1 /* dmesg.c - display/control kernel ring buffer.
2 *
3 * Copyright 2006, 2007 Rob Landley <rob@landley.net>
4 *
5 * See http://refspecs.linuxfoundation.org/LSB_4.1.0/LSB-Core-generic/LSB-Core-generic/dmesg.html
6 *
7 * Don't ask me why the horrible new dmesg API is still in "testing":
8 * http://kernel.org/doc/Documentation/ABI/testing/dev-kmsg
9
10 // We care that FLAG_c is 1, so keep c at the end.
11 USE_DMESG(NEWTOY(dmesg, "w(follow)CSTtrs#<1n#c[!Ttr][!Cc][!Sw]", TOYFLAG_BIN))
12
13 config DMESG
14 bool "dmesg"
15 default y
16 help
17 usage: dmesg [-Cc] [-r|-t|-T] [-n LEVEL] [-s SIZE] [-w]
18
19 Print or control the kernel ring buffer.
20
21 -C Clear ring buffer without printing
22 -c Clear ring buffer after printing
23 -n Set kernel logging LEVEL (1-9)
24 -r Raw output (with <level markers>)
25 -S Use syslog(2) rather than /dev/kmsg
26 -s Show the last SIZE many bytes
27 -T Human readable timestamps
28 -t Don't print timestamps
29 -w Keep waiting for more output (aka --follow)
30 */
31
32 #define FOR_dmesg
33 #include "toys.h"
34 #include <sys/klog.h>
35
GLOBALS(long n,s;int use_color;time_t tea;)36 GLOBALS(
37 long n, s;
38
39 int use_color;
40 time_t tea;
41 )
42
43 static void color(int c)
44 {
45 if (TT.use_color) printf("\033[%dm", c);
46 }
47
format_message(char * msg,int new)48 static void format_message(char *msg, int new)
49 {
50 unsigned long long time_s, time_us;
51 int facpri, subsystem, pos;
52 char *p, *text;
53
54 // The new /dev/kmsg and the old syslog(2) formats differ slightly.
55 if (new) {
56 if (sscanf(msg, "%u,%*u,%llu,%*[^;]; %n", &facpri, &time_us, &pos) != 2)
57 return;
58
59 time_s = time_us/1000000;
60 time_us %= 1000000;
61 } else if (sscanf(msg, "<%u>[%llu.%llu] %n",
62 &facpri, &time_s, &time_us, &pos) != 3) return;
63
64 // Drop extras after end of message text.
65 if ((p = strchr(text = msg+pos, '\n'))) *p = 0;
66
67 // Is there a subsystem? (The ": " is just a convention.)
68 p = strstr(text, ": ");
69 subsystem = p ? (p-text) : 0;
70
71 // To get "raw" output for /dev/kmsg we need to add priority to each line
72 if (toys.optflags&FLAG_r) {
73 color(0);
74 printf("<%d>", facpri);
75 }
76
77 // Format the time.
78 if (!(toys.optflags&FLAG_t)) {
79 color(32);
80 if (toys.optflags&FLAG_T) {
81 time_t t = TT.tea+time_s;
82 char *ts = ctime(&t);
83
84 printf("[%.*s] ", (int)(strlen(ts)-1), ts);
85 } else printf("[%5lld.%06lld] ", time_s, time_us);
86 }
87
88 // Errors (or worse) are shown in red, subsystems are shown in yellow.
89 if (subsystem) {
90 color(33);
91 printf("%.*s", subsystem, text);
92 text += subsystem;
93 }
94 color(31*((facpri&7)<=3));
95 xputs(text);
96 }
97
xklogctl(int type,char * buf,int len)98 static int xklogctl(int type, char *buf, int len)
99 {
100 int rc = klogctl(type, buf, len);
101
102 if (rc<0) perror_exit("klogctl");
103
104 return rc;
105 }
106
dmesg_cleanup(void)107 static void dmesg_cleanup(void)
108 {
109 color(0);
110 }
111
dmesg_main(void)112 void dmesg_main(void)
113 {
114 TT.use_color = isatty(1);
115
116 if (TT.use_color) sigatexit(dmesg_cleanup);
117 // If we're displaying output, is it klogctl or /dev/kmsg?
118 if (toys.optflags & (FLAG_C|FLAG_n)) goto no_output;
119
120 if (toys.optflags&FLAG_T) {
121 struct sysinfo info;
122
123 sysinfo(&info);
124 TT.tea = time(0)-info.uptime;
125 }
126
127 if (!(toys.optflags&FLAG_S)) {
128 char msg[8193]; // CONSOLE_EXT_LOG_MAX+1
129 ssize_t len;
130 int fd;
131
132 // Each read returns one message. By default, we block when there are no
133 // more messages (--follow); O_NONBLOCK is needed for for usual behavior.
134 fd = open("/dev/kmsg", O_RDONLY|(O_NONBLOCK*!(toys.optflags&FLAG_w)));
135 if (fd == -1) goto klogctl_mode;
136
137 // SYSLOG_ACTION_CLEAR(5) doesn't actually remove anything from /dev/kmsg,
138 // you need to seek to the last clear point.
139 lseek(fd, 0, SEEK_DATA);
140
141 for (;;) {
142 // why does /dev/kmesg return EPIPE instead of EAGAIN if oldest message
143 // expires as we read it?
144 if (-1==(len = read(fd, msg, sizeof(msg))) && errno==EPIPE) continue;
145 // read() from kmsg always fails on a pre-3.5 kernel.
146 if (len==-1 && errno==EINVAL) goto klogctl_mode;
147 if (len<1) break;
148
149 msg[len] = 0;
150 format_message(msg, 1);
151 }
152 close(fd);
153 } else {
154 char *data, *to, *from, *end;
155 int size;
156
157 klogctl_mode:
158 // Figure out how much data we need, and fetch it.
159 if (!(size = TT.s)) size = xklogctl(10, 0, 0);
160 data = from = xmalloc(size+1);
161 data[size = xklogctl(3+(toys.optflags&FLAG_c), data, size)] = 0;
162
163 // Send each line to format_message.
164 to = data + size;
165 while (from < to) {
166 if (!(end = memchr(from, '\n', to-from))) break;
167 *end = 0;
168 format_message(from, 0);
169 from = end + 1;
170 }
171
172 if (CFG_TOYBOX_FREE) free(data);
173 }
174
175 no_output:
176 // Set the log level?
177 if (toys.optflags & FLAG_n) xklogctl(8, 0, TT.n);
178
179 // Clear the buffer?
180 if (toys.optflags & (FLAG_C|FLAG_c)) xklogctl(5, 0, 0);
181 }
182