btrfs: send: avoid unnecessary path allocations when finding extent clone

When looking for an extent clone, at find_extent_clone(), we start by
allocating a path and then check for cases where we can't have clones
and exit immediately in those cases. It's a waste of time to allocate
the path before those cases, so reorder the logic so that we check for
those cases before allocating the path.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/send.c

@@ -1365,40 +1365,35 @@ static int find_extent_clone(struct send_ctx *sctx,
 	int compressed;
 	u32 i;
 
-	tmp_path = alloc_path_for_send();
-	if (!tmp_path)
-		return -ENOMEM;
-
-	/* We only use this path under the commit sem */
-	tmp_path->need_commit_sem = 0;
-
 	if (data_offset >= ino_size) {
 		/*
 		 * There may be extents that lie behind the file's size.
 		 * I at least had this in combination with snapshotting while
 		 * writing large files.
 		 */
-		ret = 0;
-		goto out;
+		return 0;
 	}
 
-	fi = btrfs_item_ptr(eb, path->slots[0],
-			struct btrfs_file_extent_item);
+	fi = btrfs_item_ptr(eb, path->slots[0], struct btrfs_file_extent_item);
 	extent_type = btrfs_file_extent_type(eb, fi);
-	if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
-		ret = -ENOENT;
-		goto out;
-	}
-	compressed = btrfs_file_extent_compression(eb, fi);
+	if (extent_type == BTRFS_FILE_EXTENT_INLINE)
+		return -ENOENT;
 
-	num_bytes = btrfs_file_extent_num_bytes(eb, fi);
 	disk_byte = btrfs_file_extent_disk_bytenr(eb, fi);
-	if (disk_byte == 0) {
-		ret = -ENOENT;
-		goto out;
-	}
+	if (disk_byte == 0)
+		return -ENOENT;
+
+	compressed = btrfs_file_extent_compression(eb, fi);
+	num_bytes = btrfs_file_extent_num_bytes(eb, fi);
 	logical = disk_byte + btrfs_file_extent_offset(eb, fi);
 
+	tmp_path = alloc_path_for_send();
+	if (!tmp_path)
+		return -ENOMEM;
+
+	/* We only use this path under the commit sem */
+	tmp_path->need_commit_sem = 0;
+
 	down_read(&fs_info->commit_root_sem);
 	ret = extent_from_logical(fs_info, disk_byte, tmp_path,
 				  &found_key, &flags);