btrfs: introduce btrfs_search_backwards function

It's a common practice to start a search using offset (u64)-1, which is
the u64 maximum value, meaning that we want the search_slot function to
be set in the last item with the same objectid and type.

Once we are in this position, it's a matter to start a search backwards
by calling btrfs_previous_item, which will check if we'll need to go to
a previous leaf and other necessary checks, only to be sure that we are
in last offset of the same object and type.

The new btrfs_search_backwards function does the all these steps when
necessary, and can be used to avoid code duplication.

Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

5 files changed, 40 insertions, 48 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 99b33a5b33c8..84627cbd5b5b 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -2102,6 +2102,27 @@ again:
 }
 
 /*
+ * Execute search and call btrfs_previous_item to traverse backwards if the item
+ * was not found.
+ *
+ * Return 0 if found, 1 if not found and < 0 if error.
+ */
+int btrfs_search_backwards(struct btrfs_root *root, struct btrfs_key *key,
+			   struct btrfs_path *path)
+{
+	int ret;
+
+	ret = btrfs_search_slot(NULL, root, key, path, 0, 0);
+	if (ret > 0)
+		ret = btrfs_previous_item(root, path, key->objectid, key->type);
+
+	if (ret == 0)
+		btrfs_item_key_to_cpu(path->nodes[0], key, path->slots[0]);
+
+	return ret;
+}
+
+/*
  * adjust the pointers going up the tree, starting at level
  * making sure the right key of each node is points to 'key'.
  * This is used after shifting pointers to the left, so it stops
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index f17be4b023cb..a898257ad2b5 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2908,6 +2908,10 @@ static inline int btrfs_insert_empty_item(struct btrfs_trans_handle *trans,
 int btrfs_prev_leaf(struct btrfs_root *root, struct btrfs_path *path);
 int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path,
 			u64 time_seq);
+
+int btrfs_search_backwards(struct btrfs_root *root, struct btrfs_key *key,
+			   struct btrfs_path *path);
+
 static inline int btrfs_next_old_item(struct btrfs_root *root,
 				      struct btrfs_path *p, u64 time_seq)
 {
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 85c8b5a87a6a..ba1dab6a5012 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2389,23 +2389,16 @@ static noinline int btrfs_search_path_in_tree(struct btrfs_fs_info *info,
 	key.offset = (u64)-1;
 
 	while (1) {
-		ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+		ret = btrfs_search_backwards(root, &key, path);
 		if (ret < 0)
 			goto out;
 		else if (ret > 0) {
-			ret = btrfs_previous_item(root, path, dirid,
-						  BTRFS_INODE_REF_KEY);
-			if (ret < 0)
-				goto out;
-			else if (ret > 0) {
-				ret = -ENOENT;
-				goto out;
-			}
+			ret = -ENOENT;
+			goto out;
 		}
 
 		l = path->nodes[0];
 		slot = path->slots[0];
-		btrfs_item_key_to_cpu(l, &key, slot);
 
 		iref = btrfs_item_ptr(l, slot, struct btrfs_inode_ref);
 		len = btrfs_inode_ref_name_len(l, iref);
@@ -2480,23 +2473,16 @@ static int btrfs_search_path_in_tree_user(struct inode *inode,
 		key.type = BTRFS_INODE_REF_KEY;
 		key.offset = (u64)-1;
 		while (1) {
-			ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
-			if (ret < 0) {
+			ret = btrfs_search_backwards(root, &key, path);
+			if (ret < 0)
+				goto out_put;
+			else if (ret > 0) {
+				ret = -ENOENT;
 				goto out_put;
-			} else if (ret > 0) {
-				ret = btrfs_previous_item(root, path, dirid,
-							  BTRFS_INODE_REF_KEY);
-				if (ret < 0) {
-					goto out_put;
-				} else if (ret > 0) {
-					ret = -ENOENT;
-					goto out_put;
-				}
 			}
 
 			leaf = path->nodes[0];
 			slot = path->slots[0];
-			btrfs_item_key_to_cpu(leaf, &key, slot);
 
 			iref = btrfs_item_ptr(leaf, slot, struct btrfs_inode_ref);
 			len = btrfs_inode_ref_name_len(leaf, iref);
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index d444338db3c6..409bee3e7587 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1201,21 +1201,14 @@ char *btrfs_get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
 		key.type = BTRFS_ROOT_BACKREF_KEY;
 		key.offset = (u64)-1;
 
-		ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+		ret = btrfs_search_backwards(root, &key, path);
 		if (ret < 0) {
 			goto err;
 		} else if (ret > 0) {
-			ret = btrfs_previous_item(root, path, subvol_objectid,
-						  BTRFS_ROOT_BACKREF_KEY);
-			if (ret < 0) {
-				goto err;
-			} else if (ret > 0) {
-				ret = -ENOENT;
-				goto err;
-			}
+			ret = -ENOENT;
+			goto err;
 		}
 
-		btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
 		subvol_objectid = key.offset;
 
 		root_ref = btrfs_item_ptr(path->nodes[0], path->slots[0],
@@ -1248,21 +1241,14 @@ char *btrfs_get_subvol_name_from_objectid(struct btrfs_fs_info *fs_info,
 			key.type = BTRFS_INODE_REF_KEY;
 			key.offset = (u64)-1;
 
-			ret = btrfs_search_slot(NULL, fs_root, &key, path, 0, 0);
+			ret = btrfs_search_backwards(fs_root, &key, path);
 			if (ret < 0) {
 				goto err;
 			} else if (ret > 0) {
-				ret = btrfs_previous_item(fs_root, path, dirid,
-							  BTRFS_INODE_REF_KEY);
-				if (ret < 0) {
-					goto err;
-				} else if (ret > 0) {
-					ret = -ENOENT;
-					goto err;
-				}
+				ret = -ENOENT;
+				goto err;
 			}
 
-			btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
 			dirid = key.offset;
 
 			inode_ref = btrfs_item_ptr(path->nodes[0],
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 230192d097c4..536e60c6ade3 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1586,14 +1586,9 @@ again:
 	key.offset = search_start;
 	key.type = BTRFS_DEV_EXTENT_KEY;
 
-	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	ret = btrfs_search_backwards(root, &key, path);
 	if (ret < 0)
 		goto out;
-	if (ret > 0) {
-		ret = btrfs_previous_item(root, path, key.objectid, key.type);
-		if (ret < 0)
-			goto out;
-	}
 
 	while (1) {
 		l = path->nodes[0];