SYSLOG

[Andrew Hume]

In article <10319 at alice.UUCP>, andrew at alice.UUCP (Andrew Hume) writes:
> 
> 
> has anyone running 3.2 (or 3.2.1) persuaded the syslog system to
> log disk errors? despite the obvious and default conf file,
> nothing gets logged but some whining by some networking daemons.
> i wrote a user program to log stuff; it worked.


I have a solution for anyone who wants to log their kernel printfs
(such as disk erors etc). I am running it on a 4D/240 but it should apply
to other power series. Many thanks are due to dave olson who was kind
enough to help me understand some fine points.

basically, i have a program called syslogger (spawned from S20sysetup)
that constantly scans the kernel buffer and logs any messages found there.
(isn't this what syslogd should be doing?) i made the kernel buffer
larger than normal (the define is CONBUFSIZE in master.d/kernel: default
is 1024 - mine is 4096) and i scan the buffer every minute. (in less paranoid
circumstances, say on our vaxes, we do this less often, say every 15 mins.)
to compile the following source, i use
	$CC $CFLAGS -I/usr/include/bsd -o syslogger syslogger.c -lmld -lbsd
there is some crap at the start to try and do the right thing for a daemon
process (disconnect the controlling tty etc); i never ran into any trouble
before i put it in and have no idea why it is necessary but it is apparently
the right thing to do. if i bungled, tell me.

any complaints, comments or suggestions should be sent to andrew at research.att.com

the source is:

#include	<stdio.h>
#include	<sys/param.h>
#include	<nlist.h>
#include	<signal.h>
#include	<syslog.h>
#include	<sys/termio.h>

struct	nlist nl[] = {
	{ "conbuf" },
	{ "conbufndx" },
	{ "conbufsz" },
	{ 0 }
};

int mem;
char *whoami;

main(argc, argv)
	char **argv;
{
	int i;
	int size, amt;
	int ndx;
	char *buf;
	extern errno;

	whoami = argv[0];
	/*
		fork off and find myself
	*/
	if(fork())
		exit(0);
	for(i = 0; i < 20; i++)
		close(i);		/* close a bunch */
	i = open("/dev/null", 0);	/* set std descriptors to something */
	dup2(i, 2);			/* hope i isn't 2 */
	close(i);
	dup2(2, 0);
	dup2(2, 1);
	chdir("/");
	i = open("/dev/tty", 2);
	if(i > 0){
		ioctl(i, TIOCNOTTY, (char *)0);
		close(i);
	}
	setpgrp();
	/*
		do something with my life
	*/
	signal(SIGHUP, SIG_IGN);
	nlist("/unix", nl);
	mem = 0;
	for(i = 0; nl[i].n_name; i++)
		if(nl[i].n_type == 0){
			mem = 1;
			syslog(LOG_ERR, "can't find %s\n", nl[1].n_name);
		}
		else
			nl[i].n_value &= ~0x80000000;
	if(mem)
		done("namelist problems", 1);
	if((mem = open("/dev/kmem", 0)) < 0)
		done("/dev/kmem\n", -1);
	if(getval(&nl[2], &size, sizeof(size)) != sizeof(size))
		done("reading size");
	syslog(LOG_INFO, "kernel monitor: buffer = %d bytes", size);
	if((buf = (char *)malloc(3*size)) == 0)
		done("malloc failure", 1);
	ndx = 0;		/* assume we are starting from start of the buffer */
	do {
		ndx = dobuf(ndx, size, buf);
	} while(sleep(60) >= 0);
	exit(0);
}

dobuf(ostart, size, buffer)
	char *buffer;
{
	int out;
	int ndx;

	if(getval(&nl[1], &ndx, sizeof(ndx)) != sizeof(ndx))
		done("reading ndx");
	ndx = ndx%size;		/* it should be anyway */
	if(ndx == ostart)	/* most common case: nothing happened */
		return(ostart);
	if(getval(&nl[0], buffer, size) != size)
		done("reading buf");
	/* make it a contiguous region */
	memcpy(buffer+size, buffer, size);
	if(ndx < ostart)
		ndx += size;
	out = 2*size;
	while(ostart < ndx)
		switch(buffer[ostart++])
		{
		case 0:		/* apparently not uncommon */
			break;
		case '\n':
			buffer[out] = 0;
			out = 2*size;
			syslog(LOG_ERR, "%s", buffer+out);
			break;
		default:
			buffer[out++] = buffer[ostart-1];
			break;
		}
	buffer[out] = 0;
	out = 2*size;
	if(buffer[out])
		syslog(LOG_ERR, "%s <partial line>", buffer+out);
	return(ndx%size);
}

done(s, ec)
	char *s;
{
	if(ec < 0)
		syslog(LOG_ERR, "%s: %s: %m", whoami, s);
	else
		syslog(LOG_ERR, "%s: %s", whoami, s);
	exit(1);
}

getval(nl, buf, cnt)
	struct	nlist *nl;
	char *buf;
	int cnt;
{
	if(lseek(mem, (long)nl->n_value, 0) != (long)nl->n_value){
		fprintf(stderr, "lseek to %x for %s", nl[0].n_value, nl[0].n_name);
		return(-1);
	}
/*	printf("will read %d from %#x for %s\n", cnt, nl[0].n_value, nl[0].n_name);
	/* should be min of cnt and sizeof(buf) */
	return read(mem, buf, cnt);
}