On 7.03.2018 10:20, robbieko wrote: > From: Robbie Ko <robbi...@synology.com> > > # 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. > > [FIX] > Use correct disko. > > Signed-off-by: Robbie Ko <robbi...@synology.com> > --- > 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 majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
