Re: [PATCH 1/2] Btrfs: fiemap: pass correct bytenr when fm_extent_count is zero
From: Nikolay Borisov <hidden>
Date: 2018-03-07 10:19:48
On 7.03.2018 10:20, robbieko wrote:
From: Robbie Ko <redacted> # mount /dev/vdb5 /mnt/btrfs # dd if=/dev/zero bs=16K count=4 oflag=dsync of=/mnt/btrfs/file # xfs_io -c "fiemap -v" /mnt/btrfs/file /mnt/btrfs/file: EXT: FILE-OFFSET BLOCK-RANGE TOTAL FLAGS 0: [0..127]: 25088..25215 128 0x1 Run fiemap with fm_extent_count set to 0, we'll get wrong value 4 instead of 1.
Wrong value 4 instead of 1 for which exact column, the flags? State this explicitly. Also this seems a bit bogus since fiemap's documentation states: If fm_extent_count is zero, then the fm_extents[] array is ignored (no extents will be returned), and the fm_mapped_extents count will hold the number of extents needed in fm_extents[] to hold the file's current mapping. So when fm_extent_count we shouldn't really be returning anything from kernel.
[REASON] When fm_extent_count is 0, disko is not initialized correctly, The value is 0 in this case, not the right bytenr.
This is too sparse, be more explicit i.e. that disko=0 is passed to emit_fiemap_extent which then leads to issues.
quoted hunk ↗ jump to hunk
[FIX] Use correct disko. Signed-off-by: Robbie Ko <redacted> --- fs/btrfs/extent_io.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 012d638..066b6df 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c@@ -4567,7 +4567,7 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo, offset_in_extent = em_start - em->start; em_end = extent_map_end(em); em_len = em_end - em_start; - disko = 0; + disko = em->block_start + offset_in_extent; flags = 0; /*@@ -4590,8 +4590,6 @@ int extent_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo, u64 bytenr = em->block_start - (em->start - em->orig_start); - disko = em->block_start + offset_in_extent; - /* * As btrfs supports shared space, this information * can be exported to userspace tools via --1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html