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

Marcos Paulo de Souza
2021-08-24T17:13:02Z

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)
{
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:
--
2.31.1