xref: /illumos-gate/usr/src/uts/common/io/pts.c (revision 13b136d3061155363c62c9f6568d25b8b27da8f6)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 /*
22  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
23  * Use is subject to license terms.
24  */
25 /*	Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T	*/
26 /*	  All Rights Reserved	*/
27 
28 
29 
30 /*
31  * Pseudo Terminal Slave Driver.
32  *
33  * The pseudo-tty subsystem simulates a terminal connection, where the master
34  * side represents the terminal and the slave represents the user process's
35  * special device end point. The master device is set up as a cloned device
36  * where its major device number is the major for the clone device and its minor
37  * device number is the major for the ptm driver. There are no nodes in the file
38  * system for master devices. The master pseudo driver is opened using the
39  * open(2) system call with /dev/ptmx as the device parameter.  The clone open
40  * finds the next available minor device for the ptm major device.
41  *
42  * A master device is available only if it and its corresponding slave device
43  * are not already open. When the master device is opened, the corresponding
44  * slave device is automatically locked out. Only one open is allowed on a
45  * master device.  Multiple opens are allowed on the slave device.  After both
46  * the master and slave have been opened, the user has two file descriptors
47  * which are the end points of a full duplex connection composed of two streams
48  * which are automatically connected at the master and slave drivers. The user
49  * may then push modules onto either side of the stream pair.
50  *
51  * The master and slave drivers pass all messages to their adjacent queues.
52  * Only the M_FLUSH needs some processing.  Because the read queue of one side
53  * is connected to the write queue of the other, the FLUSHR flag is changed to
54  * the FLUSHW flag and vice versa. When the master device is closed an M_HANGUP
55  * message is sent to the slave device which will render the device
56  * unusable. The process on the slave side gets the EIO when attempting to write
57  * on that stream but it will be able to read any data remaining on the stream
58  * head read queue.  When all the data has been read, read() returns 0
59  * indicating that the stream can no longer be used.  On the last close of the
60  * slave device, a 0-length message is sent to the master device. When the
61  * application on the master side issues a read() or getmsg() and 0 is returned,
62  * the user of the master device decides whether to issue a close() that
63  * dismantles the pseudo-terminal subsystem. If the master device is not closed,
64  * the pseudo-tty subsystem will be available to another user to open the slave
65  * device.
66  *
67  * Synchronization:
68  *
69  *   All global data synchronization between ptm/pts is done via global
70  *   ptms_lock mutex which is initialized at system boot time from
71  *   ptms_initspace (called from space.c).
72  *
73  *   Individual fields of pt_ttys structure (except ptm_rdq, pts_rdq and
74  *   pt_nullmsg) are protected by pt_ttys.pt_lock mutex.
75  *
76  *   PT_ENTER_READ/PT_ENTER_WRITE are reference counter based read-write locks
77  *   which allow reader locks to be reacquired by the same thread (usual
78  *   reader/writer locks can't be used for that purpose since it is illegal for
79  *   a thread to acquire a lock it already holds, even as a reader). The sole
80  *   purpose of these macros is to guarantee that the peer queue will not
81  *   disappear (due to closing peer) while it is used. It is safe to use
82  *   PT_ENTER_READ/PT_EXIT_READ brackets across calls like putq/putnext (since
83  *   they are not real locks but reference counts).
84  *
85  *   PT_ENTER_WRITE/PT_EXIT_WRITE brackets are used ONLY in master/slave
86  *   open/close paths to modify ptm_rdq and pts_rdq fields. These fields should
87  *   be set to appropriate queues *after* qprocson() is called during open (to
88  *   prevent peer from accessing the queue with incomplete plumbing) and set to
89  *   NULL before qprocsoff() is called during close.
90  *
91  *   The pt_nullmsg field is only used in open/close routines and it is also
92  *   protected by PT_ENTER_WRITE/PT_EXIT_WRITE brackets to avoid extra mutex
93  *   holds.
94  *
95  * Lock Ordering:
96  *
97  *   If both ptms_lock and per-pty lock should be held, ptms_lock should always
98  *   be entered first, followed by per-pty lock.
99  *
100  * See ptms.h, ptm.c and ptms_conf.c fore more information.
101  *
102  */
103 
104 #include <sys/types.h>
105 #include <sys/param.h>
106 #include <sys/sysmacros.h>
107 #include <sys/stream.h>
108 #include <sys/stropts.h>
109 #include <sys/stat.h>
110 #include <sys/errno.h>
111 #include <sys/debug.h>
112 #include <sys/cmn_err.h>
113 #include <sys/ptms.h>
114 #include <sys/systm.h>
115 #include <sys/modctl.h>
116 #include <sys/conf.h>
117 #include <sys/ddi.h>
118 #include <sys/sunddi.h>
119 #include <sys/cred.h>
120 #include <sys/zone.h>
121 
122 #ifdef DEBUG
123 int pts_debug = 0;
124 #define	DBG(a)	 if (pts_debug) cmn_err(CE_NOTE, a)
125 #else
126 #define	DBG(a)
127 #endif
128 
129 static int ptsopen(queue_t *, dev_t *, int, int, cred_t *);
130 static int ptsclose(queue_t *, int, cred_t *);
131 static int ptswput(queue_t *, mblk_t *);
132 static int ptsrsrv(queue_t *);
133 static int ptswsrv(queue_t *);
134 
135 /*
136  * Slave Stream Pseudo Terminal Module: stream data structure definitions
137  */
138 static struct module_info pts_info = {
139 	0xface,
140 	"pts",
141 	0,
142 	_TTY_BUFSIZ,
143 	_TTY_BUFSIZ,
144 	128
145 };
146 
147 static struct qinit ptsrint = {
148 	NULL,
149 	ptsrsrv,
150 	ptsopen,
151 	ptsclose,
152 	NULL,
153 	&pts_info,
154 	NULL
155 };
156 
157 static struct qinit ptswint = {
158 	ptswput,
159 	ptswsrv,
160 	NULL,
161 	NULL,
162 	NULL,
163 	&pts_info,
164 	NULL
165 };
166 
167 static struct streamtab ptsinfo = {
168 	&ptsrint,
169 	&ptswint,
170 	NULL,
171 	NULL
172 };
173 
174 static int pts_devinfo(dev_info_t *, ddi_info_cmd_t, void *, void **);
175 static int pts_attach(dev_info_t *, ddi_attach_cmd_t);
176 static int pts_detach(dev_info_t *, ddi_detach_cmd_t);
177 
178 #define	PTS_CONF_FLAG	(D_NEW | D_MP)
179 
180 /*
181  * this will define (struct cb_ops cb_pts_ops) and (struct dev_ops pts_ops)
182  */
183 DDI_DEFINE_STREAM_OPS(pts_ops, nulldev, nulldev,	\
184     pts_attach, pts_detach, nodev,			\
185     pts_devinfo, PTS_CONF_FLAG, &ptsinfo, ddi_quiesce_not_supported);
186 
187 /*
188  * Module linkage information for the kernel.
189  */
190 
191 static struct modldrv modldrv = {
192 	&mod_driverops, /* Type of module.  This one is a pseudo driver */
193 	"Slave Stream Pseudo Terminal driver 'pts'",
194 	&pts_ops,	/* driver ops */
195 };
196 
197 static struct modlinkage modlinkage = {
198 	MODREV_1,
199 	&modldrv,
200 	NULL
201 };
202 
203 int
204 _init(void)
205 {
206 	int rc;
207 
208 	if ((rc = mod_install(&modlinkage)) == 0)
209 		ptms_init();
210 	return (rc);
211 }
212 
213 
214 int
215 _fini(void)
216 {
217 	return (mod_remove(&modlinkage));
218 }
219 
220 int
221 _info(struct modinfo *modinfop)
222 {
223 	return (mod_info(&modlinkage, modinfop));
224 }
225 
226 static int
227 pts_attach(dev_info_t *devi, ddi_attach_cmd_t cmd)
228 {
229 	if (cmd != DDI_ATTACH)
230 		return (DDI_FAILURE);
231 
232 	mutex_enter(&ptms_lock);
233 	pts_dip = devi;
234 	mutex_exit(&ptms_lock);
235 
236 	return (DDI_SUCCESS);
237 }
238 
239 /*ARGSUSED*/
240 static int
241 pts_detach(dev_info_t *devi, ddi_detach_cmd_t cmd)
242 {
243 	if (cmd != DDI_DETACH)
244 		return (DDI_FAILURE);
245 
246 	/*
247 	 * For now, pts cannot be detached.
248 	 */
249 	return (DDI_FAILURE);
250 }
251 
252 /*ARGSUSED*/
253 static int
254 pts_devinfo(dev_info_t *dip, ddi_info_cmd_t infocmd, void *arg,
255     void **result)
256 {
257 	int error;
258 
259 	switch (infocmd) {
260 	case DDI_INFO_DEVT2DEVINFO:
261 		if (pts_dip == NULL) {
262 			error = DDI_FAILURE;
263 		} else {
264 			*result = (void *)pts_dip;
265 			error = DDI_SUCCESS;
266 		}
267 		break;
268 	case DDI_INFO_DEVT2INSTANCE:
269 		*result = (void *)0;
270 		error = DDI_SUCCESS;
271 		break;
272 	default:
273 		error = DDI_FAILURE;
274 	}
275 	return (error);
276 }
277 
278 /* ARGSUSED */
279 /*
280  * Open the slave device. Reject a clone open and do not allow the
281  * driver to be pushed. If the slave/master pair is locked or if
282  * the master is not open, return EACCESS.
283  * Upon success, store the write queue pointer in private data and
284  * set the PTSOPEN bit in the pt_state field.
285  */
286 static int
287 ptsopen(
288 	queue_t *rqp,		/* pointer to the read side queue */
289 	dev_t   *devp,		/* pointer to stream tail's dev */
290 	int	oflag,		/* the user open(2) supplied flags */
291 	int	sflag,		/* open state flag */
292 	cred_t  *credp)		/* credentials */
293 {
294 	struct pt_ttys	*ptsp;
295 	mblk_t		*mp;
296 	mblk_t		*mop;	/* ptr to a setopts message block */
297 	minor_t		dminor = getminor(*devp);
298 	struct stroptions *sop;
299 
300 	DDBG("entering ptsopen(%d)", dminor);
301 
302 	if (sflag != 0) {
303 		return (EINVAL);
304 	}
305 
306 	mutex_enter(&ptms_lock);
307 	ptsp = ptms_minor2ptty(dminor);
308 
309 	if (ptsp == NULL) {
310 		mutex_exit(&ptms_lock);
311 		return (ENXIO);
312 	}
313 	mutex_enter(&ptsp->pt_lock);
314 
315 	/*
316 	 * Prevent opens from zones other than the one blessed by ptm.  We
317 	 * can't even allow the global zone to open all pts's, as it would
318 	 * otherwise inproperly be able to claim pts's already opened by zones.
319 	 */
320 	if (ptsp->pt_zoneid != getzoneid()) {
321 		mutex_exit(&ptsp->pt_lock);
322 		mutex_exit(&ptms_lock);
323 		return (EPERM);
324 	}
325 
326 	/*
327 	 * Allow reopen of this device.
328 	 */
329 	if (rqp->q_ptr != NULL) {
330 		ASSERT(rqp->q_ptr == ptsp);
331 		ASSERT(ptsp->pts_rdq == rqp);
332 		mutex_exit(&ptsp->pt_lock);
333 		mutex_exit(&ptms_lock);
334 		return (0);
335 	}
336 
337 	DDBGP("ptsopen: p = %p\n", (uintptr_t)ptsp);
338 	DDBG("ptsopen: state = %x\n", ptsp->pt_state);
339 
340 
341 	ASSERT(ptsp->pt_minor == dminor);
342 
343 	if ((ptsp->pt_state & PTLOCK) || !(ptsp->pt_state & PTMOPEN)) {
344 		mutex_exit(&ptsp->pt_lock);
345 		mutex_exit(&ptms_lock);
346 		return (EAGAIN);
347 	}
348 
349 	/*
350 	 * if already, open simply return...
351 	 */
352 	if (ptsp->pt_state & PTSOPEN) {
353 		ASSERT(rqp->q_ptr == ptsp);
354 		ASSERT(ptsp->pts_rdq == rqp);
355 		mutex_exit(&ptsp->pt_lock);
356 		mutex_exit(&ptms_lock);
357 		return (0);
358 	}
359 
360 	/*
361 	 * Allocate message block for setting stream head options.
362 	 */
363 	if ((mop = allocb(sizeof (struct stroptions), BPRI_MED)) == NULL) {
364 		mutex_exit(&ptsp->pt_lock);
365 		mutex_exit(&ptms_lock);
366 		return (ENOMEM);
367 	}
368 
369 	/*
370 	 * Slave should send zero-length message to a master when it is
371 	 * closing. If memory is low at that time, master will not detect slave
372 	 * closes, this pty will not be deallocated. So, preallocate this
373 	 * zero-length message block early.
374 	 */
375 	if ((mp = allocb(0, BPRI_MED)) == NULL) {
376 		mutex_exit(&ptsp->pt_lock);
377 		mutex_exit(&ptms_lock);
378 		freemsg(mop);
379 		return (ENOMEM);
380 	}
381 
382 	ptsp->pt_state |= PTSOPEN;
383 
384 	WR(rqp)->q_ptr = rqp->q_ptr = ptsp;
385 
386 	mutex_exit(&ptsp->pt_lock);
387 	mutex_exit(&ptms_lock);
388 
389 	qprocson(rqp);
390 
391 	/*
392 	 * After qprocson pts driver is fully plumbed into the stream and can
393 	 * send/receive messages. Setting pts_rdq will allow master side to send
394 	 * messages to the slave. This setting can't occur before qprocson() is
395 	 * finished because slave is not ready to process them.
396 	 */
397 	PT_ENTER_WRITE(ptsp);
398 	ptsp->pts_rdq = rqp;
399 	ASSERT(ptsp->pt_nullmsg == NULL);
400 	ptsp->pt_nullmsg = mp;
401 	PT_EXIT_WRITE(ptsp);
402 
403 	/*
404 	 * set up hi/lo water marks on stream head read queue
405 	 * and add controlling tty if not set
406 	 */
407 
408 	mop->b_datap->db_type = M_SETOPTS;
409 	mop->b_wptr += sizeof (struct stroptions);
410 	sop = (struct stroptions *)mop->b_rptr;
411 	sop->so_flags = SO_HIWAT | SO_LOWAT | SO_ISTTY;
412 	sop->so_hiwat = _TTY_BUFSIZ;
413 	sop->so_lowat = 256;
414 	putnext(rqp, mop);
415 
416 	return (0);
417 }
418 
419 
420 
421 /*
422  * Find the address to private data identifying the slave's write
423  * queue. Send a 0-length msg up the slave's read queue to designate
424  * the master is closing. Uattach the master from the slave by nulling
425  * out master's write queue field in private data.
426  */
427 /*ARGSUSED1*/
428 static int
429 ptsclose(queue_t *rqp, int flag, cred_t *credp)
430 {
431 	struct pt_ttys	*ptsp;
432 	queue_t *wqp;
433 	mblk_t	*mp;
434 	mblk_t	*bp;
435 
436 	/*
437 	 * q_ptr should never be NULL in the close routine and it is checked in
438 	 * DEBUG kernel by ASSERT. For non-DEBUG kernel the attempt is made to
439 	 * behave gracefully.
440 	 */
441 	ASSERT(rqp->q_ptr != NULL);
442 	if (rqp->q_ptr == NULL) {
443 		qprocsoff(rqp);
444 		return (0);
445 	}
446 
447 	ptsp = (struct pt_ttys *)rqp->q_ptr;
448 
449 	/*
450 	 * Slave is going to close and doesn't want any new  messages coming
451 	 * from the master side, so set pts_rdq to NULL. This should be done
452 	 * before call to qprocsoff() since slave can't process additional
453 	 * messages from the master after qprocsoff is called.
454 	 */
455 	PT_ENTER_WRITE(ptsp);
456 	mp = ptsp->pt_nullmsg;
457 	ptsp->pt_nullmsg = NULL;
458 	ptsp->pts_rdq = NULL;
459 	PT_EXIT_WRITE(ptsp);
460 
461 	/*
462 	 * Drain the ouput
463 	 */
464 	wqp = WR(rqp);
465 	PT_ENTER_READ(ptsp);
466 	while ((bp = getq(wqp)) != NULL) {
467 		if (ptsp->ptm_rdq) {
468 			putnext(ptsp->ptm_rdq, bp);
469 		} else if (bp->b_datap->db_type == M_IOCTL) {
470 			bp->b_datap->db_type = M_IOCNAK;
471 			freemsg(bp->b_cont);
472 			bp->b_cont = NULL;
473 			qreply(wqp, bp);
474 		} else {
475 			freemsg(bp);
476 		}
477 	}
478 	/*
479 	 * qenable master side write queue so that it can flush
480 	 * its messages as slaves's read queue is going away
481 	 */
482 	if (ptsp->ptm_rdq) {
483 		if (mp)
484 			putnext(ptsp->ptm_rdq, mp);
485 		else
486 			qenable(WR(ptsp->ptm_rdq));
487 	} else
488 		freemsg(mp);
489 	PT_EXIT_READ(ptsp);
490 
491 	qprocsoff(rqp);
492 
493 	rqp->q_ptr = NULL;
494 	WR(rqp)->q_ptr = NULL;
495 
496 	ptms_close(ptsp, PTSOPEN | PTSTTY);
497 
498 	return (0);
499 }
500 
501 
502 /*
503  * The wput procedure will only handle flush messages.
504  * All other messages are queued and the write side
505  * service procedure sends them off to the master side.
506  */
507 static int
508 ptswput(queue_t *qp, mblk_t *mp)
509 {
510 	struct pt_ttys *ptsp;
511 	struct iocblk  *iocp;
512 	unsigned char type = mp->b_datap->db_type;
513 
514 	DBG(("entering ptswput\n"));
515 	ASSERT(qp->q_ptr);
516 
517 	ptsp = (struct pt_ttys *)qp->q_ptr;
518 	PT_ENTER_READ(ptsp);
519 	if (ptsp->ptm_rdq == NULL) {
520 		DBG(("in write put proc but no master\n"));
521 		/*
522 		 * NAK ioctl as slave side read queue is gone.
523 		 * Or else free the message.
524 		 */
525 		if (mp->b_datap->db_type == M_IOCTL) {
526 			mp->b_datap->db_type = M_IOCNAK;
527 			freemsg(mp->b_cont);
528 			mp->b_cont = NULL;
529 			qreply(qp, mp);
530 		} else
531 			freemsg(mp);
532 		PT_EXIT_READ(ptsp);
533 		return (0);
534 	}
535 
536 	if (type >= QPCTL) {
537 		switch (type) {
538 
539 		/*
540 		 * if write queue request, flush slave's write
541 		 * queue and send FLUSHR to ptm. If read queue
542 		 * request, send FLUSHR to ptm.
543 		 */
544 		case M_FLUSH:
545 		DBG(("pts got flush request\n"));
546 		if (*mp->b_rptr & FLUSHW) {
547 
548 			DBG(("got FLUSHW, flush pts write Q\n"));
549 			if (*mp->b_rptr & FLUSHBAND)
550 				/*
551 				 * if it is a FLUSHBAND, do flushband.
552 				 */
553 				flushband(qp, *(mp->b_rptr + 1), FLUSHDATA);
554 			else
555 				flushq(qp, FLUSHDATA);
556 
557 			*mp->b_rptr &= ~FLUSHW;
558 			if ((*mp->b_rptr & FLUSHR) == 0) {
559 				/*
560 				 * FLUSHW only. Change to FLUSHR and putnext
561 				 * to ptm, then we are done.
562 				 */
563 				*mp->b_rptr |= FLUSHR;
564 				if (ptsp->ptm_rdq)
565 					putnext(ptsp->ptm_rdq, mp);
566 				break;
567 			} else {
568 				mblk_t *nmp;
569 
570 				/* It is a FLUSHRW. Duplicate the mblk */
571 				nmp = copyb(mp);
572 				if (nmp) {
573 					/*
574 					 * Change FLUSHW to FLUSHR before
575 					 * putnext to ptm.
576 					 */
577 					DBG(("putnext nmp(FLUSHR) to ptm\n"));
578 					*nmp->b_rptr |= FLUSHR;
579 					if (ptsp->ptm_rdq)
580 						putnext(ptsp->ptm_rdq, nmp);
581 				}
582 			}
583 		}
584 		/*
585 		 * Since the packet module will toss any
586 		 * M_FLUSHES sent to the master's stream head
587 		 * read queue, we simply turn it around here.
588 		 */
589 		if (*mp->b_rptr & FLUSHR) {
590 			ASSERT(RD(qp)->q_first == NULL);
591 			DBG(("qreply(qp) turning FLUSHR around\n"));
592 			qreply(qp, mp);
593 		} else {
594 			freemsg(mp);
595 		}
596 		break;
597 
598 		case M_READ:
599 		/* Caused by ldterm - can not pass to master */
600 		freemsg(mp);
601 		break;
602 
603 		default:
604 		if (ptsp->ptm_rdq)
605 			putnext(ptsp->ptm_rdq, mp);
606 		break;
607 		}
608 		PT_EXIT_READ(ptsp);
609 		return (0);
610 	}
611 
612 	switch (type) {
613 
614 	case M_IOCTL:
615 		/*
616 		 * For case PTSSTTY set the flag PTSTTY and ACK
617 		 * the ioctl so that the user program can push
618 		 * the associated modules to get tty semantics.
619 		 * See bugid 4025044
620 		 */
621 		iocp = (struct iocblk *)mp->b_rptr;
622 		switch (iocp->ioc_cmd) {
623 		default:
624 			break;
625 
626 		case PTSSTTY:
627 			if (ptsp->pt_state & PTSTTY) {
628 				mp->b_datap->db_type = M_IOCNAK;
629 				iocp->ioc_error = EEXIST;
630 			} else {
631 				mp->b_datap->db_type = M_IOCACK;
632 				mutex_enter(&ptsp->pt_lock);
633 				ptsp->pt_state |= PTSTTY;
634 				mutex_exit(&ptsp->pt_lock);
635 				iocp->ioc_error = 0;
636 			}
637 			iocp->ioc_count = 0;
638 			qreply(qp, mp);
639 			PT_EXIT_READ(ptsp);
640 			return (0);
641 		}
642 		/* FALLTHROUGH */
643 	default:
644 		/*
645 		 * send other messages to the master
646 		 */
647 		DBG(("put msg on slave's write queue\n"));
648 		(void) putq(qp, mp);
649 		break;
650 	}
651 
652 	PT_EXIT_READ(ptsp);
653 	DBG(("return from ptswput()\n"));
654 	return (0);
655 }
656 
657 
658 /*
659  * enable the write side of the master. This triggers the
660  * master to send any messages queued on its write side to
661  * the read side of this slave.
662  */
663 static int
664 ptsrsrv(queue_t *qp)
665 {
666 	struct pt_ttys *ptsp;
667 
668 	DBG(("entering ptsrsrv\n"));
669 	ASSERT(qp->q_ptr);
670 
671 	ptsp = (struct pt_ttys *)qp->q_ptr;
672 	PT_ENTER_READ(ptsp);
673 	if (ptsp->ptm_rdq == NULL) {
674 		DBG(("in read srv proc but no master\n"));
675 		PT_EXIT_READ(ptsp);
676 		return (0);
677 	}
678 	qenable(WR(ptsp->ptm_rdq));
679 	PT_EXIT_READ(ptsp);
680 	DBG(("leaving ptsrsrv\n"));
681 	return (0);
682 }
683 
684 /*
685  * If there are messages on this queue that can be sent to
686  * master, send them via putnext(). Else, if queued messages
687  * cannot be sent, leave them on this queue. If priority
688  * messages on this queue, send them to master no matter what.
689  */
690 static int
691 ptswsrv(queue_t *qp)
692 {
693 	struct pt_ttys *ptsp;
694 	queue_t *ptm_rdq;
695 	mblk_t *mp;
696 
697 	DBG(("entering ptswsrv\n"));
698 	ASSERT(qp->q_ptr);
699 
700 	ptsp = (struct pt_ttys *)qp->q_ptr;
701 	PT_ENTER_READ(ptsp);
702 	if (ptsp->ptm_rdq == NULL) {
703 		DBG(("in write srv proc but no master\n"));
704 		/*
705 		 * Free messages on the write queue and send
706 		 * NAK for any M_IOCTL type messages to wakeup
707 		 * the user process waiting for ACK/NAK from
708 		 * the ioctl invocation
709 		 */
710 		while ((mp = getq(qp)) != NULL) {
711 			if (mp->b_datap->db_type == M_IOCTL) {
712 				mp->b_datap->db_type = M_IOCNAK;
713 				freemsg(mp->b_cont);
714 				mp->b_cont = NULL;
715 				qreply(qp, mp);
716 			} else
717 				freemsg(mp);
718 		}
719 		PT_EXIT_READ(ptsp);
720 		return (0);
721 	} else {
722 		ptm_rdq = ptsp->ptm_rdq;
723 	}
724 
725 	/*
726 	 * while there are messages on this write queue...
727 	 */
728 	while ((mp = getq(qp)) != NULL) {
729 		/*
730 		 * if don't have control message and cannot put
731 		 * msg. on master's read queue, put it back on
732 		 * this queue.
733 		 */
734 		if (mp->b_datap->db_type <= QPCTL &&
735 		    !bcanputnext(ptm_rdq, mp->b_band)) {
736 			DBG(("put msg. back on Q\n"));
737 			(void) putbq(qp, mp);
738 			break;
739 		}
740 		/*
741 		 * else send the message up master's stream
742 		 */
743 		DBG(("send message to master\n"));
744 		putnext(ptm_rdq, mp);
745 	}
746 	DBG(("leaving ptswsrv\n"));
747 	PT_EXIT_READ(ptsp);
748 	return (0);
749 }
750