source: vendor/3.6.0/tests/fcntl_lock.c

/* test whether fcntl locking works on this system */

#if defined(HAVE_UNISTD_H)
#include <unistd.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>

#ifdef HAVE_FCNTL_H
#include <fcntl.h>
#endif

#ifdef HAVE_SYS_FCNTL_H
#include <sys/fcntl.h>
#endif

#ifdef HAVE_SYS_WAIT_H
#include <sys/wait.h>
#endif

#include <errno.h>

static int sys_waitpid(pid_t pid,int *status,int options)
{
#ifdef HAVE_WAITPID
  return waitpid(pid,status,options);
#else /* USE_WAITPID */
  return wait4(pid, status, options, NULL);
#endif /* USE_WAITPID */
}

#define DATA "conftest.fcntl"

#ifndef SEEK_SET
#define SEEK_SET 0
#endif

/* lock a byte range in a open file */
int main(int argc, char *argv[])
{
        struct flock lock;
        int fd, ret, status=1;
        pid_t pid;
        char *testdir = NULL;

        testdir = getenv("TESTDIR");
        if (testdir) chdir(testdir);

        alarm(10);

        if (!(pid=fork())) {
                sleep(2);
                fd = open(DATA, O_RDONLY);

                if (fd == -1) {
                        fprintf(stderr,"ERROR: failed to open %s (errno=%d)\n", 
                                DATA, (int)errno);
                        exit(1);
                }

                lock.l_type = F_WRLCK;
                lock.l_whence = SEEK_SET;
                lock.l_start = 0;
                lock.l_len = 4;
                lock.l_pid = getpid();
                
                lock.l_type = F_WRLCK;
                
                /* check if a lock applies */
                ret = fcntl(fd,F_GETLK,&lock);

                if ((ret == -1) ||
                    (lock.l_type == F_UNLCK)) {
                        fprintf(stderr,"ERROR: lock test failed (ret=%d errno=%d)\n", ret, (int)errno);
                        exit(1);
                } else {
                        exit(0);
                }
        }

        unlink(DATA);
        fd = open(DATA, O_RDWR|O_CREAT|O_EXCL, 0600);

        if (fd == -1) {
                fprintf(stderr,"ERROR: failed to open %s (errno=%d)\n", 
                        DATA, (int)errno);
                exit(1);
        }

        lock.l_type = F_WRLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = 0;
        lock.l_len = 4;
        lock.l_pid = getpid();

        /* set a 4 byte write lock */
        fcntl(fd,F_SETLK,&lock);

        sys_waitpid(pid, &status, 0);

        unlink(DATA);

#if defined(WIFEXITED) && defined(WEXITSTATUS)
    if(WIFEXITED(status)) {
        status = WEXITSTATUS(status);
    } else {
        status = 1;
    }
#else /* defined(WIFEXITED) && defined(WEXITSTATUS) */
        status = (status == 0) ? 0 : 1;
#endif /* defined(WIFEXITED) && defined(WEXITSTATUS) */

        if (status) {
                fprintf(stderr,"ERROR: lock test failed with status=%d\n", 
                        status);
        }

        exit(status);
}