A friend of mine had problems with a NetBSD 1.4BETA system running out
of mbufs and locking up due to a broken application which was using
raw ip sockets.. it created ~20 ICMP sockets, sent out a few pings,
and then, under certain circumstances, wouldn't read from them
promptly due to a bug... and lots of traffic would pile up in these
sockets and the system would run out of mbuf clusters and be sad.
(this is the same system which convinced me that arp_drain is
needed..)

So, the "obvious" fix here is to add protocol drain routines to the
udp and raw protocol families to rip unread mbufs out of the socket
queues under conditions of memory shortage.  (since the protocols are
unreliable, i think you can get away with this..).  

However, this *is* fairly brutal; i'd think that it's something you'd
want to put in as a last resort.. so it might make sense to add some
sort of "despiration level" parameter to the drain routine, and change
m_reclaim to look more like:

	  for (despiration = 0; despiration < max; despiration++) {
	      for each protocol
		  if (pr->pr_drain) (*pr->pr_drain)(despiration);
	      for each interface
		  if (ifp->if_drain) (*ifp->if_drain)(ifp, despiration);
              if (there are free mbufs & free clusters)
		  break;
	  }

.. and then have {tcp,udp,rip}_drain kick in with despiration=1.

I'm not convinced this is necessary. but i'm not convinced it isn't
either.  Anyone have any opinions?

					- Bill