1/*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1991, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the University nor the names of its contributors
16 *    may be used to endorse or promote products derived from this software
17 *    without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 */
31
32#include <sys/types.h>
33#include <sys/msgbuf.h>
34#include <sys/sysctl.h>
35
36#include <ctype.h>
37#include <err.h>
38#include <errno.h>
39#include <fcntl.h>
40#include <kvm.h>
41#include <limits.h>
42#include <locale.h>
43#include <nlist.h>
44#include <stdio.h>
45#include <stdbool.h>
46#include <stdlib.h>
47#include <string.h>
48#include <unistd.h>
49#include <vis.h>
50#include <sys/syslog.h>
51
52static struct nlist nl[] = {
53#define	X_MSGBUF	0
54	{ "_msgbufp", 0, 0, 0, 0 },
55	{ NULL, 0, 0, 0, 0 },
56};
57
58void usage(void) __dead2;
59
60#define	KREAD(addr, var) \
61	kvm_read(kd, addr, &var, sizeof(var)) != sizeof(var)
62
63int
64main(int argc, char *argv[])
65{
66	struct msgbuf *bufp, cur;
67	char *bp, *ep, *memf, *nextp, *nlistf, *p, *q, *visbp;
68	kvm_t *kd;
69	size_t buflen, bufpos;
70	long pri;
71	int ch, clear;
72	bool all;
73
74	all = false;
75	clear = false;
76	(void) setlocale(LC_CTYPE, "");
77	memf = nlistf = NULL;
78	while ((ch = getopt(argc, argv, "acM:N:")) != -1)
79		switch(ch) {
80		case 'a':
81			all = true;
82			break;
83		case 'c':
84			clear = true;
85			break;
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	if (argc != 0)
98		usage();
99
100	if (memf == NULL) {
101		/*
102		 * Running kernel.  Use sysctl.  This gives an unwrapped buffer
103		 * as a side effect.  Remove nulterm (if present) so the value
104		 * returned by sysctl is formatted as the rest of the code
105		 * expects (the same as the value read from a core file below).
106		 */
107		if (sysctlbyname("kern.msgbuf", NULL, &buflen, NULL, 0) == -1)
108			err(1, "sysctl kern.msgbuf");
109		/* Allocate extra room for growth between the sysctl calls. */
110		buflen += buflen/8;
111		/* Allocate more than sysctl sees, for room to append \n\0. */
112		if ((bp = malloc(buflen + 2)) == NULL)
113			errx(1, "malloc failed");
114		if (sysctlbyname("kern.msgbuf", bp, &buflen, NULL, 0) == -1)
115			err(1, "sysctl kern.msgbuf");
116		if (buflen > 0 && bp[buflen - 1] == '\0')
117			buflen--;
118		if (clear)
119			if (sysctlbyname("kern.msgbuf_clear", NULL, NULL, &clear, sizeof(int)))
120				err(1, "sysctl kern.msgbuf_clear");
121	} else {
122		/* Read in kernel message buffer and do sanity checks. */
123		kd = kvm_open(nlistf, memf, NULL, O_RDONLY, "dmesg");
124		if (kd == NULL)
125			exit (1);
126		if (kvm_nlist(kd, nl) == -1)
127			errx(1, "kvm_nlist: %s", kvm_geterr(kd));
128		if (nl[X_MSGBUF].n_type == 0)
129			errx(1, "%s: msgbufp not found",
130			    nlistf ? nlistf : "namelist");
131		if (KREAD(nl[X_MSGBUF].n_value, bufp) || KREAD((long)bufp, cur))
132			errx(1, "kvm_read: %s", kvm_geterr(kd));
133		if (cur.msg_magic != MSG_MAGIC)
134			errx(1, "kernel message buffer has different magic "
135			    "number");
136		if ((bp = malloc(cur.msg_size + 2)) == NULL)
137			errx(1, "malloc failed");
138
139		/* Unwrap the circular buffer to start from the oldest data. */
140		bufpos = MSGBUF_SEQ_TO_POS(&cur, cur.msg_wseq);
141		if (kvm_read(kd, (long)&cur.msg_ptr[bufpos], bp,
142		    cur.msg_size - bufpos) != (ssize_t)(cur.msg_size - bufpos))
143			errx(1, "kvm_read: %s", kvm_geterr(kd));
144		if (bufpos != 0 && kvm_read(kd, (long)cur.msg_ptr,
145		    &bp[cur.msg_size - bufpos], bufpos) != (ssize_t)bufpos)
146			errx(1, "kvm_read: %s", kvm_geterr(kd));
147		kvm_close(kd);
148		buflen = cur.msg_size;
149	}
150
151	/*
152	 * Ensure that the buffer ends with a newline and a \0 to avoid
153	 * complications below.  We left space above.
154	 */
155	if (buflen == 0 || bp[buflen - 1] != '\n')
156		bp[buflen++] = '\n';
157	bp[buflen] = '\0';
158
159	if ((visbp = malloc(4 * buflen + 1)) == NULL)
160		errx(1, "malloc failed");
161
162	/*
163	 * The message buffer is circular, but has been unwrapped so that
164	 * the oldest data comes first.  The data will be preceded by \0's
165	 * if the message buffer was not full.
166	 */
167	p = bp;
168	ep = &bp[buflen];
169	if (*p == '\0') {
170		/* Strip leading \0's */
171		while (*p == '\0')
172			p++;
173	}
174	for (; p < ep; p = nextp) {
175		nextp = memchr(p, '\n', ep - p);
176		nextp++;
177
178		/* Skip ^<[0-9]+> syslog sequences. */
179		if (*p == '<' && isdigit(*(p+1))) {
180			errno = 0;
181			pri = strtol(p + 1, &q, 10);
182			if (*q == '>' && pri >= 0 && pri < INT_MAX &&
183			    errno == 0) {
184				if (LOG_FAC(pri) != LOG_KERN && !all)
185					continue;
186				p = q + 1;
187			}
188		}
189
190		(void)strvisx(visbp, p, nextp - p, 0);
191		(void)printf("%s", visbp);
192	}
193	exit(0);
194}
195
196void
197usage(void)
198{
199	fprintf(stderr, "usage: dmesg [-ac] [-M core [-N system]]\n");
200	exit(1);
201}
202