When the receive buffer fills in one socket from a
socketpair(PF_LOCAL, SOCK_DGRAM), I've noticed that
subsequent write()s to the other socket will fail with
EINVAL.  Is this by design?  If it is, is EINVAL the
correct errno to return here?   Solaris and Linux seem
to agree to block when the buffers fill, that would be
ideal in my case, but I'd even settle for a better
return errno.  EINVAL leads me to believe I'm passing
bad pointers, which I'm not.  Here's the test code
that will fail the written assert():

#include <sys/socket.h>
#include <errno.h>
#include <assert.h>

int main(void)
{
  char buf[1024];
  int sk[2];
  int ret = 0;
  socketpair(PF_LOCAL, SOCK_DGRAM, 0, sk);

  while(ret != -1)
    ret = write(sk[0], buf, 1024);
  assert(errno != EINVAL);
}

I'm running this on 1.6.1, but based on a quick look
at the code in -current from cvs I'm guessing its
present in there to.  The culprit seems to
unp_output() in uipc_usrreq.c returning the EINVAL
when the sbappendaddr() to the buddy socket's receive
buffer returns 0.

//Jesse Off

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