ext4: return hole from ext4_map_blocks()

Currently, ext4_map_blocks() just returns 0 when it finds a hole and
allocation is not requested. However we have all the information
available to tell how large the hole actually is and there are callers
of ext4_map_blocks() which would save some block-by-block hole iteration
if they knew this information. So fill in struct ext4_map_blocks even
for holes with the information we have. We keep returning 0 for holes to
maintain backward compatibility of the function.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 9 insertions, 2 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 7858fc1d2501..2730039d4742 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4374,13 +4374,20 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
         if ((flags & EXT4_GET_BLOCKS_CREATE) == 0) {
                 ext4_lblk_t hole_start, hole_len;
 
+                hole_start = map->m_lblk;
+                hole_len = ext4_ext_determine_hole(inode, path, &hole_start);
                 /*
                  * put just found gap into cache to speed up
                  * subsequent requests
                  */
-                hole_start = map->m_lblk;
-                hole_len = ext4_ext_determine_hole(inode, path, &hole_start);
                 ext4_ext_put_gap_in_cache(inode, hole_start, hole_len);
+
+                /* Update hole_len to reflect hole size after map->m_lblk */
+                if (hole_start != map->m_lblk)
+                        hole_len -= map->m_lblk - hole_start;
+                map->m_pblk = 0;
+                map->m_len = min_t(unsigned int, map->m_len, hole_len);
+
                 goto out2;
         }