[BUG] NFS no longer updates file modification times appropriately

[Joe Korty <joe.korty@ccur.com>]

Trond,
 Paraphrased from one of my inhouse customers: "The timestamp of an
NFS-mounted file does not change when written to, when the below test is
run on a 2.6.6-rc1 to 2.6.7-rc2 kernel.  The timestamp is appropriately
updated when the test is run on a 2.6.5 kernel.  This is with NFSv3.
The type of system serving up the files does not seem to be a factor."

I was not able to narrow the problem/featureset change down to a cset.

Attached is the test program my customer used.

Regards,
Joe

#include <stdio.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <errno.h>

#define PATH "./my_file"

int
main()
{
	int status;
	int count = 0;
	int fd;
	struct stat wuz;
	struct stat iz;

	(void) unlink(PATH);

	fd = open (PATH, O_RDWR+O_CREAT+O_SYNC, 0666);
	if (fd < 0) {
		fprintf (stderr, "open(%s) fails, errno = %d\n", PATH, errno);
		return 1;
	}

	status = fstat (fd, &wuz);
	if (status) {
		fprintf (stderr, "fstat(%s) fails, errno = %d\n", PATH, errno);
		return 1;
	}

	for (;;) {
		status = write (fd, &status, sizeof(status));
		if (status != sizeof(status)) {
			fprintf (stderr, "write(%s) fails, errno = %d\n", PATH, errno);
			return 1;
		}
		status = fstat (fd, &iz);
		if (status) {
			fprintf (stderr, "fstat(%s) fails, errno = %d\n", PATH, errno);
			return 1;
		}
		if (iz.st_mtime != wuz.st_mtime) break;
		count++;
		if (count % 1000 == 0) {
			printf ("count = %d\n", count);
		}
	}

	printf ("File modification time changed after %d iterations\n", count);
}