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From: "Dominic Marks" <dominic_marks@hotmail.com>
To: freebsd-hackers@freebsd.org
Subject: KEvent doesnt return and KEvent sample troubles
Date: Wed, 02 May 2001 21:24:42 -0000
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I've been looking to start using the KEvent system and I've been 
experimenting with it. However I've been having several problems, with my 
own code as well as samples from http://www.flugsvamp.org.

It appears I am able to create the correct structure's and register the 
events. However the event never returns and never responds to any action. 
For example if I use a sample which monitors the actions on a file I can 
read from, and write to the file and it shows no sign of noticing.

I was wondering if it's simply a mistake of my own, however the failure for 
the samples I've found has puzzled my further. I'm working on a 4.3-STABLE 
machine using GCC version 2.95.3.

Here is an example of code that I am using which doesn't seem to catch any 
events. Its a slightly modified version of read_test.c from flugsvamp.com 
which I edit so it would compile happily.

It doesn't seem to work however.

>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <aio.h>
#include <sys/errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/event.h>
#include <sys/time.h>
#include <sys/syscall.h>

main(int argc, char **argv)
{
	int fd, kq, n;
	struct kevent event[1];
	struct kevent *evp[1];
	char buffer[128];
	struct stat st;
	struct aiocb iocb;
  struct timespec ts = {0, 0};

	if (argc != 2)
		errx(1, "Usage: %s file\n", argv[0]);

	fd = open(argv[1], O_RDONLY);
	if (fd < 0)
		err(1, "open: %s\n", argv[1]);

	lseek(fd, 0, SEEK_END);

        kq = syscall(SYS_kqueue);
        if (kq < 0)
                err(1, "kqueue");

	event[0].ident = fd;
	event[0].filter = EVFILT_READ;
	event[0].flags = EV_ADD | EV_ENABLE;
	evp[0] = &event[0];
	n = syscall(SYS_kevent, kq, 1, evp, 0, NULL, 0);

	for (;;) {
		n = syscall(SYS_kevent, kq, 0, NULL, 1, event, ts);
		if (n < 0)
			err(1, "kevent");
		printf("kevent flags: 0x%x, data: 0x%x\n",
		    event[0].flags, event[0].data);

		n = read(fd, buffer, 128);
		buffer[n] = '\0';
		printf("%s", buffer);
	}
}
<

I'd appreciate any feedback very much.

Thank you
Dominic Marks
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