btrfs: expand btrfs_find_item() to include find_root_ref functionality

This patch is the second step in bootstrapping the btrfs_find_item
interface. The btrfs_find_root_ref() is similar to the former
__inode_info(); it accepts four of its parameters, and duplicates the
first half of its functionality.

Replace the one former call to btrfs_find_root_ref() with a call to
btrfs_find_item(), along with the defined key type that was used
internally by btrfs_find_root ref, and a null found key. In
btrfs_find_item(), add a test for the null key at the place where
the functionality of btrfs_find_root_ref() ends; btrfs_find_item()
then returns if the test passes. Finally, remove btrfs_find_root_ref().

Signed-off-by: Kelley Nielsen <kelleynnn@gmail.com>
Suggested-by: Zach Brown <zab@redhat.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/ctree.c

@@ -2464,7 +2464,13 @@ static int key_search(struct extent_buffer *b, struct btrfs_key *key,
 /* Proposed generic search function, meant to take the place of the
 * various small search helper functions throughout the code and standardize
 * the search interface. Right now, it only replaces the former __inode_info
-* in backref.c.
+* in backref.c, and the former btrfs_find_root_ref in root-tree.c.
+*
+* If a null key is passed, it returns immediately after running
+* btrfs_search_slot, leaving the path filled as it is and passing its
+* return value upward. If a real key is passed, it will set the caller's
+* path to point to the first item in the tree after its specified
+* objectid, type, and offset for which objectid and type match the input.
 */
 int btrfs_find_item(struct btrfs_root *fs_root, struct btrfs_path *path,
 		u64 iobjectid, u64 ioff, u8 key_type,
@@ -2479,7 +2485,7 @@ int btrfs_find_item(struct btrfs_root *fs_root, struct btrfs_path *path,
 	key.offset = ioff;
 
 	ret = btrfs_search_slot(NULL, fs_root, &key, path, 0, 0);
-	if (ret < 0)
+	if ((ret < 0) || (found_key == NULL))
 		return ret;
 
 	eb = path->nodes[0];

fs/btrfs/inode.c

@@ -4673,9 +4673,9 @@ static int fixup_tree_root_location(struct btrfs_root *root,
 	}
 
 	err = -ENOENT;
-	ret = btrfs_find_root_ref(root->fs_info->tree_root, path,
-				  BTRFS_I(dir)->root->root_key.objectid,
-				  location->objectid);
+	ret = btrfs_find_item(root->fs_info->tree_root, path,
+				BTRFS_I(dir)->root->root_key.objectid,
+				location->objectid, BTRFS_ROOT_REF_KEY, NULL);
 	if (ret) {
 		if (ret < 0)
 			err = ret;

fs/btrfs/root-tree.c

@@ -400,21 +400,6 @@ out:
 	return err;
 }
 
-int btrfs_find_root_ref(struct btrfs_root *tree_root,
-		   struct btrfs_path *path,
-		   u64 root_id, u64 ref_id)
-{
-	struct btrfs_key key;
-	int ret;
-
-	key.objectid = root_id;
-	key.type = BTRFS_ROOT_REF_KEY;
-	key.offset = ref_id;
-
-	ret = btrfs_search_slot(NULL, tree_root, &key, path, 0, 0);
-	return ret;
-}
-
 /*
  * add a btrfs_root_ref item.  type is either BTRFS_ROOT_REF_KEY
  * or BTRFS_ROOT_BACKREF_KEY.