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/* dmesg.c - display/control kernel ring buffer.
*
* Copyright 2006, 2007 Rob Landley <rob@landley.net>
*
* http://refspecs.linuxfoundation.org/LSB_4.1.0/LSB-Core-generic/LSB-Core-generic/dmesg.html
// We care that FLAG_c is 1, so keep c at the end.
USE_DMESG(NEWTOY(dmesg, "w(follow)Ctrs#<1n#c[!tr]", TOYFLAG_BIN))
config DMESG
bool "dmesg"
default y
help
usage: dmesg [-Cc] [-r|-t] [-n LEVEL] [-s SIZE] [-w]
Print or control the kernel ring buffer.
-C Clear ring buffer without printing
-c Clear ring buffer after printing
-n Set kernel logging LEVEL (1-9)
-r Raw output (with <level markers>)
-s Show the last SIZE many bytes
-t Don't print kernel's timestamps
-w Keep waiting for more output (aka --follow)
*/
#define FOR_dmesg
#include "toys.h"
#include <sys/klog.h>
GLOBALS(
long level;
long size;
int color;
)
static int xklogctl(int type, char *buf, int len)
{
int rc = klogctl(type, buf, len);
if (rc<0) perror_exit("klogctl");
return rc;
}
// Use klogctl for reading if we're on a pre-3.5 kernel.
static void legacy_mode() {
char *data, *to, *from;
int size;
// Figure out how much data we need, and fetch it.
if (!(size = TT.size)) size = xklogctl(10, 0, 0);
data = to = from = xmalloc(size+1);
data[size = xklogctl(3 + (toys.optflags & FLAG_c), data, size)] = 0;
// Filter out level markers and optionally time markers
if (!(toys.optflags & FLAG_r)) while ((from - data) < size) {
if (from == data || from[-1] == '\n') {
char *to;
if (*from == '<' && (to = strchr(from, '>'))) from = ++to;
if ((toys.optflags&FLAG_t) && *from == '[' && (to = strchr(from, ']')))
from = to+1+(to[1]==' ');
}
*(to++) = *(from++);
} else to = data+size;
// Write result. The odds of somebody requesting a buffer of size 3 and
// getting "<1>" are remote, but don't segfault if they do.
if (to != data) {
xwrite(1, data, to-data);
if (to[-1] != '\n') xputc('\n');
}
if (CFG_TOYBOX_FREE) free(data);
}
static void color(int c) {
if (TT.color) printf("\033[%dm", c);
}
void dmesg_main(void)
{
// For -n just tell kernel which messages to keep.
if (toys.optflags & FLAG_n) {
xklogctl(8, 0, TT.level);
return;
}
// For -C just tell kernel to throw everything out.
if (toys.optflags & FLAG_C) {
xklogctl(5, 0, 0);
return;
}
TT.color = isatty(1);
// http://kernel.org/doc/Documentation/ABI/testing/dev-kmsg
// Each read returns one message. By default, we block when there are no
// more messages (--follow); O_NONBLOCK is needed for for usual behavior.
int fd = xopen("/dev/kmsg", O_RDONLY | ((toys.optflags&FLAG_w)?0:O_NONBLOCK));
while (1) {
char msg[8192]; // CONSOLE_EXT_LOG_MAX.
unsigned long long time_us;
int facpri, subsystem, pos;
char *p, *text;
ssize_t len;
// kmsg fails with EPIPE if we try to read while the buffer moves under
// us; the next read will succeed and return the next available entry.
do {
len = read(fd, msg, sizeof(msg));
} while (len == -1 && errno == EPIPE);
// All reads from kmsg fail if you're on a pre-3.5 kernel.
if (len == -1 && errno == EINVAL) {
close(fd);
return legacy_mode();
}
if (len <= 0) break;
msg[len] = 0;
if (sscanf(msg, "%u,%*u,%llu,%*[^;];%n", &facpri, &time_us, &pos) != 2)
continue;
// Drop extras after end of message text.
text = msg + pos;
if ((p = strchr(text, '\n'))) *p = 0;
// Is there a subsystem? (The ": " is just a convention.)
p = strstr(text, ": ");
subsystem = p ? (p - text) : 0;
// "Raw" is a lie for /dev/kmsg. In practice, it just means we show the
// syslog facility/priority at the start of each line.
if (toys.optflags&FLAG_r) printf("<%d>", facpri);
if (!(toys.optflags&FLAG_t)) {
color(32);
printf("[%5lld.%06lld] ", time_us/1000000, time_us%1000000);
color(0);
}
// Errors (or worse) are shown in red, subsystems are shown in yellow.
if (subsystem) {
color(33);
printf("%.*s", subsystem, text);
text += subsystem;
color(0);
}
if (!((facpri&7) <= 3)) xputs(text);
else {
color(31);
printf("%s", text);
color(0);
xputc('\n');
}
}
close(fd);
}
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