kern_shutdown.c

Version: - FREEBSD - FREEBSD-13-STABLE - FREEBSD-13-0 - FREEBSD-12-STABLE - FREEBSD-12-0 - FREEBSD-11-STABLE - FREEBSD-11-0 - FREEBSD-10-STABLE - FREEBSD-10-0 - FREEBSD-9-STABLE - FREEBSD-9-0 - FREEBSD-8-STABLE - FREEBSD-8-0 - FREEBSD-7-STABLE - FREEBSD-7-0 - FREEBSD-6-STABLE - FREEBSD-6-0 - FREEBSD-5-STABLE - FREEBSD-5-0 - FREEBSD-4-STABLE - FREEBSD-3-STABLE - FREEBSD22 - l41 - OPENBSD - linux-2.6 - MK84 - PLAN9 - xnu-8792
SearchContext: - none - 3 - 10
    1 /*-
    2  * Copyright (c) 1986, 1988, 1991, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  * (c) UNIX System Laboratories, Inc.
    5  * All or some portions of this file are derived from material licensed
    6  * to the University of California by American Telephone and Telegraph
    7  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
    8  * the permission of UNIX System Laboratories, Inc.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 4. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      @(#)kern_shutdown.c     8.3 (Berkeley) 1/21/94
   35  */
   36 
   37 #include <sys/cdefs.h>
   38 __FBSDID("$FreeBSD: releng/5.3/sys/kern/kern_shutdown.c 136588 2004-10-16 08:43:07Z cvs2svn $");
   39 
   40 #include "opt_kdb.h"
   41 #include "opt_hw_wdog.h"
   42 #include "opt_mac.h"
   43 #include "opt_panic.h"
   44 #include "opt_show_busybufs.h"
   45 #include "opt_sched.h"
   46 
   47 #include <sys/param.h>
   48 #include <sys/systm.h>
   49 #include <sys/bio.h>
   50 #include <sys/buf.h>
   51 #include <sys/conf.h>
   52 #include <sys/cons.h>
   53 #include <sys/eventhandler.h>
   54 #include <sys/kdb.h>
   55 #include <sys/kernel.h>
   56 #include <sys/kthread.h>
   57 #include <sys/mac.h>
   58 #include <sys/malloc.h>
   59 #include <sys/mount.h>
   60 #include <sys/proc.h>
   61 #include <sys/reboot.h>
   62 #include <sys/resourcevar.h>
   63 #include <sys/smp.h>            /* smp_active */
   64 #include <sys/sysctl.h>
   65 #include <sys/sysproto.h>
   66 #include <sys/vnode.h>
   67 
   68 #include <machine/cpu.h>
   69 #include <machine/pcb.h>
   70 #include <machine/smp.h>
   71 
   72 #include <sys/signalvar.h>
   73 
   74 #ifndef PANIC_REBOOT_WAIT_TIME
   75 #define PANIC_REBOOT_WAIT_TIME 15 /* default to 15 seconds */
   76 #endif
   77 
   78 /*
   79  * Note that stdarg.h and the ANSI style va_start macro is used for both
   80  * ANSI and traditional C compilers.
   81  */
   82 #include <machine/stdarg.h>
   83 
   84 #ifdef KDB
   85 #ifdef KDB_UNATTENDED
   86 int debugger_on_panic = 0;
   87 #else
   88 int debugger_on_panic = 1;
   89 #endif
   90 SYSCTL_INT(_debug, OID_AUTO, debugger_on_panic, CTLFLAG_RW,
   91         &debugger_on_panic, 0, "Run debugger on kernel panic");
   92 
   93 #ifdef KDB_TRACE
   94 int trace_on_panic = 1;
   95 #else
   96 int trace_on_panic = 0;
   97 #endif
   98 SYSCTL_INT(_debug, OID_AUTO, trace_on_panic, CTLFLAG_RW,
   99         &trace_on_panic, 0, "Print stack trace on kernel panic");
  100 #endif /* KDB */
  101 
  102 int sync_on_panic = 0;
  103 SYSCTL_INT(_kern, OID_AUTO, sync_on_panic, CTLFLAG_RW,
  104         &sync_on_panic, 0, "Do a sync before rebooting from a panic");
  105 
  106 SYSCTL_NODE(_kern, OID_AUTO, shutdown, CTLFLAG_RW, 0, "Shutdown environment");
  107 
  108 #ifdef  HW_WDOG
  109 /*
  110  * If there is a hardware watchdog, point this at the function needed to
  111  * hold it off.
  112  * It's needed when the kernel needs to do some lengthy operations.
  113  * e.g. in wd.c when dumping core.. It's most annoying to have
  114  * your precious core-dump only half written because the wdog kicked in.
  115  */
  116 watchdog_tickle_fn wdog_tickler = NULL;
  117 #endif  /* HW_WDOG */
  118 
  119 /*
  120  * Variable panicstr contains argument to first call to panic; used as flag
  121  * to indicate that the kernel has already called panic.
  122  */
  123 const char *panicstr;
  124 
  125 int dumping;                            /* system is dumping */
  126 static struct dumperinfo dumper;        /* our selected dumper */
  127 
  128 /* Context information for dump-debuggers. */
  129 static struct pcb dumppcb;              /* Registers. */
  130 static lwpid_t dumptid;                 /* Thread ID. */
  131 
  132 static void boot(int) __dead2;
  133 static void poweroff_wait(void *, int);
  134 static void shutdown_halt(void *junk, int howto);
  135 static void shutdown_panic(void *junk, int howto);
  136 static void shutdown_reset(void *junk, int howto);
  137 
  138 /* register various local shutdown events */
  139 static void
  140 shutdown_conf(void *unused)
  141 {
  142 
  143         EVENTHANDLER_REGISTER(shutdown_final, poweroff_wait, NULL,
  144             SHUTDOWN_PRI_FIRST);
  145         EVENTHANDLER_REGISTER(shutdown_final, shutdown_halt, NULL,
  146             SHUTDOWN_PRI_LAST + 100);
  147         EVENTHANDLER_REGISTER(shutdown_final, shutdown_panic, NULL,
  148             SHUTDOWN_PRI_LAST + 100);
  149         EVENTHANDLER_REGISTER(shutdown_final, shutdown_reset, NULL,
  150             SHUTDOWN_PRI_LAST + 200);
  151 }
  152 
  153 SYSINIT(shutdown_conf, SI_SUB_INTRINSIC, SI_ORDER_ANY, shutdown_conf, NULL)
  154 
  155 /*
  156  * The system call that results in a reboot
  157  *
  158  * MPSAFE
  159  */
  160 /* ARGSUSED */
  161 int
  162 reboot(struct thread *td, struct reboot_args *uap)
  163 {
  164         int error;
  165 
  166         error = 0;
  167 #ifdef MAC
  168         error = mac_check_system_reboot(td->td_ucred, uap->opt);
  169 #endif
  170         if (error == 0)
  171                 error = suser(td);
  172         if (error == 0) {
  173                 mtx_lock(&Giant);
  174                 boot(uap->opt);
  175                 mtx_unlock(&Giant);
  176         }
  177         return (error);
  178 }
  179 
  180 /*
  181  * Called by events that want to shut down.. e.g  <CTL><ALT><DEL> on a PC
  182  */
  183 static int shutdown_howto = 0;
  184 
  185 void
  186 shutdown_nice(int howto)
  187 {
  188 
  189         shutdown_howto = howto;
  190 
  191         /* Send a signal to init(8) and have it shutdown the world */
  192         if (initproc != NULL) {
  193                 PROC_LOCK(initproc);
  194                 psignal(initproc, SIGINT);
  195                 PROC_UNLOCK(initproc);
  196         } else {
  197                 /* No init(8) running, so simply reboot */
  198                 boot(RB_NOSYNC);
  199         }
  200         return;
  201 }
  202 static int      waittime = -1;
  203 
  204 static void
  205 print_uptime(void)
  206 {
  207         int f;
  208         struct timespec ts;
  209 
  210         getnanouptime(&ts);
  211         printf("Uptime: ");
  212         f = 0;
  213         if (ts.tv_sec >= 86400) {
  214                 printf("%ldd", (long)ts.tv_sec / 86400);
  215                 ts.tv_sec %= 86400;
  216                 f = 1;
  217         }
  218         if (f || ts.tv_sec >= 3600) {
  219                 printf("%ldh", (long)ts.tv_sec / 3600);
  220                 ts.tv_sec %= 3600;
  221                 f = 1;
  222         }
  223         if (f || ts.tv_sec >= 60) {
  224                 printf("%ldm", (long)ts.tv_sec / 60);
  225                 ts.tv_sec %= 60;
  226                 f = 1;
  227         }
  228         printf("%lds\n", (long)ts.tv_sec);
  229 }
  230 
  231 static void
  232 doadump(void)
  233 {
  234 
  235         /*
  236          * Sometimes people have to call this from the kernel debugger. 
  237          * (if 'panic' can not dump)
  238          * Give them a clue as to why they can't dump.
  239          */
  240         if (dumper.dumper == NULL) {
  241                 printf("Cannot dump. No dump device defined.\n");
  242                 return;
  243         }
  244 
  245         savectx(&dumppcb);
  246         dumptid = curthread->td_tid;
  247         dumping++;
  248         dumpsys(&dumper);
  249 }
  250 
  251 /*
  252  *  Go through the rigmarole of shutting down..
  253  * this used to be in machdep.c but I'll be dammned if I could see
  254  * anything machine dependant in it.
  255  */
  256 static void
  257 boot(int howto)
  258 {
  259         static int first_buf_printf = 1;
  260 
  261         /* collect extra flags that shutdown_nice might have set */
  262         howto |= shutdown_howto;
  263 
  264         /* We are out of the debugger now. */
  265         kdb_active = 0;
  266 
  267 #ifdef SMP
  268         if (smp_active)
  269                 printf("boot() called on cpu#%d\n", PCPU_GET(cpuid));
  270 #endif
  271         /*
  272          * Do any callouts that should be done BEFORE syncing the filesystems.
  273          */
  274         EVENTHANDLER_INVOKE(shutdown_pre_sync, howto);
  275 
  276         /* 
  277          * Now sync filesystems
  278          */
  279         if (!cold && (howto & RB_NOSYNC) == 0 && waittime < 0) {
  280                 register struct buf *bp;
  281                 int iter, nbusy, pbusy;
  282 #ifndef PREEMPTION
  283                 int subiter;
  284 #endif
  285 
  286                 waittime = 0;
  287 
  288                 sync(&thread0, NULL);
  289 
  290                 /*
  291                  * With soft updates, some buffers that are
  292                  * written will be remarked as dirty until other
  293                  * buffers are written.
  294                  */
  295                 for (iter = pbusy = 0; iter < 20; iter++) {
  296                         nbusy = 0;
  297                         for (bp = &buf[nbuf]; --bp >= buf; ) {
  298                                 if ((bp->b_flags & B_INVAL) == 0 &&
  299                                     BUF_REFCNT(bp) > 0) {
  300                                         nbusy++;
  301                                 } else if ((bp->b_flags & (B_DELWRI | B_INVAL))
  302                                                 == B_DELWRI) {
  303                                         /* bawrite(bp);*/
  304                                         nbusy++;
  305                                 }
  306                         }
  307                         if (nbusy == 0) {
  308                                 if (first_buf_printf)
  309                                         printf("No buffers busy after final sync");
  310                                 break;
  311                         }
  312                         if (first_buf_printf) {
  313                                 printf("Syncing disks, buffers remaining... ");
  314                                 first_buf_printf = 0;
  315                         }
  316                         printf("%d ", nbusy);
  317                         if (nbusy < pbusy)
  318                                 iter = 0;
  319                         pbusy = nbusy;
  320                         sync(&thread0, NULL);
  321 
  322 #ifdef PREEMPTION
  323                         /*
  324                          * Drop Giant and spin for a while to allow
  325                          * interrupt threads to run.
  326                          */
  327                         DROP_GIANT();
  328                         DELAY(50000 * iter);
  329                         PICKUP_GIANT();
  330 #else
  331                         /*
  332                          * Drop Giant and context switch several times to
  333                          * allow interrupt threads to run.
  334                          */
  335                         DROP_GIANT();
  336                         for (subiter = 0; subiter < 50 * iter; subiter++) {
  337                                 mtx_lock_spin(&sched_lock);
  338                                 mi_switch(SW_VOL, NULL);
  339                                 mtx_unlock_spin(&sched_lock);
  340                                 DELAY(1000);
  341                         }
  342                         PICKUP_GIANT();
  343 #endif
  344                 }
  345                 printf("\n");
  346                 /*
  347                  * Count only busy local buffers to prevent forcing 
  348                  * a fsck if we're just a client of a wedged NFS server
  349                  */
  350                 nbusy = 0;
  351                 for (bp = &buf[nbuf]; --bp >= buf; ) {
  352                         if (((bp->b_flags&B_INVAL) == 0 && BUF_REFCNT(bp)) ||
  353                             ((bp->b_flags & (B_DELWRI|B_INVAL)) == B_DELWRI)) {
  354                                 if (bp->b_dev == NULL) {
  355                                         TAILQ_REMOVE(&mountlist,
  356                                             bp->b_vp->v_mount, mnt_list);
  357                                         continue;
  358                                 }
  359                                 nbusy++;
  360 #if defined(SHOW_BUSYBUFS) || defined(DIAGNOSTIC)
  361                                 printf(
  362                             "%d: dev:%s, flags:%0x, blkno:%ld, lblkno:%ld\n",
  363                                     nbusy, devtoname(bp->b_dev),
  364                                     bp->b_flags, (long)bp->b_blkno,
  365                                     (long)bp->b_lblkno);
  366 #endif
  367                         }
  368                 }
  369                 if (nbusy) {
  370                         /*
  371                          * Failed to sync all blocks. Indicate this and don't
  372                          * unmount filesystems (thus forcing an fsck on reboot).
  373                          */
  374                         printf("Giving up on %d buffers\n", nbusy);
  375                         DELAY(5000000); /* 5 seconds */
  376                 } else {
  377                         if (!first_buf_printf)
  378                                 printf("Final sync complete\n");
  379                         /*
  380                          * Unmount filesystems
  381                          */
  382                         if (panicstr == 0)
  383                                 vfs_unmountall();
  384                 }
  385                 DELAY(100000);          /* wait for console output to finish */
  386         }
  387 
  388         print_uptime();
  389 
  390         /*
  391          * Ok, now do things that assume all filesystem activity has
  392          * been completed.
  393          */
  394         EVENTHANDLER_INVOKE(shutdown_post_sync, howto);
  395         splhigh();
  396         if ((howto & (RB_HALT|RB_DUMP)) == RB_DUMP && !cold && !dumping) 
  397                 doadump();
  398 
  399         /* Now that we're going to really halt the system... */
  400         EVENTHANDLER_INVOKE(shutdown_final, howto);
  401 
  402         for(;;) ;       /* safety against shutdown_reset not working */
  403         /* NOTREACHED */
  404 }
  405 
  406 /*
  407  * If the shutdown was a clean halt, behave accordingly.
  408  */
  409 static void
  410 shutdown_halt(void *junk, int howto)
  411 {
  412 
  413         if (howto & RB_HALT) {
  414                 printf("\n");
  415                 printf("The operating system has halted.\n");
  416                 printf("Please press any key to reboot.\n\n");
  417                 switch (cngetc()) {
  418                 case -1:                /* No console, just die */
  419                         cpu_halt();
  420                         /* NOTREACHED */
  421                 default:
  422                         howto &= ~RB_HALT;
  423                         break;
  424                 }
  425         }
  426 }
  427 
  428 /*
  429  * Check to see if the system paniced, pause and then reboot
  430  * according to the specified delay.
  431  */
  432 static void
  433 shutdown_panic(void *junk, int howto)
  434 {
  435         int loop;
  436 
  437         if (howto & RB_DUMP) {
  438                 if (PANIC_REBOOT_WAIT_TIME != 0) {
  439                         if (PANIC_REBOOT_WAIT_TIME != -1) {
  440                                 printf("Automatic reboot in %d seconds - "
  441                                        "press a key on the console to abort\n",
  442                                         PANIC_REBOOT_WAIT_TIME);
  443                                 for (loop = PANIC_REBOOT_WAIT_TIME * 10;
  444                                      loop > 0; --loop) {
  445                                         DELAY(1000 * 100); /* 1/10th second */
  446                                         /* Did user type a key? */
  447                                         if (cncheckc() != -1)
  448                                                 break;
  449                                 }
  450                                 if (!loop)
  451                                         return;
  452                         }
  453                 } else { /* zero time specified - reboot NOW */
  454                         return;
  455                 }
  456                 printf("--> Press a key on the console to reboot,\n");
  457                 printf("--> or switch off the system now.\n");
  458                 cngetc();
  459         }
  460 }
  461 
  462 /*
  463  * Everything done, now reset
  464  */
  465 static void
  466 shutdown_reset(void *junk, int howto)
  467 {
  468 
  469         printf("Rebooting...\n");
  470         DELAY(1000000); /* wait 1 sec for printf's to complete and be read */
  471         /* cpu_boot(howto); */ /* doesn't do anything at the moment */
  472         cpu_reset();
  473         /* NOTREACHED */ /* assuming reset worked */
  474 }
  475 
  476 #ifdef SMP
  477 static u_int panic_cpu = NOCPU;
  478 #endif
  479 
  480 /*
  481  * Panic is called on unresolvable fatal errors.  It prints "panic: mesg",
  482  * and then reboots.  If we are called twice, then we avoid trying to sync
  483  * the disks as this often leads to recursive panics.
  484  *
  485  * MPSAFE
  486  */
  487 void
  488 panic(const char *fmt, ...)
  489 {
  490         struct thread *td = curthread;
  491         int bootopt, newpanic;
  492         va_list ap;
  493         static char buf[256];
  494 
  495 #ifdef SMP
  496         /*
  497          * We don't want multiple CPU's to panic at the same time, so we
  498          * use panic_cpu as a simple spinlock.  We have to keep checking
  499          * panic_cpu if we are spinning in case the panic on the first
  500          * CPU is canceled.
  501          */
  502         if (panic_cpu != PCPU_GET(cpuid))
  503                 while (atomic_cmpset_int(&panic_cpu, NOCPU,
  504                     PCPU_GET(cpuid)) == 0)
  505                         while (panic_cpu != NOCPU)
  506                                 ; /* nothing */
  507 #endif
  508 
  509         bootopt = RB_AUTOBOOT | RB_DUMP;
  510         newpanic = 0;
  511         if (panicstr)
  512                 bootopt |= RB_NOSYNC;
  513         else {
  514                 panicstr = fmt;
  515                 newpanic = 1;
  516         }
  517 
  518         va_start(ap, fmt);
  519         if (newpanic) {
  520                 (void)vsnprintf(buf, sizeof(buf), fmt, ap);
  521                 panicstr = buf;
  522                 printf("panic: %s\n", buf);
  523         } else {
  524                 printf("panic: ");
  525                 vprintf(fmt, ap);
  526                 printf("\n");
  527         }
  528         va_end(ap);
  529 #ifdef SMP
  530         printf("cpuid = %d\n", PCPU_GET(cpuid));
  531 #endif
  532 
  533 #ifdef KDB
  534         if (newpanic && trace_on_panic)
  535                 kdb_backtrace();
  536         if (debugger_on_panic)
  537                 kdb_enter("panic");
  538 #ifdef RESTARTABLE_PANICS
  539         /* See if the user aborted the panic, in which case we continue. */
  540         if (panicstr == NULL) {
  541 #ifdef SMP
  542                 atomic_store_rel_int(&panic_cpu, NOCPU);
  543 #endif
  544                 return;
  545         }
  546 #endif
  547 #endif
  548         mtx_lock_spin(&sched_lock);
  549         td->td_flags |= TDF_INPANIC;
  550         mtx_unlock_spin(&sched_lock);
  551         if (!sync_on_panic)
  552                 bootopt |= RB_NOSYNC;
  553         boot(bootopt);
  554 }
  555 
  556 /*
  557  * Support for poweroff delay.
  558  */
  559 #ifndef POWEROFF_DELAY
  560 # define POWEROFF_DELAY 5000
  561 #endif
  562 static int poweroff_delay = POWEROFF_DELAY;
  563 
  564 SYSCTL_INT(_kern_shutdown, OID_AUTO, poweroff_delay, CTLFLAG_RW,
  565         &poweroff_delay, 0, "");
  566 
  567 static void
  568 poweroff_wait(void *junk, int howto)
  569 {
  570 
  571         if (!(howto & RB_POWEROFF) || poweroff_delay <= 0)
  572                 return;
  573         DELAY(poweroff_delay * 1000);
  574 }
  575 
  576 /*
  577  * Some system processes (e.g. syncer) need to be stopped at appropriate
  578  * points in their main loops prior to a system shutdown, so that they
  579  * won't interfere with the shutdown process (e.g. by holding a disk buf
  580  * to cause sync to fail).  For each of these system processes, register
  581  * shutdown_kproc() as a handler for one of shutdown events.
  582  */
  583 static int kproc_shutdown_wait = 60;
  584 SYSCTL_INT(_kern_shutdown, OID_AUTO, kproc_shutdown_wait, CTLFLAG_RW,
  585     &kproc_shutdown_wait, 0, "");
  586 
  587 void
  588 kproc_shutdown(void *arg, int howto)
  589 {
  590         struct proc *p;
  591         char procname[MAXCOMLEN + 1];
  592         int error;
  593 
  594         if (panicstr)
  595                 return;
  596 
  597         p = (struct proc *)arg;
  598         strlcpy(procname, p->p_comm, sizeof(procname));
  599         printf("Waiting (max %d seconds) for system process `%s' to stop...",
  600             kproc_shutdown_wait, procname);
  601         error = kthread_suspend(p, kproc_shutdown_wait * hz);
  602 
  603         if (error == EWOULDBLOCK)
  604                 printf("timed out\n");
  605         else
  606                 printf("done\n");
  607 }
  608 
  609 /* Registration of dumpers */
  610 int
  611 set_dumper(struct dumperinfo *di)
  612 {
  613 
  614         if (di == NULL) {
  615                 bzero(&dumper, sizeof dumper);
  616                 return (0);
  617         }
  618         if (dumper.dumper != NULL)
  619                 return (EBUSY);
  620         dumper = *di;
  621         return (0);
  622 }
  623 
  624 #if defined(__powerpc__)
  625 void
  626 dumpsys(struct dumperinfo *di __unused)
  627 {
  628 
  629         printf("Kernel dumps not implemented on this architecture\n");
  630 }
  631 #endif
Cache object: 63ed9b574ae905ff954be02eea6cc68a
[ source navigation ] [ diff markup ] [ identifier search ] [ freetext search ] [ file search ] [ list types ] [ track identifier ]
This page is part of the FreeBSD/Linux Linux Kernel Cross-Reference, and was automatically generated using a modified version of the LXR engine.
FreeBSD/Linux Kernel Cross Reference sys/kern/kern_shutdown.c

FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_shutdown.c
