#include <stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include <fcntl.h>
#include <sys/mman.h>

#define FILENAME "/tmp/___1___"
#define MMAPSIZE 1024

int main(int argc,char **argv) {
  char *ptr;
  int fd;

  fd = open(FILENAME, O_CREAT|O_RDWR, 00666 ) ;  /* O_TRUNC ? */
  ptr = (char *) malloc (MMAPSIZE) ;
  memset (ptr, 0x00, MMAPSIZE) ;
  write(fd, ptr, MMAPSIZE) ;
  free(ptr) ;
  close(fd) ;

  fd=open(FILENAME, O_RDWR, 00666 ) ;
  ptr = (char *)
   		mmap(0, MMAPSIZE, PROT_READ|PROT_WRITE,
		MAP_SHARED,fd, 0) ;
  fork();
}