xref: /dragonfly/sys/netgraph/tty/ng_tty.c (revision 9348a738) 
1 /*
2  * (MPSAFE)
3  *
4  * ng_tty.c
5  *
6  * Copyright (c) 1996-1999 Whistle Communications, Inc.
7  * All rights reserved.
8  *
9  * Subject to the following obligations and disclaimer of warranty, use and
10  * redistribution of this software, in source or object code forms, with or
11  * without modifications are expressly permitted by Whistle Communications;
12  * provided, however, that:
13  * 1. Any and all reproductions of the source or object code must include the
14  *    copyright notice above and the following disclaimer of warranties; and
15  * 2. No rights are granted, in any manner or form, to use Whistle
16  *    Communications, Inc. trademarks, including the mark "WHISTLE
17  *    COMMUNICATIONS" on advertising, endorsements, or otherwise except as
18  *    such appears in the above copyright notice or in the software.
19  *
20  * THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
21  * TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
22  * REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
23  * INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
24  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
25  * WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
26  * REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
27  * SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
28  * IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
29  * RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
30  * WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
31  * PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
32  * SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY
33  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35  * THIS SOFTWARE, EVEN IF WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY
36  * OF SUCH DAMAGE.
37  *
38  * Author: Archie Cobbs <archie@freebsd.org>
39  *
40  * $FreeBSD: src/sys/netgraph/ng_tty.c,v 1.7.2.3 2002/02/13 00:43:12 dillon Exp $
41  * $Whistle: ng_tty.c,v 1.21 1999/11/01 09:24:52 julian Exp $
42  */
43 
44 /*
45  * This file implements a terminal line discipline that is also a
46  * netgraph node. Installing this line discipline on a terminal device
47  * instantiates a new netgraph node of this type, which allows access
48  * to the device via the "hook" hook of the node.
49  *
50  * Once the line discipline is installed, you can find out the name
51  * of the corresponding netgraph node via a NGIOCGINFO ioctl().
52  *
53  * Incoming characters are delievered to the hook one at a time, each
54  * in its own mbuf. You may optionally define a ``hotchar,'' which causes
55  * incoming characters to be buffered up until either the hotchar is
56  * seen or the mbuf is full (MHLEN bytes). Then all buffered characters
57  * are immediately delivered.
58  *
59  * NOTE: This node operates at spltty().
60  */
61 
62 #include <sys/param.h>
63 #include <sys/systm.h>
64 #include <sys/kernel.h>
65 #include <sys/conf.h>
66 #include <sys/proc.h>
67 #include <sys/priv.h>
68 #include <sys/mbuf.h>
69 #include <sys/malloc.h>
70 #include <sys/fcntl.h>
71 #include <sys/tty.h>
72 #include <sys/ttycom.h>
73 #include <sys/syslog.h>
74 #include <sys/errno.h>
75 #include <sys/thread2.h>
76 
77 #include <netgraph/ng_message.h>
78 #include <netgraph/netgraph.h>
79 #include "ng_tty.h"
80 
81 /* Misc defs */
82 #define MAX_MBUFQ		3	/* Max number of queued mbufs */
83 #define NGT_HIWATER		400	/* High water mark on output */
84 
85 /* Per-node private info */
86 struct ngt_sc {
87 	struct	tty *tp;		/* Terminal device */
88 	node_p	node;			/* Netgraph node */
89 	hook_p	hook;			/* Netgraph hook */
90 	struct	mbuf *m;		/* Incoming data buffer */
91 	struct	mbuf *qhead, **qtail;	/* Queue of outgoing mbuf's */
92 	short	qlen;			/* Length of queue */
93 	short	hotchar;		/* Hotchar, or -1 if none */
94 	u_int	flags;			/* Flags */
95 	struct	callout	ctimeout;	/* See man timeout(9) */
96 };
97 typedef struct ngt_sc *sc_p;
98 
99 /* Flags */
100 #define FLG_TIMEOUT		0x0001	/* A timeout is pending */
101 #define FLG_DEBUG		0x0002
102 
103 /* Debugging */
104 #ifdef INVARIANTS
105 #define QUEUECHECK(sc)							\
106     do {								\
107       struct mbuf	**mp;						\
108       int		k;						\
109 									\
110       for (k = 0, mp = &sc->qhead;					\
111 	k <= MAX_MBUFQ && *mp;						\
112 	k++, mp = &(*mp)->m_nextpkt);					\
113       if (k != sc->qlen || k > MAX_MBUFQ || *mp || mp != sc->qtail)	\
114 	panic("%s: queue", __func__);				\
115     } while (0)
116 #else
117 #define QUEUECHECK(sc)	do {} while (0)
118 #endif
119 
120 /* Line discipline methods */
121 static int	ngt_open(cdev_t dev, struct tty *tp);
122 static int	ngt_close(struct tty *tp, int flag);
123 static int	ngt_read(struct tty *tp, struct uio *uio, int flag);
124 static int	ngt_write(struct tty *tp, struct uio *uio, int flag);
125 static int	ngt_tioctl(struct tty *tp,
126 		    u_long cmd, caddr_t data, int flag, struct ucred *cred);
127 static int	ngt_input(int c, struct tty *tp);
128 static int	ngt_start(struct tty *tp);
129 
130 /* Netgraph methods */
131 static ng_constructor_t	ngt_constructor;
132 static ng_rcvmsg_t	ngt_rcvmsg;
133 static ng_shutdown_t	ngt_shutdown;
134 static ng_newhook_t	ngt_newhook;
135 static ng_rcvdata_t	ngt_rcvdata;
136 static ng_disconnect_t	ngt_disconnect;
137 static int	ngt_mod_event(module_t mod, int event, void *data);
138 
139 /* Other stuff */
140 static void	ngt_timeout(void *arg);
141 
142 #define ERROUT(x)		do { error = (x); goto done; } while (0)
143 
144 /* Line discipline descriptor */
145 static struct linesw ngt_disc = {
146 	ngt_open,
147 	ngt_close,
148 	ngt_read,
149 	ngt_write,
150 	ngt_tioctl,
151 	ngt_input,
152 	ngt_start,
153 	ttymodem,
154 	NG_TTY_DFL_HOTCHAR	/* XXX can't change this in serial driver */
155 };
156 
157 /* Netgraph node type descriptor */
158 static struct ng_type typestruct = {
159 	NG_VERSION,
160 	NG_TTY_NODE_TYPE,
161 	ngt_mod_event,
162 	ngt_constructor,
163 	ngt_rcvmsg,
164 	ngt_shutdown,
165 	ngt_newhook,
166 	NULL,
167 	NULL,
168 	ngt_rcvdata,
169 	ngt_rcvdata,
170 	ngt_disconnect,
171 	NULL
172 };
173 NETGRAPH_INIT(tty, &typestruct);
174 
175 static int ngt_unit;
176 static int ngt_nodeop_ok;	/* OK to create/remove node */
177 static int ngt_ldisc;
178 
179 /******************************************************************
180 		    LINE DISCIPLINE METHODS
181 ******************************************************************/
182 
183 /*
184  * Set our line discipline on the tty.
185  * Called from device open routine or ttioctl() at >= splsofttty()
186  */
187 static int
188 ngt_open(cdev_t dev, struct tty *tp)
189 {
190 	struct thread *td = curthread;	/* XXX */
191 	char name[sizeof(NG_TTY_NODE_TYPE) + 8];
192 	sc_p sc;
193 	int error;
194 
195 	/* Super-user only */
196 	if ((error = priv_check(td, PRIV_ROOT)))
197 		return (error);
198 	crit_enter();
199 	lwkt_gettoken(&tty_token);
200 
201 	/* Already installed? */
202 	if (tp->t_line == NETGRAPHDISC) {
203 		sc = (sc_p) tp->t_sc;
204 		if (sc != NULL && sc->tp == tp)
205 			goto done;
206 	}
207 
208 	/* Initialize private struct */
209 	sc = kmalloc(sizeof(*sc), M_NETGRAPH, M_WAITOK | M_ZERO);
210 	sc->tp = tp;
211 	sc->hotchar = NG_TTY_DFL_HOTCHAR;
212 	sc->qtail = &sc->qhead;
213 	QUEUECHECK(sc);
214 	callout_init_mp(&sc->ctimeout);
215 
216 	/* Setup netgraph node */
217 	ngt_nodeop_ok = 1;
218 	error = ng_make_node_common(&typestruct, &sc->node);
219 	ngt_nodeop_ok = 0;
220 	if (error) {
221 		kfree(sc, M_NETGRAPH);
222 		goto done;
223 	}
224 	ksnprintf(name, sizeof(name), "%s%d", typestruct.name, ngt_unit++);
225 
226 	/* Set back pointers */
227 	sc->node->private = sc;
228 	tp->t_sc = (caddr_t) sc;
229 
230 	/* Assign node its name */
231 	if ((error = ng_name_node(sc->node, name))) {
232 		log(LOG_ERR, "%s: node name exists?\n", name);
233 		ngt_nodeop_ok = 1;
234 		ng_rmnode(sc->node);
235 		ngt_nodeop_ok = 0;
236 		goto done;
237 	}
238 
239 	/*
240 	 * Pre-allocate cblocks to the an appropriate amount.
241 	 * I'm not sure what is appropriate.
242 	 */
243 	ttyflush(tp, FREAD | FWRITE);
244 	clist_alloc_cblocks(&tp->t_canq, 0, 0);
245 	clist_alloc_cblocks(&tp->t_rawq, 0, 0);
246 	clist_alloc_cblocks(&tp->t_outq,
247 	    MLEN + NGT_HIWATER, MLEN + NGT_HIWATER);
248 
249 done:
250 	/* Done */
251 	lwkt_reltoken(&tty_token);
252 	crit_exit();
253 	return (error);
254 }
255 
256 /*
257  * Line specific close routine, called from device close routine
258  * and from ttioctl at >= splsofttty(). This causes the node to
259  * be destroyed as well.
260  */
261 static int
262 ngt_close(struct tty *tp, int flag)
263 {
264 	const sc_p sc = (sc_p) tp->t_sc;
265 
266 	crit_enter();
267 	lwkt_gettoken(&tty_token);
268 	ttyflush(tp, FREAD | FWRITE);
269 	clist_free_cblocks(&tp->t_outq);
270 	tp->t_line = 0;
271 	if (sc != NULL) {
272 		if (sc->flags & FLG_TIMEOUT) {
273 			callout_stop(&sc->ctimeout);
274 			sc->flags &= ~FLG_TIMEOUT;
275 		}
276 		ngt_nodeop_ok = 1;
277 		ng_rmnode(sc->node);
278 		ngt_nodeop_ok = 0;
279 		tp->t_sc = NULL;
280 	}
281 	lwkt_reltoken(&tty_token);
282 	crit_exit();
283 	return (0);
284 }
285 
286 /*
287  * Once the device has been turned into a node, we don't allow reading.
288  */
289 static int
290 ngt_read(struct tty *tp, struct uio *uio, int flag)
291 {
292 	return (EIO);
293 }
294 
295 /*
296  * Once the device has been turned into a node, we don't allow writing.
297  */
298 static int
299 ngt_write(struct tty *tp, struct uio *uio, int flag)
300 {
301 	return (EIO);
302 }
303 
304 /*
305  * We implement the NGIOCGINFO ioctl() defined in ng_message.h.
306  */
307 static int
308 ngt_tioctl(struct tty *tp, u_long cmd, caddr_t data, int flag, struct ucred *cred)
309 {
310 	const sc_p sc = (sc_p) tp->t_sc;
311 	int error = 0;
312 
313 	crit_enter();
314 	lwkt_gettoken(&tty_token);
315 	switch (cmd) {
316 	case NGIOCGINFO:
317 	    {
318 		struct nodeinfo *const ni = (struct nodeinfo *) data;
319 		const node_p node = sc->node;
320 
321 		bzero(ni, sizeof(*ni));
322 		if (node->name)
323 			strncpy(ni->name, node->name, sizeof(ni->name) - 1);
324 		strncpy(ni->type, node->type->name, sizeof(ni->type) - 1);
325 		ni->id = (u_int32_t)(uintptr_t)node;
326 		ni->hooks = node->numhooks;
327 		break;
328 	    }
329 	default:
330 		ERROUT(ENOIOCTL);
331 	}
332 done:
333 	lwkt_reltoken(&tty_token);
334 	crit_exit();
335 	return (error);
336 }
337 
338 /*
339  * Receive data coming from the device. We get one character at
340  * a time, which is kindof silly.
341  * Only guaranteed to be at splsofttty() or spltty().
342  */
343 static int
344 ngt_input(int c, struct tty *tp)
345 {
346 	const sc_p sc = (sc_p) tp->t_sc;
347 	const node_p node = sc ? sc->node : NULL;
348 	struct mbuf *m;
349 	int error = 0;
350 
351 	lwkt_gettoken(&tty_token);
352 	if (!sc || tp != sc->tp) {
353 		lwkt_reltoken(&tty_token);
354 		return (0);
355 	}
356 	crit_enter();
357 	if (!sc->hook)
358 		ERROUT(0);
359 
360 	/* Check for error conditions */
361 	if ((tp->t_state & TS_CONNECTED) == 0) {
362 		if (sc->flags & FLG_DEBUG)
363 			log(LOG_DEBUG, "%s: no carrier\n", node->name);
364 		ERROUT(0);
365 	}
366 	if (c & TTY_ERRORMASK) {
367 		/* framing error or overrun on this char */
368 		if (sc->flags & FLG_DEBUG)
369 			log(LOG_DEBUG, "%s: line error %x\n",
370 			    node->name, c & TTY_ERRORMASK);
371 		ERROUT(0);
372 	}
373 	c &= TTY_CHARMASK;
374 
375 	/* Get a new header mbuf if we need one */
376 	if (!(m = sc->m)) {
377 		MGETHDR(m, M_NOWAIT, MT_DATA);
378 		if (!m) {
379 			if (sc->flags & FLG_DEBUG)
380 				log(LOG_ERR,
381 				    "%s: can't get mbuf\n", node->name);
382 			ERROUT(ENOBUFS);
383 		}
384 		m->m_len = m->m_pkthdr.len = 0;
385 		m->m_pkthdr.rcvif = NULL;
386 		sc->m = m;
387 	}
388 
389 	/* Add char to mbuf */
390 	*mtod(m, u_char *) = c;
391 	m->m_data++;
392 	m->m_len++;
393 	m->m_pkthdr.len++;
394 
395 	/* Ship off mbuf if it's time */
396 	if (sc->hotchar == -1 || c == sc->hotchar || m->m_len >= MHLEN) {
397 		m->m_data = m->m_pktdat;
398 		error = ng_queue_data(sc->hook, m, NULL);
399 		sc->m = NULL;
400 	}
401 done:
402 	crit_exit();
403 	lwkt_reltoken(&tty_token);
404 	return (error);
405 }
406 
407 /*
408  * This is called when the device driver is ready for more output.
409  * Called from tty system at splsofttty() or spltty().
410  * Also call from ngt_rcv_data() when a new mbuf is available for output.
411  */
412 static int
413 ngt_start(struct tty *tp)
414 {
415 	const sc_p sc = (sc_p) tp->t_sc;
416 
417 	crit_enter();
418 	lwkt_gettoken(&tty_token);
419 	while (tp->t_outq.c_cc < NGT_HIWATER) {	/* XXX 2.2 specific ? */
420 		struct mbuf *m = sc->qhead;
421 
422 		/* Remove first mbuf from queue */
423 		if (!m)
424 			break;
425 		if ((sc->qhead = m->m_nextpkt) == NULL)
426 			sc->qtail = &sc->qhead;
427 		sc->qlen--;
428 		QUEUECHECK(sc);
429 
430 		/* Send as much of it as possible */
431 		while (m) {
432 			int     sent;
433 
434 			sent = m->m_len
435 			    - b_to_q(mtod(m, u_char *), m->m_len, &tp->t_outq);
436 			m->m_data += sent;
437 			m->m_len -= sent;
438 			if (m->m_len > 0)
439 				break;	/* device can't take no more */
440 			m = m_free(m);
441 		}
442 
443 		/* Put remainder of mbuf chain (if any) back on queue */
444 		if (m) {
445 			m->m_nextpkt = sc->qhead;
446 			sc->qhead = m;
447 			if (sc->qtail == &sc->qhead)
448 				sc->qtail = &m->m_nextpkt;
449 			sc->qlen++;
450 			QUEUECHECK(sc);
451 			break;
452 		}
453 	}
454 
455 	/* Call output process whether or not there is any output. We are
456 	 * being called in lieu of ttstart and must do what it would. */
457 	if (tp->t_oproc != NULL)
458 		(*tp->t_oproc) (tp);
459 
460 	/* This timeout is needed for operation on a pseudo-tty, because the
461 	 * pty code doesn't call pppstart after it has drained the t_outq. */
462 	if (sc->qhead && (sc->flags & FLG_TIMEOUT) == 0) {
463 		callout_reset(&sc->ctimeout, 1, ngt_timeout, sc);
464 		sc->flags |= FLG_TIMEOUT;
465 	}
466 	lwkt_reltoken(&tty_token);
467 	crit_exit();
468 	return (0);
469 }
470 
471 /*
472  * We still have data to output to the device, so try sending more.
473  */
474 static void
475 ngt_timeout(void *arg)
476 {
477 	const sc_p sc = (sc_p) arg;
478 
479 	crit_enter();
480 	lwkt_gettoken(&tty_token);
481 	sc->flags &= ~FLG_TIMEOUT;
482 	ngt_start(sc->tp);
483 	lwkt_reltoken(&tty_token);
484 	crit_exit();
485 }
486 
487 /******************************************************************
488 		    NETGRAPH NODE METHODS
489 ******************************************************************/
490 
491 /*
492  * Initialize a new node of this type.
493  *
494  * We only allow nodes to be created as a result of setting
495  * the line discipline on a tty, so always return an error if not.
496  */
497 static int
498 ngt_constructor(node_p *nodep)
499 {
500 	if (!ngt_nodeop_ok)
501 		return (EOPNOTSUPP);
502 	return (ng_make_node_common(&typestruct, nodep));
503 }
504 
505 /*
506  * Add a new hook. There can only be one.
507  */
508 static int
509 ngt_newhook(node_p node, hook_p hook, const char *name)
510 {
511 	const sc_p sc = node->private;
512 	int error = 0;
513 
514 	if (strcmp(name, NG_TTY_HOOK))
515 		return (EINVAL);
516 	crit_enter();
517 	lwkt_gettoken(&tty_token);
518 	if (sc->hook)
519 		ERROUT(EISCONN);
520 	sc->hook = hook;
521 done:
522 	lwkt_reltoken(&tty_token);
523 	crit_exit();
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 
535 	crit_enter();
536 	lwkt_gettoken(&tty_token);
537 	if (hook != sc->hook)
538 		panic(__func__);
539 	sc->hook = NULL;
540 	m_freem(sc->m);
541 	sc->m = NULL;
542 	lwkt_reltoken(&tty_token);
543 	crit_exit();
544 	return (0);
545 }
546 
547 /*
548  * Remove this node. The does the netgraph portion of the shutdown.
549  * This should only be called indirectly from ngt_close().
550  */
551 static int
552 ngt_shutdown(node_p node)
553 {
554 	const sc_p sc = node->private;
555 
556 	if (!ngt_nodeop_ok)
557 		return (EOPNOTSUPP);
558 	lwkt_gettoken(&tty_token);
559 	ng_unname(node);
560 	ng_cutlinks(node);
561 	node->private = NULL;
562 	ng_unref(sc->node);
563 	m_freem(sc->qhead);
564 	m_freem(sc->m);
565 	bzero(sc, sizeof(*sc));
566 	kfree(sc, M_NETGRAPH);
567 	lwkt_reltoken(&tty_token);
568 	return (0);
569 }
570 
571 /*
572  * Receive incoming data from netgraph system. Put it on our
573  * output queue and start output if necessary.
574  */
575 static int
576 ngt_rcvdata(hook_p hook, struct mbuf *m, meta_p meta)
577 {
578 	const sc_p sc = hook->node->private;
579 	int error = 0;
580 
581 	if (hook != sc->hook)
582 		panic(__func__);
583 	NG_FREE_META(meta);
584 	crit_enter();
585 	lwkt_gettoken(&tty_token);
586 	if (sc->qlen >= MAX_MBUFQ)
587 		ERROUT(ENOBUFS);
588 	m->m_nextpkt = NULL;
589 	*sc->qtail = m;
590 	sc->qtail = &m->m_nextpkt;
591 	sc->qlen++;
592 	QUEUECHECK(sc);
593 	m = NULL;
594 	if (sc->qlen == 1)
595 		ngt_start(sc->tp);
596 done:
597 	lwkt_reltoken(&tty_token);
598 	crit_exit();
599 	if (m)
600 		m_freem(m);
601 	return (error);
602 }
603 
604 /*
605  * Receive control message
606  */
607 static int
608 ngt_rcvmsg(node_p node, struct ng_mesg *msg, const char *retaddr,
609 	   struct ng_mesg **rptr)
610 {
611 	const sc_p sc = (sc_p) node->private;
612 	struct ng_mesg *resp = NULL;
613 	int error = 0;
614 
615 	lwkt_gettoken(&tty_token);
616 	switch (msg->header.typecookie) {
617 	case NGM_TTY_COOKIE:
618 		switch (msg->header.cmd) {
619 		case NGM_TTY_SET_HOTCHAR:
620 		    {
621 			int     hotchar;
622 
623 			if (msg->header.arglen != sizeof(int))
624 				ERROUT(EINVAL);
625 			hotchar = *((int *) msg->data);
626 			if (hotchar != (u_char) hotchar && hotchar != -1)
627 				ERROUT(EINVAL);
628 			sc->hotchar = hotchar;	/* race condition is OK */
629 			break;
630 		    }
631 		case NGM_TTY_GET_HOTCHAR:
632 			NG_MKRESPONSE(resp, msg, sizeof(int), M_NOWAIT);
633 			if (!resp)
634 				ERROUT(ENOMEM);
635 			/* Race condition here is OK */
636 			*((int *) resp->data) = sc->hotchar;
637 			break;
638 		default:
639 			ERROUT(EINVAL);
640 		}
641 		break;
642 	default:
643 		ERROUT(EINVAL);
644 	}
645 	if (rptr)
646 		*rptr = resp;
647 	else if (resp)
648 		kfree(resp, M_NETGRAPH);
649 
650 done:
651 	kfree(msg, M_NETGRAPH);
652 	lwkt_reltoken(&tty_token);
653 	return (error);
654 }
655 
656 /******************************************************************
657 		    	INITIALIZATION
658 ******************************************************************/
659 
660 /*
661  * Handle loading and unloading for this node type
662  */
663 static int
664 ngt_mod_event(module_t mod, int event, void *data)
665 {
666 	/* struct ng_type *const type = data;*/
667 	int error = 0;
668 
669 	switch (event) {
670 	case MOD_LOAD:
671 		/* Register line discipline */
672 		crit_enter();
673 		if ((ngt_ldisc = ldisc_register(NETGRAPHDISC, &ngt_disc)) < 0) {
674 			crit_exit();
675 			log(LOG_ERR, "%s: can't register line discipline",
676 			    __func__);
677 			return (EIO);
678 		}
679 		crit_exit();
680 		break;
681 
682 	case MOD_UNLOAD:
683 
684 		/* Unregister line discipline */
685 		crit_enter();
686 		ldisc_deregister(ngt_ldisc);
687 		crit_exit();
688 		break;
689 
690 	default:
691 		error = EOPNOTSUPP;
692 		break;
693 	}
694 	return (error);
695 }
696