/* Test advisory file locking.  This program is meant to be run under
 * strace(1) or equivalent.  If its first argument is the word "fcntl"
 * it tests fcntl() locking, otherwise it tests flock() locking.
 * You are on your own for any other sort of locks and for portability
 * problems.
 *
 * Copyright 2011 Zack Weinberg.
 * Copying and distribution of this program, with or without modification,
 * are permitted in any medium without royalty provided the copyright
 * notice and this notice are preserved.  This program is offered as-is,
 * without any warranty.
 */

#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/file.h>
#include <unistd.h>

static void
alarm_handler(int unused)
{
}

int
main(int argc, char **argv)
{
    struct sigaction sa;
    char template[] = "./tstlckXXXXXX";
    int fd;

    sa.sa_handler = alarm_handler;
    sigfillset(&sa.sa_mask);
    sa.sa_flags = 0; /* _not_ SA_RESTART */
    if (sigaction(SIGALRM, &sa, 0))
    {
        fprintf(stderr, "sigaction(SIGALRM): %s\n", strerror(errno));
        return 1;
    }

    fd = mkstemp(template);
    if (fd == -1)
    {
        fprintf(stderr, "mkstemp(%s): %s\n", template, strerror(errno));
        return 1;
    }
    unlink(template);

    alarm(1);
    if (argc >= 2 && !strcmp(argv[1], "fcntl"))
    {
        struct flock lock;
        memset(&lock, 0, sizeof(struct flock));
        lock.l_type = F_WRLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = 0;
        lock.l_len = 0; /* lock entire file */

        if (fcntl(fd, F_SETLKW, &lock))
        {
            fprintf(stderr, "setting fcntl lock: %s\n", strerror(errno));
            return 1;
        }

        lock.l_type = F_UNLCK;
        if (fcntl(fd, F_SETLK, &lock))
        {
            fprintf(stderr, "releasing fcntl lock: %s\n", strerror(errno));
            return 1;
        }
    }
    else
    {
        if (flock(fd, LOCK_EX))
        {
            fprintf(stderr, "setting flock lock: %s\n", strerror(errno));
            return 1;
        }

        if (flock(fd, LOCK_UN))
        {
            fprintf(stderr, "releasing flock lock: %s\n", strerror(errno));
            return 1;
        }
    }

    return 0;
}