/*
 * Copyright (c) 2000-2022 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/* Copyright (c) 1995 NeXT Computer, Inc. All Rights Reserved */
/*
 * 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	8.3 (Berkeley) 2/14/95
 */

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

#include <machine/atomic.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc_internal.h>
#include <sys/vnode.h>
#include <stdbool.h>
#include <firehose/tracepoint_private.h>
#include <firehose/chunk_private.h>
#include <firehose/ioctl_private.h>
#include <os/firehose_buffer_private.h>

#include <os/log_private.h>
#include <sys/ioctl.h>
#include <sys/msgbuf.h>
#include <sys/file_internal.h>
#include <sys/errno.h>
#include <sys/select.h>
#include <sys/kernel.h>
#include <kern/thread.h>
#include <kern/sched_prim.h>
#include <kern/simple_lock.h>
#include <sys/lock.h>
#include <sys/signalvar.h>
#include <sys/conf.h>
#include <sys/sysctl.h>
#include <sys/queue.h>
#include <kern/kalloc.h>
#include <pexpert/pexpert.h>
#include <mach/mach_port.h>
#include <mach/mach_vm.h>
#include <mach/vm_map.h>
#include <vm/vm_kern.h>
#include <kern/task.h>
#include <kern/locks.h>

#define LOG_NBIO        0x02
#define LOG_ASYNC       0x04
#define LOG_RDWAIT      0x08

/* All globals should be accessed under bsd_log_lock() or bsd_log_lock_safe() */

/* logsoftc only valid while log_open=1 */
struct logsoftc {
	int     sc_state;               /* see above for possibilities */
	struct  selinfo sc_selp;        /* thread waiting for select */
	int     sc_pgid;                /* process/group for async I/O */
	struct msgbuf *sc_mbp;
} logsoftc;

char smsg_bufc[CONFIG_MSG_BSIZE]; /* static buffer */
struct msgbuf msgbuf = {.msg_magic  = MSG_MAGIC, .msg_size = sizeof(smsg_bufc), .msg_bufx = 0, .msg_bufr = 0, .msg_bufc = smsg_bufc};
struct msgbuf *msgbufp __attribute__((used)) = &msgbuf;

/* oslogsoftc only valid while oslog_open=true */
struct oslogsoftc {
	int     sc_state;               /* see above for possibilities */
	struct  selinfo sc_selp;        /* thread waiting for select */
	int     sc_pgid;                /* process/group for async I/O */
} oslogsoftc;

static bool log_open = false;
static bool oslog_open = false;
static bool os_log_wakeup = false;

uint32_t oslog_msgbuf_dropped_charcount = 0;

SECURITY_READ_ONLY_LATE(vm_offset_t) kernel_firehose_addr = 0;
SECURITY_READ_ONLY_LATE(uint8_t) __firehose_buffer_kernel_chunk_count =
    FIREHOSE_BUFFER_KERNEL_DEFAULT_CHUNK_COUNT;
SECURITY_READ_ONLY_LATE(uint8_t) __firehose_num_kernel_io_pages =
    FIREHOSE_BUFFER_KERNEL_DEFAULT_IO_PAGES;

/* defined in osfmk/kern/printf.c  */
extern bool bsd_log_lock(bool);
extern void bsd_log_lock_safe(void);
extern void bsd_log_unlock(void);

extern void logwakeup(void);
extern void oslogwakeup(void);
extern bool os_log_disabled(void);

/* XXX wants a linker set so these can be static */
extern d_open_t         logopen;
extern d_close_t        logclose;
extern d_read_t         logread;
extern d_ioctl_t        logioctl;
extern d_select_t       logselect;

/* XXX wants a linker set so these can be static */
extern d_open_t         oslogopen;
extern d_close_t        oslogclose;
extern d_select_t       oslogselect;
extern d_ioctl_t        oslogioctl;

/*
 * Serialize log access.  Note that the log can be written at interrupt level,
 * so any log manipulations that can be done from, or affect, another processor
 * at interrupt level must be guarded with a spin lock.
 */

static int sysctl_kern_msgbuf(struct sysctl_oid *oidp,
    void *arg1, int arg2, struct sysctl_req *req);

/*ARGSUSED*/
int
logopen(__unused dev_t dev, __unused int flags, __unused int mode, struct proc *p)
{
	bsd_log_lock_safe();

	if (log_open) {
		bsd_log_unlock();
		return EBUSY;
	}

	/*
	 * Legacy logging has to be supported as long as userspace supports it.
	 */
	if ((atm_get_diagnostic_config() & ATM_ENABLE_LEGACY_LOGGING)) {
		logsoftc.sc_mbp = msgbufp;
		logsoftc.sc_pgid = proc_getpid(p); /* signal process only */
		log_open = true;
		bsd_log_unlock();
		return 0;
	}

	bsd_log_unlock();
	return ENOTSUP;
}

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

	logsoftc.sc_state &= ~(LOG_NBIO | LOG_ASYNC);
	selthreadclear(&logsoftc.sc_selp);
	log_open = false;

	bsd_log_unlock();
	return 0;
}

int
oslogopen(__unused dev_t dev, __unused int flags, __unused int mode, struct proc *p)
{
	bsd_log_lock_safe();
	if (oslog_open) {
		bsd_log_unlock();
		return EBUSY;
	}
	oslogsoftc.sc_pgid = proc_getpid(p);          /* signal process only */
	oslog_open = true;

	bsd_log_unlock();
	return 0;
}

int
oslogclose(__unused dev_t dev, __unused int flag, __unused int devtype, __unused struct proc *p)
{
	bsd_log_lock_safe();
	oslogsoftc.sc_state &= ~(LOG_NBIO | LOG_ASYNC);
	selthreadclear(&oslogsoftc.sc_selp);
	oslog_open = false;
	bsd_log_unlock();
	return 0;
}

/*ARGSUSED*/
int
logread(__unused dev_t dev, struct uio *uio, int flag)
{
	int error;
	ssize_t resid;

	bsd_log_lock_safe();

	struct msgbuf *mbp = logsoftc.sc_mbp;

	while (mbp->msg_bufr == mbp->msg_bufx) {
		if ((flag & IO_NDELAY) || (logsoftc.sc_state & LOG_NBIO)) {
			bsd_log_unlock();
			return EWOULDBLOCK;
		}
		logsoftc.sc_state |= LOG_RDWAIT;
		bsd_log_unlock();
		/*
		 * If the wakeup is missed then wait for 5 sec and reevaluate.
		 * If it times out, carry on.
		 */
		error = tsleep((caddr_t)mbp, (PZERO + 1) | PCATCH, "klog", 5 * hz);
		if (error && error != EWOULDBLOCK) {
			return error;
		}
		bsd_log_lock_safe();
	}
	logsoftc.sc_state &= ~LOG_RDWAIT;

	while ((resid = uio_resid(uio)) > 0) {
		size_t l;

		if (mbp->msg_bufx >= mbp->msg_bufr) {
			l = mbp->msg_bufx - mbp->msg_bufr;
		} else {
			l = mbp->msg_size - mbp->msg_bufr;
		}
		if ((l = MIN(l, (size_t)resid)) == 0) {
			break;
		}

		const size_t readpos = mbp->msg_bufr;

		bsd_log_unlock();
		error = uiomove((caddr_t)&mbp->msg_bufc[readpos], (int)l, uio);
		if (error) {
			return error;
		}
		bsd_log_lock_safe();

		mbp->msg_bufr = (int)(readpos + l);
		if (mbp->msg_bufr >= mbp->msg_size) {
			mbp->msg_bufr = 0;
		}
	}

	bsd_log_unlock();
	return 0;
}

/*ARGSUSED*/
int
logselect(__unused dev_t dev, int rw, void * wql, struct proc *p)
{
	if (rw != FREAD) {
		return 0;
	}

	bsd_log_lock_safe();
	if (logsoftc.sc_mbp->msg_bufr == logsoftc.sc_mbp->msg_bufx) {
		selrecord(p, &logsoftc.sc_selp, wql);
		bsd_log_unlock();
		return 0;
	}
	bsd_log_unlock();

	return 1;
}

int
oslogselect(__unused dev_t dev, int rw, void * wql, struct proc *p)
{
	if (rw != FREAD) {
		return 0;
	}

	bsd_log_lock_safe();
	if (os_log_wakeup) {
		bsd_log_unlock();
		return 1;
	}
	selrecord(p, &oslogsoftc.sc_selp, wql);
	bsd_log_unlock();

	return 0;
}

void
logwakeup(void)
{
	/*
	 * Legacy logging is rarely enabled during a typical system run. Check
	 * log_open without taking a lock as a shortcut.
	 */
	if (!log_open || !oslog_is_safe()) {
		return;
	}

	bsd_log_lock_safe();

	if (!log_open) {
		bsd_log_unlock();
		return;
	}

	selwakeup(&logsoftc.sc_selp);
	if (logsoftc.sc_state & LOG_ASYNC) {
		int pgid = logsoftc.sc_pgid;
		bsd_log_unlock();
		if (pgid < 0) {
			gsignal(-pgid, SIGIO);
		} else {
			proc_signal(pgid, SIGIO);
		}
		bsd_log_lock_safe();
	}

	if (log_open && (logsoftc.sc_state & LOG_RDWAIT)) {
		wakeup((caddr_t)logsoftc.sc_mbp);
		logsoftc.sc_state &= ~LOG_RDWAIT;
	}

	bsd_log_unlock();
}

void
oslogwakeup(void)
{
	if (!oslog_is_safe()) {
		return;
	}

	bsd_log_lock_safe();
	if (!oslog_open) {
		bsd_log_unlock();
		return;
	}
	selwakeup(&oslogsoftc.sc_selp);
	os_log_wakeup = true;
	bsd_log_unlock();
}

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

	const struct msgbuf *mbp = logsoftc.sc_mbp;
	int l;

	switch (com) {
	/* return number of characters immediately available */
	case FIONREAD:
		l = mbp->msg_bufx - mbp->msg_bufr;
		if (l < 0) {
			l += mbp->msg_size;
		}
		*(off_t *)data = l;
		break;

	case FIONBIO:
		if (*(int *)data) {
			logsoftc.sc_state |= LOG_NBIO;
		} else {
			logsoftc.sc_state &= ~LOG_NBIO;
		}
		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;
		break;

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

	default:
		bsd_log_unlock();
		return -1;
	}

	bsd_log_unlock();
	return 0;
}

/*ARGSUSED*/
int
oslogioctl(__unused dev_t dev, u_long com, caddr_t data, __unused int flag, __unused struct proc *p)
{
	int ret = 0;
	mach_vm_size_t buffer_size = (__firehose_buffer_kernel_chunk_count * FIREHOSE_CHUNK_SIZE);
	firehose_buffer_map_info_t map_info = {0, 0};
	firehose_buffer_t kernel_firehose_buffer = NULL;
	mach_vm_address_t user_addr = 0;
	mach_port_t mem_entry_ptr = MACH_PORT_NULL;
	bool has_more;

	switch (com) {
	/* return number of characters immediately available */

	case LOGBUFFERMAP:
		kernel_firehose_buffer = (firehose_buffer_t)kernel_firehose_addr;

		ret = mach_make_memory_entry_64(kernel_map,
		    &buffer_size,
		    (mach_vm_offset_t) kernel_firehose_buffer,
		    (MAP_MEM_VM_SHARE | VM_PROT_READ),
		    &mem_entry_ptr,
		    MACH_PORT_NULL);
		if (ret == KERN_SUCCESS) {
			ret = mach_vm_map_kernel(get_task_map(current_task()),
			    &user_addr,
			    buffer_size,
			    0,               /*  mask */
			    VM_MAP_KERNEL_FLAGS_ANYWHERE(),
			    mem_entry_ptr,
			    0,               /* offset */
			    FALSE,               /* copy */
			    VM_PROT_READ,
			    VM_PROT_READ,
			    VM_INHERIT_SHARE);
		}

		if (ret == KERN_SUCCESS) {
			map_info.fbmi_addr = (uint64_t) (user_addr);
			map_info.fbmi_size = buffer_size;
			bcopy(&map_info, data, sizeof(firehose_buffer_map_info_t));
		}
		break;
	case LOGFLUSHED:
		has_more = __firehose_merge_updates(*(firehose_push_reply_t *)(data));
		bsd_log_lock_safe();
		os_log_wakeup = has_more;
		if (os_log_wakeup) {
			selwakeup(&oslogsoftc.sc_selp);
		}
		bsd_log_unlock();
		break;
	default:
		return -1;
	}
	return 0;
}

__startup_func
static void
oslog_init_firehose(void)
{
	if (os_log_disabled()) {
		printf("Firehose disabled: Logging disabled by ATM\n");
		return;
	}

	if (!PE_parse_boot_argn("firehose_chunk_count", &__firehose_buffer_kernel_chunk_count, sizeof(__firehose_buffer_kernel_chunk_count))) {
		__firehose_buffer_kernel_chunk_count = FIREHOSE_BUFFER_KERNEL_DEFAULT_CHUNK_COUNT;
	}
	if (!PE_parse_boot_argn("firehose_io_pages", &__firehose_num_kernel_io_pages, sizeof(__firehose_num_kernel_io_pages))) {
		__firehose_num_kernel_io_pages = FIREHOSE_BUFFER_KERNEL_DEFAULT_IO_PAGES;
	}
	if (!__firehose_kernel_configuration_valid(__firehose_buffer_kernel_chunk_count, __firehose_num_kernel_io_pages)) {
		printf("illegal firehose configuration %u/%u, using defaults\n", __firehose_buffer_kernel_chunk_count, __firehose_num_kernel_io_pages);
		__firehose_buffer_kernel_chunk_count = FIREHOSE_BUFFER_KERNEL_DEFAULT_CHUNK_COUNT;
		__firehose_num_kernel_io_pages = FIREHOSE_BUFFER_KERNEL_DEFAULT_IO_PAGES;
	}
	vm_size_t size = __firehose_buffer_kernel_chunk_count * FIREHOSE_CHUNK_SIZE;

	kmem_alloc(kernel_map, &kernel_firehose_addr, size + ptoa(2),
	    KMA_NOFAIL | KMA_PERMANENT | KMA_GUARD_FIRST | KMA_GUARD_LAST |
	    KMA_DATA | KMA_ZERO, VM_KERN_MEMORY_LOG);

	kernel_firehose_addr += PAGE_SIZE;
	/* register buffer with firehose */
	kernel_firehose_addr = (vm_offset_t)__firehose_buffer_create((size_t *) &size);

	printf("Firehose configured: %u chunks, %u io pages\n",
	    __firehose_buffer_kernel_chunk_count, __firehose_num_kernel_io_pages);
}
STARTUP(OSLOG, STARTUP_RANK_SECOND, oslog_init_firehose);

/*
 * log_putc_locked
 *
 * Decription:	Output a character to the log; assumes the bsd_log_lock() or
 *              bsd_log_lock_safe() is held by the caller.
 *
 * Parameters:	c				Character to output
 *
 * Returns:	(void)
 *
 * Notes:	This functions is used for multibyte output to the log; it
 *		should be used preferrentially where possible to ensure that
 *		log entries do not end up interspersed due to preemption or
 *		SMP reentrancy.
 */
void
log_putc_locked(struct msgbuf *mbp, char c)
{
	mbp->msg_bufc[mbp->msg_bufx++] = c;
	if (mbp->msg_bufx >= mbp->msg_size) {
		mbp->msg_bufx = 0;
	}
}

/*
 * log_putc
 *
 * Decription:	Output a character to the log; assumes the bsd_log_lock() or
 *              bsd_log_lock_safe() is NOT held by the caller.
 *
 * Parameters:	c				Character to output
 *
 * Returns:	(void)
 *
 * Notes:	This function is used for single byte output to the log.  It
 *		primarily exists to maintain binary backward compatibility.
 */
void
log_putc(char c)
{
	if (!bsd_log_lock(oslog_is_safe())) {
		os_atomic_inc(&oslog_msgbuf_dropped_charcount, relaxed);
		return;
	}

	log_putc_locked(msgbufp, c);
	int unread_count = msgbufp->msg_bufx - msgbufp->msg_bufr;

	bsd_log_unlock();

	if (unread_count < 0) {
		unread_count = 0 - unread_count;
	}
	if (c == '\n' || unread_count >= (msgbufp->msg_size / 2)) {
		logwakeup();
	}
}

/*
 * it is possible to increase the kernel log buffer size by adding
 *   msgbuf=n
 * to the kernel command line, and to read the current size using
 *   sysctl kern.msgbuf
 * If there is no parameter on the kernel command line, the buffer is
 * allocated statically and is CONFIG_MSG_BSIZE characters in size, otherwise
 * memory is dynamically allocated. Memory management must already be up.
 */
static int
log_setsize(size_t size)
{
	int i, count;
	char *p;

	if (size == 0 || size > MAX_MSG_BSIZE) {
		return EINVAL;
	}

	int new_logsize = (int)size;
	char *new_logdata = kalloc_data(size, Z_WAITOK | Z_ZERO);
	if (!new_logdata) {
		printf("Cannot resize system message buffer: Not enough memory\n");
		return ENOMEM;
	}

	bsd_log_lock_safe();

	char *old_logdata = msgbufp->msg_bufc;
	int old_logsize = msgbufp->msg_size;
	int old_bufr = msgbufp->msg_bufr;
	int old_bufx = msgbufp->msg_bufx;

	/* start "new_logsize" bytes before the write pointer */
	if (new_logsize <= old_bufx) {
		count = new_logsize;
		p = old_logdata + old_bufx - count;
	} else {
		/*
		 * if new buffer is bigger, copy what we have and let the
		 * bzero above handle the difference
		 */
		count = MIN(new_logsize, old_logsize);
		p = old_logdata + old_logsize - (count - old_bufx);
	}
	for (i = 0; i < count; i++) {
		if (p >= old_logdata + old_logsize) {
			p = old_logdata;
		}
		new_logdata[i] = *p++;
	}

	int new_bufx = i;
	if (new_bufx >= new_logsize) {
		new_bufx = 0;
	}
	msgbufp->msg_bufx = new_bufx;

	int new_bufr = old_bufx - old_bufr; /* how much were we trailing bufx by? */
	if (new_bufr < 0) {
		new_bufr += old_logsize;
	}
	new_bufr = new_bufx - new_bufr; /* now relative to oldest data in new buffer */
	if (new_bufr < 0) {
		new_bufr += new_logsize;
	}
	msgbufp->msg_bufr = new_bufr;

	msgbufp->msg_size = new_logsize;
	msgbufp->msg_bufc = new_logdata;

	bsd_log_unlock();

	/*
	 * This memory is now dead - clear it so that it compresses better
	 * in case of suspend to disk etc.
	 */
	bzero(old_logdata, old_logsize);
	if (old_logdata != smsg_bufc) {
		/* dynamic memory that must be freed */
		kfree_data(old_logdata, old_logsize);
	}

	printf("System message buffer configured: %lu bytes\n", size);

	return 0;
}

SYSCTL_PROC(_kern, OID_AUTO, msgbuf,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_LOCKED, 0, 0,
    sysctl_kern_msgbuf, "I", "");

static int
sysctl_kern_msgbuf(struct sysctl_oid *oidp __unused,
    void *arg1 __unused, int arg2 __unused, struct sysctl_req *req)
{
	int old_bufsize, bufsize;
	int error;

	bsd_log_lock_safe();
	old_bufsize = bufsize = msgbufp->msg_size;
	bsd_log_unlock();

	error = sysctl_io_number(req, bufsize, sizeof(bufsize), &bufsize, NULL);
	if (error) {
		return error;
	}

	if (bufsize < 0) {
		return EINVAL;
	}

	if (bufsize != old_bufsize) {
		error = log_setsize(bufsize);
	}

	return error;
}

/*
 * This should be called by /sbin/dmesg only via libproc.
 * It returns as much data still in the buffer as possible.
 */
int
log_dmesg(user_addr_t buffer, uint32_t buffersize, int32_t *retval)
{
	uint32_t i;
	uint32_t localbuff_size;
	int error = 0, newl, skip;
	char *localbuff, *p, *copystart, ch;
	size_t copysize;

	bsd_log_lock_safe();
	localbuff_size = (msgbufp->msg_size + 2); /* + '\n' + '\0' */
	bsd_log_unlock();

	/* Allocate a temporary non-circular buffer for copyout */
	localbuff = kalloc_data(localbuff_size, Z_WAITOK);
	if (!localbuff) {
		printf("log_dmesg: unable to allocate memory\n");
		return ENOMEM;
	}

	/* in between here, the log could become bigger, but that's fine */
	bsd_log_lock_safe();

	/*
	 * The message buffer is circular; start at the write pointer, and
	 * make one loop up to write pointer - 1.
	 */
	p = msgbufp->msg_bufc + msgbufp->msg_bufx;
	for (i = newl = skip = 0; p != msgbufp->msg_bufc + msgbufp->msg_bufx - 1; ++p) {
		if (p >= msgbufp->msg_bufc + msgbufp->msg_size) {
			p = msgbufp->msg_bufc;
		}
		ch = *p;
		/* Skip "\n<.*>" syslog sequences. */
		if (skip) {
			if (ch == '>') {
				newl = skip = 0;
			}
			continue;
		}
		if (newl && ch == '<') {
			skip = 1;
			continue;
		}
		if (ch == '\0') {
			continue;
		}
		newl = (ch == '\n');
		localbuff[i++] = ch;
		/* The original version of this routine contained a buffer
		 * overflow. At the time, a "small" targeted fix was desired
		 * so the change below to check the buffer bounds was made.
		 * TODO: rewrite this needlessly convoluted routine.
		 */
		if (i == (localbuff_size - 2)) {
			break;
		}
	}
	if (!newl) {
		localbuff[i++] = '\n';
	}
	localbuff[i++] = 0;

	if (buffersize >= i) {
		copystart = localbuff;
		copysize = i;
	} else {
		copystart = localbuff + i - buffersize;
		copysize = buffersize;
	}

	bsd_log_unlock();

	error = copyout(copystart, buffer, copysize);
	if (!error) {
		*retval = (int32_t)copysize;
	}

	kfree_data(localbuff, localbuff_size);
	return error;
}

#ifdef CONFIG_XNUPOST

size_t find_pattern_in_buffer(const char *, size_t, size_t);

/*
 * returns count of pattern found in systemlog buffer.
 * stops searching further if count reaches expected_count.
 */
size_t
find_pattern_in_buffer(const char *pattern, size_t len, size_t expected_count)
{
	if (pattern == NULL || len == 0 || expected_count == 0) {
		return 0;
	}

	size_t msg_bufx = msgbufp->msg_bufx;
	size_t msg_size = msgbufp->msg_size;
	size_t match_count = 0;

	for (size_t i = 0; i < msg_size; i++) {
		boolean_t match = TRUE;
		for (size_t j = 0; j < len; j++) {
			size_t pos = (msg_bufx + i + j) % msg_size;
			if (msgbufp->msg_bufc[pos] != pattern[j]) {
				match = FALSE;
				break;
			}
		}
		if (match && ++match_count >= expected_count) {
			break;
		}
	}

	return match_count;
}

__startup_func
static void
oslog_init_msgbuf(void)
{
	size_t msgbuf_size = 0;

	if (PE_parse_boot_argn("msgbuf", &msgbuf_size, sizeof(msgbuf_size))) {
		(void) log_setsize(msgbuf_size);
	}
}
STARTUP(OSLOG, STARTUP_RANK_SECOND, oslog_init_msgbuf);

#endif