kqueue.c

#include <sys/event.h>
#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char **argv)
{
    struct kevent event; /* Event we want to monitor */
    struct kevent tevent; /* Event triggered */
    int kq, fd, ret;

    if (argc != 2) {
        err(EXIT_FAILURE, "Usage: %s path\n", argv[0]);
    }
    fd = open(argv[1], O_RDONLY);
    if (fd	== -1) {
        err(EXIT_FAILURE, "Failed to open '%s'", argv[1]);
    }

    /* Create kqueue. */
    kq = kqueue();
    if (kq	== -1) {
        err(EXIT_FAILURE, "kqueue() failed");
    }

    /* Initialize kevent structure. */
    EV_SET(&event,	fd, EVFILT_VNODE, EV_ADD | EV_CLEAR, NOTE_WRITE,
        0,	NULL);
    /* Attach event to the	kqueue.	*/
    ret = kevent(kq, &event, 1, NULL, 0, NULL);
    if (ret == -1) {
        err(EXIT_FAILURE, "kevent register");
    }
    if (event.flags & EV_ERROR) {
        errx(EXIT_FAILURE,	"Event error: %s", strerror(event.data));
    }

    for (;;) {
        /* Sleep until something happens. */
        ret = kevent(kq, NULL, 0, &tevent,	1, NULL);
        if	(ret ==	-1) {
            err(EXIT_FAILURE, "kevent wait");
        } else if (ret > 0) {
            printf("Something was written in '%s'\n", argv[1]);
        }
    }
}