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btrfs: introduce btrfs_for_each_slot iterator macro

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There is a common pattern when searching for a key in btrfs:

* Call btrfs_search_slot to find the slot for the key
* Enter an endless loop:
  * If the found slot is larger than the no. of items in the current
    leaf, check the next leaf
  * If it's still not found in the next leaf, terminate the loop
  * Otherwise do something with the found key
  * Increment the current slot and continue

To reduce code duplication, we can replace this code pattern with an
iterator macro, similar to the existing for_each_X macros found
elsewhere in the kernel.  This also makes the code easier to understand
for newcomers by putting a name to the encapsulated functionality.

Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Signed-off-by: Gabriel Niebler <gniebler@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Gabriel Niebler 2022-03-09 14:50:38 +01:00 committed by David Sterba
parent e360d2f581
commit 62142be363
2 changed files with 66 additions and 0 deletions
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37
fs/btrfs/ctree.c
View file

@ -2298,6 +2298,43 @@ int btrfs_search_backwards(struct btrfs_root *root, struct btrfs_key *key,
return ret;
}
/**
* Search for a valid slot for the given path.
*
* @root: The root node of the tree.
* @key: Will contain a valid item if found.
* @path: The starting point to validate the slot.
*
* Return: 0 if the item is valid
* 1 if not found
* <0 if error.
*/
int btrfs_get_next_valid_item(struct btrfs_root *root, struct btrfs_key *key,
struct btrfs_path *path)
{
while (1) {
int ret;
const int slot = path->slots[0];
const struct extent_buffer *leaf = path->nodes[0];
/* This is where we start walking the path. */
if (slot >= btrfs_header_nritems(leaf)) {
/*
* If we've reached the last slot in this leaf we need
* to go to the next leaf and reset the path.
*/
ret = btrfs_next_leaf(root, path);
if (ret)
return ret;
continue;
}
/* Store the found, valid item in @key. */
btrfs_item_key_to_cpu(leaf, key, slot);
break;
}
return 0;
}
/*
* adjust the pointers going up the tree, starting at level
* making sure the right key of each node is points to 'key'.

29
fs/btrfs/ctree.h
View file

@ -3039,6 +3039,35 @@ int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path,
int btrfs_search_backwards(struct btrfs_root *root, struct btrfs_key *key,
struct btrfs_path *path);
int btrfs_get_next_valid_item(struct btrfs_root *root, struct btrfs_key *key,
struct btrfs_path *path);
/*
* Search in @root for a given @key, and store the slot found in @found_key.
*
* @root: The root node of the tree.
* @key: The key we are looking for.
* @found_key: Will hold the found item.
* @path: Holds the current slot/leaf.
* @iter_ret: Contains the value returned from btrfs_search_slot or
* btrfs_get_next_valid_item, whichever was executed last.
*
* The @iter_ret is an output variable that will contain the return value of
* btrfs_search_slot, if it encountered an error, or the value returned from
* btrfs_get_next_valid_item otherwise. That return value can be 0, if a valid
* slot was found, 1 if there were no more leaves, and <0 if there was an error.
*
* It's recommended to use a separate variable for iter_ret and then use it to
* set the function return value so there's no confusion of the 0/1/errno
* values stemming from btrfs_search_slot.
*/
#define btrfs_for_each_slot(root, key, found_key, path, iter_ret) \
for (iter_ret = btrfs_search_slot(NULL, (root), (key), (path), 0, 0); \
(iter_ret) >= 0 && \
(iter_ret = btrfs_get_next_valid_item((root), (found_key), (path))) == 0; \
(path)->slots[0]++ \
)
static inline int btrfs_next_old_item(struct btrfs_root *root,
struct btrfs_path *p, u64 time_seq)
{