1 /* dmesg.c - display/control kernel ring buffer.
2 *
3 * Copyright 2006, 2007 Rob Landley <rob@landley.net>
4 *
5 * http://refspecs.linuxfoundation.org/LSB_4.1.0/LSB-Core-generic/LSB-Core-generic/dmesg.html
6
7 // We care that FLAG_c is 1, so keep c at the end.
8 USE_DMESG(NEWTOY(dmesg, "w(follow)Ctrs#<1n#c[!tr][!Cc]", TOYFLAG_BIN))
9
10 config DMESG
11 bool "dmesg"
12 default n
13 help
14 usage: dmesg [-Cc] [-r|-t] [-n LEVEL] [-s SIZE] [-w]
15
16 Print or control the kernel ring buffer.
17
18 -C Clear ring buffer without printing
19 -c Clear ring buffer after printing
20 -n Set kernel logging LEVEL (1-9)
21 -r Raw output (with <level markers>)
22 -s Show the last SIZE many bytes
23 -t Don't print kernel's timestamps
24 -w Keep waiting for more output (aka --follow)
25 */
26
27 #define FOR_dmesg
28 #include "toys.h"
29 #include <sys/klog.h>
30
GLOBALS(long level;long size;int color;)31 GLOBALS(
32 long level;
33 long size;
34
35 int color;
36 )
37
38 static int xklogctl(int type, char *buf, int len)
39 {
40 int rc = klogctl(type, buf, len);
41
42 if (rc<0) perror_exit("klogctl");
43
44 return rc;
45 }
46
47 // Use klogctl for reading if we're on a pre-3.5 kernel.
legacy_mode()48 static void legacy_mode()
49 {
50 char *data, *to, *from;
51 int size;
52
53 // Figure out how much data we need, and fetch it.
54 if (!(size = TT.size)) size = xklogctl(10, 0, 0);
55 data = to = from = xmalloc(size+1);
56 data[size = xklogctl(3 + (toys.optflags & FLAG_c), data, size)] = 0;
57
58 // Filter out level markers and optionally time markers
59 if (!(toys.optflags & FLAG_r)) while ((from - data) < size) {
60 if (from == data || from[-1] == '\n') {
61 char *to;
62
63 if (*from == '<' && (to = strchr(from, '>'))) from = ++to;
64 if ((toys.optflags&FLAG_t) && *from == '[' && (to = strchr(from, ']')))
65 from = to+1+(to[1]==' ');
66 }
67 *(to++) = *(from++);
68 } else to = data+size;
69
70 // Write result. The odds of somebody requesting a buffer of size 3 and
71 // getting "<1>" are remote, but don't segfault if they do.
72 if (to != data) {
73 xwrite(1, data, to-data);
74 if (to[-1] != '\n') xputc('\n');
75 }
76 if (CFG_TOYBOX_FREE) free(data);
77 }
78
color(int c)79 static void color(int c)
80 {
81 if (TT.color) printf("\033[%dm", c);
82 }
83
print_all(void)84 static void print_all(void)
85 {
86 // http://kernel.org/doc/Documentation/ABI/testing/dev-kmsg
87
88 // Each read returns one message. By default, we block when there are no
89 // more messages (--follow); O_NONBLOCK is needed for for usual behavior.
90 int fd = xopen("/dev/kmsg", O_RDONLY | ((toys.optflags&FLAG_w)?0:O_NONBLOCK));
91
92 // With /dev/kmsg, SYSLOG_ACTION_CLEAR (5) doesn't actually remove anything;
93 // you need to seek to the last clear point.
94 lseek(fd, 0, SEEK_DATA);
95
96 while (1) {
97 char msg[8192]; // CONSOLE_EXT_LOG_MAX.
98 unsigned long long time_us;
99 int facpri, subsystem, pos;
100 char *p, *text;
101 ssize_t len;
102
103 // kmsg fails with EPIPE if we try to read while the buffer moves under
104 // us; the next read will succeed and return the next available entry.
105 do {
106 len = read(fd, msg, sizeof(msg));
107 } while (len == -1 && errno == EPIPE);
108 // All reads from kmsg fail if you're on a pre-3.5 kernel.
109 if (len == -1 && errno == EINVAL) {
110 close(fd);
111 return legacy_mode();
112 }
113 if (len <= 0) break;
114
115 msg[len] = 0;
116
117 if (sscanf(msg, "%u,%*u,%llu,%*[^;];%n", &facpri, &time_us, &pos) != 2)
118 continue;
119
120 // Drop extras after end of message text.
121 text = msg + pos;
122 if ((p = strchr(text, '\n'))) *p = 0;
123
124 // Is there a subsystem? (The ": " is just a convention.)
125 p = strstr(text, ": ");
126 subsystem = p ? (p - text) : 0;
127
128 // "Raw" is a lie for /dev/kmsg. In practice, it just means we show the
129 // syslog facility/priority at the start of each line.
130 if (toys.optflags&FLAG_r) printf("<%d>", facpri);
131
132 if (!(toys.optflags&FLAG_t)) {
133 color(32);
134 printf("[%5lld.%06lld] ", time_us/1000000, time_us%1000000);
135 color(0);
136 }
137
138 // Errors (or worse) are shown in red, subsystems are shown in yellow.
139 if (subsystem) {
140 color(33);
141 printf("%.*s", subsystem, text);
142 text += subsystem;
143 color(0);
144 }
145 if (!((facpri&7) <= 3)) xputs(text);
146 else {
147 color(31);
148 printf("%s", text);
149 color(0);
150 xputc('\n');
151 }
152 }
153 close(fd);
154 }
155
dmesg_main(void)156 void dmesg_main(void)
157 {
158 TT.color = isatty(1);
159
160 if (!(toys.optflags & (FLAG_C|FLAG_n))) print_all();
161
162 // Set the log level?
163 if (toys.optflags & FLAG_n) xklogctl(8, 0, TT.level);
164
165 // Clear the buffer?
166 if (toys.optflags & (FLAG_C|FLAG_c)) xklogctl(5, 0, 0);
167 }
168