beginner question on do_page_fault function and COW

[Vincenzo Mallozzi <vinjunior@xxxxxxxx>]

Hi all,
I've modified the do_page_fault function adding the
line

        printk(KERN_DEBUG "line added to
PAGE_FAULT!!!\n");

on top of it, then I've compiled the file and I've
rebooted my machine.
Now, I want to do a page fault in order to obtain the
string "line added to PAGE_FAULT!!!" in my
/var/log/debug file.
I've read that COW is handled by do_page_fault
function, so I've compiled and executed a simple
"fork" file (listed below) in which I do a fork and
then modify a global and a local variable in order to
obtain a COW.
At this point, I expect the searched string as output
but nothing seems matter.
Where I fail?
Can anyone help me?

Vincenzo Mallozzi.


#include <sys/types.h>
#include <unistd.h>

int glob = 6;
char buf[] = "a write to stdout\n";

int main (void)
{
  int var;
  pid_t pid;

  var = 88;
  if (write(STDOUT_FILENO, buf, sizeof(buf)-1) !=
sizeof(buf)-1)
    printf("write error");

  printf("before fork\n");
  if ((pid=fork())<0)
    printf("fork error");
  else if (pid=0){
    glob++;
    var++;
  }else{
    glob++;
    var++;
    sleep(2);
  }
  exit(0);
} 



		
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