Re: [PATCH 1/7] fs: btrfs: Introduce btrfs_for_each_slot

Johannes Thumshirn
2021-08-25T07:42:48Z

On 24/08/2021 19:13, Marcos Paulo de Souza wrote:
> There is a common pattern when search for a key in btrfs:
>
> * Call btrfs_search_slot
> * Endless loop
> * If the found slot is bigger than the current items in the leaf, check the
> next one
> * If still not found in the next leaf, return 1
> * Do something with the code
> * Increment current slot, and continue
>
> This pattern can be improved by creating an iterator macro, similar to
> those for_each_X already existing in the linux kernel. Using this
> approach means to reduce significantly boilerplate code, along making it
> easier to newcomers to understand how to code works.
>
> Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
> ---
> fs/btrfs/ctree.c | 28 ++++++++++++++++++++++++++++
> fs/btrfs/ctree.h | 25 +++++++++++++++++++++++++
> fs/btrfs/xattr.c | 40 ++++++++++++----------------------------
> 3 files changed, 65 insertions(+), 28 deletions(-)
>
> diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
> index 84627cbd5b5b..b1aa6e3987d0 100644
> --- a/fs/btrfs/ctree.c
> +++ b/fs/btrfs/ctree.c
> @@ -2122,6 +2122,34 @@ 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 start point to validate the slot.
> + *
> + * Return 0 if the item is valid, 1 if not found and < 0 if error.
> + */
> +int btrfs_valid_slot(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];
> +
> + if (slot >= btrfs_header_nritems(leaf)) {
> + ret = btrfs_next_leaf(root, path);
> + if (ret)
> + return ret;
> + continue;
> + }
> + 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'.
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index f07c82fafa04..1e3c4a7741ca 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -2912,6 +2912,31 @@ 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_valid_slot(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 returned value from btrfs_search_slot and
> + * btrfs_valid_slot, whatever is executed later.
> + *
> + * The iter_ret is an output variable that will contain the result of the
> + * btrfs_search_slot if it returns an error, or the value returned from
> + * btrfs_valid_slot otherwise. The return value can be 0 if the something was
> + * found, 1 if there weren't bigger leaves, and <0 if error.
> + */
> +#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_valid_slot(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)
> {

Shouldn't below xattr code be in a separate patch? Just like the block-group,
dev-replace, etc changes?

> diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
> index 8a4514283a4b..f85febba1891 100644
> --- a/fs/btrfs/xattr.c
> +++ b/fs/btrfs/xattr.c
> @@ -274,10 +274,12 @@ int btrfs_setxattr_trans(struct inode *inode, const char *name,
> ssize_t btrfs_listxattr(struct dentry *dentry, char *buffer, size_t size)
> {
> struct btrfs_key key;
> + struct btrfs_key found_key;
> struct inode *inode = d_inode(dentry);
> struct btrfs_root *root = BTRFS_I(inode)->root;
> struct btrfs_path *path;
> int ret = 0;
> + int iter_ret = 0;
> size_t total_size = 0, size_left = size;
>
> /*
> @@ -295,44 +297,22 @@ ssize_t btrfs_listxattr(struct dentry *dentry, char *buffer, size_t size)
> path->reada = READA_FORWARD;
>
> /* search for our xattrs */
> - ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
> - if (ret < 0)
> - goto err;
> -
> - while (1) {
> + btrfs_for_each_slot(root, &key, &found_key, path, iter_ret) {
> struct extent_buffer *leaf;
> int slot;
> struct btrfs_dir_item *di;
> - struct btrfs_key found_key;
> u32 item_size;
> u32 cur;
>
> leaf = path->nodes[0];
> slot = path->slots[0];
>
> - /* this is where we start walking through 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 everything
> - */
> - ret = btrfs_next_leaf(root, path);
> - if (ret < 0)
> - goto err;
> - else if (ret > 0)
> - break;
> - continue;
> - }
> -
> - btrfs_item_key_to_cpu(leaf, &found_key, slot);
> -
> /* check to make sure this item is what we want */
> - if (found_key.objectid != key.objectid)
> - break;
> - if (found_key.type > BTRFS_XATTR_ITEM_KEY)
> + if (found_key.objectid != key.objectid ||
> + found_key.type > BTRFS_XATTR_ITEM_KEY)
> break;
> if (found_key.type < BTRFS_XATTR_ITEM_KEY)
> - goto next_item;
> + continue;
>
> di = btrfs_item_ptr(leaf, slot, struct btrfs_dir_item);
> item_size = btrfs_item_size_nr(leaf, slot);
> @@ -365,9 +345,13 @@ ssize_t btrfs_listxattr(struct dentry *dentry, char *buffer, size_t size)
> cur += this_len;
> di = (struct btrfs_dir_item *)((char *)di + this_len);
> }
> -next_item:
> - path->slots[0]++;
> }
> +
> + if (iter_ret < 0) {
> + ret = iter_ret;
> + goto err;
> + }
> +
> ret = total_size;
>
> err:
>