/*      $NetBSD: subr_log.c,v 1.66 2025/04/09 05:38:01 rin Exp $        */

/*-
* Copyright (c) 2007, 2008 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Andrew Doran.
*
* 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.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
*/

/*
* 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  8.3 (Berkeley) 2/14/95
*/

/*
* Error log buffer for kernel printf's.
*/

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: subr_log.c,v 1.66 2025/04/09 05:38:01 rin Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/ioctl.h>
#include <sys/msgbuf.h>
#include <sys/file.h>
#include <sys/syslog.h>
#include <sys/conf.h>
#include <sys/select.h>
#include <sys/poll.h>
#include <sys/intr.h>
#include <sys/sysctl.h>
#include <sys/ktrace.h>

static int sysctl_msgbuf(SYSCTLFN_PROTO);

static void     logsoftintr(void *);

static bool     log_async;
static struct selinfo log_selp;         /* process waiting on select call */
static pid_t    log_pgid;               /* process/group for async I/O */
static kcondvar_t log_cv;
static void     *log_sih;

static kmutex_t log_lock;
int     log_open;                       /* also used in log() */
int     msgbufmapped;                   /* is the message buffer mapped */
int     msgbufenabled;                  /* is logging to the buffer enabled */
struct  kern_msgbuf *msgbufp;           /* the mapped buffer, itself. */

void
initmsgbuf(void *bf, size_t bufsize)
{
       struct kern_msgbuf *mbp;
       long new_bufs;

       /* Sanity-check the given size. */
       if (bufsize < sizeof(struct kern_msgbuf))
               return;

       mbp = msgbufp = (struct kern_msgbuf *)bf;

       new_bufs = bufsize - offsetof(struct kern_msgbuf, msg_bufc);
       if ((mbp->msg_magic != MSG_MAGIC) || (mbp->msg_bufs != new_bufs) ||
           (mbp->msg_bufr < 0) || (mbp->msg_bufr >= mbp->msg_bufs) ||
           (mbp->msg_bufx < 0) || (mbp->msg_bufx >= mbp->msg_bufs)) {
               /*
                * If the buffer magic number is wrong, has changed
                * size (which shouldn't happen often), or is
                * internally inconsistent, initialize it.
                */

               memset(bf, 0, bufsize);
               mbp->msg_magic = MSG_MAGIC;
               mbp->msg_bufs = new_bufs;
       }

       /* mark it as ready for use. */
       msgbufmapped = msgbufenabled = 1;
}

void
loginit(void)
{

       mutex_init(&log_lock, MUTEX_DEFAULT, IPL_VM);
       selinit(&log_selp);
       cv_init(&log_cv, "klog");
       log_sih = softint_establish(SOFTINT_CLOCK | SOFTINT_MPSAFE,
           logsoftintr, NULL);

       sysctl_createv(NULL, 0, NULL, NULL,
                      CTLFLAG_PERMANENT,
                      CTLTYPE_INT, "msgbufsize",
                      SYSCTL_DESCR("Size of the kernel message buffer"),
                      sysctl_msgbuf, 0, NULL, 0,
                      CTL_KERN, KERN_MSGBUFSIZE, CTL_EOL);
       sysctl_createv(NULL, 0, NULL, NULL,
                      CTLFLAG_PERMANENT,
                      CTLTYPE_INT, "msgbuf",
                      SYSCTL_DESCR("Kernel message buffer"),
                      sysctl_msgbuf, 0, NULL, 0,
                      CTL_KERN, KERN_MSGBUF, CTL_EOL);
}

/*ARGSUSED*/
static int
logopen(dev_t dev, int flags, int mode, struct lwp *l)
{
       struct kern_msgbuf *mbp = msgbufp;
       int error = 0;

       mutex_spin_enter(&log_lock);
       if (log_open) {
               error = EBUSY;
       } else {
               log_open = 1;
               log_pgid = l->l_proc->p_pid;    /* signal process only */
               /*
                * The message buffer is initialized during system
                * configuration.  If it's been clobbered, note that
                * and return an error.  (This allows a user to read
                * the buffer via /dev/kmem, and try to figure out
                * what clobbered it.
                */
               if (mbp->msg_magic != MSG_MAGIC) {
                       msgbufenabled = 0;
                       error = ENXIO;
               }
       }
       mutex_spin_exit(&log_lock);

       return error;
}

/*ARGSUSED*/
static int
logclose(dev_t dev, int flag, int mode, struct lwp *l)
{

       mutex_spin_enter(&log_lock);
       log_pgid = 0;
       log_open = 0;
       log_async = 0;
       mutex_spin_exit(&log_lock);

       return 0;
}

/*ARGSUSED*/
static int
logread(dev_t dev, struct uio *uio, int flag)
{
       struct kern_msgbuf *mbp = msgbufp;
       long l;
       int error = 0;

       mutex_spin_enter(&log_lock);
       while (mbp->msg_bufr == mbp->msg_bufx) {
               if (flag & IO_NDELAY) {
                       mutex_spin_exit(&log_lock);
                       return EWOULDBLOCK;
               }
               error = cv_wait_sig(&log_cv, &log_lock);
               if (error) {
                       mutex_spin_exit(&log_lock);
                       return error;
               }
       }
       while (uio->uio_resid > 0) {
               char buf[128]; /* taken from FreeBSD */

               l = mbp->msg_bufx - mbp->msg_bufr;
               if (l < 0)
                       l = mbp->msg_bufs - mbp->msg_bufr;
               l = ulmin(l, uio->uio_resid);
               if (l == 0)
                       break;

               l = ulmin(l, sizeof(buf));
               memcpy(buf, &mbp->msg_bufc[mbp->msg_bufr], l);
               mbp->msg_bufr += l;
               if (mbp->msg_bufr < 0 || mbp->msg_bufr >= mbp->msg_bufs)
                       mbp->msg_bufr = 0;
               mutex_spin_exit(&log_lock);
               error = uiomove(buf, l, uio);
               mutex_spin_enter(&log_lock);
               if (error)
                       break;
       }
       mutex_spin_exit(&log_lock);

       return error;
}

/*ARGSUSED*/
static int
logpoll(dev_t dev, int events, struct lwp *l)
{
       int revents = 0;

       if (events & (POLLIN | POLLRDNORM)) {
               mutex_spin_enter(&log_lock);
               if (msgbufp->msg_bufr != msgbufp->msg_bufx)
                       revents |= events & (POLLIN | POLLRDNORM);
               else
                       selrecord(l, &log_selp);
               mutex_spin_exit(&log_lock);
       }

       return revents;
}

static void
filt_logrdetach(struct knote *kn)
{

       mutex_spin_enter(&log_lock);
       selremove_knote(&log_selp, kn);
       mutex_spin_exit(&log_lock);
}

static int
filt_logread(struct knote *kn, long hint)
{
       int rv;

       if ((hint & NOTE_SUBMIT) == 0)
               mutex_spin_enter(&log_lock);
       if (msgbufp->msg_bufr == msgbufp->msg_bufx) {
               rv = 0;
       } else if (msgbufp->msg_bufr < msgbufp->msg_bufx) {
               kn->kn_data = msgbufp->msg_bufx - msgbufp->msg_bufr;
               rv = 1;
       } else {
               kn->kn_data = (msgbufp->msg_bufs - msgbufp->msg_bufr) +
                   msgbufp->msg_bufx;
               rv = 1;
       }
       if ((hint & NOTE_SUBMIT) == 0)
               mutex_spin_exit(&log_lock);

       return rv;
}

static const struct filterops logread_filtops = {
       .f_flags = FILTEROP_ISFD | FILTEROP_MPSAFE,
       .f_attach = NULL,
       .f_detach = filt_logrdetach,
       .f_event = filt_logread,
};

static int
logkqfilter(dev_t dev, struct knote *kn)
{

       switch (kn->kn_filter) {
       case EVFILT_READ:
               kn->kn_fop = &logread_filtops;
               mutex_spin_enter(&log_lock);
               selrecord_knote(&log_selp, kn);
               mutex_spin_exit(&log_lock);
               break;

       default:
               return (EINVAL);
       }

       return (0);
}

void
logwakeup(void)
{

       if (!cold && log_open) {
               mutex_spin_enter(&log_lock);
               selnotify(&log_selp, 0, NOTE_SUBMIT);
               if (log_async)
                       softint_schedule(log_sih);
               cv_broadcast(&log_cv);
               mutex_spin_exit(&log_lock);
       }
}

static void
logsoftintr(void *cookie)
{
       pid_t pid;

       if ((pid = log_pgid) != 0)
               fownsignal(pid, SIGIO, 0, 0, NULL);
}

/*ARGSUSED*/
static int
logioctl(dev_t dev, u_long com, void *data, int flag, struct lwp *lwp)
{
       long l;

       switch (com) {

       /* return number of characters immediately available */
       case FIONREAD:
               mutex_spin_enter(&log_lock);
               l = msgbufp->msg_bufx - msgbufp->msg_bufr;
               if (l < 0)
                       l += msgbufp->msg_bufs;
               mutex_spin_exit(&log_lock);
               *(int *)data = l;
               break;

       case FIONBIO:
               break;

       case FIOASYNC:
               /* No locking needed, 'thread private'. */
               log_async = (*((int *)data) != 0);
               break;

       case TIOCSPGRP:
       case FIOSETOWN:
               return fsetown(&log_pgid, com, data);

       case TIOCGPGRP:
       case FIOGETOWN:
               return fgetown(log_pgid, com, data);

       default:
               return (EPASSTHROUGH);
       }
       return (0);
}

static void
logskip(struct kern_msgbuf *mbp)
{
       /*
        * Move forward read pointer to the next line
        * in the buffer.  Note that the buffer is
        * a ring buffer so we should reset msg_bufr
        * to 0 when msg_bufr exceeds msg_bufs.
        *
        * To prevent to loop forever, give up if we
        * cannot find a newline in mbp->msg_bufs
        * characters (the max size of the buffer).
        */
       for (int i = 0; i < mbp->msg_bufs; i++) {
               char c0 = mbp->msg_bufc[mbp->msg_bufr];
               if (++mbp->msg_bufr >= mbp->msg_bufs)
                       mbp->msg_bufr = 0;
               if (c0 == '\n')
                       break;
       }
}

static void
logaddchar(struct kern_msgbuf *mbp, int c)
{
       mbp->msg_bufc[mbp->msg_bufx++] = c;
       if (mbp->msg_bufx < 0 || mbp->msg_bufx >= mbp->msg_bufs)
               mbp->msg_bufx = 0;

       /* If the buffer is full, keep the most recent data. */
       if (mbp->msg_bufr == mbp->msg_bufx)
               logskip(mbp);
}

void
logputchar(int c)
{
       struct kern_msgbuf *mbp;

       if (!cold)
               mutex_spin_enter(&log_lock);

       if (!msgbufenabled)
               goto out;

       mbp = msgbufp;
       if (mbp->msg_magic != MSG_MAGIC) {
               /*
                * Arguably should panic or somehow notify the
                * user...  but how?  Panic may be too drastic,
                * and would obliterate the message being kicked
                * out (maybe a panic itself), and printf
                * would invoke us recursively.  Silently punt
                * for now.  If syslog is running, it should
                * notice.
                */
               msgbufenabled = 0;
               goto out;

       }

       logaddchar(mbp, c);

out:
       if (!cold)
               mutex_spin_exit(&log_lock);
}

/*
* sysctl helper routine for kern.msgbufsize and kern.msgbuf. For the
* former it merely checks the message buffer is set up. For the latter,
* it also copies out the data if necessary.
*/
static int
sysctl_msgbuf(SYSCTLFN_ARGS)
{
       char *where = oldp;
       size_t len, maxlen;
       long beg, end;
       int error;

       if (!logenabled(msgbufp)) {
               msgbufenabled = 0;
               return (ENXIO);
       }

       switch (rnode->sysctl_num) {
       case KERN_MSGBUFSIZE: {
               struct sysctlnode node = *rnode;
               int msg_bufs = (int)msgbufp->msg_bufs;
               node.sysctl_data = &msg_bufs;
               return (sysctl_lookup(SYSCTLFN_CALL(&node)));
       }
       case KERN_MSGBUF:
               break;
       default:
               return (EOPNOTSUPP);
       }

       if (newp != NULL)
               return (EPERM);

       if (oldp == NULL) {
               /* always return full buffer size */
               *oldlenp = msgbufp->msg_bufs;
               return (0);
       }

       sysctl_unlock();

       /*
        * First, copy from the write pointer to the end of
        * message buffer.
        */
       error = 0;
       mutex_spin_enter(&log_lock);
       maxlen = MIN(msgbufp->msg_bufs, *oldlenp);
       beg = msgbufp->msg_bufx;
       end = msgbufp->msg_bufs;
       mutex_spin_exit(&log_lock);

       while (maxlen > 0) {
               len = MIN(end - beg, maxlen);
               if (len == 0)
                       break;
               /* XXX unlocked, but hardly matters. */
               error = copyout(&msgbufp->msg_bufc[beg], where, len);
               ktrmibio(-1, UIO_READ, where, len, error);
               if (error)
                       break;
               where += len;
               maxlen -= len;

               /*
                * ... then, copy from the beginning of message buffer to
                * the write pointer.
                */
               beg = 0;
               end = msgbufp->msg_bufx;
       }

       sysctl_relock();
       return (error);
}

const struct cdevsw log_cdevsw = {
       .d_open = logopen,
       .d_close = logclose,
       .d_read = logread,
       .d_write = nowrite,
       .d_ioctl = logioctl,
       .d_stop = nostop,
       .d_tty = notty,
       .d_poll = logpoll,
       .d_mmap = nommap,
       .d_kqfilter = logkqfilter,
       .d_discard = nodiscard,
       .d_flag = D_OTHER | D_MPSAFE
};

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