Btrfs: fix a bug when llseek for delalloc bytes behind prealloc extents

xfstests case 285 complains.

It it because btrfs did not try to find unwritten delalloc
bytes(only dirty pages, not yet writeback) behind prealloc
extents, it ends up finding nothing while we're with SEEK_DATA.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4ddcf79e7894..ac98384b174e 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5623,10 +5623,13 @@ struct extent_map *btrfs_get_extent_fiemap(struct inode *inode, struct page *pag
                 return em;
         if (em) {
                 /*
-                 * if our em maps to a hole, there might
-                 * actually be delalloc bytes behind it
+                 * if our em maps to
+                 * -  a hole or
+                 * -  a pre-alloc extent,
+                 * there might actually be delalloc bytes behind it.
                  */
-                if (em->block_start != EXTENT_MAP_HOLE)
+                if (em->block_start != EXTENT_MAP_HOLE &&
+                    !test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
                         return em;
                 else
                         hole_em = em;
@@ -5708,6 +5711,8 @@ struct extent_map *btrfs_get_extent_fiemap(struct inode *inode, struct page *pag
                          */
                         em->block_start = hole_em->block_start;
                         em->block_len = hole_len;
+                        if (test_bit(EXTENT_FLAG_PREALLOC, &hole_em->flags))
+                                set_bit(EXTENT_FLAG_PREALLOC, &em->flags);
                 } else {
                         em->start = range_start;
                         em->len = found;