common/filter: add _filter_filefrag

_filter_filefrag is a helper function to filter filefrag's output
and it can be used to get a file's file offset and physical offset.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>
1 file changed