btrfs: incorrect handling for fiemap_fill_next_extent return

fiemap_fill_next_extent returns 0 on success, -errno on error, 1 if this was
the last extent that will fit in user array. If 1 is returned, the return
value may eventually returned to user space, which should not happen, according
to manpage of ioctl.

Signed-off-by: Chengyu Song <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Reviewed-by: Liu Bo <[email protected]>
Signed-off-by: Chris Mason <[email protected]>

Author: ChengyuSong

fs/btrfs/extent_io.c

@@ -4514,8 +4514,11 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		}
 		ret = fiemap_fill_next_extent(fieinfo, em_start, disko,
 					      em_len, flags);
-		if (ret)
+		if (ret) {
+			if (ret == 1)
+				ret = 0;
 			goto out_free;
+		}
 	}
 out_free:
 	free_extent_map(em);