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

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

[Liu Bo]

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>
---
 fs/btrfs/file.c  |    9 ++++++---
 fs/btrfs/inode.c |   11 ++++++++---
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 1e16b6d..f76b1fd 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2308,9 +2308,12 @@ static int find_desired_extent(struct inode *inode, loff_t *offset, int whence)
 					}
 				}
 
-				*offset = start;
-				free_extent_map(em);
-				break;
+				if (!test_bit(EXTENT_FLAG_PREALLOC,
+					      &em->flags)) {
+					*offset = start;
+					free_extent_map(em);
+					break;
+				}
 			}
 		}
 
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 16d9e8e..7ac41aa 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5572,10 +5572,13 @@ 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;
@@ -5657,6 +5660,8 @@ 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;
-- 
1.7.7.6