Ceph

As reported by Travis Rhoden on ceph-users:

 # ceph quorum
    2013-02-20 18:22:59.327916 7f908186f700  0 monclient: hunting for
    new mon
    unknown quorum subcommand; use exit or enter

    # ceph -s
        health HEALTH_WARN 1 mons down, quorum 0,1,3,4 a,b,d,e

    Log from ceph-mon.c.log:

         -1> 2013-02-20 18:22:57.594190 7f92d84db700  0 mon.c@2(peon) e1
    handle_command mon_command(quorum v 0) v1
          0> 2013-02-20 18:22:57.721764 7f92d84db700 -1 *** Caught
    signal (Segmentation fault) **
      in thread 7f92d84db700

      ceph version 0.56.3 (6eb7e15a4783b122e9b0c85ea9ba064145958aa5)
      1: /usr/bin/ceph-mon() [0x5379da]
      2: (()+0xfcb0) [0x7f92dd8cecb0]
      3: (std::string::compare(char const*) const+0x2c) [0x7f92dcfe382c]
      4: (bool std::operator==<char, std::char_traits<char>,
    std::allocator<char> >(std::basic_string<char,
    std::char_traits<char>, std::allocator<char> > const&, char
    const*)+0x9) [0x488919]
      5: (Monitor::handle_command(MMonCommand*)+0x13a8) [0x4741e8]
      6: (Monitor::_ms_dispatch(Message*)+0x103b) [0x484bcb]
      7: (Monitor::ms_dispatch(Message*)+0x32) [0x4945c2]
      8: (DispatchQueue::entry()+0x349) [0x63d009]
      9: (DispatchQueue::DispatchThread::entry()+0xd) [0x5d67bd]
      10: (()+0x7e9a) [0x7f92dd8c6e9a]
      11: (clone()+0x6d) [0x7f92dc767cbd]
      NOTE: a copy of the executable, or `objdump -rdS <executable>` is
    needed to interpret this. 

The cause is that we weren't checking if we were provided with the required argument to 'quorum' ('enter' or 'exit') prior to trying to access its position in the array.