#define _GNU_SOURCE

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


static const char *lock_names[] = {
    [F_UNLCK] = "unlocked",
    [F_RDLCK] = "read lock in place",
    [F_WRLCK] = "write lock in place",
};


int main(void)
{
    int fd = open("foo", O_RDWR);

    struct flock fl = { .l_type = F_WRLCK };
    int ret = fcntl(fd, F_OFD_GETLK, &fl);
    printf("get lock: %i, %s; %s\n", ret, strerror(errno), lock_names[fl.l_type]);

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

    close(fd);
    return 0;
}