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b294143142
freebsd/sys/kern/subr_log.c
Ian Dowse 4784a46912 Replace the code for reading and writing the kernel message buffer 
with a new implementation that has a mostly reentrant "addchar"
routine, supports multiple message buffers in the kernel, and hides
the implementation details from callers.

The new code uses a kind of sequence number to represend the current
read and write positions in the buffer. This approach (suggested
mainly by bde) permits the read and write pointers to be maintained
separately, which reduces the number of atomic operations that are
required. The "mostly reentrant" above refers to the way that while
it is now always safe to have any number of concurrent writers,
readers could see the message buffer after a writer has advanced
the pointers but before it has witten the new character.

Discussed on:	freebsd-arch
2003-06-22 02:18:31 +00:00

258 lines
6.5 KiB
C
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/*
* 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. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. 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
#define LOG_RDWAIT 0x08
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 void logtimeout(void *arg);
#define CDEV_MAJOR 7
static struct cdevsw log_cdevsw = {
.d_open = logopen,
.d_close = logclose,
.d_read = logread,
.d_ioctl = logioctl,
.d_poll = logpoll,
.d_name = "log",
.d_maj = CDEV_MAJOR,
};
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() */
/* Times per second to check for a pending syslog wakeup. */
static int log_wakeups_per_second = 5;
SYSCTL_INT(_kern, OID_AUTO, log_wakeups_per_second, CTLFLAG_RW,
&log_wakeups_per_second, 0, "");
/*ARGSUSED*/
static int
logopen(dev_t dev, int flags, int mode, struct thread *td)
{
if (log_open)
return (EBUSY);
log_open = 1;
callout_init(&logsoftc.sc_callout, 0);
fsetown(td->td_proc->p_pid, &logsoftc.sc_sigio); /* signal process only */
if (log_wakeups_per_second < 1) {
printf("syslog wakeup is less than one. Adjusting to 1.\n");
log_wakeups_per_second = 1;
}
callout_reset(&logsoftc.sc_callout, hz / log_wakeups_per_second,
logtimeout, NULL);
return (0);
}
/*ARGSUSED*/
static int
logclose(dev_t dev, int flag, int mode, struct thread *td)
{
log_open = 0;
callout_stop(&logsoftc.sc_callout);
logsoftc.sc_state = 0;
funsetown(&logsoftc.sc_sigio);
return (0);
}
/*ARGSUSED*/
static int
logread(dev_t dev, struct uio *uio, int flag)
{
char buf[128];
struct msgbuf *mbp = msgbufp;
int error = 0, l, s;
s = splhigh();
while (msgbuf_getcount(mbp) == 0) {
if (flag & IO_NDELAY) {
splx(s);
return (EWOULDBLOCK);
}
logsoftc.sc_state |= LOG_RDWAIT;
if ((error = tsleep(mbp, LOG_RDPRI | PCATCH, "klog", 0))) {
splx(s);
return (error);
}
}
splx(s);
logsoftc.sc_state &= ~LOG_RDWAIT;
while (uio->uio_resid > 0) {
l = imin(sizeof(buf), uio->uio_resid);
l = msgbuf_getbytes(mbp, buf, l);
if (l == 0)
break;
error = uiomove(buf, l, uio);
if (error)
break;
}
return (error);
}
/*ARGSUSED*/
static int
logpoll(dev_t dev, int events, struct thread *td)
{
int s;
int revents = 0;
s = splhigh();
if (events & (POLLIN | POLLRDNORM)) {
if (msgbuf_getcount(msgbufp) > 0)
revents |= events & (POLLIN | POLLRDNORM);
else
selrecord(td, &logsoftc.sc_selp);
}
splx(s);
return (revents);
}
static void
logtimeout(void *arg)
{
if (!log_open)
return;
if (log_wakeups_per_second < 1) {
printf("syslog wakeup is less than one. Adjusting to 1.\n");
log_wakeups_per_second = 1;
}
if (msgbuftrigger == 0) {
callout_reset(&logsoftc.sc_callout,
hz / log_wakeups_per_second, logtimeout, NULL);
return;
}
msgbuftrigger = 0;
selwakeup(&logsoftc.sc_selp);
if ((logsoftc.sc_state & LOG_ASYNC) && logsoftc.sc_sigio != NULL)
pgsigio(&logsoftc.sc_sigio, SIGIO, 0);
if (logsoftc.sc_state & LOG_RDWAIT) {
wakeup(msgbufp);
logsoftc.sc_state &= ~LOG_RDWAIT;
}
callout_reset(&logsoftc.sc_callout, hz / log_wakeups_per_second,
logtimeout, NULL);
}
/*ARGSUSED*/
static int
logioctl(dev_t 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:
if (*(int *)data)
logsoftc.sc_state |= LOG_ASYNC;
else
logsoftc.sc_state &= ~LOG_ASYNC;
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)
{
make_dev(&log_cdevsw, 0, UID_ROOT, GID_WHEEL, 0600, "klog");
}
SYSINIT(logdev,SI_SUB_DRIVERS,SI_ORDER_MIDDLE+CDEV_MAJOR,log_drvinit,NULL)
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