In the check_inode_item function, the extent_end variable used to store the
end of the last file extent that has checked. When it passes to
check_file_extent, if the offset of the next file extent is not equal to
it, there is a gap between the two file extents.
In the case of a gap existing, it is wrong that only add the
extent_num_bytes of this file extent to the invalid extent_end variable as
before. Therefore, lowmem check will false alert that there are gaps
between the subsequent file extents of this inode due to the wrong
extent_end variable.
Solution:
The extent_end variable should set to the sum of the offset and the
extent_num_bytes of the file extent.
Example:
Suppose that lowmem check the following file extent of inode 257.
item 6 key (257 EXTENT_DATA 0) itemoff 15813 itemsize 53
generation 6 type 1 (regular)
extent data disk byte 13631488 nr 4096
extent data offset 0 nr 4096 ram 4096
extent compression 0 (none)
item 7 key (257 EXTENT_DATA 8192) itemoff 15760 itemsize 53
generation 6 type 1 (regular)
extent data disk byte 13631488 nr 4096
extent data offset 0 nr 4096 ram 4096
extent compression 0 (none)
item 8 key (257 EXTENT_DATA 12288) itemoff 15707 itemsize 53
generation 6 type 1 (regular)
extent data disk byte 13631488 nr 4096
extent data offset 0 nr 4096 ram 4096
extent compression 0 (none)
For inode 257, check_inode_item set extent_end to 0, then call
check_file_extent to check item {6,7,8}.
item 6)
offset(0) == extent_end(0)
extent_end = extent_end(0) + extent_num_bytes(4096)
item 7)
offset(8192) != extent_end(4096)
extent_end = extent_end(4096) + extent_num_bytes(4096)
^^^
The old extent_end should replace by offset(8192).
item 8)
offset(12288) != extent_end(8192)
^^^
But there is no gap between item {7,8}.
Fixes: d88da10ddd42 ("btrfs-progs: check: introduce function to check file
extent")
Signed-off-by: Lu Fengqi <lufq.f...@cn.fujitsu.com>
---
check/mode-lowmem.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c
index 1bce44f5658a..370318f0e631 100644
--- a/check/mode-lowmem.c
+++ b/check/mode-lowmem.c
@@ -1974,7 +1974,7 @@ static int check_file_extent(struct btrfs_root *root,
struct btrfs_path *path,
}
}
- *end += extent_num_bytes;
+ *end = fkey.offset + extent_num_bytes;
if (!is_hole)
*size += extent_num_bytes;
--
2.18.0
