diff options
Diffstat (limited to 'fs/btrfs/ctree.c')
| -rw-r--r-- | fs/btrfs/ctree.c | 127 |
1 files changed, 117 insertions, 10 deletions
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 50e81f43e6d4..ff3261ff2e19 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -1,5 +1,5 @@ /* - * Copyright (C) 2007 Oracle. All rights reserved. + * Copyright (C) 2007,2008 Oracle. All rights reserved. * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public @@ -54,12 +54,19 @@ struct btrfs_path *btrfs_alloc_path(void) return path; } +/* this also releases the path */ void btrfs_free_path(struct btrfs_path *p) { btrfs_release_path(NULL, p); kmem_cache_free(btrfs_path_cachep, p); } +/* + * path release drops references on the extent buffers in the path + * and it drops any locks held by this path + * + * It is safe to call this on paths that no locks or extent buffers held. + */ void noinline btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p) { int i; @@ -77,6 +84,16 @@ void noinline btrfs_release_path(struct btrfs_root *root, struct btrfs_path *p) } } +/* + * safely gets a reference on the root node of a tree. A lock + * is not taken, so a concurrent writer may put a different node + * at the root of the tree. See btrfs_lock_root_node for the + * looping required. + * + * The extent buffer returned by this has a reference taken, so + * it won't disappear. It may stop being the root of the tree + * at any time because there are no locks held. + */ struct extent_buffer *btrfs_root_node(struct btrfs_root *root) { struct extent_buffer *eb; @@ -87,6 +104,10 @@ struct extent_buffer *btrfs_root_node(struct btrfs_root *root) return eb; } +/* loop around taking references on and locking the root node of the + * tree until you end up with a lock on the root. A locked buffer + * is returned, with a reference held. + */ struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root) { struct extent_buffer *eb; @@ -108,6 +129,10 @@ struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root) return eb; } +/* cowonly root (everything not a reference counted cow subvolume), just get + * put onto a simple dirty list. transaction.c walks this to make sure they + * get properly updated on disk. + */ static void add_root_to_dirty_list(struct btrfs_root *root) { if (root->track_dirty && list_empty(&root->dirty_list)) { @@ -116,6 +141,11 @@ static void add_root_to_dirty_list(struct btrfs_root *root) } } +/* + * used by snapshot creation to make a copy of a root for a tree with + * a given objectid. The buffer with the new root node is returned in + * cow_ret, and this func returns zero on success or a negative error code. + */ int btrfs_copy_root(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct extent_buffer *buf, @@ -167,6 +197,22 @@ int btrfs_copy_root(struct btrfs_trans_handle *trans, return 0; } +/* + * does the dirty work in cow of a single block. The parent block + * (if supplied) is updated to point to the new cow copy. The new + * buffer is marked dirty and returned locked. If you modify the block + * it needs to be marked dirty again. + * + * search_start -- an allocation hint for the new block + * + * empty_size -- a hint that you plan on doing more cow. This is the size in bytes + * the allocator should try to find free next to the block it returns. This is + * just a hint and may be ignored by the allocator. + * + * prealloc_dest -- if you have already reserved a destination for the cow, + * this uses that block instead of allocating a new one. btrfs_alloc_reserved_extent + * is used to finish the allocation. + */ int noinline __btrfs_cow_block(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct extent_buffer *buf, @@ -311,6 +357,11 @@ int noinline __btrfs_cow_block(struct btrfs_trans_handle *trans, return 0; } +/* + * cows a single block, see __btrfs_cow_block for the real work. + * This version of it has extra checks so that a block isn't cow'd more than + * once per transaction, as long as it hasn't been written yet + */ int noinline btrfs_cow_block(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct extent_buffer *buf, struct extent_buffer *parent, int parent_slot, @@ -347,6 +398,10 @@ int noinline btrfs_cow_block(struct btrfs_trans_handle *trans, return ret; } +/* + * helper function for defrag to decide if two blocks pointed to by a + * node are actually close by + */ static int close_blocks(u64 blocknr, u64 other, u32 blocksize) { if (blocknr < other && other - (blocknr + blocksize) < 32768) @@ -381,6 +436,11 @@ static int comp_keys(struct btrfs_disk_key *disk, struct btrfs_key *k2) } +/* + * this is used by the defrag code to go through all the + * leaves pointed to by a node and reallocate them so that + * disk order is close to key order + */ 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, @@ -521,6 +581,10 @@ static inline unsigned int leaf_data_end(struct btrfs_root *root, return btrfs_item_offset_nr(leaf, nr - 1); } +/* + * extra debugging checks to make sure all the items in a key are + * well formed and in the proper order + */ static int check_node(struct btrfs_root *root, struct btrfs_path *path, int level) { @@ -561,6 +625,10 @@ static int check_node(struct btrfs_root *root, struct btrfs_path *path, return 0; } +/* + * extra checking to make sure all the items in a leaf are + * well formed and in the proper order + */ static int check_leaf(struct btrfs_root *root, struct btrfs_path *path, int level) { @@ -782,6 +850,10 @@ static int bin_search(struct extent_buffer *eb, struct btrfs_key *key, return -1; } +/* given a node and slot number, this reads the blocks it points to. The + * extent buffer is returned with a reference taken (but unlocked). + * NULL is returned on error. + */ static noinline struct extent_buffer *read_node_slot(struct btrfs_root *root, struct extent_buffer *parent, int slot) { @@ -798,6 +870,11 @@ static noinline struct extent_buffer *read_node_slot(struct btrfs_root *root, btrfs_node_ptr_generation(parent, slot)); } +/* + * node level balancing, used to make sure nodes are in proper order for + * item deletion. We balance from the top down, so we have to make sure + * that a deletion won't leave an node completely empty later on. + */ static noinline int balance_level(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct btrfs_path *path, int level) @@ -1024,7 +1101,10 @@ enospc: return ret; } -/* returns zero if the push worked, non-zero otherwise */ +/* Node balancing for insertion. Here we only split or push nodes around + * when they are completely full. This is also done top down, so we + * have to be pessimistic. + */ static int noinline push_nodes_for_insert(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct btrfs_path *path, int level) @@ -1150,7 +1230,8 @@ static int noinline push_nodes_for_insert(struct btrfs_trans_handle *trans, } /* - * readahead one full node of leaves + * readahead one full node of leaves, finding things that are close + * to the block in 'slot', and triggering ra on them. */ static noinline void reada_for_search(struct btrfs_root *root, struct btrfs_path *path, @@ -1226,6 +1307,19 @@ static noinline void reada_for_search(struct btrfs_root *root, } } +/* + * when we walk down the tree, it is usually safe to unlock the higher layers in + * the tree. The exceptions are when our path goes through slot 0, because operations + * on the tree might require changing key pointers higher up in the tree. + * + * callers might also have set path->keep_locks, which tells this code to + * keep the lock if the path points to the last slot in the block. This is + * part of walking through the tree, and selecting the next slot in the higher + * block. + * + * lowest_unlock sets the lowest level in the tree we're allowed to unlock. + * so if lowest_unlock is 1, level 0 won't be unlocked + */ static noinline void unlock_up(struct btrfs_path *path, int level, int lowest_unlock) { @@ -2705,6 +2799,12 @@ again: return ret; } +/* + * make the item pointed to by the path smaller. new_size indicates + * how small to make it, and from_end tells us if we just chop bytes + * off the end of the item or if we shift the item to chop bytes off + * the front. + */ int btrfs_truncate_item(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct btrfs_path *path, @@ -2818,6 +2918,9 @@ int btrfs_truncate_item(struct btrfs_trans_handle *trans, return ret; } +/* + * make the item pointed to by the path bigger, data_size is the new size. + */ int btrfs_extend_item(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct btrfs_path *path, u32 data_size) @@ -2897,7 +3000,7 @@ int btrfs_extend_item(struct btrfs_trans_handle *trans, } /* - * Given a key and some data, insert an item into the tree. + * Given a key and some data, insert items into the tree. * This does all the path init required, making room in the tree if needed. */ int btrfs_insert_empty_items(struct btrfs_trans_handle *trans, @@ -3046,9 +3149,8 @@ int btrfs_insert_item(struct btrfs_trans_handle *trans, struct btrfs_root /* * delete the pointer from a given node. * - * If the delete empties a node, the node is removed from the tree, - * continuing all the way the root if required. The root is converted into - * a leaf if all the nodes are emptied. + * the tree should have been previously balanced so the deletion does not + * empty a node. */ static int del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root, struct btrfs_path *path, int level, int slot) @@ -3233,6 +3335,9 @@ int btrfs_del_items(struct btrfs_trans_handle *trans, struct btrfs_root *root, * search the tree again to find a leaf with lesser keys * returns 0 if it found something or 1 if there are no lesser leaves. * returns < 0 on io errors. + * + * This may release the path, and so you may lose any locks held at the + * time you call it. */ int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path) { @@ -3265,9 +3370,7 @@ int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path) /* * A helper function to walk down the tree starting at min_key, and looking * for nodes or leaves that are either in cache or have a minimum - * transaction id. This is used by the btree defrag code, but could - * also be used to search for blocks that have changed since a given - * transaction id. + * transaction id. This is used by the btree defrag code, and tree logging * * This does not cow, but it does stuff the starting key it finds back * into min_key, so you can call btrfs_search_slot with cow=1 on the @@ -3279,6 +3382,10 @@ int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path) * This honors path->lowest_level to prevent descent past a given level * of the tree. * + * min_trans indicates the oldest transaction that you are interested + * in walking through. Any nodes or leaves older than min_trans are + * skipped over (without reading them). + * * returns zero if something useful was found, < 0 on error and 1 if there * was nothing in the tree that matched the search criteria. */ |