dmesg.c revision 36634 
1/*-
2 * Copyright (c) 1991, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 *    must display the following acknowledgement:
15 *	This product includes software developed by the University of
16 *	California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34#ifndef lint
35static const char copyright[] =
36"@(#) Copyright (c) 1991, 1993\n\
37	The Regents of the University of California.  All rights reserved.\n";
38#endif /* not lint */
39
40#ifndef lint
41#if 0
42static const char sccsid[] = "@(#)dmesg.c	8.1 (Berkeley) 6/5/93";
43#endif
44static const char rcsid[] =
45	"$Id: dmesg.c,v 1.8 1998/05/19 08:58:53 phk Exp $";
46#endif /* not lint */
47
48#include <sys/msgbuf.h>
49
50#include <err.h>
51#include <fcntl.h>
52#include <kvm.h>
53#include <locale.h>
54#include <stdio.h>
55#include <stdlib.h>
56#include <unistd.h>
57#include <vis.h>
58
59struct nlist nl[] = {
60#define	X_MSGBUF	0
61	{ "_msgbufp" },
62	{ NULL },
63};
64
65void usage __P((void));
66
67#define	KREAD(addr, var) \
68	kvm_read(kd, addr, &var, sizeof(var)) != sizeof(var)
69
70int
71main(argc, argv)
72	int argc;
73	char *argv[];
74{
75	register int ch, newl, skip;
76	register char *p, *ep;
77	struct msgbuf *bufp, cur;
78	char *bp, *memf, *nlistf;
79	kvm_t *kd;
80	char buf[5];
81
82	(void) setlocale(LC_CTYPE, "");
83	memf = nlistf = NULL;
84	while ((ch = getopt(argc, argv, "M:N:")) != -1)
85		switch(ch) {
86		case 'M':
87			memf = optarg;
88			break;
89		case 'N':
90			nlistf = optarg;
91			break;
92		case '?':
93		default:
94			usage();
95		}
96	argc -= optind;
97	argv += optind;
98
99	/*
100	 * Discard setgid privileges if not the running kernel so that bad
101	 * guys can't print interesting stuff from kernel memory.
102	 */
103	if (memf != NULL || nlistf != NULL)
104		setgid(getgid());
105
106	/* Read in kernel message buffer, do sanity checks. */
107	if ((kd = kvm_open(nlistf, memf, NULL, O_RDONLY, "dmesg")) == NULL)
108		exit (1);
109	if (kvm_nlist(kd, nl) == -1)
110		errx(1, "kvm_nlist: %s", kvm_geterr(kd));
111	if (nl[X_MSGBUF].n_type == 0)
112		errx(1, "%s: msgbufp not found", nlistf ? nlistf : "namelist");
113	if (KREAD(nl[X_MSGBUF].n_value, bufp) || KREAD((long)bufp, cur))
114		errx(1, "kvm_read: %s", kvm_geterr(kd));
115	if (cur.msg_magic != MSG_MAGIC)
116		errx(1, "magic number incorrect");
117	bp = malloc(cur.msg_size);
118	if (!bp)
119		errx(1, "malloc failed");
120	if (kvm_read(kd, (long)cur.msg_ptr, bp, cur.msg_size) !=
121	    cur.msg_size)
122		errx(1, "kvm_read: %s", kvm_geterr(kd));
123	if (cur.msg_bufx >= cur.msg_size)
124		cur.msg_bufx = 0;
125	kvm_close(kd);
126
127	/*
128	 * The message buffer is circular.  If the buffer has wrapped, the
129	 * write pointer points to the oldest data.  Otherwise, the write
130	 * pointer points to \0's following the data.  Read the entire
131	 * buffer starting at the write pointer and ignore nulls so that
132	 * we effectively start at the oldest data.
133	 */
134	p = bp + cur.msg_bufx;
135	ep = (cur.msg_bufx == 0 ? bp + cur.msg_size : p);
136	newl = skip = 0;
137	do {
138		if (p == bp + cur.msg_size)
139			p = bp;
140		ch = *p;
141		/* Skip "\n<.*>" syslog sequences. */
142		if (skip) {
143			if (ch == '>')
144				newl = skip = 0;
145			continue;
146		}
147		if (newl && ch == '<') {
148			skip = 1;
149			continue;
150		}
151		if (ch == '\0')
152			continue;
153		newl = ch == '\n';
154		(void)vis(buf, ch, 0, 0);
155		if (buf[1] == 0)
156			(void)putchar(buf[0]);
157		else
158			(void)printf("%s", buf);
159	} while (++p != ep);
160	if (!newl)
161		(void)putchar('\n');
162	exit(0);
163}
164
165void
166usage()
167{
168	(void)fprintf(stderr, "usage: dmesg [-M core] [-N system]\n");
169	exit(1);
170}
171