directory notifications lost after fork?

[Oskar Liljeblad]

The code snipper demonstrates what I consider a bug in the
dnotify facilities in the kernel. After a fork, all registered
notifications are lost in the process where they originally
where registered (the parent process). "lost" here means that
the signal specified with F_SETSIG fcntl no longer is delivered
when notified.

How to reproduce (tested with 2.4.17):
  gcc -o dnoticebug dnoticebug.c
  dnoticebug &				# run in background
  cat dnoticebug.c >/dev/null		# "notified" should now be printed
  cat dnoticebug.c >/dev/null		# nothing is printed this time
  
If you comment out the line with fork below, "notified" *will* be
printed every time you cat dnoticebug.c.

I'm not subscribed to the list so I'd appreciate if you CCed me.
(Otherwise I'd have to use the archives :) Thanks.

Oskar Liljeblad ([e-mail])

===

#define _GNU_SOURCE
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>

static void handler(int sig, siginfo_t *si, void *data)
{
	printf("notified\n");
}

int main(void)
{
	struct sigaction act;
	int fd;

	act.sa_sigaction = handler;
	sigemptyset(&act.sa_mask);
	act.sa_flags = SA_SIGINFO;
	sigaction(SIGRTMIN, &act, NULL);

	fd = open(".", O_RDONLY);
	fcntl(fd, F_SETSIG, SIGRTMIN);
	fcntl(fd, F_NOTIFY, DN_ACCESS|DN_MULTISHOT);

	while (1) {
		pause();
		if (fork() <= 0) exit(0);
		wait(NULL);
	}
}