The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/netgraph/ng_tty.c

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    1 /*
    2  * ng_tty.c
    3  */
    4 
    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 1.29.2.3 2005/02/12 09:17:31 glebius 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 
   60 #include <sys/param.h>
   61 #include <sys/systm.h>
   62 #include <sys/conf.h>
   63 #include <sys/errno.h>
   64 #include <sys/fcntl.h>
   65 #include <sys/ioccom.h>
   66 #include <sys/kernel.h>
   67 #include <sys/malloc.h>
   68 #include <sys/mbuf.h>
   69 #include <sys/socket.h>
   70 #include <sys/syslog.h>
   71 #include <sys/tty.h>
   72 #include <sys/ttycom.h>
   73 
   74 #include <net/if.h>
   75 #include <net/if_var.h>
   76 
   77 #include <netgraph/ng_message.h>
   78 #include <netgraph/netgraph.h>
   79 #include <netgraph/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  ifqueue outq;           /* Queue of outgoing data */
   91         struct  mbuf *m;                /* Incoming data buffer */
   92         short   hotchar;                /* Hotchar, or -1 if none */
   93         u_int   flags;                  /* Flags */
   94         struct  callout chand;          /* See man timeout(9) */
   95 };
   96 typedef struct ngt_sc *sc_p;
   97 
   98 /* Flags */
   99 #define FLG_DEBUG               0x0002
  100 #define FLG_DIE                 0x0004
  101 
  102 /* Line discipline methods */
  103 static int      ngt_open(struct cdev *dev, struct tty *tp);
  104 static int      ngt_close(struct tty *tp, int flag);
  105 static int      ngt_read(struct tty *tp, struct uio *uio, int flag);
  106 static int      ngt_write(struct tty *tp, struct uio *uio, int flag);
  107 static int      ngt_tioctl(struct tty *tp,
  108                     u_long cmd, caddr_t data, int flag, struct thread *);
  109 static int      ngt_input(int c, struct tty *tp);
  110 static int      ngt_start(struct tty *tp);
  111 
  112 /* Netgraph methods */
  113 static ng_constructor_t ngt_constructor;
  114 static ng_rcvmsg_t      ngt_rcvmsg;
  115 static ng_shutdown_t    ngt_shutdown;
  116 static ng_newhook_t     ngt_newhook;
  117 static ng_connect_t     ngt_connect;
  118 static ng_rcvdata_t     ngt_rcvdata;
  119 static ng_disconnect_t  ngt_disconnect;
  120 static int              ngt_mod_event(module_t mod, int event, void *data);
  121 
  122 /* Other stuff */
  123 static void     ngt_timeout(node_p node, hook_p hook, void *arg1, int arg2);
  124 
  125 #define ERROUT(x)               do { error = (x); goto done; } while (0)
  126 
  127 /* Line discipline descriptor */
  128 static struct linesw ngt_disc = {
  129         .l_open =       ngt_open,
  130         .l_close =      ngt_close,
  131         .l_read =       ngt_read,
  132         .l_write =      ngt_write,
  133         .l_ioctl =      ngt_tioctl,
  134         .l_rint =       ngt_input,
  135         .l_start =      ngt_start,
  136         .l_modem =      ttymodem,
  137 };
  138 
  139 /* Netgraph node type descriptor */
  140 static struct ng_type typestruct = {
  141         .version =      NG_ABI_VERSION,
  142         .name =         NG_TTY_NODE_TYPE,
  143         .mod_event =    ngt_mod_event,
  144         .constructor =  ngt_constructor,
  145         .rcvmsg =       ngt_rcvmsg,
  146         .shutdown =     ngt_shutdown,
  147         .newhook =      ngt_newhook,
  148         .connect =      ngt_connect,
  149         .rcvdata =      ngt_rcvdata,
  150         .disconnect =   ngt_disconnect,
  151 };
  152 NETGRAPH_INIT(tty, &typestruct);
  153 
  154 /*
  155  * Locking:
  156  *
  157  * - node private data and tp->t_sc is protected by mutex in struct
  158  *   ifqueue, locking is done using IF_XXX() macros.
  159  * - in all tty methods we should acquire node ifqueue mutex, when accessing
  160  *   private data.
  161  * - in _rcvdata() we should use locked versions of IF_{EN,DE}QUEUE() since
  162  *   we may have multiple _rcvdata() threads.
  163  * - when calling any of tty methods from netgraph methods, we should
  164  *   acquire tty locking (now Giant).
  165  *
  166  * - ngt_unit is incremented atomically.
  167  */
  168 
  169 #define NGTLOCK(sc)     IF_LOCK(&sc->outq)
  170 #define NGTUNLOCK(sc)   IF_UNLOCK(&sc->outq)
  171 
  172 static int ngt_unit;
  173 static int ngt_ldisc;
  174 
  175 /******************************************************************
  176                     LINE DISCIPLINE METHODS
  177 ******************************************************************/
  178 
  179 /*
  180  * Set our line discipline on the tty.
  181  * Called from device open routine or ttioctl()
  182  */
  183 static int
  184 ngt_open(struct cdev *dev, struct tty *tp)
  185 {
  186         struct thread *const td = curthread;    /* XXX */
  187         char name[sizeof(NG_TTY_NODE_TYPE) + 8];
  188         sc_p sc;
  189         int error;
  190 
  191         /* Super-user only */
  192         if ((error = suser(td)))
  193                 return (error);
  194 
  195         /* Initialize private struct */
  196         MALLOC(sc, sc_p, sizeof(*sc), M_NETGRAPH, M_WAITOK | M_ZERO);
  197         if (sc == NULL)
  198                 return (ENOMEM);
  199 
  200         sc->tp = tp;
  201         sc->hotchar = tp->t_hotchar = NG_TTY_DFL_HOTCHAR;
  202         mtx_init(&sc->outq.ifq_mtx, "ng_tty node+queue", NULL, MTX_DEF);
  203         IFQ_SET_MAXLEN(&sc->outq, MAX_MBUFQ);
  204 
  205         NGTLOCK(sc);
  206 
  207         /* Setup netgraph node */
  208         error = ng_make_node_common(&typestruct, &sc->node);
  209         if (error) {
  210                 NGTUNLOCK(sc);
  211                 FREE(sc, M_NETGRAPH);
  212                 return (error);
  213         }
  214 
  215         atomic_add_int(&ngt_unit, 1);
  216         snprintf(name, sizeof(name), "%s%d", typestruct.name, ngt_unit);
  217 
  218         /* Assign node its name */
  219         if ((error = ng_name_node(sc->node, name))) {
  220                 sc->flags |= FLG_DIE;
  221                 NGTUNLOCK(sc);
  222                 NG_NODE_UNREF(sc->node);
  223                 log(LOG_ERR, "%s: node name exists?\n", name);
  224                 return (error);
  225         }
  226 
  227         /* Set back pointers */
  228         NG_NODE_SET_PRIVATE(sc->node, sc);
  229         tp->t_sc = sc;
  230 
  231         ng_callout_init(&sc->chand);
  232 
  233         /*
  234          * Pre-allocate cblocks to the an appropriate amount.
  235          * I'm not sure what is appropriate.
  236          */
  237         ttyflush(tp, FREAD | FWRITE);
  238         clist_alloc_cblocks(&tp->t_canq, 0, 0);
  239         clist_alloc_cblocks(&tp->t_rawq, 0, 0);
  240         clist_alloc_cblocks(&tp->t_outq,
  241             MLEN + NGT_HIWATER, MLEN + NGT_HIWATER);
  242 
  243         NGTUNLOCK(sc);
  244 
  245         return (0);
  246 }
  247 
  248 /*
  249  * Line specific close routine, called from device close routine
  250  * and from ttioctl. This causes the node to be destroyed as well.
  251  */
  252 static int
  253 ngt_close(struct tty *tp, int flag)
  254 {
  255         const sc_p sc = (sc_p) tp->t_sc;
  256 
  257         ttyflush(tp, FREAD | FWRITE);
  258         clist_free_cblocks(&tp->t_outq);
  259         if (sc != NULL) {
  260                 NGTLOCK(sc);
  261                 if (callout_pending(&sc->chand))
  262                         ng_uncallout(&sc->chand, sc->node);
  263                 tp->t_sc = NULL;
  264                 sc->flags |= FLG_DIE;
  265                 NGTUNLOCK(sc);
  266                 ng_rmnode_self(sc->node);
  267         }
  268         return (0);
  269 }
  270 
  271 /*
  272  * Once the device has been turned into a node, we don't allow reading.
  273  */
  274 static int
  275 ngt_read(struct tty *tp, struct uio *uio, int flag)
  276 {
  277         return (EIO);
  278 }
  279 
  280 /*
  281  * Once the device has been turned into a node, we don't allow writing.
  282  */
  283 static int
  284 ngt_write(struct tty *tp, struct uio *uio, int flag)
  285 {
  286         return (EIO);
  287 }
  288 
  289 /*
  290  * We implement the NGIOCGINFO ioctl() defined in ng_message.h.
  291  */
  292 static int
  293 ngt_tioctl(struct tty *tp, u_long cmd, caddr_t data, int flag, struct thread *td)
  294 {
  295         const sc_p sc = (sc_p) tp->t_sc;
  296 
  297         if (sc == NULL)
  298                 /* No node attached */
  299                 return (0);
  300 
  301         switch (cmd) {
  302         case NGIOCGINFO:
  303             {
  304                 struct nodeinfo *const ni = (struct nodeinfo *) data;
  305                 const node_p node = sc->node;
  306 
  307                 bzero(ni, sizeof(*ni));
  308                 NGTLOCK(sc);
  309                 if (NG_NODE_HAS_NAME(node))
  310                         strncpy(ni->name, NG_NODE_NAME(node), sizeof(ni->name) - 1);
  311                 strncpy(ni->type, node->nd_type->name, sizeof(ni->type) - 1);
  312                 ni->id = (u_int32_t) ng_node2ID(node);
  313                 ni->hooks = NG_NODE_NUMHOOKS(node);
  314                 NGTUNLOCK(sc);
  315                 break;
  316             }
  317         default:
  318                 return (ENOIOCTL);
  319         }
  320 
  321         return (0);
  322 }
  323 
  324 /*
  325  * Receive data coming from the device. We get one character at
  326  * a time, which is kindof silly.
  327  *
  328  * Full locking of softc is not required, since we are the only
  329  * user of sc->m.
  330  */
  331 static int
  332 ngt_input(int c, struct tty *tp)
  333 {
  334         const sc_p sc = (sc_p) tp->t_sc;
  335         const node_p node = sc->node;
  336         struct mbuf *m;
  337         int error = 0;
  338 
  339         if (sc == NULL)
  340                 /* No node attached */
  341                 return (0);
  342 
  343         if (tp != sc->tp)
  344                 panic("ngt_input");
  345 
  346         /* Check for error conditions */
  347         if ((tp->t_state & TS_CONNECTED) == 0) {
  348                 if (sc->flags & FLG_DEBUG)
  349                         log(LOG_DEBUG, "%s: no carrier\n", NG_NODE_NAME(node));
  350                 return (0);
  351         }
  352         if (c & TTY_ERRORMASK) {
  353                 /* framing error or overrun on this char */
  354                 if (sc->flags & FLG_DEBUG)
  355                         log(LOG_DEBUG, "%s: line error %x\n",
  356                             NG_NODE_NAME(node), c & TTY_ERRORMASK);
  357                 return (0);
  358         }
  359         c &= TTY_CHARMASK;
  360 
  361         /* Get a new header mbuf if we need one */
  362         if (!(m = sc->m)) {
  363                 MGETHDR(m, M_DONTWAIT, MT_DATA);
  364                 if (!m) {
  365                         if (sc->flags & FLG_DEBUG)
  366                                 log(LOG_ERR,
  367                                     "%s: can't get mbuf\n", NG_NODE_NAME(node));
  368                         return (ENOBUFS);
  369                 }
  370                 m->m_len = m->m_pkthdr.len = 0;
  371                 m->m_pkthdr.rcvif = NULL;
  372                 sc->m = m;
  373         }
  374 
  375         /* Add char to mbuf */
  376         *mtod(m, u_char *) = c;
  377         m->m_data++;
  378         m->m_len++;
  379         m->m_pkthdr.len++;
  380 
  381         /* Ship off mbuf if it's time */
  382         if (sc->hotchar == -1 || c == sc->hotchar || m->m_len >= MHLEN) {
  383                 m->m_data = m->m_pktdat;
  384                 sc->m = NULL;
  385 
  386                 /*
  387                  * We have built our mbuf without checking that we actually
  388                  * have a hook to send it. This was done to avoid
  389                  * acquiring mutex on each character. Check now.
  390                  *
  391                  */
  392 
  393                 NGTLOCK(sc);
  394                 if (sc->hook == NULL) {
  395                         NGTUNLOCK(sc);
  396                         m_freem(m);
  397                         return (0);             /* XXX: original behavior */
  398                 }
  399                 NG_SEND_DATA_ONLY(error, sc->hook, m);  /* Will queue */
  400                 NGTUNLOCK(sc);
  401         }
  402 
  403         return (error);
  404 }
  405 
  406 /*
  407  * This is called when the device driver is ready for more output.
  408  * Also called from ngt_rcv_data() when a new mbuf is available for output.
  409  */
  410 static int
  411 ngt_start(struct tty *tp)
  412 {
  413         const sc_p sc = (sc_p) tp->t_sc;
  414 
  415         while (tp->t_outq.c_cc < NGT_HIWATER) { /* XXX 2.2 specific ? */
  416                 struct mbuf *m;
  417 
  418                 /* Remove first mbuf from queue */
  419                 IF_DEQUEUE(&sc->outq, m);
  420                 if (m == NULL)
  421                         break;
  422 
  423                 /* Send as much of it as possible */
  424                 while (m != NULL) {
  425                         int     sent;
  426 
  427                         sent = m->m_len
  428                             - b_to_q(mtod(m, u_char *), m->m_len, &tp->t_outq);
  429                         m->m_data += sent;
  430                         m->m_len -= sent;
  431                         if (m->m_len > 0)
  432                                 break;  /* device can't take no more */
  433                         m = m_free(m);
  434                 }
  435 
  436                 /* Put remainder of mbuf chain (if any) back on queue */
  437                 if (m != NULL) {
  438                         IF_PREPEND(&sc->outq, m);
  439                         break;
  440                 }
  441         }
  442 
  443         /* Call output process whether or not there is any output. We are
  444          * being called in lieu of ttstart and must do what it would. */
  445         if (tp->t_oproc != NULL)
  446                 (*tp->t_oproc) (tp);
  447 
  448         /* This timeout is needed for operation on a pseudo-tty, because the
  449          * pty code doesn't call pppstart after it has drained the t_outq. */
  450         /* XXX: outq not locked */
  451         if (!IFQ_IS_EMPTY(&sc->outq) && !callout_pending(&sc->chand))
  452                 ng_callout(&sc->chand, sc->node, NULL, 1, ngt_timeout, NULL, 0);
  453 
  454         return (0);
  455 }
  456 
  457 /*
  458  * We still have data to output to the device, so try sending more.
  459  */
  460 static void
  461 ngt_timeout(node_p node, hook_p hook, void *arg1, int arg2)
  462 {
  463         const sc_p sc = NG_NODE_PRIVATE(node);
  464 
  465         mtx_lock(&Giant);
  466         ngt_start(sc->tp);
  467         mtx_unlock(&Giant);
  468 }
  469 
  470 /******************************************************************
  471                     NETGRAPH NODE METHODS
  472 ******************************************************************/
  473 
  474 /*
  475  * Initialize a new node of this type.
  476  *
  477  * We only allow nodes to be created as a result of setting
  478  * the line discipline on a tty, so always return an error if not.
  479  */
  480 static int
  481 ngt_constructor(node_p node)
  482 {
  483         return (EOPNOTSUPP);
  484 }
  485 
  486 /*
  487  * Add a new hook. There can only be one.
  488  */
  489 static int
  490 ngt_newhook(node_p node, hook_p hook, const char *name)
  491 {
  492         const sc_p sc = NG_NODE_PRIVATE(node);
  493 
  494         if (strcmp(name, NG_TTY_HOOK))
  495                 return (EINVAL);
  496 
  497         if (sc->hook)
  498                 return (EISCONN);
  499 
  500         NGTLOCK(sc);
  501         sc->hook = hook;
  502         NGTUNLOCK(sc);
  503 
  504         return (0);
  505 }
  506 
  507 /*
  508  * Set the hook into queueing mode (for outgoing packets),
  509  * so that we wont deliver mbuf thru the whole graph holding
  510  * tty locks.
  511  */
  512 static int
  513 ngt_connect(hook_p hook)
  514 {
  515         NG_HOOK_FORCE_QUEUE(NG_HOOK_PEER(hook));
  516         /*
  517          * XXX: While ngt_start() is Giant-locked, queue incoming
  518          * packets, too. Otherwise we acquire Giant holding some
  519          * IP stack locks, e.g. divinp, and this makes WITNESS scream.
  520          */
  521         NG_HOOK_FORCE_QUEUE(hook);
  522         return (0);
  523 }
  524 
  525 /*
  526  * Disconnect the hook
  527  */
  528 static int
  529 ngt_disconnect(hook_p hook)
  530 {
  531         const sc_p sc = NG_NODE_PRIVATE(NG_HOOK_NODE(hook));
  532 
  533         if (hook != sc->hook)
  534                 panic(__func__);
  535 
  536         NGTLOCK(sc);
  537         sc->hook = NULL;
  538         NGTUNLOCK(sc);
  539 
  540         return (0);
  541 }
  542 
  543 /*
  544  * Remove this node. The does the netgraph portion of the shutdown.
  545  * This should only be called indirectly from ngt_close().
  546  *
  547  * tp->t_sc is already NULL, so we should be protected from
  548  * tty calls now.
  549  */
  550 static int
  551 ngt_shutdown(node_p node)
  552 {
  553         const sc_p sc = NG_NODE_PRIVATE(node);
  554 
  555         NGTLOCK(sc);
  556         if (!(sc->flags & FLG_DIE)) {
  557                 NGTUNLOCK(sc);
  558                 return (EOPNOTSUPP);
  559         }
  560         NGTUNLOCK(sc);
  561 
  562         /* Free resources */
  563         _IF_DRAIN(&sc->outq);
  564         mtx_destroy(&(sc)->outq.ifq_mtx);
  565         m_freem(sc->m);
  566         NG_NODE_UNREF(sc->node);
  567         FREE(sc, M_NETGRAPH);
  568 
  569         return (0);
  570 }
  571 
  572 /*
  573  * Receive incoming data from netgraph system. Put it on our
  574  * output queue and start output if necessary.
  575  */
  576 static int
  577 ngt_rcvdata(hook_p hook, item_p item)
  578 {
  579         const sc_p sc = NG_NODE_PRIVATE(NG_HOOK_NODE(hook));
  580         struct mbuf *m;
  581         int qlen;
  582 
  583         if (hook != sc->hook)
  584                 panic(__func__);
  585 
  586         NGI_GET_M(item, m);
  587         NG_FREE_ITEM(item);
  588 
  589         IF_LOCK(&sc->outq);
  590         if (_IF_QFULL(&sc->outq)) {
  591                 _IF_DROP(&sc->outq);
  592                 IF_UNLOCK(&sc->outq);
  593                 NG_FREE_M(m);
  594                 return (ENOBUFS);
  595         }
  596 
  597         _IF_ENQUEUE(&sc->outq, m);
  598         qlen = sc->outq.ifq_len;
  599         IF_UNLOCK(&sc->outq);
  600 
  601         /*
  602          * If qlen > 1, then we should already have a scheduled callout.
  603          */
  604         if (qlen == 1) {
  605                 mtx_lock(&Giant);
  606                 ngt_start(sc->tp);
  607                 mtx_unlock(&Giant);
  608         }
  609 
  610         return (0);
  611 }
  612 
  613 /*
  614  * Receive control message
  615  */
  616 static int
  617 ngt_rcvmsg(node_p node, item_p item, hook_p lasthook)
  618 {
  619         const sc_p sc = NG_NODE_PRIVATE(node);
  620         struct ng_mesg *msg, *resp = NULL;
  621         int error = 0;
  622 
  623         NGI_GET_MSG(item, msg);
  624         switch (msg->header.typecookie) {
  625         case NGM_TTY_COOKIE:
  626                 switch (msg->header.cmd) {
  627                 case NGM_TTY_SET_HOTCHAR:
  628                     {
  629                         int     hotchar;
  630 
  631                         if (msg->header.arglen != sizeof(int))
  632                                 ERROUT(EINVAL);
  633                         hotchar = *((int *) msg->data);
  634                         if (hotchar != (u_char) hotchar && hotchar != -1)
  635                                 ERROUT(EINVAL);
  636                         sc->hotchar = hotchar;  /* race condition is OK */
  637                         break;
  638                     }
  639                 case NGM_TTY_GET_HOTCHAR:
  640                         NG_MKRESPONSE(resp, msg, sizeof(int), M_NOWAIT);
  641                         if (!resp)
  642                                 ERROUT(ENOMEM);
  643                         /* Race condition here is OK */
  644                         *((int *) resp->data) = sc->hotchar;
  645                         break;
  646                 default:
  647                         ERROUT(EINVAL);
  648                 }
  649                 break;
  650         default:
  651                 ERROUT(EINVAL);
  652         }
  653 done:
  654         NG_RESPOND_MSG(error, node, item, resp);
  655         NG_FREE_MSG(msg);
  656         return (error);
  657 }
  658 
  659 /******************************************************************
  660                         INITIALIZATION
  661 ******************************************************************/
  662 
  663 /*
  664  * Handle loading and unloading for this node type
  665  */
  666 static int
  667 ngt_mod_event(module_t mod, int event, void *data)
  668 {
  669         int error = 0;
  670 
  671         switch (event) {
  672         case MOD_LOAD:
  673 
  674                 /* Register line discipline */
  675                 mtx_lock(&Giant);
  676                 if ((ngt_ldisc = ldisc_register(NETGRAPHDISC, &ngt_disc)) < 0) {
  677                         mtx_unlock(&Giant);
  678                         log(LOG_ERR, "%s: can't register line discipline",
  679                             __func__);
  680                         return (EIO);
  681                 }
  682                 mtx_unlock(&Giant);
  683                 break;
  684 
  685         case MOD_UNLOAD:
  686 
  687                 /* Unregister line discipline */
  688                 mtx_lock(&Giant);
  689                 ldisc_deregister(ngt_ldisc);
  690                 mtx_unlock(&Giant);
  691                 break;
  692 
  693         default:
  694                 error = EOPNOTSUPP;
  695                 break;
  696         }
  697         return (error);
  698 }

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