smart memcpy

[Michael Trimarchi]

Hi all,
is it possible to map a region on memory copy on write using this idea? 
I have an invalid argument in the mmap call.
Why?
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>

#define MAXPATH 255

int main (int argc, char **argv)
{
   char *s,*x;
   int i;
   int addr;
   int fd;   
   int size=40960; 
   char file_memory[MAXPATH];
   pid_t p=getpid();
   s=malloc(size);
   sprintf(file_memory,"/proc/%d/mem",(int)p);
   fd = open(file_memory,O_RDONLY);
   if (fd < 0) {
           perror(file_memory);
           exit(-1);
   }
   printf ("start %s\n",file_memory);
   printf("s = %p\n",s);
   memset(s, 'X', size);
   //lseek(fd,(int)s,SEEK_SET);
   //read(fd,&addr,1);
   //printf("%c", addr);
        
    x = mmap(0,size,PROT_READ|PROT_WRITE,MAP_PRIVATE,fd,(int)s);
    if ((int)(x)>0) {
        printf("x = %p\n",x);
        *x='P';
        for (i=0;i<40; i++)
           printf("sval=%c;xval=%c;",*(x+i),*(s+i));     
   } else {
         printf("%s\n",strerror(errno));
   }  
    return 0;
}