On 7.03.2018 12:27, robbieko wrote: > Nikolay Borisov 於 2018-03-07 18:19 寫到: >> 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. >> > > Sorry I did not explain clearly. > The value is fm_mapped_extents.
But fm_mapped_extents is tagged as an OUT member, meaning the user has no job writing to it. > If fm_extent_count is zero, the fm_mapped_extents count will hold the > number of extents needed. > > >> >>> >>> [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 > -- 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
