Adding SIGIO support for /dev/tapX and other netlink-based drivers.

Use the following program to test it:

	#include <stdio.h>
	#include <stdlib.h>
	#include <unistd.h>
	#include <signal.h>
	
	#define __USE_GNU
	#include <fcntl.h>
	
	#define DEVNAME	"/dev/tap0"
	#define SIGNUM	SIGIO
	
	void sigio (int signum)
	{
		printf ("Got signal %d\n", signum);
		fflush (stdout);
	}
	
	int main (int argc, char **argv)
	{
		int fd, flags;
	
		fd = open (DEVNAME, O_RDWR);
		if (fd < 0) {
			perror (DEVNAME);
			exit (1);
		}
		signal (SIGNUM, sigio);
		fcntl (fd, F_SETOWN, getpid());
		fcntl (fd, F_SETSIG, SIGNUM);
	
		flags = fcntl (fd, F_GETFL, 0);
		fcntl (fd, F_SETFL, flags | O_ASYNC);
	
		printf ("Waiting for i/o signal.\n");
		printf ("Ping /dev/tap0 interface.\n");
		for (;;)
			pause ();
	}
___
Best wishes,
Serge Vakulenko <vak@cronyx.ru>


--- /usr/src/linux-2.2.5/net/netlink/netlink_dev.c	Fri Aug 28 06:33:09 1998
+++ netlink_dev.c	Fri Mar  1 21:20:17 2002
@@ -25,6 +25,7 @@
 #include <linux/netlink.h>
 #include <linux/poll.h>
 #include <linux/init.h>
+#include <net/sock.h>
 
 #include <asm/system.h>
 #include <asm/uaccess.h>
@@ -148,11 +149,27 @@
 	return err;
 }
 
+static int netlink_fasync(int fd, struct file *filp, int on)
+{
+	struct inode *inode = filp->f_dentry->d_inode;
+	struct socket *sock = netlink_user[MINOR(inode->i_rdev)];
+	int retval;
+
+	lock_sock(sock->sk);
+	retval = fasync_helper(fd, filp, on, &sock->fasync_list);
+	release_sock(sock->sk);
+
+	if (retval <= 0)
+		return retval;
+	return 0;
+}
+
 static int netlink_release(struct inode * inode, struct file * file)
 {
 	unsigned int minor = MINOR(inode->i_rdev);
 	struct socket *sock = netlink_user[minor];
 
+	netlink_fasync(-1, file, 0);
 	netlink_user[minor] = NULL;
 	open_map &= ~(1<<minor);
 	sock_release(sock);
@@ -187,7 +204,9 @@
 	NULL,		/* netlink_mmap */
 	netlink_open,
 	NULL,		/* flush */
-	netlink_release
+	netlink_release,
+	NULL,		/* no fsync */
+	netlink_fasync
 };
 
 __initfunc(int init_netlink(void))