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To: freebsd-hackers@FreeBSD.org
cc: elh@spnet.com
Subject: controllable-predictable slip interface units
Date: Sat, 04 Feb 1995 18:29:59 +0000
From: Ed Hudson <elh@p5.spnet.com>
Sender: hackers-owner@FreeBSD.org
Precedence: bulk


  howdy.

	old issue:
	management of multiple slip interfaces is simpler if the
	slip unit number returned by slattach is controllable

	i'd like to ask you folks to consider adding the following
	patch to the kernel slip interface, which makes the interface
	unit assigned by slattach controllable (well, predictable) under
	most circumstances.

	the patch takes the last four bits of the minor device number,
	and, if it is within the range of the slip interface indices,
	and that slip interface is available, it is returned as the
	slip unit.  if none of these conditions are met, the behaviour
	defaults to the current one: return the first available
	slip interface unit. ie,

		sl# = ((minor&0xf)<NSL && slip_free(minor&0xf)) ?
			(minor&0xf) :
			first_slip_free

	with this, patch, slattach applied to /dev/cuaa0 uses slip
	interface sl0, slattach applied to /dev/cuaa1 uses sl1, and
	so on.

	yes, this is an imperfect solution to this problem
	in that it places requirements on minor device numbers, and
	fails (softly, with the old behaviour) in the face of more
	than min(NSL,16) slip interfaces, etc, but i think that it is easier
	to use than the current scheme(s) typically employed.


	thanks for considering adding this patch.

			-elh
			elh@spnet.com

based on 950202-SNAP, /usr/src/sys/net/if_sl.c

*** Orig/if_sl.c	Sun Nov 27 15:29:57 1994
--- if_sl.c	Sat Feb  4 18:15:45 1995
***************
*** 264,274 ****
  
  	if (tp->t_line == SLIPDISC)
  		return (0);
! 
  	for (nsl = NSL, sc = sl_softc; --nsl >= 0; sc++)
  		if (sc->sc_ttyp == NULL) {
  			if (slinit(sc) == 0)
  				return (ENOBUFS);
  			tp->t_sc = (caddr_t)sc;
  			sc->sc_ttyp = tp;
  			sc->sc_if.if_baudrate = tp->t_ospeed;
--- 264,307 ----
  
  	if (tp->t_line == SLIPDISC)
  		return (0);
!   
! #ifdef	PREDICTABLE_SL
!     {
!     /*
!      * elh 9.19.1994
!      * make the interface number returned by slattach
!      * predictable - make it equal to the last four bits
!      * of the minor tty/cua number, if the last four bits are
!      * less than NSL
!      *
!      *        thus    cuaa0	->	sl0
!      *                ttyd1	->	sl1
!      *                cuaa2	->	sl2		(if NSL >= 3)
!      *                cuaa45	->	old algorithm.
!      *
!      * if the interface is already taken (how? nunits > NSL,
!      *   or multiports?) then
!      * the behaviour defaults to the old: it looks for
!      * the lowest available sl interface
!      */
!       unsigned int sl_num;
!       sl_num=	(unsigned int) dev;
! 	  sl_num=	sl_num & 0x0f;
! 	  if (sl_num < NSL) {
!         sc=	&(sl_softc[sl_num]);
!         if (sc->sc_ttyp == NULL) {
!           if (slinit(sc) == 0) { } else goto got_sl;
! 	    }
! 	  }
!     }
! #endif
  	for (nsl = NSL, sc = sl_softc; --nsl >= 0; sc++)
  		if (sc->sc_ttyp == NULL) {
  			if (slinit(sc) == 0)
  				return (ENOBUFS);
+ #ifdef	PREDICTABLE_SL
+ 		  got_sl:
+ #endif
  			tp->t_sc = (caddr_t)sc;
  			sc->sc_ttyp = tp;
  			sc->sc_if.if_baudrate = tp->t_ospeed;