kqueue_test.cpp

#ifdef __cplusplus
extern "C" {
#endif
#include <sys/types.h>
#include <sys/event.h>
#include <sys/time.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#ifdef __cplusplus
}
#endif

int
register_watch_file(char* filename) {
  // target
  struct kevent kev;
  memset(&kev, 0, sizeof(struct kevent));
  int fd = open(filename, O_RDONLY, 0);
  EV_SET(&kev, fd, EVFILT_VNODE, EV_ADD|EV_ENABLE|EV_CLEAR, NOTE_WRITE, 0, NULL);

  // register
  int kq = kqueue();
  kevent(kq, &kev, 1, NULL, 0, NULL);
  return kq;
}

int
main(int argc, char** argv) {
  if (argc != 2) {
    perror("usage: ./kqueue_test <file>");
    printf("argc: %d\n", argc);
    return 1;
  }
  int kq = register_watch_file(argv[1]);
  struct kevent kev;
  time_t timer;
  memset(&kev, 0, sizeof(struct kevent));
  for (;;) {
    if (kevent(kq, NULL, 0, &kev, 1, NULL) > 0) {
      if ((kev.fflags & NOTE_WRITE) == NOTE_WRITE) {
        timer = time(NULL);
        printf("%swrite! %s\n", asctime(localtime(&timer)), argv[1]);
      }
    }
  }
  
  close(kq);
  return 0;
}