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Replace select backends with poll backends.  selscan() and pollscan()
now call the poll backend.  With this change we implement greater
poll(2) functionality instead of emulating it via the select backend.
Adapted from NetBSD and including some changes from FreeBSD.
Tested by many, deraadt@ OK

/*	$OpenBSD: subr_log.c,v 1.11 2003/09/23 16:51:12 millert Exp $	*/
/*	$NetBSD: subr_log.c,v 1.11 1996/03/30 22:24:44 christos Exp $	*/

/*
 * 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/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/vnode.h>
#include <sys/ioctl.h>
#include <sys/msgbuf.h>
#include <sys/file.h>
#include <sys/signalvar.h>
#include <sys/syslog.h>
#include <sys/conf.h>
#include <sys/poll.h>

#define LOG_RDPRI	(PZERO + 1)

#define LOG_ASYNC	0x04
#define LOG_RDWAIT	0x08

struct logsoftc {
	int	sc_state;		/* see above for possibilities */
	struct	selinfo sc_selp;	/* process waiting on select call */
	int	sc_pgid;		/* process/group for async I/O */
	uid_t	sc_siguid;		/* uid for process that set sc_pgid */
	uid_t	sc_sigeuid;		/* euid for process that set sc_pgid */
} logsoftc;

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

void filt_logrdetach(struct knote *kn);
int filt_logread(struct knote *kn, long hint);
   
struct filterops logread_filtops =
	{ 1, NULL, filt_logrdetach, filt_logread};

void
initmsgbuf(buf, bufsize)
	caddr_t buf;
	size_t bufsize;
{
	register struct msgbuf *mbp;
	long new_bufs;

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

	mbp = msgbufp = (struct msgbuf *)buf;

	new_bufs = bufsize - offsetof(struct 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.
		 */

		bzero(buf, bufsize);
		mbp->msg_magic = MSG_MAGIC;
		mbp->msg_bufs = new_bufs;
	}

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

/*ARGSUSED*/
int
logopen(dev, flags, mode, p)
	dev_t dev;
	int flags, mode;
	struct proc *p;
{
	if (log_open)
		return (EBUSY);
	log_open = 1;
	return (0);
}

/*ARGSUSED*/
int
logclose(dev, flag, mode, p)
	dev_t dev;
	int flag, mode;
	struct proc *p;
{

	log_open = 0;
	logsoftc.sc_state = 0;
	return (0);
}

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

	s = splhigh();
	while (mbp->msg_bufr == mbp->msg_bufx) {
		if (flag & IO_NDELAY) {
			splx(s);
			return (EWOULDBLOCK);
		}
		logsoftc.sc_state |= LOG_RDWAIT;
		error = tsleep(mbp, LOG_RDPRI | PCATCH,
			       "klog", 0);
		if (error) {
			splx(s);
			return (error);
		}
	}
	splx(s);
	logsoftc.sc_state &= ~LOG_RDWAIT;

	while (uio->uio_resid > 0) {
		l = mbp->msg_bufx - mbp->msg_bufr;
		if (l < 0)
			l = mbp->msg_bufs - mbp->msg_bufr;
		l = min(l, uio->uio_resid);
		if (l == 0)
			break;
		error = uiomove(&mbp->msg_bufc[mbp->msg_bufr], (int)l, uio);
		if (error)
			break;
		mbp->msg_bufr += l;
		if (mbp->msg_bufr < 0 || mbp->msg_bufr >= mbp->msg_bufs)
			mbp->msg_bufr = 0;
	}
	return (error);
}

/*ARGSUSED*/
int
logpoll(dev, events, p)
	dev_t dev;
	int events;
	struct proc *p;
{
	int revents = 0;
	int s = splhigh();

	if (events & (POLLIN | POLLRDNORM)) {
		if (msgbufp->msg_bufr != msgbufp->msg_bufx)
			revents |= events & (POLLIN | POLLRDNORM);
		else
			selrecord(p, &logsoftc.sc_selp);
	}
	splx(s);
	return (revents);
}

int
logkqfilter(dev_t dev, struct knote *kn)
{
	struct klist *klist;
	int s;

	switch (kn->kn_filter) {
	case EVFILT_READ:
		klist = &logsoftc.sc_selp.si_note;
		kn->kn_fop = &logread_filtops;
		break;
	default:
		return (1);
	}

	kn->kn_hook = (void *)msgbufp;

	s = splhigh();
	SLIST_INSERT_HEAD(klist, kn, kn_selnext);
	splx(s);

	return (0);
}

void
filt_logrdetach(struct knote *kn)
{
	int s = splhigh();

	SLIST_REMOVE(&logsoftc.sc_selp.si_note, kn, knote, kn_selnext);
	splx(s);
}

int
filt_logread(struct knote *kn, long hint)
{
	struct  msgbuf *p = (struct  msgbuf *)kn->kn_hook;

	kn->kn_data = (int)(p->msg_bufx - p->msg_bufr);

	return (p->msg_bufx != p->msg_bufr);
}

void
logwakeup()
{
	if (!log_open)
		return;
	selwakeup(&logsoftc.sc_selp);
	if (logsoftc.sc_state & LOG_ASYNC)
		csignal(logsoftc.sc_pgid, SIGIO,
		    logsoftc.sc_siguid, logsoftc.sc_sigeuid);
	if (logsoftc.sc_state & LOG_RDWAIT) {
		wakeup(msgbufp);
		logsoftc.sc_state &= ~LOG_RDWAIT;
	}
	KNOTE(&logsoftc.sc_selp.si_note, 0);
}

/*ARGSUSED*/
int
logioctl(dev, com, data, flag, p)
	dev_t dev;
	u_long com;
	caddr_t data;
	int flag;
	struct proc *p;
{
	long l;
	int s;

	switch (com) {

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

	case FIONBIO:
		break;

	case FIOASYNC:
		if (*(int *)data)
			logsoftc.sc_state |= LOG_ASYNC;
		else
			logsoftc.sc_state &= ~LOG_ASYNC;
		break;

	case TIOCSPGRP:
		logsoftc.sc_pgid = *(int *)data;
		logsoftc.sc_siguid = p->p_cred->p_ruid;
		logsoftc.sc_sigeuid = p->p_ucred->cr_uid;
		break;

	case TIOCGPGRP:
		*(int *)data = logsoftc.sc_pgid;
		break;

	default:
		return (-1);
	}
	return (0);
}