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logger: support for -k, early log to /dev/kmsg

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This patch adds support for logging to /dev/kmsg, which can be highly
useful for early scripts that run long before syslogd has started and
/dev/log is available.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
This commit is contained in:
Joachim Wiberg 2021-06-20 14:09:00 +02:00
parent 10ccdc3da1
commit 36778bee4a
1 changed files with 44 additions and 1 deletions
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45
src/logger.c
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@ -31,6 +31,7 @@
#include "config.h"
#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <getopt.h>
@ -112,6 +113,15 @@ static int logrotate(char *file, int num, off_t sz)
return 0;
}
static void log_kmsg(FILE *fp, char *ident, int pri, int opts, char *buf)
{
while (isspace(*buf))
buf++;
/* Always add [PID] so syslogd can find this later on */
fprintf(fp, "<%d>%s[%d]:%s\n", pri, ident, getpid(), buf);
}
static int checksz(FILE *fp, off_t sz)
{
struct stat st;
@ -187,6 +197,9 @@ static int usage(int code)
" -d SD Log SD as RFC5424 style 'structured data' in message\n"
" -f FILE Log file to write messages to, instead of syslog daemon\n"
" -i Log process ID of the logger process with each line (LOG_PID)\n"
#ifdef __linux__
" -k Log to kernel /dev/kmsg if /dev/log doesn't exist yet\m"
#endif
" -m MSGID Log message using this RFC5424 style MSGID\n"
" -n Open log file immediately (LOG_NDELAY)\n"
" -p PRIO Log message priority (numeric or facility.severity pair)\n"
@ -213,13 +226,14 @@ int main(int argc, char *argv[])
int severity = LOG_INFO;
int log_opts = 0;
int rotate = 0;
int allow_kmsg = 0;
off_t size = 200 * 1024;
char *ident = NULL, *logfile = NULL;
char *msgid = NULL, *sd = NULL;
char *sockpath = NULL;
char buf[512] = "";
while ((c = getopt(argc, argv, "?cd:f:im:np:r:st:u:v")) != EOF) {
while ((c = getopt(argc, argv, "?cd:f:ikm:np:r:st:u:v")) != EOF) {
switch (c) {
case 'c':
log_opts |= LOG_CONS;
@ -237,6 +251,14 @@ int main(int argc, char *argv[])
log_opts |= LOG_PID;
break;
case 'k':
#ifdef __linux__
allow_kmsg = 1;
#else
errx(1, "-k is not supported on non-Linux systems.");
#endif
break;
case 'm':
msgid = optarg;
break;
@ -308,6 +330,27 @@ int main(int argc, char *argv[])
if (access(sockpath, W_OK))
err(1, "Socket path %s", sockpath);
log.log_sockpath = sockpath;
} else if (allow_kmsg && access(_PATH_LOG, W_OK)) {
/*
* -k and /dev/log is not yet up, user wants to prevent
* logging to console and instead use the detour around
* the kernel logger until syslogd has started.
*/
while (!access("/dev/kmsg", W_OK)) {
int pri = facility | severity;
fp = fopen("/dev/kmsg", "w");
if (!fp)
break; /* fall back to log syslogp_r() */
if (!buf[0]) {
while ((fgets(buf, sizeof(buf), stdin)))
log_kmsg(fp, ident, pri, log_opts, chomp(buf));
} else
log_kmsg(fp, ident, pri, log_opts, buf);
return fclose(fp);
}
}
openlog_r(ident, log_opts, facility, &log);