/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1991, 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.
 */

#include <sys/types.h>
#include <sys/msgbuf.h>
#include <sys/sysctl.h>

#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <kvm.h>
#include <limits.h>
#include <locale.h>
#include <nlist.h>
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <vis.h>
#include <sys/syslog.h>

static struct nlist nl[] = {
#define X_MSGBUF        0
        { "_msgbufp", 0, 0, 0, 0 },
        { NULL, 0, 0, 0, 0 },
};

void usage(void) __dead2;

#define KREAD(addr, var) \
        kvm_read(kd, addr, &var, sizeof(var)) != sizeof(var)

int
main(int argc, char *argv[])
{
        struct msgbuf *bufp, cur;
        char *bp, *ep, *memf, *nextp, *nlistf, *p, *q, *visbp;
        kvm_t *kd;
        size_t buflen, bufpos;
        long pri;
        int ch, clear;
        bool all;

        all = false;
        clear = false;
        (void) setlocale(LC_CTYPE, "");
        memf = nlistf = NULL;
        while ((ch = getopt(argc, argv, "acM:N:")) != -1)
                switch(ch) {
                case 'a':
                        all = true;
                        break;
                case 'c':
                        clear = true;
                        break;
                case 'M':
                        memf = optarg;
                        break;
                case 'N':
                        nlistf = optarg;
                        break;
                case '?':
                default:
                        usage();
                }
        argc -= optind;
        if (argc != 0)
                usage();

        if (memf == NULL) {
                /*
                 * Running kernel.  Use sysctl.  This gives an unwrapped buffer
                 * as a side effect.  Remove nulterm (if present) so the value
                 * returned by sysctl is formatted as the rest of the code
                 * expects (the same as the value read from a core file below).
                 */
                if (sysctlbyname("kern.msgbuf", NULL, &buflen, NULL, 0) == -1)
                        err(1, "sysctl kern.msgbuf");
                /* Allocate extra room for growth between the sysctl calls. */
                buflen += buflen/8;
                /* Allocate more than sysctl sees, for room to append \n\0. */
                if ((bp = malloc(buflen + 2)) == NULL)
                        errx(1, "malloc failed");
                if (sysctlbyname("kern.msgbuf", bp, &buflen, NULL, 0) == -1)
                        err(1, "sysctl kern.msgbuf");
                if (buflen > 0 && bp[buflen - 1] == '\0')
                        buflen--;
                if (clear)
                        if (sysctlbyname("kern.msgbuf_clear", NULL, NULL, &clear, sizeof(int)))
                                err(1, "sysctl kern.msgbuf_clear");
        } else {
                /* Read in kernel message buffer and do sanity checks. */
                kd = kvm_open(nlistf, memf, NULL, O_RDONLY, "dmesg");
                if (kd == NULL)
                        exit (1);
                if (kvm_nlist(kd, nl) == -1)
                        errx(1, "kvm_nlist: %s", kvm_geterr(kd));
                if (nl[X_MSGBUF].n_type == 0)
                        errx(1, "%s: msgbufp not found",
                            nlistf ? nlistf : "namelist");
                if (KREAD(nl[X_MSGBUF].n_value, bufp) || KREAD((long)bufp, cur))
                        errx(1, "kvm_read: %s", kvm_geterr(kd));
                if (cur.msg_magic != MSG_MAGIC)
                        errx(1, "kernel message buffer has different magic "
                            "number");
                if ((bp = malloc(cur.msg_size + 2)) == NULL)
                        errx(1, "malloc failed");

                /* Unwrap the circular buffer to start from the oldest data. */
                bufpos = MSGBUF_SEQ_TO_POS(&cur, cur.msg_wseq);
                if (kvm_read(kd, (long)&cur.msg_ptr[bufpos], bp,
                    cur.msg_size - bufpos) != (ssize_t)(cur.msg_size - bufpos))
                        errx(1, "kvm_read: %s", kvm_geterr(kd));
                if (bufpos != 0 && kvm_read(kd, (long)cur.msg_ptr,
                    &bp[cur.msg_size - bufpos], bufpos) != (ssize_t)bufpos)
                        errx(1, "kvm_read: %s", kvm_geterr(kd));
                kvm_close(kd);
                buflen = cur.msg_size;
        }

        /*
         * Ensure that the buffer ends with a newline and a \0 to avoid
         * complications below.  We left space above.
         */
        if (buflen == 0 || bp[buflen - 1] != '\n')
                bp[buflen++] = '\n';
        bp[buflen] = '\0';

        if ((visbp = malloc(4 * buflen + 1)) == NULL)
                errx(1, "malloc failed");

        /*
         * The message buffer is circular, but has been unwrapped so that
         * the oldest data comes first.  The data will be preceded by \0's
         * if the message buffer was not full.
         */
        p = bp;
        ep = &bp[buflen];
        if (*p == '\0') {
                /* Strip leading \0's */
                while (*p == '\0')
                        p++;
        }
        for (; p < ep; p = nextp) {
                nextp = memchr(p, '\n', ep - p);
                nextp++;

                /* Skip ^<[0-9]+> syslog sequences. */
                if (*p == '<' && isdigit(*(p+1))) {
                        errno = 0;
                        pri = strtol(p + 1, &q, 10);
                        if (*q == '>' && pri >= 0 && pri < INT_MAX &&
                            errno == 0) {
                                if (LOG_FAC(pri) != LOG_KERN && !all)
                                        continue;
                                p = q + 1;
                        }
                }

                (void)strvisx(visbp, p, nextp - p, 0);
                (void)printf("%s", visbp);
        }
        exit(0);
}

void
usage(void)
{
        fprintf(stderr, "usage: dmesg [-ac] [-M core [-N system]]\n");
        exit(1);
}