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

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1986, 1988, 1991, 1993
      *      The Regents of the University of California.  All rights reserved.
      * (c) UNIX System Laboratories, Inc.
      * All or some portions of this file are derived from material licensed
      * to the University of California by American Telephone and Telegraph
      * Co. or Unix System Laboratories, Inc. and are reproduced herein with
     * the permission of UNIX System Laboratories, Inc.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)kern_shutdown.c     8.3 (Berkeley) 1/21/94
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_ddb.h"
    #include "opt_ekcd.h"
    #include "opt_kdb.h"
    #include "opt_panic.h"
    #include "opt_sched.h"
    #include "opt_watchdog.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/bio.h>
    #include <sys/buf.h>
    #include <sys/conf.h>
    #include <sys/compressor.h>
    #include <sys/cons.h>
    #include <sys/eventhandler.h>
    #include <sys/filedesc.h>
    #include <sys/jail.h>
    #include <sys/kdb.h>
    #include <sys/kernel.h>
    #include <sys/kerneldump.h>
    #include <sys/kthread.h>
    #include <sys/ktr.h>
    #include <sys/malloc.h>
    #include <sys/mbuf.h>
    #include <sys/mount.h>
    #include <sys/priv.h>
    #include <sys/proc.h>
    #include <sys/reboot.h>
    #include <sys/resourcevar.h>
    #include <sys/rwlock.h>
    #include <sys/sched.h>
    #include <sys/smp.h>
    #include <sys/sysctl.h>
    #include <sys/sysproto.h>
    #include <sys/taskqueue.h>
    #include <sys/vnode.h>
    #include <sys/watchdog.h>
    
    #include <crypto/rijndael/rijndael-api-fst.h>
    #include <crypto/sha2/sha256.h>
    
    #include <ddb/ddb.h>
    
    #include <machine/cpu.h>
    #include <machine/dump.h>
    #include <machine/pcb.h>
    #include <machine/smp.h>
    
    #include <security/mac/mac_framework.h>
    
    #include <vm/vm.h>
    #include <vm/vm_object.h>
    #include <vm/vm_page.h>
    #include <vm/vm_pager.h>
    #include <vm/swap_pager.h>
    
    #include <sys/signalvar.h>
    
   static MALLOC_DEFINE(M_DUMPER, "dumper", "dumper block buffer");
   
   #ifndef PANIC_REBOOT_WAIT_TIME
   #define PANIC_REBOOT_WAIT_TIME 15 /* default to 15 seconds */
   #endif
   static int panic_reboot_wait_time = PANIC_REBOOT_WAIT_TIME;
   SYSCTL_INT(_kern, OID_AUTO, panic_reboot_wait_time, CTLFLAG_RWTUN,
       &panic_reboot_wait_time, 0,
       "Seconds to wait before rebooting after a panic");
   
   /*
    * Note that stdarg.h and the ANSI style va_start macro is used for both
    * ANSI and traditional C compilers.
    */
   #include <machine/stdarg.h>
   
   #ifdef KDB
   #ifdef KDB_UNATTENDED
   int debugger_on_panic = 0;
   #else
   int debugger_on_panic = 1;
   #endif
   SYSCTL_INT(_debug, OID_AUTO, debugger_on_panic,
       CTLFLAG_RWTUN | CTLFLAG_SECURE,
       &debugger_on_panic, 0, "Run debugger on kernel panic");
   
   int debugger_on_trap = 0;
   SYSCTL_INT(_debug, OID_AUTO, debugger_on_trap,
       CTLFLAG_RWTUN | CTLFLAG_SECURE,
       &debugger_on_trap, 0, "Run debugger on kernel trap before panic");
   
   #ifdef KDB_TRACE
   static int trace_on_panic = 1;
   static bool trace_all_panics = true;
   #else
   static int trace_on_panic = 0;
   static bool trace_all_panics = false;
   #endif
   SYSCTL_INT(_debug, OID_AUTO, trace_on_panic,
       CTLFLAG_RWTUN | CTLFLAG_SECURE,
       &trace_on_panic, 0, "Print stack trace on kernel panic");
   SYSCTL_BOOL(_debug, OID_AUTO, trace_all_panics, CTLFLAG_RWTUN,
       &trace_all_panics, 0, "Print stack traces on secondary kernel panics");
   #endif /* KDB */
   
   static int sync_on_panic = 0;
   SYSCTL_INT(_kern, OID_AUTO, sync_on_panic, CTLFLAG_RWTUN,
           &sync_on_panic, 0, "Do a sync before rebooting from a panic");
   
   static bool poweroff_on_panic = 0;
   SYSCTL_BOOL(_kern, OID_AUTO, poweroff_on_panic, CTLFLAG_RWTUN,
           &poweroff_on_panic, 0, "Do a power off instead of a reboot on a panic");
   
   static bool powercycle_on_panic = 0;
   SYSCTL_BOOL(_kern, OID_AUTO, powercycle_on_panic, CTLFLAG_RWTUN,
           &powercycle_on_panic, 0, "Do a power cycle instead of a reboot on a panic");
   
   static SYSCTL_NODE(_kern, OID_AUTO, shutdown, CTLFLAG_RW, 0,
       "Shutdown environment");
   
   #ifndef DIAGNOSTIC
   static int show_busybufs;
   #else
   static int show_busybufs = 1;
   #endif
   SYSCTL_INT(_kern_shutdown, OID_AUTO, show_busybufs, CTLFLAG_RW,
           &show_busybufs, 0, "");
   
   int suspend_blocked = 0;
   SYSCTL_INT(_kern, OID_AUTO, suspend_blocked, CTLFLAG_RW,
           &suspend_blocked, 0, "Block suspend due to a pending shutdown");
   
   #ifdef EKCD
   FEATURE(ekcd, "Encrypted kernel crash dumps support");
   
   MALLOC_DEFINE(M_EKCD, "ekcd", "Encrypted kernel crash dumps data");
   
   struct kerneldumpcrypto {
           uint8_t                 kdc_encryption;
           uint8_t                 kdc_iv[KERNELDUMP_IV_MAX_SIZE];
           keyInstance             kdc_ki;
           cipherInstance          kdc_ci;
           uint32_t                kdc_dumpkeysize;
           struct kerneldumpkey    kdc_dumpkey[];
   };
   #endif
   
   struct kerneldumpcomp {
           uint8_t                 kdc_format;
           struct compressor       *kdc_stream;
           uint8_t                 *kdc_buf;
           size_t                  kdc_resid;
   };
   
   static struct kerneldumpcomp *kerneldumpcomp_create(struct dumperinfo *di,
                       uint8_t compression);
   static void     kerneldumpcomp_destroy(struct dumperinfo *di);
   static int      kerneldumpcomp_write_cb(void *base, size_t len, off_t off, void *arg);
   
   static int kerneldump_gzlevel = 6;
   SYSCTL_INT(_kern, OID_AUTO, kerneldump_gzlevel, CTLFLAG_RWTUN,
       &kerneldump_gzlevel, 0,
       "Kernel crash dump compression level");
   
   /*
    * Variable panicstr contains argument to first call to panic; used as flag
    * to indicate that the kernel has already called panic.
    */
   const char __read_mostly *panicstr;
   
   int __read_mostly dumping;              /* system is dumping */
   int rebooting;                          /* system is rebooting */
   static struct dumperinfo dumper;        /* our selected dumper */
   
   /* Context information for dump-debuggers. */
   static struct pcb dumppcb;              /* Registers. */
   lwpid_t dumptid;                        /* Thread ID. */
   
   static struct cdevsw reroot_cdevsw = {
        .d_version = D_VERSION,
        .d_name    = "reroot",
   };
   
   static void poweroff_wait(void *, int);
   static void shutdown_halt(void *junk, int howto);
   static void shutdown_panic(void *junk, int howto);
   static void shutdown_reset(void *junk, int howto);
   static int kern_reroot(void);
   
   /* register various local shutdown events */
   static void
   shutdown_conf(void *unused)
   {
   
           EVENTHANDLER_REGISTER(shutdown_final, poweroff_wait, NULL,
               SHUTDOWN_PRI_FIRST);
           EVENTHANDLER_REGISTER(shutdown_final, shutdown_halt, NULL,
               SHUTDOWN_PRI_LAST + 100);
           EVENTHANDLER_REGISTER(shutdown_final, shutdown_panic, NULL,
               SHUTDOWN_PRI_LAST + 100);
           EVENTHANDLER_REGISTER(shutdown_final, shutdown_reset, NULL,
               SHUTDOWN_PRI_LAST + 200);
   }
   
   SYSINIT(shutdown_conf, SI_SUB_INTRINSIC, SI_ORDER_ANY, shutdown_conf, NULL);
   
   /*
    * The only reason this exists is to create the /dev/reroot/ directory,
    * used by reroot code in init(8) as a mountpoint for tmpfs.
    */
   static void
   reroot_conf(void *unused)
   {
           int error;
           struct cdev *cdev;
   
           error = make_dev_p(MAKEDEV_CHECKNAME | MAKEDEV_WAITOK, &cdev,
               &reroot_cdevsw, NULL, UID_ROOT, GID_WHEEL, 0600, "reroot/reroot");
           if (error != 0) {
                   printf("%s: failed to create device node, error %d",
                       __func__, error);
           }
   }
   
   SYSINIT(reroot_conf, SI_SUB_DEVFS, SI_ORDER_ANY, reroot_conf, NULL);
   
   /*
    * The system call that results in a reboot.
    */
   /* ARGSUSED */
   int
   sys_reboot(struct thread *td, struct reboot_args *uap)
   {
           int error;
   
           error = 0;
   #ifdef MAC
           error = mac_system_check_reboot(td->td_ucred, uap->opt);
   #endif
           if (error == 0)
                   error = priv_check(td, PRIV_REBOOT);
           if (error == 0) {
                   if (uap->opt & RB_REROOT)
                           error = kern_reroot();
                   else
                           kern_reboot(uap->opt);
           }
           return (error);
   }
   
   static void
   shutdown_nice_task_fn(void *arg, int pending __unused)
   {
           int howto;
   
           howto = (uintptr_t)arg;
           /* Send a signal to init(8) and have it shutdown the world. */
           PROC_LOCK(initproc);
           if (howto & RB_POWEROFF)
                   kern_psignal(initproc, SIGUSR2);
           else if (howto & RB_POWERCYCLE)
                   kern_psignal(initproc, SIGWINCH);
           else if (howto & RB_HALT)
                   kern_psignal(initproc, SIGUSR1);
           else
                   kern_psignal(initproc, SIGINT);
           PROC_UNLOCK(initproc);
   }
   
   static struct task shutdown_nice_task = TASK_INITIALIZER(0,
       &shutdown_nice_task_fn, NULL);
   
   /*
    * Called by events that want to shut down.. e.g  <CTL><ALT><DEL> on a PC
    */
   void
   shutdown_nice(int howto)
   {
   
           if (initproc != NULL && !SCHEDULER_STOPPED()) {
                   shutdown_nice_task.ta_context = (void *)(uintptr_t)howto;
                   taskqueue_enqueue(taskqueue_fast, &shutdown_nice_task);
           } else {
                   /*
                    * No init(8) running, or scheduler would not allow it
                    * to run, so simply reboot.
                    */
                   kern_reboot(howto | RB_NOSYNC);
           }
   }
   
   static void
   print_uptime(void)
   {
           int f;
           struct timespec ts;
   
           getnanouptime(&ts);
           printf("Uptime: ");
           f = 0;
           if (ts.tv_sec >= 86400) {
                   printf("%ldd", (long)ts.tv_sec / 86400);
                   ts.tv_sec %= 86400;
                   f = 1;
           }
           if (f || ts.tv_sec >= 3600) {
                   printf("%ldh", (long)ts.tv_sec / 3600);
                   ts.tv_sec %= 3600;
                   f = 1;
           }
           if (f || ts.tv_sec >= 60) {
                   printf("%ldm", (long)ts.tv_sec / 60);
                   ts.tv_sec %= 60;
                   f = 1;
           }
           printf("%lds\n", (long)ts.tv_sec);
   }
   
   int
   doadump(boolean_t textdump)
   {
           boolean_t coredump;
           int error;
   
           error = 0;
           if (dumping)
                   return (EBUSY);
           if (dumper.dumper == NULL)
                   return (ENXIO);
   
           savectx(&dumppcb);
           dumptid = curthread->td_tid;
           dumping++;
   
           coredump = TRUE;
   #ifdef DDB
           if (textdump && textdump_pending) {
                   coredump = FALSE;
                   textdump_dumpsys(&dumper);
           }
   #endif
           if (coredump)
                   error = dumpsys(&dumper);
   
           dumping--;
           return (error);
   }
   
   /*
    * kern_reboot(9): Shut down the system cleanly to prepare for reboot, halt, or
    * power off.
    */
   void
   kern_reboot(int howto)
   {
           static int once = 0;
   
           /*
            * Normal paths here don't hold Giant, but we can wind up here
            * unexpectedly with it held.  Drop it now so we don't have to
            * drop and pick it up elsewhere. The paths it is locking will
            * never be returned to, and it is preferable to preclude
            * deadlock than to lock against code that won't ever
            * continue.
            */
           while (mtx_owned(&Giant))
                   mtx_unlock(&Giant);
   
   #if defined(SMP)
           /*
            * Bind us to the first CPU so that all shutdown code runs there.  Some
            * systems don't shutdown properly (i.e., ACPI power off) if we
            * run on another processor.
            */
           if (!SCHEDULER_STOPPED()) {
                   thread_lock(curthread);
                   sched_bind(curthread, CPU_FIRST());
                   thread_unlock(curthread);
                   KASSERT(PCPU_GET(cpuid) == CPU_FIRST(),
                       ("%s: not running on cpu 0", __func__));
           }
   #endif
           /* We're in the process of rebooting. */
           rebooting = 1;
   
           /* We are out of the debugger now. */
           kdb_active = 0;
   
           /*
            * Do any callouts that should be done BEFORE syncing the filesystems.
            */
           EVENTHANDLER_INVOKE(shutdown_pre_sync, howto);
   
           /* 
            * Now sync filesystems
            */
           if (!cold && (howto & RB_NOSYNC) == 0 && once == 0) {
                   once = 1;
                   bufshutdown(show_busybufs);
           }
   
           print_uptime();
   
           cngrab();
   
           /*
            * Ok, now do things that assume all filesystem activity has
            * been completed.
            */
           EVENTHANDLER_INVOKE(shutdown_post_sync, howto);
   
           if ((howto & (RB_HALT|RB_DUMP)) == RB_DUMP && !cold && !dumping) 
                   doadump(TRUE);
   
           /* Now that we're going to really halt the system... */
           EVENTHANDLER_INVOKE(shutdown_final, howto);
   
           for(;;) ;       /* safety against shutdown_reset not working */
           /* NOTREACHED */
   }
   
   /*
    * The system call that results in changing the rootfs.
    */
   static int
   kern_reroot(void)
   {
           struct vnode *oldrootvnode, *vp;
           struct mount *mp, *devmp;
           int error;
   
           if (curproc != initproc)
                   return (EPERM);
   
           /*
            * Mark the filesystem containing currently-running executable
            * (the temporary copy of init(8)) busy.
            */
           vp = curproc->p_textvp;
           error = vn_lock(vp, LK_SHARED);
           if (error != 0)
                   return (error);
           mp = vp->v_mount;
           error = vfs_busy(mp, MBF_NOWAIT);
           if (error != 0) {
                   vfs_ref(mp);
                   VOP_UNLOCK(vp, 0);
                   error = vfs_busy(mp, 0);
                   vn_lock(vp, LK_SHARED | LK_RETRY);
                   vfs_rel(mp);
                   if (error != 0) {
                           VOP_UNLOCK(vp, 0);
                           return (ENOENT);
                   }
                   if (vp->v_iflag & VI_DOOMED) {
                           VOP_UNLOCK(vp, 0);
                           vfs_unbusy(mp);
                           return (ENOENT);
                   }
           }
           VOP_UNLOCK(vp, 0);
   
           /*
            * Remove the filesystem containing currently-running executable
            * from the mount list, to prevent it from being unmounted
            * by vfs_unmountall(), and to avoid confusing vfs_mountroot().
            *
            * Also preserve /dev - forcibly unmounting it could cause driver
            * reinitialization.
            */
   
           vfs_ref(rootdevmp);
           devmp = rootdevmp;
           rootdevmp = NULL;
   
           mtx_lock(&mountlist_mtx);
           TAILQ_REMOVE(&mountlist, mp, mnt_list);
           TAILQ_REMOVE(&mountlist, devmp, mnt_list);
           mtx_unlock(&mountlist_mtx);
   
           oldrootvnode = rootvnode;
   
           /*
            * Unmount everything except for the two filesystems preserved above.
            */
           vfs_unmountall();
   
           /*
            * Add /dev back; vfs_mountroot() will move it into its new place.
            */
           mtx_lock(&mountlist_mtx);
           TAILQ_INSERT_HEAD(&mountlist, devmp, mnt_list);
           mtx_unlock(&mountlist_mtx);
           rootdevmp = devmp;
           vfs_rel(rootdevmp);
   
           /*
            * Mount the new rootfs.
            */
           vfs_mountroot();
   
           /*
            * Update all references to the old rootvnode.
            */
           mountcheckdirs(oldrootvnode, rootvnode);
   
           /*
            * Add the temporary filesystem back and unbusy it.
            */
           mtx_lock(&mountlist_mtx);
           TAILQ_INSERT_TAIL(&mountlist, mp, mnt_list);
           mtx_unlock(&mountlist_mtx);
           vfs_unbusy(mp);
   
           return (0);
   }
   
   /*
    * If the shutdown was a clean halt, behave accordingly.
    */
   static void
   shutdown_halt(void *junk, int howto)
   {
   
           if (howto & RB_HALT) {
                   printf("\n");
                   printf("The operating system has halted.\n");
                   printf("Please press any key to reboot.\n\n");
   
                   wdog_kern_pat(WD_TO_NEVER);
   
                   switch (cngetc()) {
                   case -1:                /* No console, just die */
                           cpu_halt();
                           /* NOTREACHED */
                   default:
                           break;
                   }
           }
   }
   
   /*
    * Check to see if the system panicked, pause and then reboot
    * according to the specified delay.
    */
   static void
   shutdown_panic(void *junk, int howto)
   {
           int loop;
   
           if (howto & RB_DUMP) {
                   if (panic_reboot_wait_time != 0) {
                           if (panic_reboot_wait_time != -1) {
                                   printf("Automatic reboot in %d seconds - "
                                          "press a key on the console to abort\n",
                                           panic_reboot_wait_time);
                                   for (loop = panic_reboot_wait_time * 10;
                                        loop > 0; --loop) {
                                           DELAY(1000 * 100); /* 1/10th second */
                                           /* Did user type a key? */
                                           if (cncheckc() != -1)
                                                   break;
                                   }
                                   if (!loop)
                                           return;
                           }
                   } else { /* zero time specified - reboot NOW */
                           return;
                   }
                   printf("--> Press a key on the console to reboot,\n");
                   printf("--> or switch off the system now.\n");
                   cngetc();
           }
   }
   
   /*
    * Everything done, now reset
    */
   static void
   shutdown_reset(void *junk, int howto)
   {
   
           printf("Rebooting...\n");
           DELAY(1000000); /* wait 1 sec for printf's to complete and be read */
   
           /*
            * Acquiring smp_ipi_mtx here has a double effect:
            * - it disables interrupts avoiding CPU0 preemption
            *   by fast handlers (thus deadlocking  against other CPUs)
            * - it avoids deadlocks against smp_rendezvous() or, more 
            *   generally, threads busy-waiting, with this spinlock held,
            *   and waiting for responses by threads on other CPUs
            *   (ie. smp_tlb_shootdown()).
            *
            * For the !SMP case it just needs to handle the former problem.
            */
   #ifdef SMP
           mtx_lock_spin(&smp_ipi_mtx);
   #else
           spinlock_enter();
   #endif
   
           /* cpu_boot(howto); */ /* doesn't do anything at the moment */
           cpu_reset();
           /* NOTREACHED */ /* assuming reset worked */
   }
   
   #if defined(WITNESS) || defined(INVARIANT_SUPPORT)
   static int kassert_warn_only = 0;
   #ifdef KDB
   static int kassert_do_kdb = 0;
   #endif
   #ifdef KTR
   static int kassert_do_ktr = 0;
   #endif
   static int kassert_do_log = 1;
   static int kassert_log_pps_limit = 4;
   static int kassert_log_mute_at = 0;
   static int kassert_log_panic_at = 0;
   static int kassert_suppress_in_panic = 0;
   static int kassert_warnings = 0;
   
   SYSCTL_NODE(_debug, OID_AUTO, kassert, CTLFLAG_RW, NULL, "kassert options");
   
   #ifdef KASSERT_PANIC_OPTIONAL
   #define KASSERT_RWTUN   CTLFLAG_RWTUN
   #else
   #define KASSERT_RWTUN   CTLFLAG_RDTUN
   #endif
   
   SYSCTL_INT(_debug_kassert, OID_AUTO, warn_only, KASSERT_RWTUN,
       &kassert_warn_only, 0,
       "KASSERT triggers a panic (0) or just a warning (1)");
   
   #ifdef KDB
   SYSCTL_INT(_debug_kassert, OID_AUTO, do_kdb, KASSERT_RWTUN,
       &kassert_do_kdb, 0, "KASSERT will enter the debugger");
   #endif
   
   #ifdef KTR
   SYSCTL_UINT(_debug_kassert, OID_AUTO, do_ktr, KASSERT_RWTUN,
       &kassert_do_ktr, 0,
       "KASSERT does a KTR, set this to the KTRMASK you want");
   #endif
   
   SYSCTL_INT(_debug_kassert, OID_AUTO, do_log, KASSERT_RWTUN,
       &kassert_do_log, 0,
       "If warn_only is enabled, log (1) or do not log (0) assertion violations");
   
   SYSCTL_INT(_debug_kassert, OID_AUTO, warnings, CTLFLAG_RD | CTLFLAG_STATS,
       &kassert_warnings, 0, "number of KASSERTs that have been triggered");
   
   SYSCTL_INT(_debug_kassert, OID_AUTO, log_panic_at, KASSERT_RWTUN,
       &kassert_log_panic_at, 0, "max number of KASSERTS before we will panic");
   
   SYSCTL_INT(_debug_kassert, OID_AUTO, log_pps_limit, KASSERT_RWTUN,
       &kassert_log_pps_limit, 0, "limit number of log messages per second");
   
   SYSCTL_INT(_debug_kassert, OID_AUTO, log_mute_at, KASSERT_RWTUN,
       &kassert_log_mute_at, 0, "max number of KASSERTS to log");
   
   SYSCTL_INT(_debug_kassert, OID_AUTO, suppress_in_panic, KASSERT_RWTUN,
       &kassert_suppress_in_panic, 0,
       "KASSERTs will be suppressed while handling a panic");
   #undef KASSERT_RWTUN
   
   static int kassert_sysctl_kassert(SYSCTL_HANDLER_ARGS);
   
   SYSCTL_PROC(_debug_kassert, OID_AUTO, kassert,
       CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_SECURE, NULL, 0,
       kassert_sysctl_kassert, "I", "set to trigger a test kassert");
   
   static int
   kassert_sysctl_kassert(SYSCTL_HANDLER_ARGS)
   {
           int error, i;
   
           error = sysctl_wire_old_buffer(req, sizeof(int));
           if (error == 0) {
                   i = 0;
                   error = sysctl_handle_int(oidp, &i, 0, req);
           }
           if (error != 0 || req->newptr == NULL)
                   return (error);
           KASSERT(0, ("kassert_sysctl_kassert triggered kassert %d", i));
           return (0);
   }
   
   #ifdef KASSERT_PANIC_OPTIONAL
   /*
    * Called by KASSERT, this decides if we will panic
    * or if we will log via printf and/or ktr.
    */
   void
   kassert_panic(const char *fmt, ...)
   {
           static char buf[256];
           va_list ap;
   
           va_start(ap, fmt);
           (void)vsnprintf(buf, sizeof(buf), fmt, ap);
           va_end(ap);
   
           /*
            * If we are suppressing secondary panics, log the warning but do not
            * re-enter panic/kdb.
            */
           if (panicstr != NULL && kassert_suppress_in_panic) {
                   if (kassert_do_log) {
                           printf("KASSERT failed: %s\n", buf);
   #ifdef KDB
                           if (trace_all_panics && trace_on_panic)
                                   kdb_backtrace();
   #endif
                   }
                   return;
           }
   
           /*
            * panic if we're not just warning, or if we've exceeded
            * kassert_log_panic_at warnings.
            */
           if (!kassert_warn_only ||
               (kassert_log_panic_at > 0 &&
                kassert_warnings >= kassert_log_panic_at)) {
                   va_start(ap, fmt);
                   vpanic(fmt, ap);
                   /* NORETURN */
           }
   #ifdef KTR
           if (kassert_do_ktr)
                   CTR0(ktr_mask, buf);
   #endif /* KTR */
           /*
            * log if we've not yet met the mute limit.
            */
           if (kassert_do_log &&
               (kassert_log_mute_at == 0 ||
                kassert_warnings < kassert_log_mute_at)) {
                   static  struct timeval lasterr;
                   static  int curerr;
   
                   if (ppsratecheck(&lasterr, &curerr, kassert_log_pps_limit)) {
                           printf("KASSERT failed: %s\n", buf);
                           kdb_backtrace();
                   }
           }
   #ifdef KDB
           if (kassert_do_kdb) {
                   kdb_enter(KDB_WHY_KASSERT, buf);
           }
   #endif
           atomic_add_int(&kassert_warnings, 1);
   }
   #endif /* KASSERT_PANIC_OPTIONAL */
   #endif
   
   /*
    * Panic is called on unresolvable fatal errors.  It prints "panic: mesg",
    * and then reboots.  If we are called twice, then we avoid trying to sync
    * the disks as this often leads to recursive panics.
    */
   void
   panic(const char *fmt, ...)
   {
           va_list ap;
   
           va_start(ap, fmt);
           vpanic(fmt, ap);
   }
   
   void
   vpanic(const char *fmt, va_list ap)
   {
   #ifdef SMP
           cpuset_t other_cpus;
   #endif
           struct thread *td = curthread;
           int bootopt, newpanic;
           static char buf[256];
   
           spinlock_enter();
   
   #ifdef SMP
           /*
            * stop_cpus_hard(other_cpus) should prevent multiple CPUs from
            * concurrently entering panic.  Only the winner will proceed
            * further.
            */
           if (panicstr == NULL && !kdb_active) {
                   other_cpus = all_cpus;
                   CPU_CLR(PCPU_GET(cpuid), &other_cpus);
                   stop_cpus_hard(other_cpus);
           }
   #endif
   
           /*
            * Ensure that the scheduler is stopped while panicking, even if panic
            * has been entered from kdb.
            */
           td->td_stopsched = 1;
   
           bootopt = RB_AUTOBOOT;
           newpanic = 0;
           if (panicstr)
                   bootopt |= RB_NOSYNC;
           else {
                   bootopt |= RB_DUMP;
                   panicstr = fmt;
                   newpanic = 1;
           }
   
           if (newpanic) {
                   (void)vsnprintf(buf, sizeof(buf), fmt, ap);
                   panicstr = buf;
                   cngrab();
                   printf("panic: %s\n", buf);
           } else {
                   printf("panic: ");
                   vprintf(fmt, ap);
                   printf("\n");
           }
   #ifdef SMP
           printf("cpuid = %d\n", PCPU_GET(cpuid));
   #endif
           printf("time = %jd\n", (intmax_t )time_second);
   #ifdef KDB
           if ((newpanic || trace_all_panics) && trace_on_panic)
                   kdb_backtrace();
           if (debugger_on_panic)
                   kdb_enter(KDB_WHY_PANIC, "panic");
   #endif
           /*thread_lock(td); */
           td->td_flags |= TDF_INPANIC;
           /* thread_unlock(td); */
           if (!sync_on_panic)
                   bootopt |= RB_NOSYNC;
           if (poweroff_on_panic)
                   bootopt |= RB_POWEROFF;
           if (powercycle_on_panic)
                   bootopt |= RB_POWERCYCLE;
           kern_reboot(bootopt);
   }
   
   /*
    * Support for poweroff delay.
    *
    * Please note that setting this delay too short might power off your machine
    * before the write cache on your hard disk has been flushed, leading to
    * soft-updates inconsistencies.
    */
   #ifndef POWEROFF_DELAY
   # define POWEROFF_DELAY 5000
   #endif
   static int poweroff_delay = POWEROFF_DELAY;
   
   SYSCTL_INT(_kern_shutdown, OID_AUTO, poweroff_delay, CTLFLAG_RW,
       &poweroff_delay, 0, "Delay before poweroff to write disk caches (msec)");
   
   static void
   poweroff_wait(void *junk, int howto)
   {
   
           if ((howto & (RB_POWEROFF | RB_POWERCYCLE)) == 0 || poweroff_delay <= 0)
                   return;
           DELAY(poweroff_delay * 1000);
   }
   
   /*
    * Some system processes (e.g. syncer) need to be stopped at appropriate
    * points in their main loops prior to a system shutdown, so that they
    * won't interfere with the shutdown process (e.g. by holding a disk buf
    * to cause sync to fail).  For each of these system processes, register
    * shutdown_kproc() as a handler for one of shutdown events.
    */
   static int kproc_shutdown_wait = 60;
   SYSCTL_INT(_kern_shutdown, OID_AUTO, kproc_shutdown_wait, CTLFLAG_RW,
       &kproc_shutdown_wait, 0, "Max wait time (sec) to stop for each process");
   
   void
   kproc_shutdown(void *arg, int howto)
   {
           struct proc *p;
           int error;
   
           if (panicstr)
                   return;
   
           p = (struct proc *)arg;
           printf("Waiting (max %d seconds) for system process `%s' to stop... ",
               kproc_shutdown_wait, p->p_comm);
           error = kproc_suspend(p, kproc_shutdown_wait * hz);
   
           if (error == EWOULDBLOCK)
                   printf("timed out\n");
           else
                   printf("done\n");
   }
   
   void
   kthread_shutdown(void *arg, int howto)
   {
           struct thread *td;
           int error;
   
           if (panicstr)
                   return;
   
           td = (struct thread *)arg;
           printf("Waiting (max %d seconds) for system thread `%s' to stop... ",
               kproc_shutdown_wait, td->td_name);
           error = kthread_suspend(td, kproc_shutdown_wait * hz);
   
           if (error == EWOULDBLOCK)
                   printf("timed out\n");
           else
                   printf("done\n");
   }
   
   static char dumpdevname[sizeof(((struct cdev*)NULL)->si_name)];
   SYSCTL_STRING(_kern_shutdown, OID_AUTO, dumpdevname, CTLFLAG_RD,
       dumpdevname, 0, "Device for kernel dumps");
   
   static int      _dump_append(struct dumperinfo *di, void *virtual,
                       vm_offset_t physical, size_t length);
   
   #ifdef EKCD
   static struct kerneldumpcrypto *
   kerneldumpcrypto_create(size_t blocksize, uint8_t encryption,
       const uint8_t *key, uint32_t encryptedkeysize, const uint8_t *encryptedkey)
   {
           struct kerneldumpcrypto *kdc;
           struct kerneldumpkey *kdk;
           uint32_t dumpkeysize;
   
           dumpkeysize = roundup2(sizeof(*kdk) + encryptedkeysize, blocksize);
           kdc = malloc(sizeof(*kdc) + dumpkeysize, M_EKCD, M_WAITOK | M_ZERO);
   
           arc4rand(kdc->kdc_iv, sizeof(kdc->kdc_iv), 0);
   
           kdc->kdc_encryption = encryption;
           switch (kdc->kdc_encryption) {
           case KERNELDUMP_ENC_AES_256_CBC:
                   if (rijndael_makeKey(&kdc->kdc_ki, DIR_ENCRYPT, 256, key) <= 0)
                           goto failed;
                   break;
           default:
                   goto failed;
           }
   
           kdc->kdc_dumpkeysize = dumpkeysize;
           kdk = kdc->kdc_dumpkey;
           kdk->kdk_encryption = kdc->kdc_encryption;
           memcpy(kdk->kdk_iv, kdc->kdc_iv, sizeof(kdk->kdk_iv));
           kdk->kdk_encryptedkeysize = htod32(encryptedkeysize);
           memcpy(kdk->kdk_encryptedkey, encryptedkey, encryptedkeysize);
   
           return (kdc);
   failed:
           explicit_bzero(kdc, sizeof(*kdc) + dumpkeysize);
          free(kdc, M_EKCD);
          return (NULL);
  }
  
  static int
  kerneldumpcrypto_init(struct kerneldumpcrypto *kdc)
  {
          uint8_t hash[SHA256_DIGEST_LENGTH];
          SHA256_CTX ctx;
          struct kerneldumpkey *kdk;
          int error;
  
          error = 0;
  
          if (kdc == NULL)
                  return (0);
  
          /*
           * When a user enters ddb it can write a crash dump multiple times.
           * Each time it should be encrypted using a different IV.
           */
          SHA256_Init(&ctx);
          SHA256_Update(&ctx, kdc->kdc_iv, sizeof(kdc->kdc_iv));
          SHA256_Final(hash, &ctx);
          bcopy(hash, kdc->kdc_iv, sizeof(kdc->kdc_iv));
  
          switch (kdc->kdc_encryption) {
          case KERNELDUMP_ENC_AES_256_CBC:
                  if (rijndael_cipherInit(&kdc->kdc_ci, MODE_CBC,
                      kdc->kdc_iv) <= 0) {
                          error = EINVAL;
                          goto out;
                  }
                  break;
          default:
                  error = EINVAL;
                  goto out;
          }
  
          kdk = kdc->kdc_dumpkey;
          memcpy(kdk->kdk_iv, kdc->kdc_iv, sizeof(kdk->kdk_iv));
  out:
          explicit_bzero(hash, sizeof(hash));
          return (error);
  }
  
  static uint32_t
  kerneldumpcrypto_dumpkeysize(const struct kerneldumpcrypto *kdc)
  {
  
          if (kdc == NULL)
                  return (0);
          return (kdc->kdc_dumpkeysize);
  }
  #endif /* EKCD */
  
  static struct kerneldumpcomp *
  kerneldumpcomp_create(struct dumperinfo *di, uint8_t compression)
  {
          struct kerneldumpcomp *kdcomp;
          int format;
  
          switch (compression) {
          case KERNELDUMP_COMP_GZIP:
                  format = COMPRESS_GZIP;
                  break;
          case KERNELDUMP_COMP_ZSTD:
                  format = COMPRESS_ZSTD;
                  break;
          default:
                  return (NULL);
          }
  
          kdcomp = malloc(sizeof(*kdcomp), M_DUMPER, M_WAITOK | M_ZERO);
          kdcomp->kdc_format = compression;
          kdcomp->kdc_stream = compressor_init(kerneldumpcomp_write_cb,
              format, di->maxiosize, kerneldump_gzlevel, di);
          if (kdcomp->kdc_stream == NULL) {
                  free(kdcomp, M_DUMPER);
                  return (NULL);
          }
          kdcomp->kdc_buf = malloc(di->maxiosize, M_DUMPER, M_WAITOK | M_NODUMP);
          return (kdcomp);
  }
  
  static void
  kerneldumpcomp_destroy(struct dumperinfo *di)
  {
          struct kerneldumpcomp *kdcomp;
  
          kdcomp = di->kdcomp;
          if (kdcomp == NULL)
                  return;
          compressor_fini(kdcomp->kdc_stream);
          explicit_bzero(kdcomp->kdc_buf, di->maxiosize);
          free(kdcomp->kdc_buf, M_DUMPER);
          free(kdcomp, M_DUMPER);
  }
  
  /* Registration of dumpers */
  int
  set_dumper(struct dumperinfo *di, const char *devname, struct thread *td,
      uint8_t compression, uint8_t encryption, const uint8_t *key,
      uint32_t encryptedkeysize, const uint8_t *encryptedkey)
  {
          size_t wantcopy;
          int error;
  
          error = priv_check(td, PRIV_SETDUMPER);
          if (error != 0)
                  return (error);
  
          if (dumper.dumper != NULL)
                  return (EBUSY);
          dumper = *di;
          dumper.blockbuf = NULL;
          dumper.kdcrypto = NULL;
          dumper.kdcomp = NULL;
  
          if (encryption != KERNELDUMP_ENC_NONE) {
  #ifdef EKCD
                  dumper.kdcrypto = kerneldumpcrypto_create(di->blocksize,
                      encryption, key, encryptedkeysize, encryptedkey);
                  if (dumper.kdcrypto == NULL) {
                          error = EINVAL;
                          goto cleanup;
                  }
  #else
                  error = EOPNOTSUPP;
                  goto cleanup;
  #endif
          }
  
          wantcopy = strlcpy(dumpdevname, devname, sizeof(dumpdevname));
          if (wantcopy >= sizeof(dumpdevname)) {
                  printf("set_dumper: device name truncated from '%s' -> '%s'\n",
                      devname, dumpdevname);
          }
  
          if (compression != KERNELDUMP_COMP_NONE) {
                  /*
                   * We currently can't support simultaneous encryption and
                   * compression.
                   */
                  if (encryption != KERNELDUMP_ENC_NONE) {
                          error = EOPNOTSUPP;
                          goto cleanup;
                  }
                  dumper.kdcomp = kerneldumpcomp_create(&dumper, compression);
                  if (dumper.kdcomp == NULL) {
                          error = EINVAL;
                          goto cleanup;
                  }
          }
  
          dumper.blockbuf = malloc(di->blocksize, M_DUMPER, M_WAITOK | M_ZERO);
          return (0);
  
  cleanup:
          (void)clear_dumper(td);
          return (error);
  }
  
  int
  clear_dumper(struct thread *td)
  {
          int error;
  
          error = priv_check(td, PRIV_SETDUMPER);
          if (error != 0)
                  return (error);
  
  #ifdef NETDUMP
          netdump_mbuf_drain();
  #endif
  
  #ifdef EKCD
          if (dumper.kdcrypto != NULL) {
                  explicit_bzero(dumper.kdcrypto, sizeof(*dumper.kdcrypto) +
                      dumper.kdcrypto->kdc_dumpkeysize);
                  free(dumper.kdcrypto, M_EKCD);
          }
  #endif
  
          kerneldumpcomp_destroy(&dumper);
  
          if (dumper.blockbuf != NULL) {
                  explicit_bzero(dumper.blockbuf, dumper.blocksize);
                  free(dumper.blockbuf, M_DUMPER);
          }
          explicit_bzero(&dumper, sizeof(dumper));
          dumpdevname[0] = '\0';
          return (0);
  }
  
  static int
  dump_check_bounds(struct dumperinfo *di, off_t offset, size_t length)
  {
  
          if (di->mediasize > 0 && length != 0 && (offset < di->mediaoffset ||
              offset - di->mediaoffset + length > di->mediasize)) {
                  if (di->kdcomp != NULL && offset >= di->mediaoffset) {
                          printf(
                      "Compressed dump failed to fit in device boundaries.\n");
                          return (E2BIG);
                  }
  
                  printf("Attempt to write outside dump device boundaries.\n"
              "offset(%jd), mediaoffset(%jd), length(%ju), mediasize(%jd).\n",
                      (intmax_t)offset, (intmax_t)di->mediaoffset,
                      (uintmax_t)length, (intmax_t)di->mediasize);
                  return (ENOSPC);
          }
          if (length % di->blocksize != 0) {
                  printf("Attempt to write partial block of length %ju.\n",
                      (uintmax_t)length);
                  return (EINVAL);
          }
          if (offset % di->blocksize != 0) {
                  printf("Attempt to write at unaligned offset %jd.\n",
                      (intmax_t)offset);
                  return (EINVAL);
          }
  
          return (0);
  }
  
  #ifdef EKCD
  static int
  dump_encrypt(struct kerneldumpcrypto *kdc, uint8_t *buf, size_t size)
  {
  
          switch (kdc->kdc_encryption) {
          case KERNELDUMP_ENC_AES_256_CBC:
                  if (rijndael_blockEncrypt(&kdc->kdc_ci, &kdc->kdc_ki, buf,
                      8 * size, buf) <= 0) {
                          return (EIO);
                  }
                  if (rijndael_cipherInit(&kdc->kdc_ci, MODE_CBC,
                      buf + size - 16 /* IV size for AES-256-CBC */) <= 0) {
                          return (EIO);
                  }
                  break;
          default:
                  return (EINVAL);
          }
  
          return (0);
  }
  
  /* Encrypt data and call dumper. */
  static int
  dump_encrypted_write(struct dumperinfo *di, void *virtual,
      vm_offset_t physical, off_t offset, size_t length)
  {
          static uint8_t buf[KERNELDUMP_BUFFER_SIZE];
          struct kerneldumpcrypto *kdc;
          int error;
          size_t nbytes;
  
          kdc = di->kdcrypto;
  
          while (length > 0) {
                  nbytes = MIN(length, sizeof(buf));
                  bcopy(virtual, buf, nbytes);
  
                  if (dump_encrypt(kdc, buf, nbytes) != 0)
                          return (EIO);
  
                  error = dump_write(di, buf, physical, offset, nbytes);
                  if (error != 0)
                          return (error);
  
                  offset += nbytes;
                  virtual = (void *)((uint8_t *)virtual + nbytes);
                  length -= nbytes;
          }
  
          return (0);
  }
  #endif /* EKCD */
  
  static int
  kerneldumpcomp_write_cb(void *base, size_t length, off_t offset, void *arg)
  {
          struct dumperinfo *di;
          size_t resid, rlength;
          int error;
  
          di = arg;
  
          if (length % di->blocksize != 0) {
                  /*
                   * This must be the final write after flushing the compression
                   * stream. Write as many full blocks as possible and stash the
                   * residual data in the dumper's block buffer. It will be
                   * padded and written in dump_finish().
                   */
                  rlength = rounddown(length, di->blocksize);
                  if (rlength != 0) {
                          error = _dump_append(di, base, 0, rlength);
                          if (error != 0)
                                  return (error);
                  }
                  resid = length - rlength;
                  memmove(di->blockbuf, (uint8_t *)base + rlength, resid);
                  bzero((uint8_t *)di->blockbuf + resid, di->blocksize - resid);
                  di->kdcomp->kdc_resid = resid;
                  return (EAGAIN);
          }
          return (_dump_append(di, base, 0, length));
  }
  
  /*
   * Write kernel dump headers at the beginning and end of the dump extent.
   * Write the kernel dump encryption key after the leading header if we were
   * configured to do so.
   */
  static int
  dump_write_headers(struct dumperinfo *di, struct kerneldumpheader *kdh)
  {
  #ifdef EKCD
          struct kerneldumpcrypto *kdc;
  #endif
          void *buf, *key;
          size_t hdrsz;
          uint64_t extent;
          uint32_t keysize;
          int error;
  
          hdrsz = sizeof(*kdh);
          if (hdrsz > di->blocksize)
                  return (ENOMEM);
  
  #ifdef EKCD
          kdc = di->kdcrypto;
          key = kdc->kdc_dumpkey;
          keysize = kerneldumpcrypto_dumpkeysize(kdc);
  #else
          key = NULL;
          keysize = 0;
  #endif
  
          /*
           * If the dump device has special handling for headers, let it take care
           * of writing them out.
           */
          if (di->dumper_hdr != NULL)
                  return (di->dumper_hdr(di, kdh, key, keysize));
  
          if (hdrsz == di->blocksize)
                  buf = kdh;
          else {
                  buf = di->blockbuf;
                  memset(buf, 0, di->blocksize);
                  memcpy(buf, kdh, hdrsz);
          }
  
          extent = dtoh64(kdh->dumpextent);
  #ifdef EKCD
          if (kdc != NULL) {
                  error = dump_write(di, kdc->kdc_dumpkey, 0,
                      di->mediaoffset + di->mediasize - di->blocksize - extent -
                      keysize, keysize);
                  if (error != 0)
                          return (error);
          }
  #endif
  
          error = dump_write(di, buf, 0,
              di->mediaoffset + di->mediasize - 2 * di->blocksize - extent -
              keysize, di->blocksize);
          if (error == 0)
                  error = dump_write(di, buf, 0, di->mediaoffset + di->mediasize -
                      di->blocksize, di->blocksize);
          return (error);
  }
  
  /*
   * Don't touch the first SIZEOF_METADATA bytes on the dump device.  This is to
   * protect us from metadata and metadata from us.
   */
  #define SIZEOF_METADATA         (64 * 1024)
  
  /*
   * Do some preliminary setup for a kernel dump: initialize state for encryption,
   * if requested, and make sure that we have enough space on the dump device.
   *
   * We set things up so that the dump ends before the last sector of the dump
   * device, at which the trailing header is written.
   *
   *     +-----------+------+-----+----------------------------+------+
   *     |           | lhdr | key |    ... kernel dump ...     | thdr |
   *     +-----------+------+-----+----------------------------+------+
   *                   1 blk  opt <------- dump extent --------> 1 blk
   *
   * Dumps written using dump_append() start at the beginning of the extent.
   * Uncompressed dumps will use the entire extent, but compressed dumps typically
   * will not. The true length of the dump is recorded in the leading and trailing
   * headers once the dump has been completed.
   *
   * The dump device may provide a callback, in which case it will initialize
   * dumpoff and take care of laying out the headers.
   */
  int
  dump_start(struct dumperinfo *di, struct kerneldumpheader *kdh)
  {
          uint64_t dumpextent, span;
          uint32_t keysize;
          int error;
  
  #ifdef EKCD
          error = kerneldumpcrypto_init(di->kdcrypto);
          if (error != 0)
                  return (error);
          keysize = kerneldumpcrypto_dumpkeysize(di->kdcrypto);
  #else
          error = 0;
          keysize = 0;
  #endif
  
          if (di->dumper_start != NULL) {
                  error = di->dumper_start(di);
          } else {
                  dumpextent = dtoh64(kdh->dumpextent);
                  span = SIZEOF_METADATA + dumpextent + 2 * di->blocksize +
                      keysize;
                  if (di->mediasize < span) {
                          if (di->kdcomp == NULL)
                                  return (E2BIG);
  
                          /*
                           * We don't yet know how much space the compressed dump
                           * will occupy, so try to use the whole swap partition
                           * (minus the first 64KB) in the hope that the
                           * compressed dump will fit. If that doesn't turn out to
                           * be enough, the bounds checking in dump_write()
                           * will catch us and cause the dump to fail.
                           */
                          dumpextent = di->mediasize - span + dumpextent;
                          kdh->dumpextent = htod64(dumpextent);
                  }
  
                  /*
                   * The offset at which to begin writing the dump.
                   */
                  di->dumpoff = di->mediaoffset + di->mediasize - di->blocksize -
                      dumpextent;
          }
          di->origdumpoff = di->dumpoff;
          return (error);
  }
  
  static int
  _dump_append(struct dumperinfo *di, void *virtual, vm_offset_t physical,
      size_t length)
  {
          int error;
  
  #ifdef EKCD
          if (di->kdcrypto != NULL)
                  error = dump_encrypted_write(di, virtual, physical, di->dumpoff,
                      length);
          else
  #endif
                  error = dump_write(di, virtual, physical, di->dumpoff, length);
          if (error == 0)
                  di->dumpoff += length;
          return (error);
  }
  
  /*
   * Write to the dump device starting at dumpoff. When compression is enabled,
   * writes to the device will be performed using a callback that gets invoked
   * when the compression stream's output buffer is full.
   */
  int
  dump_append(struct dumperinfo *di, void *virtual, vm_offset_t physical,
      size_t length)
  {
          void *buf;
  
          if (di->kdcomp != NULL) {
                  /* Bounce through a buffer to avoid CRC errors. */
                  if (length > di->maxiosize)
                          return (EINVAL);
                  buf = di->kdcomp->kdc_buf;
                  memmove(buf, virtual, length);
                  return (compressor_write(di->kdcomp->kdc_stream, buf, length));
          }
          return (_dump_append(di, virtual, physical, length));
  }
  
  /*
   * Write to the dump device at the specified offset.
   */
  int
  dump_write(struct dumperinfo *di, void *virtual, vm_offset_t physical,
      off_t offset, size_t length)
  {
          int error;
  
          error = dump_check_bounds(di, offset, length);
          if (error != 0)
                  return (error);
          return (di->dumper(di->priv, virtual, physical, offset, length));
  }
  
  /*
   * Perform kernel dump finalization: flush the compression stream, if necessary,
   * write the leading and trailing kernel dump headers now that we know the true
   * length of the dump, and optionally write the encryption key following the
   * leading header.
   */
  int
  dump_finish(struct dumperinfo *di, struct kerneldumpheader *kdh)
  {
          int error;
  
          if (di->kdcomp != NULL) {
                  error = compressor_flush(di->kdcomp->kdc_stream);
                  if (error == EAGAIN) {
                          /* We have residual data in di->blockbuf. */
                          error = _dump_append(di, di->blockbuf, 0, di->blocksize);
                          if (error == 0)
                                  /* Compensate for _dump_append()'s adjustment. */
                                  di->dumpoff -= di->blocksize - di->kdcomp->kdc_resid;
                          di->kdcomp->kdc_resid = 0;
                  }
                  if (error != 0)
                          return (error);
  
                  /*
                   * We now know the size of the compressed dump, so update the
                   * header accordingly and recompute parity.
                   */
                  kdh->dumplength = htod64(di->dumpoff - di->origdumpoff);
                  kdh->parity = 0;
                  kdh->parity = kerneldump_parity(kdh);
  
                  compressor_reset(di->kdcomp->kdc_stream);
          }
  
          error = dump_write_headers(di, kdh);
          if (error != 0)
                  return (error);
  
          (void)dump_write(di, NULL, 0, 0, 0);
          return (0);
  }
  
  void
  dump_init_header(const struct dumperinfo *di, struct kerneldumpheader *kdh,
      char *magic, uint32_t archver, uint64_t dumplen)
  {
          size_t dstsize;
  
          bzero(kdh, sizeof(*kdh));
          strlcpy(kdh->magic, magic, sizeof(kdh->magic));
          strlcpy(kdh->architecture, MACHINE_ARCH, sizeof(kdh->architecture));
          kdh->version = htod32(KERNELDUMPVERSION);
          kdh->architectureversion = htod32(archver);
          kdh->dumplength = htod64(dumplen);
          kdh->dumpextent = kdh->dumplength;
          kdh->dumptime = htod64(time_second);
  #ifdef EKCD
          kdh->dumpkeysize = htod32(kerneldumpcrypto_dumpkeysize(di->kdcrypto));
  #else
          kdh->dumpkeysize = 0;
  #endif
          kdh->blocksize = htod32(di->blocksize);
          strlcpy(kdh->hostname, prison0.pr_hostname, sizeof(kdh->hostname));
          dstsize = sizeof(kdh->versionstring);
          if (strlcpy(kdh->versionstring, version, dstsize) >= dstsize)
                  kdh->versionstring[dstsize - 2] = '\n';
          if (panicstr != NULL)
                  strlcpy(kdh->panicstring, panicstr, sizeof(kdh->panicstring));
          if (di->kdcomp != NULL)
                  kdh->compression = di->kdcomp->kdc_format;
          kdh->parity = kerneldump_parity(kdh);
  }
  
  #ifdef DDB
  DB_SHOW_COMMAND(panic, db_show_panic)
  {
  
          if (panicstr == NULL)
                  db_printf("panicstr not set\n");
          else
                  db_printf("panic: %s\n", panicstr);
  }
  #endif

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