subr_log.c

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/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1982, 1986, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * 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.
 *
 *      @(#)subr_log.c  8.1 (Berkeley) 6/10/93
 */
 
/*
 * Error log buffer for kernel printf's.
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/conf.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/filio.h>
#include <sys/ttycom.h>
#include <sys/msgbuf.h>
#include <sys/signalvar.h>
#include <sys/kernel.h>
#include <sys/poll.h>
#include <sys/filedesc.h>
#include <sys/sysctl.h>
 
#define LOG_RDPRI       (PZERO + 1)
 
#define LOG_ASYNC       0x04
 
static  d_open_t        logopen;
static  d_close_t       logclose;
static  d_read_t        logread;
static  d_ioctl_t       logioctl;
static  d_poll_t        logpoll;
static  d_kqfilter_t    logkqfilter;
 
static  void logtimeout(void *arg);
 
static struct cdevsw log_cdevsw = {
        .d_version =    D_VERSION,
        .d_open =       logopen,
        .d_close =      logclose,
        .d_read =       logread,
        .d_ioctl =      logioctl,
        .d_poll =       logpoll,
        .d_kqfilter =   logkqfilter,
        .d_name =       "log",
};
 
static int      logkqread(struct knote *note, long hint);
static void     logkqdetach(struct knote *note);
 
static struct filterops log_read_filterops = {
        .f_isfd =       1,
        .f_attach =     NULL,
        .f_detach =     logkqdetach,
        .f_event =      logkqread,
};
 
static struct logsoftc {
        int     sc_state;               /* see above for possibilities */
        struct  selinfo sc_selp;        /* process waiting on select call */
        struct  sigio *sc_sigio;        /* information for async I/O */
        struct  callout sc_callout;     /* callout to wakeup syslog  */
} logsoftc;
 
int                     log_open;       /* also used in log() */
static struct cv        log_wakeup;
struct mtx              msgbuf_lock;
MTX_SYSINIT(msgbuf_lock, &msgbuf_lock, "msgbuf lock", MTX_DEF);
 
static int      log_wakeups_per_second = 5;
SYSCTL_INT(_kern, OID_AUTO, log_wakeups_per_second, CTLFLAG_RW,
    &log_wakeups_per_second, 0,
    "How often (times per second) to check for /dev/log waiters.");
 
/*ARGSUSED*/
static  int
logopen(struct cdev *dev, int flags, int mode, struct thread *td)
{
 
        if (log_wakeups_per_second < 1) {
                printf("syslog wakeup is less than one.  Adjusting to 1.\n");
                log_wakeups_per_second = 1;
        }
 
        mtx_lock(&msgbuf_lock);
        if (log_open) {
                mtx_unlock(&msgbuf_lock);
                return (EBUSY);
        }
        log_open = 1;
        callout_reset_sbt(&logsoftc.sc_callout,
            SBT_1S / log_wakeups_per_second, 0, logtimeout, NULL, C_PREL(1));
        mtx_unlock(&msgbuf_lock);
 
        fsetown(td->td_proc->p_pid, &logsoftc.sc_sigio);        /* signal process only */
        return (0);
}
 
/*ARGSUSED*/
static  int
logclose(struct cdev *dev, int flag, int mode, struct thread *td)
{
 
        funsetown(&logsoftc.sc_sigio);
 
        mtx_lock(&msgbuf_lock);
        callout_stop(&logsoftc.sc_callout);
        logsoftc.sc_state = 0;
        log_open = 0;
        mtx_unlock(&msgbuf_lock);
 
        return (0);
}
 
/*ARGSUSED*/
static  int
logread(struct cdev *dev, struct uio *uio, int flag)
{
        char buf[128];
        struct msgbuf *mbp = msgbufp;
        int error = 0, l;
 
        mtx_lock(&msgbuf_lock);
        while (msgbuf_getcount(mbp) == 0) {
                if (flag & IO_NDELAY) {
                        mtx_unlock(&msgbuf_lock);
                        return (EWOULDBLOCK);
                }
                if ((error = cv_wait_sig(&log_wakeup, &msgbuf_lock)) != 0) {
                        mtx_unlock(&msgbuf_lock);
                        return (error);
                }
        }
 
        while (uio->uio_resid > 0) {
                l = imin(sizeof(buf), uio->uio_resid);
                l = msgbuf_getbytes(mbp, buf, l);
                if (l == 0)
                        break;
                mtx_unlock(&msgbuf_lock);
                error = uiomove(buf, l, uio);
                if (error || uio->uio_resid == 0)
                        return (error);
                mtx_lock(&msgbuf_lock);
        }
        mtx_unlock(&msgbuf_lock);
        return (error);
}
 
/*ARGSUSED*/
static  int
logpoll(struct cdev *dev, int events, struct thread *td)
{
        int revents = 0;
 
        if (events & (POLLIN | POLLRDNORM)) {
                mtx_lock(&msgbuf_lock);
                if (msgbuf_getcount(msgbufp) > 0)
                        revents |= events & (POLLIN | POLLRDNORM);
                else
                        selrecord(td, &logsoftc.sc_selp);
                mtx_unlock(&msgbuf_lock);
        }
        return (revents);
}
 
static int
logkqfilter(struct cdev *dev, struct knote *kn)
{
 
        if (kn->kn_filter != EVFILT_READ)
                return (EINVAL);
 
        kn->kn_fop = &log_read_filterops;
        kn->kn_hook = NULL;
 
        mtx_lock(&msgbuf_lock);
        knlist_add(&logsoftc.sc_selp.si_note, kn, 1);
        mtx_unlock(&msgbuf_lock);
        return (0);
}
 
static int
logkqread(struct knote *kn, long hint)
{
 
        mtx_assert(&msgbuf_lock, MA_OWNED);
        kn->kn_data = msgbuf_getcount(msgbufp);
        return (kn->kn_data != 0);
}
 
static void
logkqdetach(struct knote *kn)
{
 
        mtx_lock(&msgbuf_lock);
        knlist_remove(&logsoftc.sc_selp.si_note, kn, 1);
        mtx_unlock(&msgbuf_lock);
}
 
static void
logtimeout(void *arg)
{
 
        if (!log_open)
                return;
        if (msgbuftrigger == 0)
                goto done;
        msgbuftrigger = 0;
        selwakeuppri(&logsoftc.sc_selp, LOG_RDPRI);
        KNOTE_LOCKED(&logsoftc.sc_selp.si_note, 0);
        if ((logsoftc.sc_state & LOG_ASYNC) && logsoftc.sc_sigio != NULL)
                pgsigio(&logsoftc.sc_sigio, SIGIO, 0);
        cv_broadcastpri(&log_wakeup, LOG_RDPRI);
done:
        if (log_wakeups_per_second < 1) {
                printf("syslog wakeup is less than one.  Adjusting to 1.\n");
                log_wakeups_per_second = 1;
        }
        callout_reset_sbt(&logsoftc.sc_callout,
            SBT_1S / log_wakeups_per_second, 0, logtimeout, NULL, C_PREL(1));
}
 
/*ARGSUSED*/
static  int
logioctl(struct cdev *dev, u_long com, caddr_t data, int flag, struct thread *td)
{
 
        switch (com) {
        /* return number of characters immediately available */
        case FIONREAD:
                *(int *)data = msgbuf_getcount(msgbufp);
                break;
 
        case FIONBIO:
                break;
 
        case FIOASYNC:
                mtx_lock(&msgbuf_lock);
                if (*(int *)data)
                        logsoftc.sc_state |= LOG_ASYNC;
                else
                        logsoftc.sc_state &= ~LOG_ASYNC;
                mtx_unlock(&msgbuf_lock);
                break;
 
        case FIOSETOWN:
                return (fsetown(*(int *)data, &logsoftc.sc_sigio));
 
        case FIOGETOWN:
                *(int *)data = fgetown(&logsoftc.sc_sigio);
                break;
 
        /* This is deprecated, FIOSETOWN should be used instead. */
        case TIOCSPGRP:
                return (fsetown(-(*(int *)data), &logsoftc.sc_sigio));
 
        /* This is deprecated, FIOGETOWN should be used instead */
        case TIOCGPGRP:
                *(int *)data = -fgetown(&logsoftc.sc_sigio);
                break;
 
        default:
                return (ENOTTY);
        }
        return (0);
}
 
static void
log_drvinit(void *unused)
{
 
        cv_init(&log_wakeup, "klog");
        callout_init_mtx(&logsoftc.sc_callout, &msgbuf_lock, 0);
        knlist_init_mtx(&logsoftc.sc_selp.si_note, &msgbuf_lock);
        make_dev_credf(MAKEDEV_ETERNAL, &log_cdevsw, 0, NULL, UID_ROOT,
            GID_WHEEL, 0600, "klog");
}
 
SYSINIT(logdev,SI_SUB_DRIVERS,SI_ORDER_MIDDLE,log_drvinit,NULL);