usr/src/uts/common/io/ptm.c

   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 (c) 1988, 2010, Oracle and/or its affiliates. All rights reserved.
  23  */
  24 /*      Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T */
  25 /*        All Rights Reserved   */
  26
  27
  28
  29 /*
  30  * Pseudo Terminal Master Driver.
  31  *
  32  * The pseudo-tty subsystem simulates a terminal connection, where the master
  33  * side represents the terminal and the slave represents the user process's
  34  * special device end point. The master device is set up as a cloned device
  35  * where its major device number is the major for the clone device and its minor
  36  * device number is the major for the ptm driver. There are no nodes in the file
  37  * system for master devices. The master pseudo driver is opened using the
  38  * open(2) system call with /dev/ptmx as the device parameter.  The clone open
  39  * finds the next available minor device for the ptm major device.
  40  *
  41  * A master device is available only if it and its corresponding slave device
  42  * are not already open. When the master device is opened, the corresponding
  43  * slave device is automatically locked out. Only one open is allowed on a
  44  * master device.  Multiple opens are allowed on the slave device.  After both
  45  * the master and slave have been opened, the user has two file descriptors
  46  * which are the end points of a full duplex connection composed of two streams
  47  * which are automatically connected at the master and slave drivers. The user
  48  * may then push modules onto either side of the stream pair.
  49  *
  50  * The master and slave drivers pass all messages to their adjacent queues.
  51  * Only the M_FLUSH needs some processing.  Because the read queue of one side
  52  * is connected to the write queue of the other, the FLUSHR flag is changed to
  53  * the FLUSHW flag and vice versa. When the master device is closed an M_HANGUP
  54  * message is sent to the slave device which will render the device
  55  * unusable. The process on the slave side gets the EIO when attempting to write
  56  * on that stream but it will be able to read any data remaining on the stream
  57  * head read queue.  When all the data has been read, read() returns 0
  58  * indicating that the stream can no longer be used.  On the last close of the
  59  * slave device, a 0-length message is sent to the master device. When the
  60  * application on the master side issues a read() or getmsg() and 0 is returned,
  61  * the user of the master device decides whether to issue a close() that
  62  * dismantles the pseudo-terminal subsystem. If the master device is not closed,
  63  * the pseudo-tty subsystem will be available to another user to open the slave
  64  * device.
  65  *
  66  * If O_NONBLOCK or O_NDELAY is set, read on the master side returns -1 with
  67  * errno set to EAGAIN if no data is available, and write returns -1 with errno
  68  * set to EAGAIN if there is internal flow control.
  69  *
  70  * IOCTLS:
  71  *
  72  *  ISPTM: determines whether the file descriptor is that of an open master
  73  *         device. Return code of zero indicates that the file descriptor
  74  *         represents master device.
  75  *
  76  *  UNLKPT: unlocks the master and slave devices.  It returns 0 on success. On
  77  *          failure, the errno is set to EINVAL indicating that the master
  78  *          device is not open.
  79  *
  80  *  ZONEPT: sets the zone membership of the associated pts device.
  81  *
  82  *  GRPPT:  sets the group owner of the associated pts device.
  83  *
  84  * Synchronization:
  85  *
  86  *   All global data synchronization between ptm/pts is done via global
  87  *   ptms_lock mutex which is initialized at system boot time from
  88  *   ptms_initspace (called from space.c).
  89  *
  90  *   Individual fields of pt_ttys structure (except ptm_rdq, pts_rdq and
  91  *   pt_nullmsg) are protected by pt_ttys.pt_lock mutex.
  92  *
  93  *   PT_ENTER_READ/PT_ENTER_WRITE are reference counter based read-write locks
  94  *   which allow reader locks to be reacquired by the same thread (usual
  95  *   reader/writer locks can't be used for that purpose since it is illegal for
  96  *   a thread to acquire a lock it already holds, even as a reader). The sole
  97  *   purpose of these macros is to guarantee that the peer queue will not
  98  *   disappear (due to closing peer) while it is used. It is safe to use
  99  *   PT_ENTER_READ/PT_EXIT_READ brackets across calls like putq/putnext (since
 100  *   they are not real locks but reference counts).
 101  *
 102  *   PT_ENTER_WRITE/PT_EXIT_WRITE brackets are used ONLY in master/slave
 103  *   open/close paths to modify ptm_rdq and pts_rdq fields. These fields should
 104  *   be set to appropriate queues *after* qprocson() is called during open (to
 105  *   prevent peer from accessing the queue with incomplete plumbing) and set to
 106  *   NULL before qprocsoff() is called during close.
 107  *
 108  *   The pt_nullmsg field is only used in open/close routines and it is also
 109  *   protected by PT_ENTER_WRITE/PT_EXIT_WRITE brackets to avoid extra mutex
 110  *   holds.
 111  *
 112  * Lock Ordering:
 113  *
 114  *   If both ptms_lock and per-pty lock should be held, ptms_lock should always
 115  *   be entered first, followed by per-pty lock.
 116  *
 117  * See ptms.h, pts.c and ptms_conf.c for more information.
 118  */
 119
 120 #include <sys/types.h>
 121 #include <sys/param.h>
 122 #include <sys/file.h>
 123 #include <sys/sysmacros.h>
 124 #include <sys/stream.h>
 125 #include <sys/stropts.h>
 126 #include <sys/proc.h>
 127 #include <sys/errno.h>
 128 #include <sys/debug.h>
 129 #include <sys/cmn_err.h>
 130 #include <sys/ptms.h>
 131 #include <sys/stat.h>
 132 #include <sys/strsun.h>
 133 #include <sys/systm.h>
 134 #include <sys/modctl.h>
 135 #include <sys/conf.h>
 136 #include <sys/ddi.h>
 137 #include <sys/sunddi.h>
 138 #include <sys/zone.h>
 139
 140 #ifdef DEBUG
 141 int ptm_debug = 0;
 142 #define DBG(a)   if (ptm_debug) cmn_err(CE_NOTE, a)
 143 #else
 144 #define DBG(a)
 145 #endif
 146
 147 static int ptmopen(queue_t *, dev_t *, int, int, cred_t *);
 148 static int ptmclose(queue_t *, int, cred_t *);
 149 static void ptmwput(queue_t *, mblk_t *);
 150 static void ptmrsrv(queue_t *);
 151 static void ptmwsrv(queue_t *);
 152
 153 /*
 154  * Master Stream Pseudo Terminal Module: stream data structure definitions
 155  */
 156
 157 static struct module_info ptm_info = {
 158         0xdead,
 159         "ptm",
 160         0,
 161         512,
 162         512,
 163         128
 164 };
 165
 166 static struct qinit ptmrint = {
 167         NULL,
 168         (int (*)()) ptmrsrv,
 169         ptmopen,
 170         ptmclose,
 171         NULL,
 172         &ptm_info,
 173         NULL
 174 };
 175
 176 static struct qinit ptmwint = {
 177         (int (*)()) ptmwput,
 178         (int (*)()) ptmwsrv,
 179         NULL,
 180         NULL,
 181         NULL,
 182         &ptm_info,
 183         NULL
 184 };
 185
 186 static struct streamtab ptminfo = {
 187         &ptmrint,
 188         &ptmwint,
 189         NULL,
 190         NULL
 191 };
 192
 193 static int ptm_attach(dev_info_t *, ddi_attach_cmd_t);
 194 static int ptm_detach(dev_info_t *, ddi_detach_cmd_t);
 195 static int ptm_devinfo(dev_info_t *, ddi_info_cmd_t, void *, void **);
 196
 197 static dev_info_t       *ptm_dip;               /* private devinfo pointer */
 198
 199 /*
 200  * this will define (struct cb_ops cb_ptm_ops) and (struct dev_ops ptm_ops)
 201  */
 202 DDI_DEFINE_STREAM_OPS(ptm_ops, nulldev, nulldev, ptm_attach, ptm_detach,
 203     nodev, ptm_devinfo, D_MP, &ptminfo, ddi_quiesce_not_supported);
 204
 205 /*
 206  * Module linkage information for the kernel.
 207  */
 208
 209 static struct modldrv modldrv = {
 210         &mod_driverops, /* Type of module.  This one is a pseudo driver */
 211         "Master streams driver 'ptm'",
 212         &ptm_ops,       /* driver ops */
 213 };
 214
 215 static struct modlinkage modlinkage = {
 216         MODREV_1,
 217         &modldrv,
 218         NULL
 219 };
 220
 221 int
 222 _init(void)
 223 {
 224         int rc;
 225
 226         if ((rc = mod_install(&modlinkage)) == 0)
 227                 ptms_init();
 228         return (rc);
 229 }
 230
 231 int
 232 _fini(void)
 233 {
 234         return (mod_remove(&modlinkage));
 235 }
 236
 237 int
 238 _info(struct modinfo *modinfop)
 239 {
 240         return (mod_info(&modlinkage, modinfop));
 241 }
 242
 243 static int
 244 ptm_attach(dev_info_t *devi, ddi_attach_cmd_t cmd)
 245 {
 246         if (cmd != DDI_ATTACH)
 247                 return (DDI_FAILURE);
 248
 249         if (ddi_create_minor_node(devi, "ptmajor", S_IFCHR,
 250             0, DDI_PSEUDO, NULL) == DDI_FAILURE) {
 251                 ddi_remove_minor_node(devi, NULL);
 252                 return (DDI_FAILURE);
 253         }
 254         if (ddi_create_minor_node(devi, "ptmx", S_IFCHR,
 255             0, DDI_PSEUDO, CLONE_DEV) == DDI_FAILURE) {
 256                 ddi_remove_minor_node(devi, NULL);
 257                 return (DDI_FAILURE);
 258         }
 259         ptm_dip = devi;
 260
 261         return (DDI_SUCCESS);
 262 }
 263
 264 static int
 265 ptm_detach(dev_info_t *devi, ddi_detach_cmd_t cmd)
 266 {
 267         if (cmd != DDI_DETACH)
 268                 return (DDI_FAILURE);
 269
 270         ddi_remove_minor_node(devi, NULL);
 271         return (DDI_SUCCESS);
 272 }
 273
 274 /*ARGSUSED*/
 275 static int
 276 ptm_devinfo(dev_info_t *dip, ddi_info_cmd_t infocmd, void *arg,
 277     void **result)
 278 {
 279         int error;
 280
 281         switch (infocmd) {
 282         case DDI_INFO_DEVT2DEVINFO:
 283                 if (ptm_dip == NULL) {
 284                         error = DDI_FAILURE;
 285                 } else {
 286                         *result = (void *)ptm_dip;
 287                         error = DDI_SUCCESS;
 288                 }
 289                 break;
 290         case DDI_INFO_DEVT2INSTANCE:
 291                 *result = (void *)0;
 292                 error = DDI_SUCCESS;
 293                 break;
 294         default:
 295                 error = DDI_FAILURE;
 296         }
 297         return (error);
 298 }
 299
 300
 301 /* ARGSUSED */
 302 /*
 303  * Open a minor of the master device. Store the write queue pointer and set the
 304  * pt_state field to (PTMOPEN | PTLOCK).
 305  * This code will work properly with both clone opens and direct opens of the
 306  * master device.
 307  */
 308 static int
 309 ptmopen(
 310         queue_t *rqp,           /* pointer to the read side queue */
 311         dev_t   *devp,          /* pointer to stream tail's dev */
 312         int     oflag,          /* the user open(2) supplied flags */
 313         int     sflag,          /* open state flag */
 314         cred_t  *credp)         /* credentials */
 315 {
 316         struct pt_ttys  *ptmp;
 317         mblk_t          *mop;           /* ptr to a setopts message block */
 318         struct stroptions *sop;
 319         minor_t         dminor = getminor(*devp);
 320
 321         /* Allow reopen */
 322         if (rqp->q_ptr != NULL)
 323                 return (0);
 324
 325         if (sflag & MODOPEN)
 326                 return (ENXIO);
 327
 328         if (!(sflag & CLONEOPEN) && dminor != 0) {
 329                 /*
 330                  * This is a direct open to specific master device through an
 331                  * artificially created entry with specific minor in
 332                  * /dev/directory. Such behavior is not supported.
 333                  */
 334                 return (ENXIO);
 335         }
 336
 337         /*
 338          * The master open requires that the slave be attached
 339          * before it returns so that attempts to open the slave will
 340          * succeeed
 341          */
 342         if (ptms_attach_slave() != 0) {
 343                 return (ENXIO);
 344         }
 345
 346         mop = allocb(sizeof (struct stroptions), BPRI_MED);
 347         if (mop == NULL) {
 348                 DDBG("ptmopen(): mop allocation failed\n", 0);
 349                 return (ENOMEM);
 350         }
 351
 352         if ((ptmp = pt_ttys_alloc()) == NULL) {
 353                 DDBG("ptmopen(): pty allocation failed\n", 0);
 354                 freemsg(mop);
 355                 return (ENOMEM);
 356         }
 357
 358         dminor = ptmp->pt_minor;
 359
 360         DDBGP("ptmopen(): allocated ptmp %p\n", (uintptr_t)ptmp);
 361         DDBG("ptmopen(): allocated minor %d\n", dminor);
 362
 363         WR(rqp)->q_ptr = rqp->q_ptr = ptmp;
 364
 365         qprocson(rqp);
 366
 367         /* Allow slave to send messages to master */
 368         PT_ENTER_WRITE(ptmp);
 369         ptmp->ptm_rdq = rqp;
 370         PT_EXIT_WRITE(ptmp);
 371
 372         /*
 373          * set up hi/lo water marks on stream head read queue
 374          * and add controlling tty if not set
 375          */
 376         mop->b_datap->db_type = M_SETOPTS;
 377         mop->b_wptr += sizeof (struct stroptions);
 378         sop = (struct stroptions *)mop->b_rptr;
 379         if (oflag & FNOCTTY)
 380                 sop->so_flags = SO_HIWAT | SO_LOWAT;
 381         else
 382                 sop->so_flags = SO_HIWAT | SO_LOWAT | SO_ISTTY;
 383         sop->so_hiwat = _TTY_BUFSIZ;
 384         sop->so_lowat = 256;
 385         putnext(rqp, mop);
 386
 387         /*
 388          * The input, devp, is a major device number, the output is put
 389          * into the same parm as a major,minor pair.
 390          */
 391         *devp = makedevice(getmajor(*devp), dminor);
 392
 393         return (0);
 394 }
 395
 396
 397 /*
 398  * Find the address to private data identifying the slave's write queue.
 399  * Send a hang-up message up the slave's read queue to designate the
 400  * master/slave pair is tearing down. Uattach the master and slave by
 401  * nulling out the write queue fields in the private data structure.
 402  * Finally, unlock the master/slave pair and mark the master as closed.
 403  */
 404 /*ARGSUSED1*/
 405 static int
 406 ptmclose(queue_t *rqp, int flag, cred_t *credp)
 407 {
 408         struct pt_ttys  *ptmp;
 409         queue_t *pts_rdq;
 410
 411         ASSERT(rqp->q_ptr);
 412
 413         ptmp = (struct pt_ttys *)rqp->q_ptr;
 414         PT_ENTER_READ(ptmp);
 415         if (ptmp->pts_rdq) {
 416                 pts_rdq = ptmp->pts_rdq;
 417                 if (pts_rdq->q_next) {
 418                         DBG(("send hangup message to slave\n"));
 419                         (void) putnextctl(pts_rdq, M_HANGUP);
 420                 }
 421         }
 422         PT_EXIT_READ(ptmp);
 423         /*
 424          * ptm_rdq should be cleared before call to qprocsoff() to prevent pts
 425          * write procedure to attempt using ptm_rdq after qprocsoff.
 426          */
 427         PT_ENTER_WRITE(ptmp);
 428         ptmp->ptm_rdq = NULL;
 429         freemsg(ptmp->pt_nullmsg);
 430         ptmp->pt_nullmsg = NULL;
 431         /*
 432          * qenable slave side write queue so that it can flush
 433          * its messages as master's read queue is going away
 434          */
 435         if (ptmp->pts_rdq)
 436                 qenable(WR(ptmp->pts_rdq));
 437         PT_EXIT_WRITE(ptmp);
 438
 439         qprocsoff(rqp);
 440
 441         /* Finish the close */
 442         rqp->q_ptr = NULL;
 443         WR(rqp)->q_ptr = NULL;
 444
 445         ptms_close(ptmp, PTMOPEN | PTLOCK);
 446
 447         return (0);
 448 }
 449
 450 /*
 451  * The wput procedure will only handle ioctl and flush messages.
 452  */
 453 static void
 454 ptmwput(queue_t *qp, mblk_t *mp)
 455 {
 456         struct pt_ttys  *ptmp;
 457         struct iocblk   *iocp;
 458
 459         DBG(("entering ptmwput\n"));
 460         ASSERT(qp->q_ptr);
 461
 462         ptmp = (struct pt_ttys *)qp->q_ptr;
 463         PT_ENTER_READ(ptmp);
 464
 465         switch (mp->b_datap->db_type) {
 466         /*
 467          * if write queue request, flush master's write
 468          * queue and send FLUSHR up slave side. If read
 469          * queue request, convert to FLUSHW and putnext().
 470          */
 471         case M_FLUSH:
 472                 {
 473                         unsigned char flush_flg = 0;
 474
 475                         DBG(("ptm got flush request\n"));
 476                         if (*mp->b_rptr & FLUSHW) {
 477                                 DBG(("got FLUSHW, flush ptm write Q\n"));
 478                                 if (*mp->b_rptr & FLUSHBAND)
 479                                         /*
 480                                          * if it is a FLUSHBAND, do flushband.
 481                                          */
 482                                         flushband(qp, *(mp->b_rptr + 1),
 483                                             FLUSHDATA);
 484                                 else
 485                                         flushq(qp, FLUSHDATA);
 486                                 flush_flg = (*mp->b_rptr & ~FLUSHW) | FLUSHR;
 487                         }
 488                         if (*mp->b_rptr & FLUSHR) {
 489                                 DBG(("got FLUSHR, set FLUSHW\n"));
 490                                 flush_flg |= (*mp->b_rptr & ~FLUSHR) | FLUSHW;
 491                         }
 492                         if (flush_flg != 0 && ptmp->pts_rdq &&
 493                             !(ptmp->pt_state & PTLOCK)) {
 494                                 DBG(("putnext to pts\n"));
 495                                 *mp->b_rptr = flush_flg;
 496                                 putnext(ptmp->pts_rdq, mp);
 497                         } else
 498                                 freemsg(mp);
 499                         break;
 500                 }
 501
 502         case M_IOCTL:
 503                 iocp = (struct iocblk *)mp->b_rptr;
 504                 switch (iocp->ioc_cmd) {
 505                 default:
 506                         if ((ptmp->pt_state & PTLOCK) ||
 507                             (ptmp->pts_rdq == NULL)) {
 508                                 DBG(("got M_IOCTL but no slave\n"));
 509                                 miocnak(qp, mp, 0, EINVAL);
 510                                 PT_EXIT_READ(ptmp);
 511                                 return;
 512                         }
 513                         (void) putq(qp, mp);
 514                         break;
 515                 case UNLKPT:
 516                         mutex_enter(&ptmp->pt_lock);
 517                         ptmp->pt_state &= ~PTLOCK;
 518                         mutex_exit(&ptmp->pt_lock);
 519                         /*FALLTHROUGH*/
 520                 case ISPTM:
 521                         DBG(("ack the UNLKPT/ISPTM\n"));
 522                         miocack(qp, mp, 0, 0);
 523                         break;
 524                 case ZONEPT:
 525                 {
 526                         zoneid_t z;
 527                         int error;
 528
 529                         if ((error = drv_priv(iocp->ioc_cr)) != 0) {
 530                                 miocnak(qp, mp, 0, error);
 531                                 break;
 532                         }
 533                         if ((error = miocpullup(mp, sizeof (zoneid_t))) != 0) {
 534                                 miocnak(qp, mp, 0, error);
 535                                 break;
 536                         }
 537                         z = *((zoneid_t *)mp->b_cont->b_rptr);
 538                         if (z < MIN_ZONEID || z > MAX_ZONEID) {
 539                                 miocnak(qp, mp, 0, EINVAL);
 540                                 break;
 541                         }
 542
 543                         mutex_enter(&ptmp->pt_lock);
 544                         ptmp->pt_zoneid = z;
 545                         mutex_exit(&ptmp->pt_lock);
 546                         miocack(qp, mp, 0, 0);
 547                         break;
 548                 }
 549                 case OWNERPT:
 550                 {
 551                         pt_own_t *ptop;
 552                         int error;
 553                         zone_t *zone;
 554
 555                         if ((error = miocpullup(mp, sizeof (pt_own_t))) != 0) {
 556                                 miocnak(qp, mp, 0, error);
 557                                 break;
 558                         }
 559
 560                         zone = zone_find_by_id(ptmp->pt_zoneid);
 561                         ptop = (pt_own_t *)mp->b_cont->b_rptr;
 562
 563                         if (!VALID_UID(ptop->pto_ruid, zone) ||
 564                             !VALID_GID(ptop->pto_rgid, zone)) {
 565                                 zone_rele(zone);
 566                                 miocnak(qp, mp, 0, EINVAL);
 567                                 break;
 568                         }
 569                         zone_rele(zone);
 570                         mutex_enter(&ptmp->pt_lock);
 571                         ptmp->pt_ruid = ptop->pto_ruid;
 572                         ptmp->pt_rgid = ptop->pto_rgid;
 573                         mutex_exit(&ptmp->pt_lock);
 574                         miocack(qp, mp, 0, 0);
 575                         break;
 576                 }
 577                 }
 578                 break;
 579
 580         case M_READ:
 581                 /* Caused by ldterm - can not pass to slave */
 582                 freemsg(mp);
 583                 break;
 584
 585         /*
 586          * send other messages to slave
 587          */
 588         default:
 589                 if ((ptmp->pt_state  & PTLOCK) || (ptmp->pts_rdq == NULL)) {
 590                         DBG(("got msg. but no slave\n"));
 591                         mp = mexchange(NULL, mp, 2, M_ERROR, -1);
 592                         if (mp != NULL) {
 593                                 mp->b_rptr[0] = NOERROR;
 594                                 mp->b_rptr[1] = EINVAL;
 595                                 qreply(qp, mp);
 596                         }
 597                         PT_EXIT_READ(ptmp);
 598                         return;
 599                 }
 600                 DBG(("put msg on master's write queue\n"));
 601                 (void) putq(qp, mp);
 602                 break;
 603         }
 604         DBG(("return from ptmwput()\n"));
 605         PT_EXIT_READ(ptmp);
 606 }
 607
 608
 609 /*
 610  * enable the write side of the slave. This triggers the
 611  * slave to send any messages queued on its write side to
 612  * the read side of this master.
 613  */
 614 static void
 615 ptmrsrv(queue_t *qp)
 616 {
 617         struct pt_ttys  *ptmp;
 618
 619         DBG(("entering ptmrsrv\n"));
 620         ASSERT(qp->q_ptr);
 621
 622         ptmp = (struct pt_ttys *)qp->q_ptr;
 623         PT_ENTER_READ(ptmp);
 624         if (ptmp->pts_rdq) {
 625                 qenable(WR(ptmp->pts_rdq));
 626         }
 627         PT_EXIT_READ(ptmp);
 628         DBG(("leaving ptmrsrv\n"));
 629 }
 630
 631
 632 /*
 633  * If there are messages on this queue that can be sent to
 634  * slave, send them via putnext(). Else, if queued messages
 635  * cannot be sent, leave them on this queue. If priority
 636  * messages on this queue, send them to slave no matter what.
 637  */
 638 static void
 639 ptmwsrv(queue_t *qp)
 640 {
 641         struct pt_ttys  *ptmp;
 642         mblk_t          *mp;
 643
 644         DBG(("entering ptmwsrv\n"));
 645         ASSERT(qp->q_ptr);
 646
 647         ptmp = (struct pt_ttys *)qp->q_ptr;
 648
 649         if ((mp = getq(qp)) == NULL) {
 650                 /* If there are no messages there's nothing to do. */
 651                 DBG(("leaving ptmwsrv (no messages)\n"));
 652                 return;
 653         }
 654
 655         PT_ENTER_READ(ptmp);
 656         if ((ptmp->pt_state  & PTLOCK) || (ptmp->pts_rdq == NULL)) {
 657                 DBG(("in master write srv proc but no slave\n"));
 658                 /*
 659                  * Free messages on the write queue and send
 660                  * NAK for any M_IOCTL type messages to wakeup
 661                  * the user process waiting for ACK/NAK from
 662                  * the ioctl invocation
 663                  */
 664                 do {
 665                         if (mp->b_datap->db_type == M_IOCTL)
 666                                 miocnak(qp, mp, 0, EINVAL);
 667                         else
 668                                 freemsg(mp);
 669                 } while ((mp = getq(qp)) != NULL);
 670                 flushq(qp, FLUSHALL);
 671
 672                 mp = mexchange(NULL, NULL, 2, M_ERROR, -1);
 673                 if (mp != NULL) {
 674                         mp->b_rptr[0] = NOERROR;
 675                         mp->b_rptr[1] = EINVAL;
 676                         qreply(qp, mp);
 677                 }
 678                 PT_EXIT_READ(ptmp);
 679                 return;
 680         }
 681         /*
 682          * while there are messages on this write queue...
 683          */
 684         do {
 685                 /*
 686                  * if don't have control message and cannot put
 687                  * msg. on slave's read queue, put it back on
 688                  * this queue.
 689                  */
 690                 if (mp->b_datap->db_type <= QPCTL &&
 691                     !bcanputnext(ptmp->pts_rdq, mp->b_band)) {
 692                         DBG(("put msg. back on queue\n"));
 693                         (void) putbq(qp, mp);
 694                         break;
 695                 }
 696                 /*
 697                  * else send the message up slave's stream
 698                  */
 699                 DBG(("send message to slave\n"));
 700                 putnext(ptmp->pts_rdq, mp);
 701         } while ((mp = getq(qp)) != NULL);
 702         DBG(("leaving ptmwsrv\n"));
 703         PT_EXIT_READ(ptmp);
 704 }