msyncing时的分段错误

我只是在学习msync的使用，但是我遇到了分割错误的问题。当我将MAPSTEP更改为一个小数字时，错误就消失了。这个代码怎么了

#define MAPSTEP 1 * 4096
main(void) {
  size_t bytesWritten =0;
  int fd;
  const char text[MAPSTEP];
  memset(text, '-', sizeof(char) * MAPSTEP);

  fd = open("/tmp/mmsyncTest", (O_CREAT | O_TRUNC | O_RDWR), 
            (S_IRWXU | S_IRWXG | S_IRWXO));
  if ( fd < 0 ) {
    perror("open() error");
    return fd;
  }

  off_t lastoffset = lseek( fd, MAPSTEP, SEEK_SET);
  bytesWritten = write(fd, " ", 1 );
  if (bytesWritten != 1 ) {
    perror("write error. ");
    return -1;
  }

  /* mmap the file. */
  void *address;
  int len;
  off_t my_offset = 0;
  len = MAPSTEP;   /* Map page */
  address = mmap(NULL, len, PROT_WRITE, MAP_SHARED, fd, my_offset);

  if ( address == MAP_FAILED ) {
    perror("mmap error. " );
    return -1;
  }

  /* Move some data into the file using memory map. */
  (void) strcpy( (char*) address, text);
  /* use msync to write changes to disk. */
  if ( msync( address, MAPSTEP , MS_SYNC ) < 0 ) {
    perror("msync failed with error:");
    return -1;
  }
  else (void) printf("%s","msync completed successfully.\n");

  close(fd);
  unlink("/tmp/msyncTest");
}

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功能unlink/tmp/msyncTest中的一个观察结果；是的，文件名与您之前打开的文件名不同。这也可能会造成分段错误