SunOS bug list/4.1 problems with locking

[Casper H.S. Dik]

In article <10194 at brazos.Rice.edu>, kdenning at ksun.naitc.com writes:

|> 1) We've run into a really strange problem with file locks.  From time to
|>    time we'll see messages of the form "fcntl: no record locks available"
|>    followed (usually) by "rpc.lockd: out of lock".

I've seen this problem to and am about to file a bug report. If you have
source to the program that uses the locks, there's an easy work around.

The bug is caused (presumably) by the lock client code.  If you test for
the existence of a non existent lock with fcntl/lockf, rpc.lockdistance!
relinquishes the file descriptor refering to the 'locked' file.

The workaround is to do a lockf(fd,F_ULOCK,size) after a
lockf(fd,F_TEST,size) returns 0.  Internally, i.e. in libc, lockf(F_TEST)
is translated to an equivalent call to fcntl (F_GETLK).

If you don't have the source there are some things you can do:

a) complain complain, COMPLAIN
b) Write a wrapper around rpc.lockd to increase the soft limit on fd's to 256:
#!/bin/csh -f
limit desc 256
exec /usr/etc/rpc.lockd.org
c) Try:
   Use ofiles/fstat to find the inodes of the files kept open by rpc.lockd.
   Use ncheck to find the filenames.
   Use the program below (on an NFS client) compiled with -DZAPLOCK and the
     files found in step 2 as arguments. This will cause rpc.lockd to forget
     about those files.

This is a program to demonstrate the bug:

#include <errno.h>
#include <sys/file.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>

main (argc,argv)
int argc;
char **argv;

{
	int fd;

	if (argc < 2) {
		(void) fprintf(stderr,"Usage: %s filename ...\n", *argv);
		exit(1);
	}
	while(*++argv) {
		if ((fd = open(*argv,O_RDWR)) < 0) {
			perror(*argv);
			continue;
		}
		/*
		 * this is what causes the bug
                 */
		if (lockf(fd,F_TEST,0) < 0) {
			perror("TESTLK");
			close(fd);
			continue;
		}
#if ZAPLOCK
		if (lockf(fd,F_ULOCK,0) < 0) {
			perror("UNLOCK");
		}
#endif
		close(fd);
	}
	exit(0);
}


|> Secondly, we (and I'm sure lots of other people) would REALLY like to have
|> a list of fixed bugs in a nice compendium somewhere.

There's the customer distributed buglist.  As a non American user I have
no access to the Online Bugs Database.  (Wish it were accessable over the
Internet, like rlogin odb.sun.com -l guest)

My main problem is tmpfs. This really is a (last minute?) hack.  (Can't
use lockf/flock on a tmpfs, can't make pipes on tmpfs, sticky bit on
directories won't work (it was invented for /tmp!))

Casper H.S. Dik				VCP/HIP: +31205922022
University of Amsterdam     |		casper at fwi.uva.nl
The Netherlands             |		casper%fwi.uva.nl at hp4nl.nluug.nl