quick C program to re-read a partition table on Linux:

  #include <stdio.h>
  #include <sys/ioctl.h>
  
  #include <linux/fs.h>
  
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <fcntl.h>
  
  int main (int argc, char **argv) {
        int fd= open("/dev/hda",O_RDWR);
        ioctl (fd, BLKRRPART);
        ioctl (fd, BLKFLSBUF);
        close(fd);
  }