The Design and Implementation of the FreeBSD Operating System, Second Edition
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sys/kern/kern_acct.c

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    1 /*-
    2  * Copyright (c) 1982, 1986, 1989, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  * (c) UNIX System Laboratories, Inc.
    5  * Copyright (c) 2005 Robert N. M. Watson
    6  * All rights reserved.
    7  *
    8  * All or some portions of this file are derived from material licensed
    9  * to the University of California by American Telephone and Telegraph
   10  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
   11  * the permission of UNIX System Laboratories, Inc.
   12  *
   13  * Redistribution and use in source and binary forms, with or without
   14  * modification, are permitted provided that the following conditions
   15  * are met:
   16  * 1. Redistributions of source code must retain the above copyright
   17  *    notice, this list of conditions and the following disclaimer.
   18  * 2. Redistributions in binary form must reproduce the above copyright
   19  *    notice, this list of conditions and the following disclaimer in the
   20  *    documentation and/or other materials provided with the distribution.
   21  * 4. Neither the name of the University nor the names of its contributors
   22  *    may be used to endorse or promote products derived from this software
   23  *    without specific prior written permission.
   24  *
   25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   35  * SUCH DAMAGE.
   36  *
   37  * Copyright (c) 1994 Christopher G. Demetriou
   38  *
   39  * Redistribution and use in source and binary forms, with or without
   40  * modification, are permitted provided that the following conditions
   41  * are met:
   42  * 1. Redistributions of source code must retain the above copyright
   43  *    notice, this list of conditions and the following disclaimer.
   44  * 2. Redistributions in binary form must reproduce the above copyright
   45  *    notice, this list of conditions and the following disclaimer in the
   46  *    documentation and/or other materials provided with the distribution.
   47  * 3. All advertising materials mentioning features or use of this software
   48  *    must display the following acknowledgement:
   49  *      This product includes software developed by the University of
   50  *      California, Berkeley and its contributors.
   51  * 4. Neither the name of the University nor the names of its contributors
   52  *    may be used to endorse or promote products derived from this software
   53  *    without specific prior written permission.
   54  *
   55  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   56  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   57  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   58  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   59  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   60  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   61  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   62  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   63  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   64  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   65  * SUCH DAMAGE.
   66  *
   67  *      @(#)kern_acct.c 8.1 (Berkeley) 6/14/93
   68  */
   69 
   70 #include <sys/cdefs.h>
   71 __FBSDID("$FreeBSD: stable/10/sys/kern/kern_acct.c 252422 2013-06-30 19:08:06Z mjg $");
   72 
   73 #include <sys/param.h>
   74 #include <sys/systm.h>
   75 #include <sys/acct.h>
   76 #include <sys/fcntl.h>
   77 #include <sys/kernel.h>
   78 #include <sys/kthread.h>
   79 #include <sys/limits.h>
   80 #include <sys/lock.h>
   81 #include <sys/mount.h>
   82 #include <sys/mutex.h>
   83 #include <sys/namei.h>
   84 #include <sys/priv.h>
   85 #include <sys/proc.h>
   86 #include <sys/resourcevar.h>
   87 #include <sys/sched.h>
   88 #include <sys/sx.h>
   89 #include <sys/sysctl.h>
   90 #include <sys/sysent.h>
   91 #include <sys/syslog.h>
   92 #include <sys/sysproto.h>
   93 #include <sys/tty.h>
   94 #include <sys/vnode.h>
   95 
   96 #include <security/mac/mac_framework.h>
   97 
   98 /*
   99  * The routines implemented in this file are described in:
  100  *      Leffler, et al.: The Design and Implementation of the 4.3BSD
  101  *          UNIX Operating System (Addison Welley, 1989)
  102  * on pages 62-63.
  103  * On May 2007 the historic 3 bits base 8 exponent, 13 bit fraction
  104  * compt_t representation described in the above reference was replaced
  105  * with that of IEEE-754 floats.
  106  *
  107  * Arguably, to simplify accounting operations, this mechanism should
  108  * be replaced by one in which an accounting log file (similar to /dev/klog)
  109  * is read by a user process, etc.  However, that has its own problems.
  110  */
  111 
  112 /* Floating point definitions from <float.h>. */
  113 #define FLT_MANT_DIG    24              /* p */
  114 #define FLT_MAX_EXP     128             /* emax */
  115 
  116 /*
  117  * Internal accounting functions.
  118  * The former's operation is described in Leffler, et al., and the latter
  119  * was provided by UCB with the 4.4BSD-Lite release
  120  */
  121 static uint32_t encode_timeval(struct timeval);
  122 static uint32_t encode_long(long);
  123 static void     acctwatch(void);
  124 static void     acct_thread(void *);
  125 static int      acct_disable(struct thread *, int);
  126 
  127 /*
  128  * Accounting vnode pointer, saved vnode pointer, and flags for each.
  129  * acct_sx protects against changes to the active vnode and credentials
  130  * while accounting records are being committed to disk.
  131  */
  132 static int               acct_configured;
  133 static int               acct_suspended;
  134 static struct vnode     *acct_vp;
  135 static struct ucred     *acct_cred;
  136 static struct plimit    *acct_limit;
  137 static int               acct_flags;
  138 static struct sx         acct_sx;
  139 
  140 SX_SYSINIT(acct, &acct_sx, "acct_sx");
  141 
  142 /*
  143  * State of the accounting kthread.
  144  */
  145 static int               acct_state;
  146 
  147 #define ACCT_RUNNING    1       /* Accounting kthread is running. */
  148 #define ACCT_EXITREQ    2       /* Accounting kthread should exit. */
  149 
  150 /*
  151  * Values associated with enabling and disabling accounting
  152  */
  153 static int acctsuspend = 2;     /* stop accounting when < 2% free space left */
  154 SYSCTL_INT(_kern, OID_AUTO, acct_suspend, CTLFLAG_RW,
  155         &acctsuspend, 0, "percentage of free disk space below which accounting stops");
  156 
  157 static int acctresume = 4;      /* resume when free space risen to > 4% */
  158 SYSCTL_INT(_kern, OID_AUTO, acct_resume, CTLFLAG_RW,
  159         &acctresume, 0, "percentage of free disk space above which accounting resumes");
  160 
  161 static int acctchkfreq = 15;    /* frequency (in seconds) to check space */
  162 
  163 static int
  164 sysctl_acct_chkfreq(SYSCTL_HANDLER_ARGS)
  165 {
  166         int error, value;
  167 
  168         /* Write out the old value. */
  169         error = SYSCTL_OUT(req, &acctchkfreq, sizeof(int));
  170         if (error || req->newptr == NULL)
  171                 return (error);
  172 
  173         /* Read in and verify the new value. */
  174         error = SYSCTL_IN(req, &value, sizeof(int));
  175         if (error)
  176                 return (error);
  177         if (value <= 0)
  178                 return (EINVAL);
  179         acctchkfreq = value;
  180         return (0);
  181 }
  182 SYSCTL_PROC(_kern, OID_AUTO, acct_chkfreq, CTLTYPE_INT|CTLFLAG_RW,
  183     &acctchkfreq, 0, sysctl_acct_chkfreq, "I",
  184     "frequency for checking the free space");
  185 
  186 SYSCTL_INT(_kern, OID_AUTO, acct_configured, CTLFLAG_RD, &acct_configured, 0,
  187         "Accounting configured or not");
  188 
  189 SYSCTL_INT(_kern, OID_AUTO, acct_suspended, CTLFLAG_RD, &acct_suspended, 0,
  190         "Accounting suspended or not");
  191 
  192 /*
  193  * Accounting system call.  Written based on the specification and previous
  194  * implementation done by Mark Tinguely.
  195  */
  196 int
  197 sys_acct(struct thread *td, struct acct_args *uap)
  198 {
  199         struct nameidata nd;
  200         int error, flags, i, replacing;
  201 
  202         error = priv_check(td, PRIV_ACCT);
  203         if (error)
  204                 return (error);
  205 
  206         /*
  207          * If accounting is to be started to a file, open that file for
  208          * appending and make sure it's a 'normal'.
  209          */
  210         if (uap->path != NULL) {
  211                 NDINIT(&nd, LOOKUP, NOFOLLOW | AUDITVNODE1,
  212                     UIO_USERSPACE, uap->path, td);
  213                 flags = FWRITE | O_APPEND;
  214                 error = vn_open(&nd, &flags, 0, NULL);
  215                 if (error)
  216                         return (error);
  217                 NDFREE(&nd, NDF_ONLY_PNBUF);
  218 #ifdef MAC
  219                 error = mac_system_check_acct(td->td_ucred, nd.ni_vp);
  220                 if (error) {
  221                         VOP_UNLOCK(nd.ni_vp, 0);
  222                         vn_close(nd.ni_vp, flags, td->td_ucred, td);
  223                         return (error);
  224                 }
  225 #endif
  226                 VOP_UNLOCK(nd.ni_vp, 0);
  227                 if (nd.ni_vp->v_type != VREG) {
  228                         vn_close(nd.ni_vp, flags, td->td_ucred, td);
  229                         return (EACCES);
  230                 }
  231 #ifdef MAC
  232         } else {
  233                 error = mac_system_check_acct(td->td_ucred, NULL);
  234                 if (error)
  235                         return (error);
  236 #endif
  237         }
  238 
  239         /*
  240          * Disallow concurrent access to the accounting vnode while we swap
  241          * it out, in order to prevent access after close.
  242          */
  243         sx_xlock(&acct_sx);
  244 
  245         /*
  246          * Don't log spurious disable/enable messages if we are
  247          * switching from one accounting file to another due to log
  248          * rotation.
  249          */
  250         replacing = (acct_vp != NULL && uap->path != NULL);
  251 
  252         /*
  253          * If accounting was previously enabled, kill the old space-watcher,
  254          * close the file, and (if no new file was specified, leave).  Reset
  255          * the suspended state regardless of whether accounting remains
  256          * enabled.
  257          */
  258         acct_suspended = 0;
  259         if (acct_vp != NULL)
  260                 error = acct_disable(td, !replacing);
  261         if (uap->path == NULL) {
  262                 if (acct_state & ACCT_RUNNING) {
  263                         acct_state |= ACCT_EXITREQ;
  264                         wakeup(&acct_state);
  265                 }
  266                 sx_xunlock(&acct_sx);
  267                 return (error);
  268         }
  269 
  270         /*
  271          * Create our own plimit object without limits. It will be assigned
  272          * to exiting processes.
  273          */
  274         acct_limit = lim_alloc();
  275         for (i = 0; i < RLIM_NLIMITS; i++)
  276                 acct_limit->pl_rlimit[i].rlim_cur =
  277                     acct_limit->pl_rlimit[i].rlim_max = RLIM_INFINITY;
  278 
  279         /*
  280          * Save the new accounting file vnode, and schedule the new
  281          * free space watcher.
  282          */
  283         acct_vp = nd.ni_vp;
  284         acct_cred = crhold(td->td_ucred);
  285         acct_flags = flags;
  286         if (acct_state & ACCT_RUNNING)
  287                 acct_state &= ~ACCT_EXITREQ;
  288         else {
  289                 /*
  290                  * Try to start up an accounting kthread.  We may start more
  291                  * than one, but if so the extras will commit suicide as
  292                  * soon as they start up.
  293                  */
  294                 error = kproc_create(acct_thread, NULL, NULL, 0, 0,
  295                     "accounting");
  296                 if (error) {
  297                         (void) acct_disable(td, 0);
  298                         sx_xunlock(&acct_sx);
  299                         log(LOG_NOTICE, "Unable to start accounting thread\n");
  300                         return (error);
  301                 }
  302         }
  303         acct_configured = 1;
  304         sx_xunlock(&acct_sx);
  305         if (!replacing)
  306                 log(LOG_NOTICE, "Accounting enabled\n");
  307         return (error);
  308 }
  309 
  310 /*
  311  * Disable currently in-progress accounting by closing the vnode, dropping
  312  * our reference to the credential, and clearing the vnode's flags.
  313  */
  314 static int
  315 acct_disable(struct thread *td, int logging)
  316 {
  317         int error;
  318 
  319         sx_assert(&acct_sx, SX_XLOCKED);
  320         error = vn_close(acct_vp, acct_flags, acct_cred, td);
  321         crfree(acct_cred);
  322         lim_free(acct_limit);
  323         acct_configured = 0;
  324         acct_vp = NULL;
  325         acct_cred = NULL;
  326         acct_flags = 0;
  327         if (logging)
  328                 log(LOG_NOTICE, "Accounting disabled\n");
  329         return (error);
  330 }
  331 
  332 /*
  333  * Write out process accounting information, on process exit.
  334  * Data to be written out is specified in Leffler, et al.
  335  * and are enumerated below.  (They're also noted in the system
  336  * "acct.h" header file.)
  337  */
  338 int
  339 acct_process(struct thread *td)
  340 {
  341         struct acctv2 acct;
  342         struct timeval ut, st, tmp;
  343         struct plimit *oldlim;
  344         struct proc *p;
  345         struct rusage ru;
  346         int t, ret;
  347 
  348         /*
  349          * Lockless check of accounting condition before doing the hard
  350          * work.
  351          */
  352         if (acct_vp == NULL || acct_suspended)
  353                 return (0);
  354 
  355         sx_slock(&acct_sx);
  356 
  357         /*
  358          * If accounting isn't enabled, don't bother.  Have to check again
  359          * once we own the lock in case we raced with disabling of accounting
  360          * by another thread.
  361          */
  362         if (acct_vp == NULL || acct_suspended) {
  363                 sx_sunlock(&acct_sx);
  364                 return (0);
  365         }
  366 
  367         p = td->td_proc;
  368 
  369         /*
  370          * Get process accounting information.
  371          */
  372 
  373         sx_slock(&proctree_lock);
  374         PROC_LOCK(p);
  375 
  376         /* (1) The terminal from which the process was started */
  377         if ((p->p_flag & P_CONTROLT) && p->p_pgrp->pg_session->s_ttyp)
  378                 acct.ac_tty = tty_udev(p->p_pgrp->pg_session->s_ttyp);
  379         else
  380                 acct.ac_tty = NODEV;
  381         sx_sunlock(&proctree_lock);
  382 
  383         /* (2) The name of the command that ran */
  384         bcopy(p->p_comm, acct.ac_comm, sizeof acct.ac_comm);
  385 
  386         /* (3) The amount of user and system time that was used */
  387         rufetchcalc(p, &ru, &ut, &st);
  388         acct.ac_utime = encode_timeval(ut);
  389         acct.ac_stime = encode_timeval(st);
  390 
  391         /* (4) The elapsed time the command ran (and its starting time) */
  392         tmp = boottime;
  393         timevaladd(&tmp, &p->p_stats->p_start);
  394         acct.ac_btime = tmp.tv_sec;
  395         microuptime(&tmp);
  396         timevalsub(&tmp, &p->p_stats->p_start);
  397         acct.ac_etime = encode_timeval(tmp);
  398 
  399         /* (5) The average amount of memory used */
  400         tmp = ut;
  401         timevaladd(&tmp, &st);
  402         /* Convert tmp (i.e. u + s) into hz units to match ru_i*. */
  403         t = tmp.tv_sec * hz + tmp.tv_usec / tick;
  404         if (t)
  405                 acct.ac_mem = encode_long((ru.ru_ixrss + ru.ru_idrss +
  406                     + ru.ru_isrss) / t);
  407         else
  408                 acct.ac_mem = 0;
  409 
  410         /* (6) The number of disk I/O operations done */
  411         acct.ac_io = encode_long(ru.ru_inblock + ru.ru_oublock);
  412 
  413         /* (7) The UID and GID of the process */
  414         acct.ac_uid = p->p_ucred->cr_ruid;
  415         acct.ac_gid = p->p_ucred->cr_rgid;
  416 
  417         /* (8) The boolean flags that tell how the process terminated, etc. */
  418         acct.ac_flagx = p->p_acflag;
  419 
  420         /* Setup ancillary structure fields. */
  421         acct.ac_flagx |= ANVER;
  422         acct.ac_zero = 0;
  423         acct.ac_version = 2;
  424         acct.ac_len = acct.ac_len2 = sizeof(acct);
  425 
  426         /*
  427          * Eliminate rlimits (file size limit in particular).
  428          */
  429         oldlim = p->p_limit;
  430         p->p_limit = lim_hold(acct_limit);
  431         PROC_UNLOCK(p);
  432         lim_free(oldlim);
  433 
  434         /*
  435          * Write the accounting information to the file.
  436          */
  437         ret = vn_rdwr(UIO_WRITE, acct_vp, (caddr_t)&acct, sizeof (acct),
  438             (off_t)0, UIO_SYSSPACE, IO_APPEND|IO_UNIT, acct_cred, NOCRED,
  439             NULL, td);
  440         sx_sunlock(&acct_sx);
  441         return (ret);
  442 }
  443 
  444 /* FLOAT_CONVERSION_START (Regression testing; don't remove this line.) */
  445 
  446 /* Convert timevals and longs into IEEE-754 bit patterns. */
  447 
  448 /* Mantissa mask (MSB is implied, so subtract 1). */
  449 #define MANT_MASK ((1 << (FLT_MANT_DIG - 1)) - 1)
  450 
  451 /*
  452  * We calculate integer values to a precision of approximately
  453  * 28 bits.
  454  * This is high-enough precision to fill the 24 float bits
  455  * and low-enough to avoid overflowing the 32 int bits.
  456  */
  457 #define CALC_BITS 28
  458 
  459 /* log_2(1000000). */
  460 #define LOG2_1M 20
  461 
  462 /*
  463  * Convert the elements of a timeval into a 32-bit word holding
  464  * the bits of a IEEE-754 float.
  465  * The float value represents the timeval's value in microsecond units.
  466  */
  467 static uint32_t
  468 encode_timeval(struct timeval tv)
  469 {
  470         int log2_s;
  471         int val, exp;   /* Unnormalized value and exponent */
  472         int norm_exp;   /* Normalized exponent */
  473         int shift;
  474 
  475         /*
  476          * First calculate value and exponent to about CALC_BITS precision.
  477          * Note that the following conditionals have been ordered so that
  478          * the most common cases appear first.
  479          */
  480         if (tv.tv_sec == 0) {
  481                 if (tv.tv_usec == 0)
  482                         return (0);
  483                 exp = 0;
  484                 val = tv.tv_usec;
  485         } else {
  486                 /*
  487                  * Calculate the value to a precision of approximately
  488                  * CALC_BITS.
  489                  */
  490                 log2_s = fls(tv.tv_sec) - 1;
  491                 if (log2_s + LOG2_1M < CALC_BITS) {
  492                         exp = 0;
  493                         val = 1000000 * tv.tv_sec + tv.tv_usec;
  494                 } else {
  495                         exp = log2_s + LOG2_1M - CALC_BITS;
  496                         val = (unsigned int)(((uint64_t)1000000 * tv.tv_sec +
  497                             tv.tv_usec) >> exp);
  498                 }
  499         }
  500         /* Now normalize and pack the value into an IEEE-754 float. */
  501         norm_exp = fls(val) - 1;
  502         shift = FLT_MANT_DIG - norm_exp - 1;
  503 #ifdef ACCT_DEBUG
  504         printf("val=%d exp=%d shift=%d log2(val)=%d\n",
  505             val, exp, shift, norm_exp);
  506         printf("exp=%x mant=%x\n", FLT_MAX_EXP - 1 + exp + norm_exp,
  507             ((shift > 0 ? (val << shift) : (val >> -shift)) & MANT_MASK));
  508 #endif
  509         return (((FLT_MAX_EXP - 1 + exp + norm_exp) << (FLT_MANT_DIG - 1)) |
  510             ((shift > 0 ? val << shift : val >> -shift) & MANT_MASK));
  511 }
  512 
  513 /*
  514  * Convert a non-negative long value into the bit pattern of
  515  * an IEEE-754 float value.
  516  */
  517 static uint32_t
  518 encode_long(long val)
  519 {
  520         int norm_exp;   /* Normalized exponent */
  521         int shift;
  522 
  523         if (val == 0)
  524                 return (0);
  525         if (val < 0) {
  526                 log(LOG_NOTICE,
  527                     "encode_long: negative value %ld in accounting record\n",
  528                     val);
  529                 val = LONG_MAX;
  530         }
  531         norm_exp = fls(val) - 1;
  532         shift = FLT_MANT_DIG - norm_exp - 1;
  533 #ifdef ACCT_DEBUG
  534         printf("val=%d shift=%d log2(val)=%d\n",
  535             val, shift, norm_exp);
  536         printf("exp=%x mant=%x\n", FLT_MAX_EXP - 1 + exp + norm_exp,
  537             ((shift > 0 ? (val << shift) : (val >> -shift)) & MANT_MASK));
  538 #endif
  539         return (((FLT_MAX_EXP - 1 + norm_exp) << (FLT_MANT_DIG - 1)) |
  540             ((shift > 0 ? val << shift : val >> -shift) & MANT_MASK));
  541 }
  542 
  543 /* FLOAT_CONVERSION_END (Regression testing; don't remove this line.) */
  544 
  545 /*
  546  * Periodically check the filesystem to see if accounting
  547  * should be turned on or off.  Beware the case where the vnode
  548  * has been vgone()'d out from underneath us, e.g. when the file
  549  * system containing the accounting file has been forcibly unmounted.
  550  */
  551 /* ARGSUSED */
  552 static void
  553 acctwatch(void)
  554 {
  555         struct statfs sb;
  556 
  557         sx_assert(&acct_sx, SX_XLOCKED);
  558 
  559         /*
  560          * If accounting was disabled before our kthread was scheduled,
  561          * then acct_vp might be NULL.  If so, just ask our kthread to
  562          * exit and return.
  563          */
  564         if (acct_vp == NULL) {
  565                 acct_state |= ACCT_EXITREQ;
  566                 return;
  567         }
  568 
  569         /*
  570          * If our vnode is no longer valid, tear it down and signal the
  571          * accounting thread to die.
  572          */
  573         if (acct_vp->v_type == VBAD) {
  574                 (void) acct_disable(NULL, 1);
  575                 acct_state |= ACCT_EXITREQ;
  576                 return;
  577         }
  578 
  579         /*
  580          * Stopping here is better than continuing, maybe it will be VBAD
  581          * next time around.
  582          */
  583         if (VFS_STATFS(acct_vp->v_mount, &sb) < 0)
  584                 return;
  585         if (acct_suspended) {
  586                 if (sb.f_bavail > (int64_t)(acctresume * sb.f_blocks /
  587                     100)) {
  588                         acct_suspended = 0;
  589                         log(LOG_NOTICE, "Accounting resumed\n");
  590                 }
  591         } else {
  592                 if (sb.f_bavail <= (int64_t)(acctsuspend * sb.f_blocks /
  593                     100)) {
  594                         acct_suspended = 1;
  595                         log(LOG_NOTICE, "Accounting suspended\n");
  596                 }
  597         }
  598 }
  599 
  600 /*
  601  * The main loop for the dedicated kernel thread that periodically calls
  602  * acctwatch().
  603  */
  604 static void
  605 acct_thread(void *dummy)
  606 {
  607         u_char pri;
  608 
  609         /* This is a low-priority kernel thread. */
  610         pri = PRI_MAX_KERN;
  611         thread_lock(curthread);
  612         sched_prio(curthread, pri);
  613         thread_unlock(curthread);
  614 
  615         /* If another accounting kthread is already running, just die. */
  616         sx_xlock(&acct_sx);
  617         if (acct_state & ACCT_RUNNING) {
  618                 sx_xunlock(&acct_sx);
  619                 kproc_exit(0);
  620         }
  621         acct_state |= ACCT_RUNNING;
  622 
  623         /* Loop until we are asked to exit. */
  624         while (!(acct_state & ACCT_EXITREQ)) {
  625 
  626                 /* Perform our periodic checks. */
  627                 acctwatch();
  628 
  629                 /*
  630                  * We check this flag again before sleeping since the
  631                  * acctwatch() might have shut down accounting and asked us
  632                  * to exit.
  633                  */
  634                 if (!(acct_state & ACCT_EXITREQ)) {
  635                         sx_sleep(&acct_state, &acct_sx, 0, "-",
  636                             acctchkfreq * hz);
  637                 }
  638         }
  639 
  640         /*
  641          * Acknowledge the exit request and shutdown.  We clear both the
  642          * exit request and running flags.
  643          */
  644         acct_state = 0;
  645         sx_xunlock(&acct_sx);
  646         kproc_exit(0);
  647 }

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