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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);
}

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