#define _GNU_SOURCE

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>


int main(void)
{
    system("touch foo");


    int fd = open("foo", O_RDWR);

    int ret = fcntl(fd, F_OFD_SETLK, &(struct flock){ .l_type = F_RDLCK });
    printf("set rd lock: %i, %s\n", ret, strerror(errno));

    system("./test2");

    printf("===\n");

    ret = fcntl(fd, F_OFD_SETLK, &(struct flock){ .l_type = F_UNLCK });
    printf("unset lock: %i, %s\n", ret, strerror(errno));

    system("./test2");

    printf("===\n");

    ret = fcntl(fd, F_OFD_SETLK, &(struct flock){ .l_type = F_WRLCK });
    printf("set wr lock: %i, %s\n", ret, strerror(errno));

    system("./test2");

    close(fd);
    return 0;
}