1. 07 Jun, 2018 1 commit
    • Robbie Ko's avatar
      Btrfs: fiemap: pass correct bytenr when fm_extent_count is zero · 9d311e11
      Robbie Ko authored
      [BUG]
      fm_mapped_extents is not correct when fm_extent_count is 0
      Like:
         # 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
      
      When user space wants to get the number of file extents,
      set fm_extent_count to 0 to run fiemap and then read fm_mapped_extents.
      
      In the above example, fiemap will return with fm_mapped_extents set to 4,
      but it should be 1 since there's only one entry in the output.
      
      [REASON]
      The problem seems to be that disko is only set if
      fieinfo->fi_extents_max is set. And this member is initialized, in the
      generic ioctl_fiemap function, to the value of used-passed
      fm_extent_count. So when the user passes 0 then fi_extent_max is also
      set to zero and this causes btrfs to not initialize disko at all.
      Eventually this leads emit_fiemap_extent being called with a bogus
      'phys' argument preventing proper fiemap entries merging.
      
      [FIX]
      Move the disko initialization earlier in extent_fiemap making it
      independent of user-passed arguments, allowing emit_fiemap_extent to
      properly handle consecutive extent entries.
      Signed-off-by: default avatarRobbie Ko <robbieko@synology.com>
      Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
      9d311e11
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