From 5d9e75c41d11ca79b1d1ff6ed17c88c9047d1fea Mon Sep 17 00:00:00 2001 From: Jan Schmidt Date: Wed, 16 May 2012 18:25:47 +0200 Subject: [PATCH] Btrfs: add btrfs_search_old_slot The tree modification log together with the current state of the tree gives a consistent, old version of the tree. btrfs_search_old_slot is used to search through this old version and return old (dummy!) extent buffers. Naturally, this function cannot do any tree modifications. Signed-off-by: Jan Schmidt --- fs/btrfs/ctree.c | 319 ++++++++++++++++++++++++++++++++++++++++++++++++++++++- fs/btrfs/ctree.h | 2 + 2 files changed, 317 insertions(+), 4 deletions(-) diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 69ce3f7..0954f17 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -960,6 +960,207 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans, return 0; } +/* + * returns the logical address of the oldest predecessor of the given root. + * entries older than time_seq are ignored. + */ +static struct tree_mod_elem * +__tree_mod_log_oldest_root(struct btrfs_fs_info *fs_info, + struct btrfs_root *root, u64 time_seq) +{ + struct tree_mod_elem *tm; + struct tree_mod_elem *found = NULL; + u64 root_logical = root->node->start; + int looped = 0; + + if (!time_seq) + return 0; + + /* + * the very last operation that's logged for a root is the replacement + * operation (if it is replaced at all). this has the index of the *new* + * root, making it the very first operation that's logged for this root. + */ + while (1) { + tm = tree_mod_log_search_oldest(fs_info, root_logical, + time_seq); + if (!looped && !tm) + return 0; + /* + * we must have key remove operations in the log before the + * replace operation. + */ + BUG_ON(!tm); + + if (tm->op != MOD_LOG_ROOT_REPLACE) + break; + + found = tm; + root_logical = tm->old_root.logical; + BUG_ON(root_logical == root->node->start); + looped = 1; + } + + return found; +} + +/* + * tm is a pointer to the first operation to rewind within eb. then, all + * previous operations will be rewinded (until we reach something older than + * time_seq). + */ +static void +__tree_mod_log_rewind(struct extent_buffer *eb, u64 time_seq, + struct tree_mod_elem *first_tm) +{ + u32 n; + struct rb_node *next; + struct tree_mod_elem *tm = first_tm; + unsigned long o_dst; + unsigned long o_src; + unsigned long p_size = sizeof(struct btrfs_key_ptr); + + n = btrfs_header_nritems(eb); + while (tm && tm->elem.seq >= time_seq) { + /* + * all the operations are recorded with the operator used for + * the modification. as we're going backwards, we do the + * opposite of each operation here. + */ + switch (tm->op) { + case MOD_LOG_KEY_REMOVE_WHILE_FREEING: + BUG_ON(tm->slot < n); + case MOD_LOG_KEY_REMOVE_WHILE_MOVING: + case MOD_LOG_KEY_REMOVE: + btrfs_set_node_key(eb, &tm->key, tm->slot); + btrfs_set_node_blockptr(eb, tm->slot, tm->blockptr); + btrfs_set_node_ptr_generation(eb, tm->slot, + tm->generation); + n++; + break; + case MOD_LOG_KEY_REPLACE: + BUG_ON(tm->slot >= n); + btrfs_set_node_key(eb, &tm->key, tm->slot); + btrfs_set_node_blockptr(eb, tm->slot, tm->blockptr); + btrfs_set_node_ptr_generation(eb, tm->slot, + tm->generation); + break; + case MOD_LOG_KEY_ADD: + if (tm->slot != n - 1) { + o_dst = btrfs_node_key_ptr_offset(tm->slot); + o_src = btrfs_node_key_ptr_offset(tm->slot + 1); + memmove_extent_buffer(eb, o_dst, o_src, p_size); + } + n--; + break; + case MOD_LOG_MOVE_KEYS: + memmove_extent_buffer(eb, tm->slot, tm->move.dst_slot, + tm->move.nr_items * p_size); + break; + case MOD_LOG_ROOT_REPLACE: + /* + * this operation is special. for roots, this must be + * handled explicitly before rewinding. + * for non-roots, this operation may exist if the node + * was a root: root A -> child B; then A gets empty and + * B is promoted to the new root. in the mod log, we'll + * have a root-replace operation for B, a tree block + * that is no root. we simply ignore that operation. + */ + break; + } + next = rb_next(&tm->node); + if (!next) + break; + tm = container_of(next, struct tree_mod_elem, node); + if (tm->index != first_tm->index) + break; + } + btrfs_set_header_nritems(eb, n); +} + +static struct extent_buffer * +tree_mod_log_rewind(struct btrfs_fs_info *fs_info, struct extent_buffer *eb, + u64 time_seq) +{ + struct extent_buffer *eb_rewin; + struct tree_mod_elem *tm; + + if (!time_seq) + return eb; + + if (btrfs_header_level(eb) == 0) + return eb; + + tm = tree_mod_log_search(fs_info, eb->start, time_seq); + if (!tm) + return eb; + + if (tm->op == MOD_LOG_KEY_REMOVE_WHILE_FREEING) { + BUG_ON(tm->slot != 0); + eb_rewin = alloc_dummy_extent_buffer(eb->start, + fs_info->tree_root->nodesize); + BUG_ON(!eb_rewin); + btrfs_set_header_bytenr(eb_rewin, eb->start); + btrfs_set_header_backref_rev(eb_rewin, + btrfs_header_backref_rev(eb)); + btrfs_set_header_owner(eb_rewin, btrfs_header_owner(eb)); + } else { + eb_rewin = btrfs_clone_extent_buffer(eb); + BUG_ON(!eb_rewin); + } + + extent_buffer_get(eb_rewin); + free_extent_buffer(eb); + + __tree_mod_log_rewind(eb_rewin, time_seq, tm); + + return eb_rewin; +} + +static inline struct extent_buffer * +get_old_root(struct btrfs_root *root, u64 time_seq) +{ + struct tree_mod_elem *tm; + struct extent_buffer *eb; + struct tree_mod_root *old_root; + u64 old_generation; + + tm = __tree_mod_log_oldest_root(root->fs_info, root, time_seq); + if (!tm) + return root->node; + + old_root = &tm->old_root; + old_generation = tm->generation; + + tm = tree_mod_log_search(root->fs_info, old_root->logical, time_seq); + /* + * there was an item in the log when __tree_mod_log_oldest_root + * returned. this one must not go away, because the time_seq passed to + * us must be blocking its removal. + */ + BUG_ON(!tm); + + if (old_root->logical == root->node->start) { + /* there are logged operations for the current root */ + eb = btrfs_clone_extent_buffer(root->node); + } else { + /* there's a root replace operation for the current root */ + eb = alloc_dummy_extent_buffer(tm->index << PAGE_CACHE_SHIFT, + root->nodesize); + btrfs_set_header_bytenr(eb, eb->start); + btrfs_set_header_backref_rev(eb, BTRFS_MIXED_BACKREF_REV); + btrfs_set_header_owner(eb, root->root_key.objectid); + } + if (!eb) + return NULL; + btrfs_set_header_level(eb, old_root->level); + btrfs_set_header_generation(eb, old_generation); + __tree_mod_log_rewind(eb, time_seq, tm); + + return eb; +} + static inline int should_cow_block(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct extent_buffer *buf) @@ -1930,7 +2131,7 @@ static int read_block_for_search(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct btrfs_path *p, struct extent_buffer **eb_ret, int level, int slot, - struct btrfs_key *key) + struct btrfs_key *key, u64 time_seq) { u64 blocknr; u64 gen; @@ -2284,7 +2485,7 @@ cow_done: } err = read_block_for_search(trans, root, p, - &b, level, slot, key); + &b, level, slot, key, 0); if (err == -EAGAIN) goto again; if (err) { @@ -2356,6 +2557,116 @@ done: } /* + * Like btrfs_search_slot, this looks for a key in the given tree. It uses the + * current state of the tree together with the operations recorded in the tree + * modification log to search for the key in a previous version of this tree, as + * denoted by the time_seq parameter. + * + * Naturally, there is no support for insert, delete or cow operations. + * + * The resulting path and return value will be set up as if we called + * btrfs_search_slot at that point in time with ins_len and cow both set to 0. + */ +int btrfs_search_old_slot(struct btrfs_root *root, struct btrfs_key *key, + struct btrfs_path *p, u64 time_seq) +{ + struct extent_buffer *b; + int slot; + int ret; + int err; + int level; + int lowest_unlock = 1; + u8 lowest_level = 0; + + lowest_level = p->lowest_level; + WARN_ON(p->nodes[0] != NULL); + + if (p->search_commit_root) { + BUG_ON(time_seq); + return btrfs_search_slot(NULL, root, key, p, 0, 0); + } + +again: + level = 0; + b = get_old_root(root, time_seq); + extent_buffer_get(b); + level = btrfs_header_level(b); + btrfs_tree_read_lock(b); + p->locks[level] = BTRFS_READ_LOCK; + + while (b) { + level = btrfs_header_level(b); + p->nodes[level] = b; + btrfs_clear_path_blocking(p, NULL, 0); + + /* + * we have a lock on b and as long as we aren't changing + * the tree, there is no way to for the items in b to change. + * It is safe to drop the lock on our parent before we + * go through the expensive btree search on b. + */ + btrfs_unlock_up_safe(p, level + 1); + + ret = bin_search(b, key, level, &slot); + + if (level != 0) { + int dec = 0; + if (ret && slot > 0) { + dec = 1; + slot -= 1; + } + p->slots[level] = slot; + unlock_up(p, level, lowest_unlock, 0, NULL); + + if (level == lowest_level) { + if (dec) + p->slots[level]++; + goto done; + } + + err = read_block_for_search(NULL, root, p, &b, level, + slot, key, time_seq); + if (err == -EAGAIN) + goto again; + if (err) { + ret = err; + goto done; + } + + level = btrfs_header_level(b); + err = btrfs_try_tree_read_lock(b); + if (!err) { + btrfs_set_path_blocking(p); + btrfs_tree_read_lock(b); + btrfs_clear_path_blocking(p, b, + BTRFS_READ_LOCK); + } + p->locks[level] = BTRFS_READ_LOCK; + p->nodes[level] = b; + b = tree_mod_log_rewind(root->fs_info, b, time_seq); + if (b != p->nodes[level]) { + btrfs_tree_unlock_rw(p->nodes[level], + p->locks[level]); + p->locks[level] = 0; + p->nodes[level] = b; + } + } else { + p->slots[level] = slot; + unlock_up(p, level, lowest_unlock, 0, NULL); + goto done; + } + } + ret = 1; +done: + if (!p->leave_spinning) + btrfs_set_path_blocking(p); + if (ret < 0) + btrfs_release_path(p); + + return ret; +} + +/* * adjust the pointers going up the tree, starting at level * making sure the right key of each node is points to 'key'. * This is used after shifting pointers to the left, so it stops @@ -4735,7 +5046,7 @@ again: next = c; next_rw_lock = path->locks[level]; ret = read_block_for_search(NULL, root, path, &next, level, - slot, &key); + slot, &key, 0); if (ret == -EAGAIN) goto again; @@ -4772,7 +5083,7 @@ again: break; ret = read_block_for_search(NULL, root, path, &next, level, - 0, &key); + 0, &key, 0); if (ret == -EAGAIN) goto again; diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index e53bfb9..6ba21b1 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -2668,6 +2668,8 @@ int btrfs_duplicate_item(struct btrfs_trans_handle *trans, int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct btrfs_key *key, struct btrfs_path *p, int ins_len, int cow); +int btrfs_search_old_slot(struct btrfs_root *root, struct btrfs_key *key, + struct btrfs_path *p, u64 time_seq); int btrfs_realloc_node(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct extent_buffer *parent, int start_slot, int cache_only, u64 *last_ret, -- 2.7.4