Otherwise impl is unpopulated and we risk segfaults in several
methods. It also seems like it would always indicate a bug.
Signed-off-by: Samuel Just <sjust@redhat.com>
Track a set of hash values, either explicitly or using a bloom_filter. Hide
the implementation and allow us to transparently encode and decode.
Signed-off-by: Sage Weil <sage@inktank.com>
Signed-off-by: Greg Farnum <greg@inktank.com>