// Copyright 2025 Justine Alexandra Roberts Tunney

//

// Permission to use, copy, modify, and/or distribute this software for

// any purpose with or without fee is hereby granted, provided that the

// above copyright notice and this permission notice appear in all copies.

//

// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL

// WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED

// WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE

// AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL

// DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR

// PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER

// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR

// PERFORMANCE OF THIS SOFTWARE.

#include <errno.h>

#include <fcntl.h>

#include <stdlib.h>

#include <sys/wait.h>

#include <unistd.h>

int main() {

int fd;

pid_t pid;

struct flock lock;

char path[] = "/tmp/fcntl_lock_test.XXXXXX";

if ((fd = mkstemp(path)) == -1)

return 1;

lock.l_type = F_WRLCK;

lock.l_whence = SEEK_SET;

lock.l_start = 0;

lock.l_len = 0;

if (fcntl(fd, F_SETLK, &lock) != 0)

return 2;

pid = fork();

if (pid == 0) {

int fd2 = open(path, O_RDWR);

if (fd2 < 0)

_exit(10);

if (fcntl(fd2, F_SETLK, &lock) == 0)

_exit(11);

if (errno != EACCES && errno != EAGAIN)

_exit(12);

close(fd2);

_exit(0);

} else if (pid > 0) {

int status;

wait(&status);

if (WEXITSTATUS(status) != 0)

return 3;

} else {

return 4;

}

lock.l_type = F_UNLCK;

if (fcntl(fd, F_SETLK, &lock) != 0)

return 5;

close(fd);

unlink(path);

return 0;

}