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 * Linux 6.0 celebrates the 10th anniversary of this being in "testing":
8 * http://kernel.org/doc/Documentation/ABI/testing/dev-kmsg
9
10 USE_DMESG(NEWTOY(dmesg, "w(follow)CSTtrs#<1n#c[!Ttr][!Cc][!Sw]", TOYFLAG_BIN))
11
12 config DMESG
13 bool "dmesg"
14 default y
15 help
16 usage: dmesg [-Cc] [-r|-t|-T] [-n LEVEL] [-s SIZE] [-w]
17
18 Print or control the kernel ring buffer.
19
20 -C Clear ring buffer without printing
21 -c Clear ring buffer after printing
22 -n Set kernel logging LEVEL (1-9)
23 -r Raw output (with <level markers>)
24 -S Use syslog(2) rather than /dev/kmsg
25 -s Show the last SIZE many bytes
26 -T Human readable timestamps
27 -t Don't print timestamps
28 -w Keep waiting for more output (aka --follow)
29 */
30
31 #define FOR_dmesg
32 #include "toys.h"
33 #include <sys/klog.h>
34
GLOBALS(long n,s;int use_color;time_t tea;)35 GLOBALS(
36 long n, s;
37
38 int use_color;
39 time_t tea;
40 )
41
42 static void color(int c)
43 {
44 if (TT.use_color) printf("\e[%dm", c);
45 }
46
format_message(char * msg,int new)47 static void format_message(char *msg, int new)
48 {
49 unsigned long long time_s, time_us;
50 int facpri, subsystem, pos, ii, jj, in, out;
51 char *p, *text;
52
53 // The new /dev/kmsg and the old syslog(2) formats differ slightly.
54 if (new) {
55 if (sscanf(msg, "%u,%*u,%llu,%*[^;]; %n", &facpri, &time_us, &pos) != 2)
56 return;
57
58 time_s = time_us/1000000;
59 time_us %= 1000000;
60 } else if (sscanf(msg, "<%u>[%llu.%llu] %n",
61 &facpri, &time_s, &time_us, &pos) != 3) return;
62
63 // Drop extras after end of message text.
64 if ((p = strchr(text = msg+pos, '\n'))) *p = 0;
65
66 // Is there a subsystem? (The ": " is just a convention.)
67 p = strstr(text, ": ");
68 subsystem = p ? (p-text) : 0;
69
70 // To get "raw" output for /dev/kmsg we need to add priority to each line
71 if (FLAG(r)) {
72 color(0);
73 printf("<%d>", facpri);
74 } else for (in = out = subsystem;; ) {
75 jj = 0;
76 if (text[in]=='\\'&& 1==sscanf(text+in, "\\x%2x%n", &ii, &jj) && jj==4) {
77 in += 4;
78 text[out++] = ii;
79 } else if (!(text[out++] = text[in++])) break;
80 }
81
82 // Format the time.
83 if (!FLAG(t)) {
84 color(32);
85 if (FLAG(T)) {
86 time_t t = TT.tea+time_s;
87 char *ts = ctime(&t);
88
89 printf("[%.*s] ", (int)(strlen(ts)-1), ts);
90 } else printf("[%5lld.%06lld] ", time_s, time_us);
91 }
92
93 // Errors (or worse) are shown in red, subsystems are shown in yellow.
94 if (subsystem) {
95 color(33);
96 printf("%.*s", subsystem, text);
97 text += subsystem;
98 }
99 color(31*((facpri&7)<=3));
100 xputs(text);
101 }
102
xklogctl(int type,char * buf,int len)103 static int xklogctl(int type, char *buf, int len)
104 {
105 int rc = klogctl(type, buf, len);
106
107 if (rc<0) perror_exit("klogctl");
108
109 return rc;
110 }
111
dmesg_cleanup(void)112 static void dmesg_cleanup(void)
113 {
114 color(0);
115 }
116
dmesg_main(void)117 void dmesg_main(void)
118 {
119 TT.use_color = isatty(1);
120
121 if (TT.use_color) sigatexit(dmesg_cleanup);
122 // If we're displaying output, is it klogctl or /dev/kmsg?
123 if (FLAG(C)||FLAG(n)) goto no_output;
124
125 if (FLAG(T)) {
126 struct sysinfo info;
127
128 sysinfo(&info);
129 TT.tea = time(0)-info.uptime;
130 }
131
132 if (!FLAG(S)) {
133 char msg[8193]; // CONSOLE_EXT_LOG_MAX+1
134 ssize_t len;
135 int fd;
136
137 // Each read returns one message. By default, we block when there are no
138 // more messages (--follow); O_NONBLOCK is needed for for usual behavior.
139 fd = open("/dev/kmsg", O_RDONLY|O_NONBLOCK*!FLAG(w));
140 if (fd == -1) goto klogctl_mode;
141
142 // SYSLOG_ACTION_CLEAR(5) doesn't actually remove anything from /dev/kmsg,
143 // you need to seek to the last clear point.
144 lseek(fd, 0, SEEK_DATA);
145
146 for (;;) {
147 // why does /dev/kmesg return EPIPE instead of EAGAIN if oldest message
148 // expires as we read it?
149 if (-1==(len = read(fd, msg, sizeof(msg)-1)) && errno==EPIPE) continue;
150 // read() from kmsg always fails on a pre-3.5 kernel.
151 if (len==-1 && errno==EINVAL) goto klogctl_mode;
152 if (len<1) break;
153
154 msg[len] = 0;
155 format_message(msg, 1);
156 }
157 close(fd);
158 } else {
159 char *data, *to, *from, *end;
160 int size;
161
162 klogctl_mode:
163 // Figure out how much data we need, and fetch it.
164 if (!(size = TT.s)) size = xklogctl(10, 0, 0);
165 data = from = xmalloc(size+1);
166 data[size = xklogctl(3+FLAG(c), data, size)] = 0;
167
168 // Send each line to format_message.
169 to = data + size;
170 while (from < to) {
171 if (!(end = memchr(from, '\n', to-from))) break;
172 *end = 0;
173 format_message(from, 0);
174 from = end + 1;
175 }
176
177 if (CFG_TOYBOX_FREE) free(data);
178 }
179
180 no_output:
181 // Set the log level?
182 if (FLAG(n)) xklogctl(8, 0, TT.n);
183
184 // Clear the buffer?
185 if (FLAG(C)||FLAG(c)) xklogctl(5, 0, 0);
186 }
187