
3346                         rollback_lock_file(&reflog_lock);
3347                 } else if (commit_lock_file(&reflog_lock)) {
3348                         status |= error("unable to write reflog '%s' (%s)",
3349                                         log_file, strerror(errno));
3350                 } else if (update && commit_ref(lock)) {
3351                         status |= error("couldn't set %s", lock->ref_name);
3352                 }
3353         }
3354         free(log_file);
3355         unlock_ref(lock);
3356         return status;
3357
3358  failure:
3359         rollback_lock_file(&reflog_lock);
3360         free(log_file);
3361         unlock_ref(lock);
3362         return -1;
3363 }
3364
3365 static int files_init_db(struct ref_store *ref_store, struct strbuf *err)
3366 {
3367         struct files_ref_store *refs =
3368                 files_downcast(ref_store, REF_STORE_WRITE, "init_db");
3369         struct strbuf sb = STRBUF_INIT;
3370
3371         /*
3372          * Create .git/refs/{heads,tags}
3373          */
3374         files_ref_path(refs, &sb, "refs/heads");
3375         safe_create_dir(sb.buf, 1);
3376
3377         strbuf_reset(&sb);
3378         files_ref_path(refs, &sb, "refs/tags");
3379         safe_create_dir(sb.buf, 1);
3380
3381         strbuf_release(&sb);
3382         return 0;
3383 }
3384
3385 struct ref_storage_be refs_be_files = {
3386         NULL,
3387         "files",
3388         files_ref_store_create,
3389         files_init_db,
3390         files_transaction_prepare,
3391         files_transaction_finish,
3392         files_transaction_abort,
3393         files_initial_transaction_commit,
3394
3395         files_pack_refs,
3396         files_peel_ref,
3397         files_create_symref,
3398         files_delete_refs,
3399         files_rename_ref,
3400
3401         files_ref_iterator_begin,
3402         files_read_raw_ref,
3403
3404         files_reflog_iterator_begin,
3405         files_for_each_reflog_ent,
3406         files_for_each_reflog_ent_reverse,
3407         files_reflog_exists,
3408         files_create_reflog,
3409         files_delete_reflog,
3410         files_reflog_expire
3411 };