The FIONREAD ioctl is wrong for the tunnel driver. It only returns
the first link of the mbuf chain whereas the read will return the
lot. I admit that I haven't tested this under netbsd. This patch
applies to the SunOS 4.1.x version of if_tun.c. It should be
easy to apply the equivalent patch to the netbsd version. I presume
netbsd is the repository of BSD correctness these days.

Bob Smart

*** OLD/andrew/sunos/if_tun.c	Fri Dec  8 18:31:12 1995
--- if_tun.c	Sun Dec 10 13:14:20 1995
***************
*** 13,18 ****
--- 13,21 ----
   *
   * $Header: if_tun.c,v 1.13 88/07/11 08:28:51 jpo Exp $
   * 
+  * Revision 1.14 95/12/10 rks
+  * fix for FIONREAD ioctl
+  *
   * $Log:	if_tun.c,v $
   * Revision 1.13  88/07/11  08:28:51  jpo
   * Some tidying up
***************
*** 422,429 ****
  
  	    case FIONREAD:
  		s = splimp ();
! 		if (tp->tun_if.if_snd.ifq_head)
! 			*(int *)data = tp->tun_if.if_snd.ifq_head->m_len;
  		else	*(int *)data = 0;
  		splx (s);
  		break;
--- 425,435 ----
  
  	    case FIONREAD:
  		s = splimp ();
! 		if (tp->tun_if.if_snd.ifq_head) {
! 			struct mbuf *mb = tp->tun_if.if_snd.ifq_head;
! 			for( *(int *)data = 0; mb != 0; mb = mb->m_next) 
! 				*(int *)data += mb->m_len;
! 		}
  		else	*(int *)data = 0;
  		splx (s);
  		break;