File:  [DragonFly] / src / sys / kern / kern_device.c
Revision 1.11: download - view: text, annotated - select for diffs
Wed May 19 22:52:58 2004 UTC (10 years, 6 months ago) by dillon
Branches: MAIN
CVS tags: HEAD, DragonFly_Snap13Sep2004, DragonFly_1_0_REL, DragonFly_1_0_RC1, DragonFly_1_0A_REL
Device layer rollup commit.

* cdevsw_add() is now required.  cdevsw_add() and cdevsw_remove() may specify
  a mask/match indicating the range of supported minor numbers.  Multiple
  cdevsw_add()'s using the same major number, but distinctly different
  ranges, may be issued.  All devices that failed to call cdevsw_add() before
  now do.

* cdevsw_remove() now automatically marks all devices within its supported
  range as being destroyed.

* vnode->v_rdev is no longer resolved when the vnode is created.  Instead,
  only v_udev (a newly added field) is resolved.  v_rdev is resolved when
  the vnode is opened and cleared on the last close.

* A great deal of code was making rather dubious assumptions with regards
  to the validity of devices associated with vnodes, primarily due to
  the persistence of a device structure due to being indexed by (major, minor)
  instead of by (cdevsw, major, minor).  In particular, if you run a program
  which connects to a USB device and then you pull the USB device and plug
  it back in, the vnode subsystem will continue to believe that the device
  is open when, in fact, it isn't (because it was destroyed and recreated).

  In particular, note that all the VFS mount procedures now check devices
  via v_udev instead of v_rdev prior to calling VOP_OPEN(), since v_rdev
  is NULL prior to the first open.

* The disk layer's device interaction has been rewritten.  The disk layer
  (i.e. the slice and disklabel management layer) no longer overloads
  its data onto the device structure representing the underlying physical
  disk.  Instead, the disk layer uses the new cdevsw_add() functionality
  to register its own cdevsw using the underlying device's major number,
  and simply does NOT register the underlying device's cdevsw.  No
  confusion is created because the device hash is now based on
  (cdevsw,major,minor) rather then (major,minor).

  NOTE: This also means that underlying raw disk devices may use the entire
  device minor number instead of having to reserve the bits used by the disk
  layer, and also means that can we (theoretically) stack a fully
  disklabel-supported 'disk' on top of any block device.

* The new reference counting scheme prevents this by associating a device
  with a cdevsw and disconnecting the device from its cdevsw when the cdevsw
  is removed.  Additionally, all udev2dev() lookups run through the cdevsw
  mask/match and only successfully find devices still associated with an
  active cdevsw.

* Major work on MFS:  MFS no longer shortcuts vnode and device creation.  It
  now creates a real vnode and a real device and implements real open and
  close VOPs.  Additionally, due to the disk layer changes, MFS is no longer
  limited to 255 mounts.  The new limit is 16 million.  Since MFS creates a
  real device node, mount_mfs will now create a real /dev/mfs<PID> device
  that can be read from userland (e.g. so you can dump an MFS filesystem).

* BUF AND DEVICE STRATEGY changes.  The struct buf contains a b_dev field.
  In order to properly handle stacked devices we now require that the b_dev
  field be initialized before the device strategy routine is called.  This
  required some additional work in various VFS implementations.  To enforce
  this requirement, biodone() now sets b_dev to NODEV.  The new disk layer
  will adjust b_dev before forwarding a request to the actual physical
  device.

* A bug in the ISO CD boot sequence which resulted in a panic has been fixed.

Testing by: lots of people, but David Rhodus found the most aggregious bugs.

    1: /*
    2:  * Copyright (c) 2003 Matthew Dillon <dillon@backplane.com> All rights reserved.
    3:  * cdevsw from kern/kern_conf.c Copyright (c) 1995 Terrence R. Lambert
    4:  * cdevsw from kern/kern_conf.c Copyright (c) 1995 Julian R. Elishcer,
    5:  *							All rights reserved.
    6:  *
    7:  * Redistribution and use in source and binary forms, with or without
    8:  * modification, are permitted provided that the following conditions
    9:  * are met:
   10:  * 1. Redistributions of source code must retain the above copyright
   11:  *    notice, this list of conditions and the following disclaimer.
   12:  * 2. Redistributions in binary form must reproduce the above copyright
   13:  *    notice, this list of conditions and the following disclaimer in the
   14:  *    documentation and/or other materials provided with the distribution.
   15:  *
   16:  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   17:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   18:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   19:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   20:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   21:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   22:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   23:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   24:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   25:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   26:  * SUCH DAMAGE.
   27:  *
   28:  * $DragonFly: src/sys/kern/kern_device.c,v 1.11 2004/05/19 22:52:58 dillon Exp $
   29:  */
   30: #include <sys/param.h>
   31: #include <sys/kernel.h>
   32: #include <sys/sysctl.h>
   33: #include <sys/systm.h>
   34: #include <sys/module.h>
   35: #include <sys/malloc.h>
   36: #include <sys/conf.h>
   37: #include <sys/vnode.h>
   38: #include <sys/queue.h>
   39: #include <sys/msgport.h>
   40: #include <sys/device.h>
   41: #include <machine/stdarg.h>
   42: #include <sys/proc.h>
   43: #include <sys/thread2.h>
   44: #include <sys/msgport2.h>
   45: 
   46: static struct cdevlink 	*cdevbase[NUMCDEVSW];
   47: 
   48: static int cdevsw_putport(lwkt_port_t port, lwkt_msg_t msg);
   49: 
   50: struct cdevsw dead_cdevsw;
   51: 
   52: /*
   53:  * Initialize a message port to serve as the default message-handling port
   54:  * for device operations.  This message port provides compatibility with
   55:  * traditional cdevsw dispatch functions by running them synchronously.
   56:  *
   57:  * YYY NOTE: ms_cmd can now hold a function pointer, should this code be
   58:  * converted from an integer op to a function pointer with a flag to
   59:  * indicate legacy operation?
   60:  */
   61: static void
   62: init_default_cdevsw_port(lwkt_port_t port)
   63: {
   64:     lwkt_initport(port, NULL);
   65:     port->mp_putport = cdevsw_putport;
   66: }
   67: 
   68: static
   69: int
   70: cdevsw_putport(lwkt_port_t port, lwkt_msg_t lmsg)
   71: {
   72:     cdevallmsg_t msg = (cdevallmsg_t)lmsg;
   73:     struct cdevsw *devsw = msg->am_msg.dev->si_devsw;
   74:     int error;
   75: 
   76:     /*
   77:      * Run the device switch function synchronously in the context of the
   78:      * caller and return a synchronous error code (anything not EASYNC).
   79:      */
   80:     switch(msg->am_lmsg.ms_cmd.cm_op) {
   81:     case CDEV_CMD_OPEN:
   82: 	error = devsw->old_open(
   83: 		    msg->am_open.msg.dev,
   84: 		    msg->am_open.oflags,
   85: 		    msg->am_open.devtype,
   86: 		    msg->am_open.td);
   87: 	break;
   88:     case CDEV_CMD_CLOSE:
   89: 	error = devsw->old_close(
   90: 		    msg->am_close.msg.dev,
   91: 		    msg->am_close.fflag,
   92: 		    msg->am_close.devtype,
   93: 		    msg->am_close.td);
   94: 	break;
   95:     case CDEV_CMD_STRATEGY:
   96: 	devsw->old_strategy(msg->am_strategy.bp);
   97: 	error = 0;
   98: 	break;
   99:     case CDEV_CMD_IOCTL:
  100: 	error = devsw->old_ioctl(
  101: 		    msg->am_ioctl.msg.dev,
  102: 		    msg->am_ioctl.cmd,
  103: 		    msg->am_ioctl.data,
  104: 		    msg->am_ioctl.fflag,
  105: 		    msg->am_ioctl.td);
  106: 	break;
  107:     case CDEV_CMD_DUMP:
  108: 	error = devsw->old_dump(
  109: 		    msg->am_dump.msg.dev,
  110: 		    msg->am_dump.count,
  111: 		    msg->am_dump.blkno,
  112: 		    msg->am_dump.secsize);
  113: 	break;
  114:     case CDEV_CMD_PSIZE:
  115: 	msg->am_psize.result = devsw->old_psize(msg->am_psize.msg.dev);
  116: 	error = 0;	/* XXX */
  117: 	break;
  118:     case CDEV_CMD_READ:
  119: 	error = devsw->old_read(
  120: 		    msg->am_read.msg.dev,
  121: 		    msg->am_read.uio,
  122: 		    msg->am_read.ioflag);
  123: 	break;
  124:     case CDEV_CMD_WRITE:
  125: 	error = devsw->old_write(
  126: 		    msg->am_read.msg.dev,
  127: 		    msg->am_read.uio,
  128: 		    msg->am_read.ioflag);
  129: 	break;
  130:     case CDEV_CMD_POLL:
  131: 	msg->am_poll.events = devsw->old_poll(
  132: 				msg->am_poll.msg.dev,
  133: 				msg->am_poll.events,
  134: 				msg->am_poll.td);
  135: 	error = 0;
  136: 	break;
  137:     case CDEV_CMD_KQFILTER:
  138: 	msg->am_kqfilter.result = devsw->old_kqfilter(
  139: 				msg->am_kqfilter.msg.dev,
  140: 				msg->am_kqfilter.kn);
  141: 	error = 0;
  142: 	break;
  143:     case CDEV_CMD_MMAP:
  144: 	msg->am_mmap.result = devsw->old_mmap(
  145: 		    msg->am_mmap.msg.dev,
  146: 		    msg->am_mmap.offset,
  147: 		    msg->am_mmap.nprot);
  148: 	error = 0;	/* XXX */
  149: 	break;
  150:     default:
  151: 	error = ENOSYS;
  152: 	break;
  153:     }
  154:     KKASSERT(error != EASYNC);
  155:     return(error);
  156: }
  157: 
  158: static __inline
  159: lwkt_port_t
  160: _init_cdevmsg(dev_t dev, cdevmsg_t msg, int cmd)
  161: {
  162:     lwkt_initmsg_simple(&msg->msg, cmd);
  163:     msg->dev = dev;
  164:     return(dev->si_port);
  165: }
  166: 
  167: int
  168: dev_dopen(dev_t dev, int oflags, int devtype, thread_t td)
  169: {
  170:     struct cdevmsg_open	msg;
  171:     lwkt_port_t port;
  172: 
  173:     port = _init_cdevmsg(dev, &msg.msg, CDEV_CMD_OPEN);
  174:     if (port == NULL)
  175: 	return(ENXIO);
  176:     msg.oflags = oflags;
  177:     msg.devtype = devtype;
  178:     msg.td = td;
  179:     return(lwkt_domsg(port, &msg.msg.msg));
  180: }
  181: 
  182: int
  183: dev_dclose(dev_t dev, int fflag, int devtype, thread_t td)
  184: {
  185:     struct cdevmsg_close msg;
  186:     lwkt_port_t port;
  187: 
  188:     port = _init_cdevmsg(dev, &msg.msg, CDEV_CMD_CLOSE);
  189:     if (port == NULL)
  190: 	return(ENXIO);
  191:     msg.fflag = fflag;
  192:     msg.devtype = devtype;
  193:     msg.td = td;
  194:     return(lwkt_domsg(port, &msg.msg.msg));
  195: }
  196: 
  197: void
  198: dev_dstrategy(dev_t dev, struct buf *bp)
  199: {
  200:     struct cdevmsg_strategy msg;
  201:     lwkt_port_t port;
  202: 
  203:     port = _init_cdevmsg(dev, &msg.msg, CDEV_CMD_STRATEGY);
  204:     KKASSERT(port);	/* 'nostrategy' function is NULL YYY */
  205:     msg.bp = bp;
  206:     lwkt_domsg(port, &msg.msg.msg);
  207: }
  208: 
  209: int
  210: dev_dioctl(dev_t dev, u_long cmd, caddr_t data, int fflag, thread_t td)
  211: {
  212:     struct cdevmsg_ioctl msg;
  213:     lwkt_port_t port;
  214: 
  215:     port = _init_cdevmsg(dev, &msg.msg, CDEV_CMD_IOCTL);
  216:     if (port == NULL)
  217: 	return(ENXIO);
  218:     msg.cmd = cmd;
  219:     msg.data = data;
  220:     msg.fflag = fflag;
  221:     msg.td = td;
  222:     return(lwkt_domsg(port, &msg.msg.msg));
  223: }
  224: 
  225: /*
  226:  * note: the disk layer is expected to set count, blkno, and secsize before
  227:  * forwarding the message.
  228:  */
  229: int
  230: dev_ddump(dev_t dev)
  231: {
  232:     struct cdevmsg_dump	msg;
  233:     lwkt_port_t port;
  234: 
  235:     port = _init_cdevmsg(dev, &msg.msg, CDEV_CMD_DUMP);
  236:     if (port == NULL)
  237: 	return(ENXIO);
  238:     msg.count = 0;
  239:     msg.blkno = 0;
  240:     msg.secsize = 0;
  241:     return(lwkt_domsg(port, &msg.msg.msg));
  242: }
  243: 
  244: int
  245: dev_dpsize(dev_t dev)
  246: {
  247:     struct cdevmsg_psize msg;
  248:     lwkt_port_t port;
  249:     int error;
  250: 
  251:     port = _init_cdevmsg(dev, &msg.msg, CDEV_CMD_PSIZE);
  252:     if (port == NULL)
  253: 	return(-1);
  254:     error = lwkt_domsg(port, &msg.msg.msg);
  255:     if (error == 0)
  256: 	return(msg.result);
  257:     return(-1);
  258: }
  259: 
  260: int
  261: dev_dread(dev_t dev, struct uio *uio, int ioflag)
  262: {
  263:     struct cdevmsg_read msg;
  264:     lwkt_port_t port;
  265: 
  266:     port = _init_cdevmsg(dev, &msg.msg, CDEV_CMD_READ);
  267:     if (port == NULL)
  268: 	return(ENXIO);
  269:     msg.uio = uio;
  270:     msg.ioflag = ioflag;
  271:     return(lwkt_domsg(port, &msg.msg.msg));
  272: }
  273: 
  274: int
  275: dev_dwrite(dev_t dev, struct uio *uio, int ioflag)
  276: {
  277:     struct cdevmsg_write msg;
  278:     lwkt_port_t port;
  279: 
  280:     port = _init_cdevmsg(dev, &msg.msg, CDEV_CMD_WRITE);
  281:     if (port == NULL)
  282: 	return(ENXIO);
  283:     msg.uio = uio;
  284:     msg.ioflag = ioflag;
  285:     return(lwkt_domsg(port, &msg.msg.msg));
  286: }
  287: 
  288: int
  289: dev_dpoll(dev_t dev, int events, thread_t td)
  290: {
  291:     struct cdevmsg_poll msg;
  292:     lwkt_port_t port;
  293:     int error;
  294: 
  295:     port = _init_cdevmsg(dev, &msg.msg, CDEV_CMD_POLL);
  296:     if (port == NULL)
  297: 	return(ENXIO);
  298:     msg.events = events;
  299:     msg.td = td;
  300:     error = lwkt_domsg(port, &msg.msg.msg);
  301:     if (error == 0)
  302: 	return(msg.events);
  303:     return(seltrue(dev, msg.events, td));
  304: }
  305: 
  306: int
  307: dev_dkqfilter(dev_t dev, struct knote *kn)
  308: {
  309:     struct cdevmsg_kqfilter msg;
  310:     lwkt_port_t port;
  311:     int error;
  312: 
  313:     port = _init_cdevmsg(dev, &msg.msg, CDEV_CMD_KQFILTER);
  314:     if (port == NULL)
  315: 	return(ENXIO);
  316:     msg.kn = kn;
  317:     error = lwkt_domsg(port, &msg.msg.msg);
  318:     if (error == 0)
  319: 	return(msg.result);
  320:     return(ENODEV);
  321: }
  322: 
  323: int
  324: dev_dmmap(dev_t dev, vm_offset_t offset, int nprot)
  325: {
  326:     struct cdevmsg_mmap msg;
  327:     lwkt_port_t port;
  328:     int error;
  329: 
  330:     port = _init_cdevmsg(dev, &msg.msg, CDEV_CMD_MMAP);
  331:     if (port == NULL)
  332: 	return(-1);
  333:     msg.offset = offset;
  334:     msg.nprot = nprot;
  335:     error = lwkt_domsg(port, &msg.msg.msg);
  336:     if (error == 0)
  337: 	return(msg.result);
  338:     return(-1);
  339: }
  340: 
  341: const char *
  342: dev_dname(dev_t dev)
  343: {
  344:     return(dev->si_devsw->d_name);
  345: }
  346: 
  347: int
  348: dev_dflags(dev_t dev)
  349: {
  350:     return(dev->si_devsw->d_flags);
  351: }
  352: 
  353: int
  354: dev_dmaj(dev_t dev)
  355: {
  356:     return(dev->si_devsw->d_maj);
  357: }
  358: 
  359: lwkt_port_t
  360: dev_dport(dev_t dev)
  361: {
  362:     return(dev->si_port);
  363: }
  364: 
  365: /*
  366:  * Convert a cdevsw template into the real thing, filling in fields the
  367:  * device left empty with appropriate defaults.
  368:  */
  369: void
  370: compile_devsw(struct cdevsw *devsw)
  371: {
  372:     static lwkt_port devsw_compat_port;
  373: 
  374:     if (devsw_compat_port.mp_putport == NULL)
  375: 	init_default_cdevsw_port(&devsw_compat_port);
  376:     
  377:     if (devsw->old_open == NULL)
  378: 	devsw->old_open = noopen;
  379:     if (devsw->old_close == NULL)
  380: 	devsw->old_close = noclose;
  381:     if (devsw->old_read == NULL)
  382: 	devsw->old_read = noread;
  383:     if (devsw->old_write == NULL)
  384: 	devsw->old_write = nowrite;
  385:     if (devsw->old_ioctl == NULL)
  386: 	devsw->old_ioctl = noioctl;
  387:     if (devsw->old_poll == NULL)
  388: 	devsw->old_poll = nopoll;
  389:     if (devsw->old_mmap == NULL)
  390: 	devsw->old_mmap = nommap;
  391:     if (devsw->old_strategy == NULL)
  392: 	devsw->old_strategy = nostrategy;
  393:     if (devsw->old_dump == NULL)
  394: 	devsw->old_dump = nodump;
  395:     if (devsw->old_psize == NULL)
  396: 	devsw->old_psize = nopsize;
  397:     if (devsw->old_kqfilter == NULL)
  398: 	devsw->old_kqfilter = nokqfilter;
  399: 
  400:     if (devsw->d_port == NULL)
  401: 	devsw->d_port = &devsw_compat_port;
  402:     if (devsw->d_clone == NULL)
  403: 	devsw->d_clone = noclone;
  404: }
  405: 
  406: /*
  407:  * This makes a cdevsw entry visible to userland (e.g /dev/<blah>).
  408:  *
  409:  * The kernel can overload a major number with multiple cdevsw's but only
  410:  * the one installed in cdevbase[] is visible to userland.  make_dev() does
  411:  * not automatically call cdevsw_add() (nor do we want it to, since 
  412:  * partition-managed disk devices are overloaded on top of the raw device).
  413:  */
  414: int
  415: cdevsw_add(struct cdevsw *devsw, u_int mask, u_int match)
  416: {
  417:     int maj;
  418:     struct cdevlink *link;
  419: 
  420:     compile_devsw(devsw);
  421:     maj = devsw->d_maj;
  422:     if (maj < 0 || maj >= NUMCDEVSW) {
  423: 	printf("%s: ERROR: driver has bogus cdevsw->d_maj = %d\n",
  424: 	    devsw->d_name, maj);
  425: 	return (EINVAL);
  426:     }
  427:     for (link = cdevbase[maj]; link; link = link->next) {
  428: 	/*
  429: 	 * If we get an exact match we usurp the target, but we only print
  430: 	 * a warning message if a different device switch is installed.
  431: 	 */
  432: 	if (link->mask == mask && link->match == match) {
  433: 	    if (link->devsw != devsw) {
  434: 		    printf("WARNING: \"%s\" (%p) is usurping \"%s\"'s (%p)"
  435: 			" cdevsw[]\n",
  436: 			devsw->d_name, devsw, 
  437: 			link->devsw->d_name, link->devsw);
  438: 		    link->devsw = devsw;
  439: 		    ++devsw->d_refs;
  440: 	    }
  441: 	    return(0);
  442: 	}
  443: 	/*
  444: 	 * XXX add additional warnings for overlaps
  445: 	 */
  446:     }
  447: 
  448:     link = malloc(sizeof(struct cdevlink), M_DEVBUF, M_INTWAIT|M_ZERO);
  449:     link->mask = mask;
  450:     link->match = match;
  451:     link->devsw = devsw;
  452:     link->next = cdevbase[maj];
  453:     cdevbase[maj] = link;
  454:     ++devsw->d_refs;
  455:     return(0);
  456: }
  457: 
  458: /*
  459:  * Should only be used by udev2dev().
  460:  *
  461:  * If the minor number is -1, we match the first cdevsw we find for this
  462:  * major. 
  463:  *
  464:  * Note that this function will return NULL if the minor number is not within
  465:  * the bounds of the installed mask(s).
  466:  */
  467: struct cdevsw *
  468: cdevsw_get(int x, int y)
  469: {
  470:     struct cdevlink *link;
  471: 
  472:     if (x < 0 || x >= NUMCDEVSW)
  473: 	return(NULL);
  474:     for (link = cdevbase[x]; link; link = link->next) {
  475: 	if (y == -1 || (link->mask & y) == link->match)
  476: 	    return(link->devsw);
  477:     }
  478:     return(NULL);
  479: }
  480: 
  481: /*
  482:  * Use the passed cdevsw as a template to create our intercept cdevsw,
  483:  * and install and return ours.
  484:  */
  485: struct cdevsw *
  486: cdevsw_add_override(dev_t backing_dev, u_int mask, u_int match)
  487: {
  488:     struct cdevsw *devsw;
  489:     struct cdevsw *bsw = backing_dev->si_devsw;
  490: 
  491:     devsw = malloc(sizeof(struct cdevsw), M_DEVBUF, M_INTWAIT|M_ZERO);
  492:     devsw->d_name = bsw->d_name;
  493:     devsw->d_maj = bsw->d_maj;
  494:     devsw->d_flags = bsw->d_flags;
  495:     compile_devsw(devsw);
  496:     cdevsw_add(devsw, mask, match);
  497: 
  498:     return(devsw);
  499: }
  500: 
  501: /*
  502:  * Override a device's port, returning the previously installed port.  This
  503:  * is XXX very dangerous.
  504:  */
  505: lwkt_port_t
  506: cdevsw_dev_override(dev_t dev, lwkt_port_t port)
  507: {
  508:     lwkt_port_t oport;
  509: 
  510:     oport = dev->si_port;
  511:     dev->si_port = port;
  512:     return(oport);
  513: }
  514: 
  515: /*
  516:  * Remove a cdevsw entry from the cdevbase[] major array so no new user opens
  517:  * can be performed, and destroy all devices installed in the hash table
  518:  * which are associated with this cdevsw.  (see destroy_all_dev()).
  519:  */
  520: int
  521: cdevsw_remove(struct cdevsw *devsw, u_int mask, u_int match)
  522: {
  523:     int maj = devsw->d_maj;
  524:     struct cdevlink *link;
  525:     struct cdevlink **plink;
  526:  
  527:     if (maj < 0 || maj >= NUMCDEVSW) {
  528: 	printf("%s: ERROR: driver has bogus cdevsw->d_maj = %d\n",
  529: 	    devsw->d_name, maj);
  530: 	return EINVAL;
  531:     }
  532:     if (devsw != &dead_cdevsw)
  533: 	destroy_all_dev(devsw, mask, match);
  534:     for (plink = &cdevbase[maj]; (link = *plink) != NULL; plink = &link->next) {
  535: 	if (link->mask == mask && link->match == match) {
  536: 	    if (link->devsw == devsw)
  537: 		break;
  538: 	    printf("%s: ERROR: cannot remove from cdevsw[], its major"
  539: 		    " number %d was stolen by %s\n",
  540: 		    devsw->d_name, maj,
  541: 		    link->devsw->d_name
  542: 	    );
  543: 	}
  544:     }
  545:     if (link == NULL) {
  546: 	printf("%s(%d): WARNING: cdevsw removed multiple times!\n",
  547: 		devsw->d_name, maj);
  548:     } else {
  549: 	*plink = link->next;
  550: 	--devsw->d_refs; /* XXX cdevsw_release() / record refs */
  551: 	free(link, M_DEVBUF);
  552:     }
  553:     if (devsw->d_refs != 0) {
  554: 	printf("%s: Warning: cdevsw_remove() called while %d device refs"
  555: 		" still exist! (major %d)\n", 
  556: 		devsw->d_name,
  557: 		devsw->d_refs,
  558: 		maj);
  559:     } else {
  560: 	printf("%s: cdevsw removed\n", devsw->d_name);
  561:     }
  562:     return 0;
  563: }
  564: 
  565: /*
  566:  * Release a cdevsw entry.  When the ref count reaches zero, recurse
  567:  * through the stack.
  568:  */
  569: void
  570: cdevsw_release(struct cdevsw *devsw)
  571: {
  572:     --devsw->d_refs;
  573:     if (devsw->d_refs == 0) {
  574: 	/* XXX */
  575:     }
  576: }
  577: