/***********************************************************************
 * This is a STC to show that fcntl fails.
 *
 * It tries to use fcntl() for file locking. It creates a temporary
 * file and tries to lock and then unlock the file.
 *
 * This produces "lock: Bad address" with Cygwin 1.7.19 x86_64.
 *
 * Compile: gcc -Wall -o stc-fcntl stc-fcntl.c
 ***********************************************************************/

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/wait.h>
#include <sys/file.h>

/* A temporary file used for fcntl. */
char tmpfilename[] = "/tmp/fcntlXXXXXX";

struct flock mutex_lock_it;
struct flock mutex_unlock_it;

int main(int argc, const char * const * argv, const char * const *env)
{
    int fd;
    int rc;
 
    /* Create the temporary file. */
    fd = mkstemp(tmpfilename);
    if (fd < 0) {
        perror("open failed");
        exit(1);
    }

    /* Setup mutexes */
    mutex_lock_it.l_whence = SEEK_SET;   /* from current point */
    mutex_lock_it.l_start = 0;           /* -"- */
    mutex_lock_it.l_len = 0;             /* until end of file */
    mutex_lock_it.l_type = F_WRLCK;      /* set exclusive/write lock */
    mutex_lock_it.l_pid = 0;             /* pid not actually interesting */
    mutex_unlock_it.l_whence = SEEK_SET; /* from current point */
    mutex_unlock_it.l_start = 0;         /* -"- */
    mutex_unlock_it.l_len = 0;           /* until end of file */
    mutex_unlock_it.l_type = F_UNLCK;    /* set exclusive/write lock */
    mutex_unlock_it.l_pid = 0;           /* pid not actually interesting */

    /* Get the lock. */
    do {
        rc = fcntl(fd, F_SETLKW, &mutex_lock_it);
    } while (rc < 0 && errno == EINTR);
    if (rc < 0) {
        perror("lock");
        exit(1);
    }

    /* Release the lock. */
    do {
        rc = fcntl(fd, F_SETLKW, &mutex_unlock_it);
    } while (rc < 0 && errno == EINTR);
    if (rc < 0) {
        perror("unlock");
        exit(1);
    }

    /* Clean up. */
    close(fd);
    unlink(tmpfilename);
    return 0;
}