btrfs: introduce btrfs_for_each_slot iterator macro

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>

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index a795e89de3f1e7b4c7015127f301f7311f2d8225..6ae1bf7ab27f5f16646531bc3b1ea084036b7f8f 100644 (file)
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -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'.

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 077c95e9baa50648ad027c78e4b9fb77dbe19853..1c50e051641d865781be7c72d944900b93813dc1 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -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)
 {