FreeBSD C言語 kqueue/keventで簡易tail -fコマンドを作る

#include <stdio.h>
#include <stdlib.h>
#include <err.h>
#include <unistd.h>

#include <sys/types.h>
#include <sys/event.h>
#include <sys/time.h>
#include <fcntl.h>

int
main (int argc, char *argv[])
{
	char	*filename = "/tmp/a";
	struct kevent kev;
	struct kevent kev2;
	int fd = open(filename , O_RDONLY);
	if(fd == -1)
	{
		err(1, filename);
	}
	int kq = kqueue();
	if(kq == -1)
	{
		err(1, "kqueue");
	}
	EV_SET(&kev, fd, EVFILT_READ, EV_ADD, 0, 0, NULL);
	if(kevent(kq, &kev, 1, NULL, 0, NULL) == -1)
	{
		err(1, "kevent");
	}

	for ( ; ; ) {
		int r = kevent(kq, NULL, 0, &kev2, 1, NULL);
		if(r == -1) {
			err(1, "kevent");
		}
		char buf[256];
		ssize_t len = read(fd, buf, sizeof(buf));
		if(len == 0) {
			break;
		} else if (len == -1) {
			err(1, "read");
		}
		(void) printf ("%.*s", len, buf);
	}

	exit (EXIT_SUCCESS);
}

cc mytail.c

実行方法

./a.out