进程间通信，共享内存，mmap操作文件指针

此代码来自...[反正不是自己写的]
nginx使用了mmap（）来操作共享内存，但是没有使用文件指针，对于不使用文件指针的第二个进程怎么获取内存

/**************************************************************************************/
/*简介：mmap_write共享内存，写操作子程序 */
/*************************************************************************************/
#include <sys/mman.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

typedef struct
{
 char name[4];
 int age;
}people;

int main(int argc, char** argv)
{
 int fd,i;
 people *p_map;
 char name[4];
 if (argc != 2)
 {
    perror("usage: mmap_write ");
    return 1;
 }

 fd=open(argv[1],O_CREAT|O_RDWR|O_TRUNC,00777);
 lseek(fd,sizeof(people)*5-1,SEEK_SET);
 write(fd,"",1);

 p_map = (people*) mmap( NULL,sizeof(people)*10,\
  PROT_READ|PROT_WRITE,MAP_SHARED,fd,0 );
 close( fd );
 name[0] = 'a';
 name[1] = '\0';
 for(i=0; i<10; i++)
 {
  name[0] ++;
  memcpy( ( *(p_map+i) ).name, &name,sizeof(name) );
  ( *(p_map+i) ).age = 20+i;
 }
 printf(" initialize over \n ");
 sleep(10);

 munmap( p_map, sizeof(people)*10 );
 printf( "umap ok \n" );
 return 0;
}

/**************************************************************************************/
/*简介：mmap_read共享内存，读操作子程序 */
/*************************************************************************************/
#include <sys/mman.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

typedef struct
{
 char name[4];
 int age;
}people;

int main(int argc, char** argv)
{
 int fd,i;
 people *p_map;
 if (argc != 2)
 {
  perror("usage: mmap_read ");
  return 1;
 }
 fd=open( argv[1],O_CREAT|O_RDWR,00777 );
 p_map = (people*)mmap(NULL,sizeof(people)*10,\
  PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);
 close(fd);
 for(i = 0;i<10;i++)
 {
  printf( "name: %s age %d;\n",(*(p_map+i)).name, (*(p_map+i)).age );
 }
 munmap( p_map,sizeof(people)*10 );
 return 0;
}