usr/src/sbin/dmesg/dmesg.c

/*-
 * Copyright (c) 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * %sccs.include.redist.c%
 */

#ifndef lint
static char copyright[] =
"@(#) Copyright (c) 1991, 1993\n\
        The Regents of the University of California.  All rights reserved.\n";
#endif /* not lint */

#ifndef lint
static char sccsid[] = "@(#)dmesg.c     8.1 (Berkeley) %G%";
#endif /* not lint */

#include <sys/cdefs.h>
#include <sys/msgbuf.h>

#include <fcntl.h>
#include <kvm.h>
#include <limits.h>
#include <nlist.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <vis.h>

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

void usage __P((void));

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

int
main(argc, argv)
        int argc;
        char *argv[];
{
        register int ch, newl, skip;
        register char *p, *ep;
        struct msgbuf *bufp, cur;
        char *memf, *nlistf;
        kvm_t *kd;
        char buf[5];

        memf = nlistf = NULL;
        while ((ch = getopt(argc, argv, "M:N:")) != EOF)
                switch(ch) {
                case 'M':
                        memf = optarg;
                        break;
                case 'N':
                        nlistf = optarg;
                        break;
                case '?':
                default:
                        usage();
                }
        argc -= optind;
        argv += optind;

        /*
         * Discard setgid privileges if not the running kernel so that bad
         * guys can't print interesting stuff from kernel memory.
         */
        if (memf != NULL || nlistf != NULL)
                setgid(getgid());

        /* Read in kernel message buffer, do sanity checks. */
        if ((kd = kvm_open(nlistf, memf, NULL, O_RDONLY, "dmesg")) == 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));
        kvm_close(kd);
        if (cur.msg_magic != MSG_MAGIC)
                errx(1, "magic number incorrect");
        if (cur.msg_bufx >= MSG_BSIZE)
                cur.msg_bufx = 0;

        /*
         * The message buffer is circular; start at the read pointer, and
         * go to the write pointer - 1.
         */
        p = cur.msg_bufc + cur.msg_bufx;
        ep = cur.msg_bufc + cur.msg_bufx - 1;
        for (newl = skip = 0; p != ep; ++p) {
                if (p == cur.msg_bufc + MSG_BSIZE)
                        p = cur.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';
                (void)vis(buf, ch, 0, 0);
                if (buf[1] == 0)
                        (void)putchar(buf[0]);
                else
                        (void)printf("%s", buf);
        }
        if (!newl)
                (void)putchar('\n');
        exit(0);
}

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