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

[Marcos Paulo de Souza <mpdesouza@suse.com>]

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