Date: Thu, 11 Nov 1999 14:55:01 -0800 (PST) From: Doug Barton <Doug@gorean.org> To: freebsd-hackers@freebsd.org Subject: Serious locking problem over NFS Message-ID: <Pine.BSF.4.20.9911111429310.37830-100000@dt054n7c.san.rr.com>
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Greetings,
The following small program illustrates an obscure problem with
file locking with freebsd as an NFS client. I'm aware of the problems with
NFS client side locking, but this is a slightly different problem. If you
compile this program, then place it on the NFS server machine and access
it twice from the same NFS client, it does what you'd expect, namely the
second process hangs till the first releases the lock. However if you run
this program from two different FreeBSD NFS clients, both clients get a
lock, which is bad. This is true whether all 3 machines are freebsd, or if
two clients are freebsd and the server is sun (which is how our
machines are set up in reality). However, if two sun clients run the
binary located on a sun server, it works as expected, namely the second
one hangs till the first one releases the lock.
Any insights into this situation are welcome, including
suggestions on different ways to do the locking that will work over
freebsd. Of course, if there is a bug in our NFS code fixing that would be
a good thing too.
I'm a bit behind on my FreeBSD mail, so my apologies if this has
come up recently. Thanks in advance for any help or suggestions.
Doug
--
"Stop it, I'm gettin' misty."
- Mel Gibson as Porter, "Payback"
#include <unistd.h>
#include <fcntl.h>
#include <sys/time.h>
int main( int argc, char *argv[] )
{
int fd;
struct flock fl;
fd = open( "test.lck", O_CREAT | O_TRUNC | O_WRONLY, 0644 );
fl.l_type = F_WRLCK;
fl.l_whence = SEEK_SET;
fl.l_start = 0;
fl.l_len = 1;
fcntl( fd, F_SETLKW, &fl );
printf( "Got lock\n" );
sleep( 30 );
fl.l_type = F_UNLCK;
fcntl( fd, F_SETLKW, &fl );
close( fd );
}
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