HAMMER Utilities: Sync with recent work.

[dragonfly.git] / sys / kern / subr_prf.c

/*-
 * Copyright (c) 1986, 1988, 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * 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_prf.c  8.3 (Berkeley) 1/21/94
 * $FreeBSD: src/sys/kern/subr_prf.c,v 1.61.2.5 2002/08/31 18:22:08 dwmalone Exp $
 * $DragonFly: src/sys/kern/subr_prf.c,v 1.20 2008/01/04 12:16:19 matthias Exp $
 */

#include "opt_ddb.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/msgbuf.h>
#include <sys/malloc.h>
#include <sys/proc.h>
#include <sys/tty.h>
#include <sys/tprintf.h>
#include <sys/stdint.h>
#include <sys/syslog.h>
#include <sys/cons.h>
#include <sys/uio.h>
#include <sys/sysctl.h>
#include <sys/lock.h>
#include <sys/ctype.h>

#ifdef DDB
#include <ddb/ddb.h>
#endif

/*
 * Note that stdarg.h and the ANSI style va_start macro is used for both
 * ANSI and traditional C compilers.  We use the __ machine version to stay
 * within the kernel header file set.
 */
#include <machine/stdarg.h>

#define TOCONS  0x01
#define TOTTY   0x02
#define TOLOG   0x04

/* Max number conversion buffer length: a u_quad_t in base 2, plus NUL byte. */
#define MAXNBUF (sizeof(intmax_t) * NBBY + 1)

struct putchar_arg {
        int     flags;
        int     pri;
        struct  tty *tty;
};

struct snprintf_arg {
        char    *str;
        size_t  remain;
};

extern  int log_open;

struct  tty *constty;                   /* pointer to console "window" tty */

static void (*v_putc)(int) = cnputc;    /* routine to putc on virtual console */
static void  msglogchar(int c, int pri);
static void  msgaddchar(int c, void *dummy);
static void  kputchar (int ch, void *arg);
static char *ksprintn (char *nbuf, uintmax_t num, int base, int *lenp,
                       int upper);
static void  snprintf_func (int ch, void *arg);

static int consintr = 1;                /* Ok to handle console interrupts? */
static int msgbufmapped;                /* Set when safe to use msgbuf */
int msgbuftrigger;

static int      log_console_output = 1;
TUNABLE_INT("kern.log_console_output", &log_console_output);
SYSCTL_INT(_kern, OID_AUTO, log_console_output, CTLFLAG_RW,
    &log_console_output, 0, "");

static int unprivileged_read_msgbuf = 1;
SYSCTL_INT(_security, OID_AUTO, unprivileged_read_msgbuf, CTLFLAG_RW,
    &unprivileged_read_msgbuf, 0,
    "Unprivileged processes may read the kernel message buffer");

/*
 * Warn that a system table is full.
 */
void
tablefull(const char *tab)
{

        log(LOG_ERR, "%s: table is full\n", tab);
}

/*
 * Uprintf prints to the controlling terminal for the current process.
 */
int
uprintf(const char *fmt, ...)
{
        struct proc *p = curproc;
        __va_list ap;
        struct putchar_arg pca;
        int retval = 0;

        if (p && p->p_flag & P_CONTROLT &&
            p->p_session->s_ttyvp) {
                __va_start(ap, fmt);
                pca.tty = p->p_session->s_ttyp;
                pca.flags = TOTTY;

                retval = kvcprintf(fmt, kputchar, &pca, 10, ap);
                __va_end(ap);
        }
        return (retval);
}

tpr_t
tprintf_open(struct proc *p)
{

        if ((p->p_flag & P_CONTROLT) && p->p_session->s_ttyvp) {
                sess_hold(p->p_session);
                return ((tpr_t) p->p_session);
        }
        return ((tpr_t) NULL);
}

void
tprintf_close(tpr_t sess)
{
        if (sess)
                sess_rele((struct session *) sess);
}

/*
 * tprintf prints on the controlling terminal associated
 * with the given session.
 */
int
tprintf(tpr_t tpr, const char *fmt, ...)
{
        struct session *sess = (struct session *)tpr;
        struct tty *tp = NULL;
        int flags = TOLOG;
        __va_list ap;
        struct putchar_arg pca;
        int retval;

        if (sess && sess->s_ttyvp && ttycheckoutq(sess->s_ttyp, 0)) {
                flags |= TOTTY;
                tp = sess->s_ttyp;
        }
        __va_start(ap, fmt);
        pca.tty = tp;
        pca.flags = flags;
        pca.pri = LOG_INFO;
        retval = kvcprintf(fmt, kputchar, &pca, 10, ap);
        __va_end(ap);
        msgbuftrigger = 1;
        return (retval);
}

/*
 * Ttyprintf displays a message on a tty; it should be used only by
 * the tty driver, or anything that knows the underlying tty will not
 * be revoke(2)'d away.  Other callers should use tprintf.
 */
int
ttyprintf(struct tty *tp, const char *fmt, ...)
{
        __va_list ap;
        struct putchar_arg pca;
        int retval;

        __va_start(ap, fmt);
        pca.tty = tp;
        pca.flags = TOTTY;
        retval = kvcprintf(fmt, kputchar, &pca, 10, ap);
        __va_end(ap);
        return (retval);
}

/*
 * Log writes to the log buffer, and guarantees not to sleep (so can be
 * called by interrupt routines).  If there is no process reading the
 * log yet, it writes to the console also.
 */
int
log(int level, const char *fmt, ...)
{
        __va_list ap;
        int retval;
        struct putchar_arg pca;

        pca.tty = NULL;
        pca.pri = level;
        pca.flags = log_open ? TOLOG : TOCONS;

        __va_start(ap, fmt);
        retval = kvcprintf(fmt, kputchar, &pca, 10, ap);
        __va_end(ap);

        msgbuftrigger = 1;
        return (retval);
}

#define CONSCHUNK 128

void
log_console(struct uio *uio)
{
        int c, i, error, iovlen, nl;
        struct uio muio;
        struct iovec *miov = NULL;
        char *consbuffer;
        int pri;

        if (!log_console_output)
                return;

        pri = LOG_INFO | LOG_CONSOLE;
        muio = *uio;
        iovlen = uio->uio_iovcnt * sizeof (struct iovec);
        MALLOC(miov, struct iovec *, iovlen, M_TEMP, M_WAITOK);
        MALLOC(consbuffer, char *, CONSCHUNK, M_TEMP, M_WAITOK);
        bcopy((caddr_t)muio.uio_iov, (caddr_t)miov, iovlen);
        muio.uio_iov = miov;
        uio = &muio;

        nl = 0;
        while (uio->uio_resid > 0) {
                c = imin(uio->uio_resid, CONSCHUNK);
                error = uiomove(consbuffer, c, uio);
                if (error != 0)
                        break;
                for (i = 0; i < c; i++) {
                        msglogchar(consbuffer[i], pri);
                        if (consbuffer[i] == '\n')
                                nl = 1;
                        else
                                nl = 0;
                }
        }
        if (!nl)
                msglogchar('\n', pri);
        msgbuftrigger = 1;
        FREE(miov, M_TEMP);
        FREE(consbuffer, M_TEMP);
        return;
}

/*
 * Output to the console.
 *
 * NOT YET ENTIRELY MPSAFE
 */
int
kprintf(const char *fmt, ...)
{
        __va_list ap;
        int savintr;
        struct putchar_arg pca;
        int retval;

        savintr = consintr;             /* disable interrupts */
        consintr = 0;
        __va_start(ap, fmt);
        pca.tty = NULL;
        pca.flags = TOCONS | TOLOG;
        pca.pri = -1;
        cons_lock();
        retval = kvcprintf(fmt, kputchar, &pca, 10, ap);
        cons_unlock();
        __va_end(ap);
        if (!panicstr)
                msgbuftrigger = 1;
        consintr = savintr;             /* reenable interrupts */
        return (retval);
}

int
kvprintf(const char *fmt, __va_list ap)
{
        int savintr;
        struct putchar_arg pca;
        int retval;

        savintr = consintr;             /* disable interrupts */
        consintr = 0;
        pca.tty = NULL;
        pca.flags = TOCONS | TOLOG;
        pca.pri = -1;
        cons_lock();
        retval = kvcprintf(fmt, kputchar, &pca, 10, ap);
        cons_unlock();
        if (!panicstr)
                msgbuftrigger = 1;
        consintr = savintr;             /* reenable interrupts */
        return (retval);
}

/*
 * Limited rate kprintf.  The passed rate structure must be initialized
 * with the desired reporting frequency.  A frequency of 0 will result in
 * no output.
 */
void
krateprintf(struct krate *rate, const char *fmt, ...)
{
        __va_list ap;

        if (rate->ticks != (int)time_second) {
                rate->ticks = (int)time_second;
                rate->count = 0;
        }
        if (rate->count < rate->freq) {
                ++rate->count;
                __va_start(ap, fmt);
                kvprintf(fmt, ap);
                __va_end(ap);
        }
}

/*
 * Print a character on console or users terminal.  If destination is
 * the console then the last bunch of characters are saved in msgbuf for
 * inspection later.
 *
 * NOT YET ENTIRELY MPSAFE, EVEN WHEN LOGGING JUST TO THE SYSCONSOLE.
 */
static void
kputchar(int c, void *arg)
{
        struct putchar_arg *ap = (struct putchar_arg*) arg;
        int flags = ap->flags;
        struct tty *tp = ap->tty;
        if (panicstr)
                constty = NULL;
        if ((flags & TOCONS) && tp == NULL && constty) {
                tp = constty;
                flags |= TOTTY;
        }
        if ((flags & TOTTY) && tp && tputchar(c, tp) < 0 &&
            (flags & TOCONS) && tp == constty)
                constty = NULL;
        if ((flags & TOLOG))
                msglogchar(c, ap->pri);
        if ((flags & TOCONS) && constty == NULL && c != '\0')
                (*v_putc)(c);
}

/*
 * Scaled down version of sprintf(3).
 */
int
ksprintf(char *buf, const char *cfmt, ...)
{
        int retval;
        __va_list ap;

        __va_start(ap, cfmt);
        retval = kvcprintf(cfmt, NULL, (void *)buf, 10, ap);
        buf[retval] = '\0';
        __va_end(ap);
        return (retval);
}

/*
 * Scaled down version of vsprintf(3).
 */
int
kvsprintf(char *buf, const char *cfmt, __va_list ap)
{
        int retval;

        retval = kvcprintf(cfmt, NULL, (void *)buf, 10, ap);
        buf[retval] = '\0';
        return (retval);
}

/*
 * Scaled down version of snprintf(3).
 */
int
ksnprintf(char *str, size_t size, const char *format, ...)
{
        int retval;
        __va_list ap;

        __va_start(ap, format);
        retval = kvsnprintf(str, size, format, ap);
        __va_end(ap);
        return(retval);
}

/*
 * Scaled down version of vsnprintf(3).
 */
int
kvsnprintf(char *str, size_t size, const char *format, __va_list ap)
{
        struct snprintf_arg info;
        int retval;

        info.str = str;
        info.remain = size;
        retval = kvcprintf(format, snprintf_func, &info, 10, ap);
        if (info.remain >= 1)
                *info.str++ = '\0';
        return (retval);
}

static void
snprintf_func(int ch, void *arg)
{
        struct snprintf_arg *const info = arg;

        if (info->remain >= 2) {
                *info->str++ = ch;
                info->remain--;
        }
}

/*
 * Put a NUL-terminated ASCII number (base <= 36) in a buffer in reverse
 * order; return an optional length and a pointer to the last character
 * written in the buffer (i.e., the first character of the string).
 * The buffer pointed to by `nbuf' must have length >= MAXNBUF.
 */
static char *
ksprintn(char *nbuf, uintmax_t num, int base, int *lenp, int upper)
{
        char *p, c;

        p = nbuf;
        *p = '\0';
        do {
                c = hex2ascii(num % base);
                *++p = upper ? toupper(c) : c;
        } while (num /= base);
        if (lenp)
                *lenp = p - nbuf;
        return (p);
}

/*
 * Scaled down version of printf(3).
 *
 * Two additional formats:
 *
 * The format %b is supported to decode error registers.
 * Its usage is:
 *
 *      kprintf("reg=%b\n", regval, "<base><arg>*");
 *
 * where <base> is the output base expressed as a control character, e.g.
 * \10 gives octal; \20 gives hex.  Each arg is a sequence of characters,
 * the first of which gives the bit number to be inspected (origin 1), and
 * the next characters (up to a control character, i.e. a character <= 32),
 * give the name of the register.  Thus:
 *
 *      kvcprintf("reg=%b\n", 3, "\10\2BITTWO\1BITONE\n");
 *
 * would produce output:
 *
 *      reg=3<BITTWO,BITONE>
 *
 * XXX:  %D  -- Hexdump, takes pointer and separator string:
 *              ("%6D", ptr, ":")   -> XX:XX:XX:XX:XX:XX
 *              ("%*D", len, ptr, " " -> XX XX XX XX ...
 */
int
kvcprintf(char const *fmt, void (*func)(int, void*), void *arg, int radix, __va_list ap)
{
#define PCHAR(c) {int cc=(c); if (func) (*func)(cc,arg); else *d++ = cc; retval++; }
        char nbuf[MAXNBUF];
        char *d;
        const char *p, *percent, *q;
        u_char *up;
        int ch, n;
        uintmax_t num;
        int base, tmp, width, ladjust, sharpflag, neg, sign, dot;
        int jflag, lflag, qflag, tflag;
        int dwidth, upper;
        char padc;
        int retval = 0, stop = 0;

        num = 0;
        if (!func)
                d = (char *) arg;
        else
                d = NULL;

        if (fmt == NULL)
                fmt = "(fmt null)\n";

        if (radix < 2 || radix > 36)
                radix = 10;

        for (;;) {
                padc = ' ';
                width = 0;
                while ((ch = (u_char)*fmt++) != '%' || stop) {
                        if (ch == '\0')
                                return (retval);
                        PCHAR(ch);
                }
                percent = fmt - 1;
                dot = dwidth = ladjust = neg = sharpflag = sign = upper = 0;
                jflag = lflag = qflag = tflag = 0;

reswitch:
                switch (ch = (u_char)*fmt++) {
                case '.':
                        dot = 1;
                        goto reswitch;
                case '#':
                        sharpflag = 1;
                        goto reswitch;
                case '+':
                        sign = 1;
                        goto reswitch;
                case '-':
                        ladjust = 1;
                        goto reswitch;
                case '%':
                        PCHAR(ch);
                        break;
                case '*':
                        if (!dot) {
                                width = __va_arg(ap, int);
                                if (width < 0) {
                                        ladjust = !ladjust;
                                        width = -width;
                                }
                        } else {
                                dwidth = __va_arg(ap, int);
                        }
                        goto reswitch;
                case '0':
                        if (!dot) {
                                padc = '0';
                                goto reswitch;
                        }
                case '1': case '2': case '3': case '4':
                case '5': case '6': case '7': case '8': case '9':
                                for (n = 0;; ++fmt) {
                                        n = n * 10 + ch - '0';
                                        ch = *fmt;
                                        if (ch < '0' || ch > '9')
                                                break;
                                }
                        if (dot)
                                dwidth = n;
                        else
                                width = n;
                        goto reswitch;
                case 'b':
                        num = (u_int)__va_arg(ap, int);
                        p = __va_arg(ap, char *);
                        for (q = ksprintn(nbuf, num, *p++, NULL, 0); *q;)
                                PCHAR(*q--);

                        if (num == 0)
                                break;

                        for (tmp = 0; *p;) {
                                n = *p++;
                                if (num & (1 << (n - 1))) {
                                        PCHAR(tmp ? ',' : '<');
                                        for (; (n = *p) > ' '; ++p)
                                                PCHAR(n);
                                        tmp = 1;
                                } else
                                        for (; *p > ' '; ++p)
                                                continue;
                        }
                        if (tmp)
                                PCHAR('>');
                        break;
                case 'c':
                        PCHAR(__va_arg(ap, int));
                        break;
                case 'D':
                        up = __va_arg(ap, u_char *);
                        p = __va_arg(ap, char *);
                        if (!width)
                                width = 16;
                        while(width--) {
                                PCHAR(hex2ascii(*up >> 4));
                                PCHAR(hex2ascii(*up & 0x0f));
                                up++;
                                if (width)
                                        for (q=p;*q;q++)
                                                PCHAR(*q);
                        }
                        break;
                case 'd':
                case 'i':
                        base = 10;
                        sign = 1;
                        goto handle_sign;
                case 'j':
                        jflag = 1;
                        goto reswitch;
                case 'l':
                        if (lflag) {
                                lflag = 0;
                                qflag = 1;
                        } else
                                lflag = 1;
                        goto reswitch;
                case 'n':
                        if (jflag)
                                *(__va_arg(ap, intmax_t *)) = retval;
                        else if (lflag)
                                *(__va_arg(ap, long *)) = retval;
                        else if (qflag)
                                *(__va_arg(ap, quad_t *)) = retval;
                        else
                                *(__va_arg(ap, int *)) = retval;
                        break;
                case 'o':
                        base = 8;
                        goto handle_nosign;
                case 'p':
                        base = 16;
                        sharpflag = (width == 0);
                        sign = 0;
                        num = (uintptr_t)__va_arg(ap, void *);
                        goto number;
                case 'q':
                        qflag = 1;
                        goto reswitch;
                case 'r':
                        base = radix;
                        if (sign)
                                goto handle_sign;
                        goto handle_nosign;
                case 's':
                        p = __va_arg(ap, char *);
                        if (p == NULL)
                                p = "(null)";
                        if (!dot)
                                n = strlen (p);
                        else
                                for (n = 0; n < dwidth && p[n]; n++)
                                        continue;

                        width -= n;

                        if (!ladjust && width > 0)
                                while (width--)
                                        PCHAR(padc);
                        while (n--)
                                PCHAR(*p++);
                        if (ladjust && width > 0)
                                while (width--)
                                        PCHAR(padc);
                        break;
                case 't':
                        tflag = 1;
                        goto reswitch;
                case 'u':
                        base = 10;
                        goto handle_nosign;
                case 'X':
                        upper = 1;
                        /* FALLTHROUGH */
                case 'x':
                        base = 16;
                        goto handle_nosign;
                case 'z':
                        base = 16;
                        sign = 1;
                        goto handle_sign;
handle_nosign:
                        sign = 0;
                        if (jflag)
                                num = __va_arg(ap, uintmax_t);
                        else if (lflag)
                                num = __va_arg(ap, u_long);
                        else if (qflag)
                                num = __va_arg(ap, u_quad_t);
                        else if (tflag)
                                num = __va_arg(ap, ptrdiff_t);
                        else
                                num = __va_arg(ap, u_int);
                        goto number;
handle_sign:
                        if (jflag)
                                num = __va_arg(ap, intmax_t);
                        else if (lflag)
                                num = __va_arg(ap, long);
                        else if (qflag)
                                num = __va_arg(ap, quad_t);
                        else if (tflag)
                                num = __va_arg(ap, ptrdiff_t);
                        else
                                num = __va_arg(ap, int);
number:
                        if (sign && (intmax_t)num < 0) {
                                neg = 1;
                                num = -(intmax_t)num;
                        }
                        p = ksprintn(nbuf, num, base, &tmp, upper);
                        if (sharpflag && num != 0) {
                                if (base == 8)
                                        tmp++;
                                else if (base == 16)
                                        tmp += 2;
                        }
                        if (neg)
                                tmp++;

                        if (!ladjust && padc != '0' && width &&
                            (width -= tmp) > 0) {
                                while (width--)
                                        PCHAR(padc);
                        }
                        if (neg)
                                PCHAR('-');
                        if (sharpflag && num != 0) {
                                if (base == 8) {
                                        PCHAR('0');
                                } else if (base == 16) {
                                        PCHAR('0');
                                        PCHAR('x');
                                }
                        }
                        if (!ladjust && width && (width -= tmp) > 0)
                                while (width--)
                                        PCHAR(padc);

                        while (*p)
                                PCHAR(*p--);

                        if (ladjust && width && (width -= tmp) > 0)
                                while (width--)
                                        PCHAR(padc);

                        break;
                default:
                        while (percent < fmt)
                                PCHAR(*percent++);
                        /*
                         * Since we ignore an formatting argument it is no 
                         * longer safe to obey the remaining formatting
                         * arguments as the arguments will no longer match
                         * the format specs.
                         */
                        stop = 1;
                        break;
                }
        }
#undef PCHAR
}

/*
 * Put character in log buffer with a particular priority.
 *
 * MPSAFE
 */
static void
msglogchar(int c, int pri)
{
        static int lastpri = -1;
        static int dangling;
        char nbuf[MAXNBUF];
        char *p;

        if (!msgbufmapped)
                return;
        if (c == '\0' || c == '\r')
                return;
        if (pri != -1 && pri != lastpri) {
                if (dangling) {
                        msgaddchar('\n', NULL);
                        dangling = 0;
                }
                msgaddchar('<', NULL);
                for (p = ksprintn(nbuf, (uintmax_t)pri, 10, NULL, 0); *p;)
                        msgaddchar(*p--, NULL);
                msgaddchar('>', NULL);
                lastpri = pri;
        }
        msgaddchar(c, NULL);
        if (c == '\n') {
                dangling = 0;
                lastpri = -1;
        } else {
                dangling = 1;
        }
}

/*
 * Put char in log buffer.   Make sure nothing blows up beyond repair if
 * we have an MP race.
 *
 * MPSAFE.
 */
static void
msgaddchar(int c, void *dummy)
{
        struct msgbuf *mbp;
        int rindex;
        int windex;

        if (!msgbufmapped)
                return;
        mbp = msgbufp;
        windex = mbp->msg_bufx;
        mbp->msg_ptr[windex] = c;
        if (++windex >= mbp->msg_size)
                windex = 0;
        rindex = mbp->msg_bufr;
        if (windex == rindex) {
                rindex += 32;
                if (rindex >= mbp->msg_size)
                        rindex -= mbp->msg_size;
                mbp->msg_bufr = rindex;
        }
        mbp->msg_bufx = windex;
}

static void
msgbufcopy(struct msgbuf *oldp)
{
        int pos;

        pos = oldp->msg_bufr;
        while (pos != oldp->msg_bufx) {
                msglogchar(oldp->msg_ptr[pos], -1);
                if (++pos >= oldp->msg_size)
                        pos = 0;
        }
}

void
msgbufinit(void *ptr, size_t size)
{
        char *cp;
        static struct msgbuf *oldp = NULL;

        size -= sizeof(*msgbufp);
        cp = (char *)ptr;
        msgbufp = (struct msgbuf *) (cp + size);
        if (msgbufp->msg_magic != MSG_MAGIC || msgbufp->msg_size != size ||
            msgbufp->msg_bufx >= size || msgbufp->msg_bufr >= size) {
                bzero(cp, size);
                bzero(msgbufp, sizeof(*msgbufp));
                msgbufp->msg_magic = MSG_MAGIC;
                msgbufp->msg_size = (char *)msgbufp - cp;
        }
        msgbufp->msg_ptr = cp;
        if (msgbufmapped && oldp != msgbufp)
                msgbufcopy(oldp);
        msgbufmapped = 1;
        oldp = msgbufp;
}

/* Sysctls for accessing/clearing the msgbuf */

static int
sysctl_kern_msgbuf(SYSCTL_HANDLER_ARGS)
{
        struct ucred *cred;
        int error;

        /*
         * Only wheel or root can access the message log.
         */
        if (unprivileged_read_msgbuf == 0) {
                KKASSERT(req->td->td_proc);
                cred = req->td->td_proc->p_ucred;

                if ((cred->cr_prison || groupmember(0, cred) == 0) &&
                    suser(req->td) != 0
                ) {
                        return (EPERM);
                }
        }

        /*
         * Unwind the buffer, so that it's linear (possibly starting with
         * some initial nulls).
         */
        error = sysctl_handle_opaque(oidp, msgbufp->msg_ptr + msgbufp->msg_bufx,
            msgbufp->msg_size - msgbufp->msg_bufx, req);
        if (error)
                return (error);
        if (msgbufp->msg_bufx > 0) {
                error = sysctl_handle_opaque(oidp, msgbufp->msg_ptr,
                    msgbufp->msg_bufx, req);
        }
        return (error);
}

SYSCTL_PROC(_kern, OID_AUTO, msgbuf, CTLTYPE_STRING | CTLFLAG_RD,
    0, 0, sysctl_kern_msgbuf, "A", "Contents of kernel message buffer");

static int msgbuf_clear;

static int
sysctl_kern_msgbuf_clear(SYSCTL_HANDLER_ARGS)
{
        int error;
        error = sysctl_handle_int(oidp, oidp->oid_arg1, oidp->oid_arg2, req);
        if (!error && req->newptr) {
                /* Clear the buffer and reset write pointer */
                bzero(msgbufp->msg_ptr, msgbufp->msg_size);
                msgbufp->msg_bufr = msgbufp->msg_bufx = 0;
                msgbuf_clear = 0;
        }
        return (error);
}

SYSCTL_PROC(_kern, OID_AUTO, msgbuf_clear,
    CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_SECURE, &msgbuf_clear, 0,
    sysctl_kern_msgbuf_clear, "I", "Clear kernel message buffer");

#ifdef DDB

DB_SHOW_COMMAND(msgbuf, db_show_msgbuf)
{
        int i, j;

        if (!msgbufmapped) {
                db_printf("msgbuf not mapped yet\n");
                return;
        }
        db_printf("msgbufp = %p\n", msgbufp);
        db_printf("magic = %x, size = %d, r= %d, w = %d, ptr = %p\n",
            msgbufp->msg_magic, msgbufp->msg_size, msgbufp->msg_bufr,
            msgbufp->msg_bufx, msgbufp->msg_ptr);
        for (i = 0; i < msgbufp->msg_size; i++) {
                j = (i + msgbufp->msg_bufr) % msgbufp->msg_size;
                db_printf("%c", msgbufp->msg_ptr[j]);
        }
        db_printf("\n");
}

#endif /* DDB */