xref: /freebsd/sys/netgraph/ng_tty.c (revision 7f9d26bd9d1b2754da8429257edbde0a8237f84f) 
1 
2 /*
3  * ng_tty.c
4  *
5  * Copyright (c) 1996-1999 Whistle Communications, Inc.
6  * All rights reserved.
7  *
8  * Subject to the following obligations and disclaimer of warranty, use and
9  * redistribution of this software, in source or object code forms, with or
10  * without modifications are expressly permitted by Whistle Communications;
11  * provided, however, that:
12  * 1. Any and all reproductions of the source or object code must include the
13  *    copyright notice above and the following disclaimer of warranties; and
14  * 2. No rights are granted, in any manner or form, to use Whistle
15  *    Communications, Inc. trademarks, including the mark "WHISTLE
16  *    COMMUNICATIONS" on advertising, endorsements, or otherwise except as
17  *    such appears in the above copyright notice or in the software.
18  *
19  * THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
20  * TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
21  * REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
22  * INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
23  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
24  * WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
25  * REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
26  * SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
27  * IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
28  * RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
29  * WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
30  * PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
31  * SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY
32  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
34  * THIS SOFTWARE, EVEN IF WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY
35  * OF SUCH DAMAGE.
36  *
37  * Author: Archie Cobbs <archie@whistle.com>
38  *
39  * $FreeBSD$
40  * $Whistle: ng_tty.c,v 1.18 1999/01/28 23:54:54 julian Exp $
41  */
42 
43 /*
44  * This file implements a terminal line discipline that is also a
45  * netgraph node. Installing this line discipline on a terminal device
46  * instantiates a new netgraph node of this type, which allows access
47  * to the device via the "hook" hook of the node.
48  *
49  * Once the line discipline is installed, you can find out the name
50  * of the corresponding netgraph node via a NGIOCGINFO ioctl().
51  *
52  * Incoming characters are delievered to the hook one at a time, each
53  * in its own mbuf. You may optionally define a ``hotchar,'' which causes
54  * incoming characters to be buffered up until either the hotchar is
55  * seen or the mbuf is full (MHLEN bytes). Then all buffered characters
56  * are immediately delivered.
57  *
58  * NOTE: This node operates at spltty().
59  */
60 
61 #include <sys/param.h>
62 #include <sys/systm.h>
63 #include <sys/kernel.h>
64 #include <sys/conf.h>
65 #include <sys/proc.h>
66 #include <sys/mbuf.h>
67 #include <sys/malloc.h>
68 #include <sys/socket.h>
69 #include <sys/fcntl.h>
70 #include <sys/file.h>
71 #include <sys/tty.h>
72 #include <sys/ttycom.h>
73 #include <sys/syslog.h>
74 #include <sys/errno.h>
75 #include <sys/ioccom.h>
76 
77 #include <netgraph/ng_message.h>
78 #include <netgraph/netgraph.h>
79 #include <netgraph/ng_tty.h>
80 
81 #ifdef __i386__			/* fiddle with the spl locking */
82 #include <machine/ipl.h>
83 #include <i386/isa/intr_machdep.h>
84 #endif
85 
86 /* Misc defs */
87 #define MAX_MBUFQ		3	/* Max number of queued mbufs */
88 #define NGT_HIWATER		400	/* High water mark on output */
89 
90 /* Per-node private info */
91 struct ngt_sc {
92 	struct tty *tp;		/* Terminal device */
93 	node_p  node;		/* Netgraph node */
94 	hook_p  hook;		/* Netgraph hook */
95 	struct mbuf *m;		/* Incoming data buffer */
96 	struct mbuf *qhead, **qtail;	/* Queue of outgoing mbuf's */
97 	short   qlen;		/* Length of queue */
98 	short   hotchar;	/* Hotchar, or -1 if none */
99 	u_int   flags;		/* Flags */
100 	struct callout_handle chand;	/* See man timeout(9) */
101 };
102 typedef struct ngt_sc *sc_p;
103 
104 /* Flags */
105 #define FLG_TIMEOUT		0x0001	/* A timeout is pending */
106 #define FLG_DEBUG		0x0002
107 
108 /* Debugging */
109 #ifdef DIAGNOSTICS
110 #define QUEUECHECK(sc)							\
111     do {								\
112       struct mbuf	**mp;						\
113       int		k;						\
114 									\
115       for (k = 0, mp = &sc->qhead;					\
116 	k <= MAX_MBUFQ && *mp;						\
117 	k++, mp = &(*mp)->m_nextpkt);					\
118       if (k != sc->qlen || k > MAX_MBUFQ || *mp || mp != sc->qtail)	\
119 	panic(__FUNCTION__ ": queue");					\
120     } while (0)
121 #else
122 #define QUEUECHECK(sc)	do {} while (0)
123 #endif
124 
125 /* Line discipline methods */
126 static int	ngt_open(dev_t dev, struct tty *tp);
127 static int	ngt_close(struct tty *tp, int flag);
128 static int	ngt_read(struct tty *tp, struct uio *uio, int flag);
129 static int	ngt_write(struct tty *tp, struct uio *uio, int flag);
130 static int	ngt_tioctl(struct tty *tp,
131 		    u_long cmd, caddr_t data, int flag, struct proc *);
132 static int	ngt_input(int c, struct tty *tp);
133 static int	ngt_start(struct tty *tp);
134 
135 /* Netgraph methods */
136 static int	ngt_constructor(node_p *node);
137 static int	ngt_rcvmsg(node_p node, struct ng_mesg *msg,
138 		    const char *retaddr, struct ng_mesg **resp);
139 static int	ngt_shutdown(node_p node);
140 static int	ngt_newhook(node_p node, hook_p hook, const char *name);
141 static int	ngt_rcvdata(hook_p hook, struct mbuf *m, meta_p meta);
142 static int	ngt_disconnect(hook_p hook);
143 static int	ngt_mod_event(module_t mod, int event, void *data);
144 
145 /* Other stuff */
146 static void	ngt_timeout(void *arg);
147 
148 #define ERROUT(x)		do { error = (x); goto done; } while (0)
149 
150 /* Line discipline descriptor */
151 static struct linesw ngt_disc = {
152 	ngt_open,
153 	ngt_close,
154 	ngt_read,
155 	ngt_write,
156 	ngt_tioctl,
157 	ngt_input,
158 	ngt_start,
159 	ttymodem,
160 	NG_TTY_DFL_HOTCHAR	/* XXX can't change this in serial driver */
161 };
162 
163 /* Netgraph node type descriptor */
164 static struct ng_type typestruct = {
165 	NG_VERSION,
166 	NG_TTY_NODE_TYPE,
167 	ngt_mod_event,
168 	ngt_constructor,
169 	ngt_rcvmsg,
170 	ngt_shutdown,
171 	ngt_newhook,
172 	NULL,
173 	NULL,
174 	ngt_rcvdata,
175 	ngt_rcvdata,
176 	ngt_disconnect,
177 };
178 NETGRAPH_INIT(tty, &typestruct);
179 
180 static int ngt_unit;
181 static int ngt_nodeop_ok;	/* OK to create/remove node */
182 static int ngt_ldisc;
183 
184 /******************************************************************
185 		    LINE DISCIPLINE METHODS
186 ******************************************************************/
187 
188 /*
189  * Set our line discipline on the tty.
190  * Called from device open routine or ttioctl() at >= splsofttty()
191  */
192 static int
193 ngt_open(dev_t dev, struct tty *tp)
194 {
195 	struct proc *const p = curproc;	/* XXX */
196 	char name[sizeof(NG_TTY_NODE_TYPE) + 8];
197 	sc_p sc;
198 	int s, error;
199 
200 	/* Super-user only */
201 	if ((error = suser(p)))
202 		return (error);
203 	s = splnet();
204 	(void) spltty();	/* XXX is this necessary? */
205 
206 	/* Already installed? */
207 	if (tp->t_line == NETGRAPHDISC) {
208 		sc = (sc_p) tp->t_sc;
209 		if (sc != NULL && sc->tp == tp)
210 			goto done;
211 	}
212 
213 	/* Initialize private struct */
214 	MALLOC(sc, sc_p, sizeof(*sc), M_NETGRAPH, M_WAITOK);
215 	if (sc == NULL) {
216 		error = ENOMEM;
217 		goto done;
218 	}
219 	bzero(sc, sizeof(*sc));
220 	sc->tp = tp;
221 	sc->hotchar = NG_TTY_DFL_HOTCHAR;
222 	sc->qtail = &sc->qhead;
223 	QUEUECHECK(sc);
224 	callout_handle_init(&sc->chand);
225 
226 	/* Setup netgraph node */
227 	ngt_nodeop_ok = 1;
228 	error = ng_make_node_common(&typestruct, &sc->node);
229 	ngt_nodeop_ok = 0;
230 	if (error) {
231 		FREE(sc, M_NETGRAPH);
232 		goto done;
233 	}
234 	sprintf(name, "%s%d", typestruct.name, ngt_unit++);
235 
236 	/* Set back pointers */
237 	sc->node->private = sc;
238 	tp->t_sc = (caddr_t) sc;
239 
240 	/* Assign node its name */
241 	if ((error = ng_name_node(sc->node, name))) {
242 		log(LOG_ERR, "%s: node name exists?\n", name);
243 		ngt_nodeop_ok = 1;
244 		ng_rmnode(sc->node);
245 		ngt_nodeop_ok = 0;
246 		goto done;
247 	}
248 
249 	/*
250 	 * Pre-allocate cblocks to the an appropriate amount.
251 	 * I'm not sure what is appropriate.
252 	 */
253 	ttyflush(tp, FREAD | FWRITE);
254 	clist_alloc_cblocks(&tp->t_canq, 0, 0);
255 	clist_alloc_cblocks(&tp->t_rawq, 0, 0);
256 	clist_alloc_cblocks(&tp->t_outq,
257 	    MLEN + NGT_HIWATER, MLEN + NGT_HIWATER);
258 
259 done:
260 	/* Done */
261 	splx(s);
262 	return (error);
263 }
264 
265 /*
266  * Line specific close routine, called from device close routine
267  * and from ttioctl at >= splsofttty(). This causes the node to
268  * be destroyed as well.
269  */
270 static int
271 ngt_close(struct tty *tp, int flag)
272 {
273 	const sc_p sc = (sc_p) tp->t_sc;
274 	int s;
275 
276 	s = spltty();
277 	ttyflush(tp, FREAD | FWRITE);
278 	clist_free_cblocks(&tp->t_outq);
279 	tp->t_line = 0;
280 	if (sc != NULL) {
281 		if (sc->flags & FLG_TIMEOUT) {
282 			untimeout(ngt_timeout, sc, sc->chand);
283 			sc->flags &= ~FLG_TIMEOUT;
284 		}
285 		ngt_nodeop_ok = 1;
286 		ng_rmnode(sc->node);
287 		ngt_nodeop_ok = 0;
288 		tp->t_sc = NULL;
289 	}
290 	splx(s);
291 	return (0);
292 }
293 
294 /*
295  * Once the device has been turned into a node, we don't allow reading.
296  */
297 static int
298 ngt_read(struct tty *tp, struct uio *uio, int flag)
299 {
300 	return (EIO);
301 }
302 
303 /*
304  * Once the device has been turned into a node, we don't allow writing.
305  */
306 static int
307 ngt_write(struct tty *tp, struct uio *uio, int flag)
308 {
309 	return (EIO);
310 }
311 
312 /*
313  * We implement the NGIOCGINFO ioctl() defined in ng_message.h.
314  */
315 static int
316 ngt_tioctl(struct tty *tp, u_long cmd, caddr_t data, int flag, struct proc *p)
317 {
318 	const sc_p sc = (sc_p) tp->t_sc;
319 	int s, error = 0;
320 
321 	s = spltty();
322 	switch (cmd) {
323 	case NGIOCGINFO:
324 	    {
325 		struct nodeinfo *const ni = (struct nodeinfo *) data;
326 		const node_p node = sc->node;
327 
328 		bzero(ni, sizeof(*ni));
329 		if (node->name)
330 			strncpy(ni->name, node->name, sizeof(ni->name) - 1);
331 		strncpy(ni->type, node->type->name, sizeof(ni->type) - 1);
332 		ni->id = (u_int32_t) node;
333 		ni->hooks = node->numhooks;
334 		break;
335 	    }
336 	default:
337 		ERROUT(ENOIOCTL);
338 	}
339 done:
340 	splx(s);
341 	return (error);
342 }
343 
344 /*
345  * Receive data coming from the device. We get one character at
346  * a time, which is kindof silly.
347  * Only guaranteed to be at splsofttty() or spltty().
348  */
349 static int
350 ngt_input(int c, struct tty *tp)
351 {
352 	const sc_p sc = (sc_p) tp->t_sc;
353 	const node_p node = sc->node;
354 	struct mbuf *m;
355 	int s, error = 0;
356 
357 	if (!sc || tp != sc->tp)
358 		return (0);
359 	s = spltty();
360 	if (!sc->hook)
361 		ERROUT(0);
362 
363 	/* Check for error conditions */
364 	if ((tp->t_state & TS_CONNECTED) == 0) {
365 		if (sc->flags & FLG_DEBUG)
366 			log(LOG_DEBUG, "%s: no carrier\n", node->name);
367 		ERROUT(0);
368 	}
369 	if (c & TTY_ERRORMASK) {
370 		/* framing error or overrun on this char */
371 		if (sc->flags & FLG_DEBUG)
372 			log(LOG_DEBUG, "%s: line error %x\n",
373 			    node->name, c & TTY_ERRORMASK);
374 		ERROUT(0);
375 	}
376 	c &= TTY_CHARMASK;
377 
378 	/* Get a new header mbuf if we need one */
379 	if (!(m = sc->m)) {
380 		MGETHDR(m, M_DONTWAIT, MT_DATA);
381 		if (!m) {
382 			if (sc->flags & FLG_DEBUG)
383 				log(LOG_ERR,
384 				    "%s: can't get mbuf\n", node->name);
385 			ERROUT(ENOBUFS);
386 		}
387 		m->m_len = 0;
388 		m->m_pkthdr.len = 0;
389 		sc->m = m;
390 	}
391 
392 	/* Add char to mbuf */
393 	*mtod(m, u_char *) = c;
394 	m->m_data++;
395 	m->m_len++;
396 	m->m_pkthdr.len++;
397 
398 	/* Ship off mbuf if it's time */
399 	if (sc->hotchar == -1 || c == sc->hotchar || m->m_len >= MHLEN) {
400 		m->m_data = m->m_pktdat;
401 		error = ng_queue_data(sc->hook, m, NULL);
402 		sc->m = NULL;
403 	}
404 done:
405 	splx(s);
406 	return (error);
407 }
408 
409 /*
410  * This is called when the device driver is ready for more output.
411  * Called from tty system at splsofttty() or spltty().
412  * Also call from ngt_rcv_data() when a new mbuf is available for output.
413  */
414 static int
415 ngt_start(struct tty *tp)
416 {
417 	const sc_p sc = (sc_p) tp->t_sc;
418 	int s;
419 
420 	s = spltty();
421 	while (tp->t_outq.c_cc < NGT_HIWATER) {	/* XXX 2.2 specific ? */
422 		struct mbuf *m = sc->qhead;
423 
424 		/* Remove first mbuf from queue */
425 		if (!m)
426 			break;
427 		if ((sc->qhead = m->m_nextpkt) == NULL)
428 			sc->qtail = &sc->qhead;
429 		sc->qlen--;
430 		QUEUECHECK(sc);
431 
432 		/* Send as much of it as possible */
433 		while (m) {
434 			struct mbuf *m2;
435 			int     sent;
436 
437 			sent = m->m_len
438 			    - b_to_q(mtod(m, u_char *), m->m_len, &tp->t_outq);
439 			m->m_data += sent;
440 			m->m_len -= sent;
441 			if (m->m_len > 0)
442 				break;	/* device can't take no more */
443 			MFREE(m, m2);
444 			m = m2;
445 		}
446 
447 		/* Put remainder of mbuf chain (if any) back on queue */
448 		if (m) {
449 			m->m_nextpkt = sc->qhead;
450 			sc->qhead = m;
451 			if (sc->qtail == &sc->qhead)
452 				sc->qtail = &m->m_nextpkt;
453 			sc->qlen++;
454 			QUEUECHECK(sc);
455 			break;
456 		}
457 	}
458 
459 	/* Call output process whether or not there is any output. We are
460 	 * being called in lieu of ttstart and must do what it would. */
461 	if (tp->t_oproc != NULL)
462 		(*tp->t_oproc) (tp);
463 
464 	/* This timeout is needed for operation on a pseudo-tty, because the
465 	 * pty code doesn't call pppstart after it has drained the t_outq. */
466 	if (sc->qhead && (sc->flags & FLG_TIMEOUT) == 0) {
467 		sc->chand = timeout(ngt_timeout, sc, 1);
468 		sc->flags |= FLG_TIMEOUT;
469 	}
470 	splx(s);
471 	return (0);
472 }
473 
474 /*
475  * We still have data to output to the device, so try sending more.
476  */
477 static void
478 ngt_timeout(void *arg)
479 {
480 	const sc_p sc = (sc_p) arg;
481 	int s;
482 
483 	s = spltty();
484 	sc->flags &= ~FLG_TIMEOUT;
485 	ngt_start(sc->tp);
486 	splx(s);
487 }
488 
489 /******************************************************************
490 		    NETGRAPH NODE METHODS
491 ******************************************************************/
492 
493 /*
494  * Initialize a new node of this type.
495  *
496  * We only allow nodes to be created as a result of setting
497  * the line discipline on a tty, so always return an error if not.
498  */
499 static int
500 ngt_constructor(node_p *nodep)
501 {
502 	if (!ngt_nodeop_ok)
503 		return (EOPNOTSUPP);
504 	return (ng_make_node_common(&typestruct, nodep));
505 }
506 
507 /*
508  * Add a new hook. There can only be one.
509  */
510 static int
511 ngt_newhook(node_p node, hook_p hook, const char *name)
512 {
513 	const sc_p sc = node->private;
514 	int s, error = 0;
515 
516 	if (strcmp(name, NG_TTY_HOOK))
517 		return (EINVAL);
518 	s = spltty();
519 	if (sc->hook)
520 		ERROUT(EISCONN);
521 	sc->hook = hook;
522 done:
523 	splx(s);
524 	return (error);
525 }
526 
527 /*
528  * Disconnect the hook
529  */
530 static int
531 ngt_disconnect(hook_p hook)
532 {
533 	const sc_p sc = hook->node->private;
534 	int s;
535 
536 	s = spltty();
537 	if (hook != sc->hook)
538 		panic(__FUNCTION__);
539 	sc->hook = NULL;
540 	m_freem(sc->m);
541 	sc->m = NULL;
542 	splx(s);
543 	return (0);
544 }
545 
546 /*
547  * Remove this node. The does the netgraph portion of the shutdown.
548  * This should only be called indirectly from ngt_close().
549  */
550 static int
551 ngt_shutdown(node_p node)
552 {
553 	const sc_p sc = node->private;
554 
555 	if (!ngt_nodeop_ok)
556 		return (EOPNOTSUPP);
557 	ng_unname(node);
558 	ng_cutlinks(node);
559 	node->private = NULL;
560 	ng_unref(sc->node);
561 	m_freem(sc->qhead);
562 	m_freem(sc->m);
563 	bzero(sc, sizeof(*sc));
564 	FREE(sc, M_NETGRAPH);
565 	return (0);
566 }
567 
568 /*
569  * Receive incoming data from netgraph system. Put it on our
570  * output queue and start output if necessary.
571  */
572 static int
573 ngt_rcvdata(hook_p hook, struct mbuf *m, meta_p meta)
574 {
575 	const sc_p sc = hook->node->private;
576 	int s, error = 0;
577 
578 	if (hook != sc->hook)
579 		panic(__FUNCTION__);
580 	NG_FREE_META(meta);
581 	s = spltty();
582 	if (sc->qlen >= MAX_MBUFQ)
583 		ERROUT(ENOBUFS);
584 	m->m_nextpkt = NULL;
585 	*sc->qtail = m;
586 	sc->qtail = &m->m_nextpkt;
587 	sc->qlen++;
588 	QUEUECHECK(sc);
589 	m = NULL;
590 	if (sc->qlen == 1)
591 		ngt_start(sc->tp);
592 done:
593 	splx(s);
594 	if (m)
595 		m_freem(m);
596 	return (error);
597 }
598 
599 /*
600  * Receive control message
601  */
602 static int
603 ngt_rcvmsg(node_p node, struct ng_mesg *msg, const char *retaddr,
604 	   struct ng_mesg **rptr)
605 {
606 	const sc_p sc = (sc_p) node->private;
607 	struct ng_mesg *resp = NULL;
608 	int error = 0;
609 
610 	switch (msg->header.typecookie) {
611 	case NGM_TTY_COOKIE:
612 		switch (msg->header.cmd) {
613 		case NGM_TTY_SET_HOTCHAR:
614 		    {
615 			int     hotchar;
616 
617 			if (msg->header.arglen != sizeof(int))
618 				ERROUT(EINVAL);
619 			hotchar = *((int *) msg->data);
620 			if (hotchar != (u_char) hotchar && hotchar != -1)
621 				ERROUT(EINVAL);
622 			sc->hotchar = hotchar;	/* race condition is OK */
623 			break;
624 		    }
625 		case NGM_TTY_GET_HOTCHAR:
626 			NG_MKRESPONSE(resp, msg, sizeof(int), M_NOWAIT);
627 			if (!resp)
628 				ERROUT(ENOMEM);
629 			/* Race condition here is OK */
630 			*((int *) resp->data) = sc->hotchar;
631 			break;
632 		default:
633 			ERROUT(EINVAL);
634 		}
635 		break;
636 	default:
637 		ERROUT(EINVAL);
638 	}
639 	if (rptr)
640 		*rptr = resp;
641 	else if (resp)
642 		FREE(resp, M_NETGRAPH);
643 
644 done:
645 	FREE(msg, M_NETGRAPH);
646 	return (error);
647 }
648 
649 /******************************************************************
650 		    	INITIALIZATION
651 ******************************************************************/
652 
653 /*
654  * Handle loading and unloading for this node type
655  */
656 static int
657 ngt_mod_event(module_t mod, int event, void *data)
658 {
659 	/* struct ng_type *const type = data;*/
660 	int s, error = 0;
661 
662 	switch (event) {
663 	case MOD_LOAD:
664 #ifdef __i386__
665 		/* Insure the soft net "engine" can't run during spltty code */
666 		s = splhigh();
667 		tty_imask |= softnet_imask; /* spltty() block spl[soft]net() */
668 		net_imask |= softtty_imask; /* splimp() block splsofttty() */
669 		net_imask |= tty_imask;	    /* splimp() block spltty() */
670 		update_intr_masks();
671 		splx(s);
672 
673 		if (bootverbose)
674 			log(LOG_DEBUG, "new masks: bio %x, tty %x, net %x\n",
675 			    bio_imask, tty_imask, net_imask);
676 #endif
677 
678 		/* Register line discipline */
679 		s = spltty();
680 		if ((ngt_ldisc = ldisc_register(NETGRAPHDISC, &ngt_disc)) < 0) {
681 			splx(s);
682 			log(LOG_ERR, "%s: can't register line discipline",
683 			    __FUNCTION__);
684 			return (EIO);
685 		}
686 		splx(s);
687 		break;
688 
689 	case MOD_UNLOAD:
690 
691 		/* Unregister line discipline */
692 		s = spltty();
693 		ldisc_deregister(ngt_ldisc);
694 		splx(s);
695 		break;
696 
697 	default:
698 		error = EOPNOTSUPP;
699 		break;
700 	}
701 	return (error);
702 }
703 
704