xref: /freebsd/sbin/dmesg/dmesg.c (revision ae477ca7da55f76d28859e1bd01cd1051e36f28f)
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 
52 static struct nlist nl[] = {
53 #define	X_MSGBUF	0
54 	{ "_msgbufp", 0, 0, 0, 0 },
55 	{ NULL, 0, 0, 0, 0 },
56 };
57 
58 void usage(void) __dead2;
59 
60 #define	KREAD(addr, var) \
61 	kvm_read(kd, addr, &var, sizeof(var)) != sizeof(var)
62 
63 int
64 main(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 
196 void
197 usage(void)
198 {
199 	fprintf(stderr, "usage: dmesg [-ac] [-M core [-N system]]\n");
200 	exit(1);
201 }
202