From: Subhobroto Sinha <[EMAIL PROTECTED]>
I wanna know indepth about the COW implementation of
fork() in Linux 2.4 and higher - all including page
table stuff..
You need a book ;) not a LUG for that.
Oh, and a quickie :
When we print an address of a variable, is it the
virtual address or the physical one which is printed ?
printf("%04X", &i); /* Is virtual address of 'i'
This statement invokes UB. See below.
printed or the physical one ?*/
And what exactly do you mean by virtual/physical address?
Methinks it's the virtual address as from the page
table. Am I right ?
AFAIK, C does not have any idea of virtual/physical address.
If you didn't get it, or think I am on dope, consider
this :
#include <stdio.h>
int main()
{
int i = 5, pid, count, *p = &i;
char choice[4] = {0};
printf("\ni = %d (%X)\n", i, &i);
printf("\nFork ?\n");
scanf("%s", choice);
if(choice[0] == 'y')
{
pid = fork();
if(pid < 0)
{
printf("\nfork() failed\n");
}
else if(pid == 0)
{
i = 6;
printf("\nChild : %d (%X)\n", i, &i);
}
else
{
printf("\n[1]Spawned child pid = %d, i = %d
(%X)\n", pid, i, &i);
wait(0);
printf("\n[2]Spawned child pid = %d, i = %d
(%X)\n", pid, i, &i);
printf("\nDone waiting for child\n");
}
printf("{%d} ", pid);
for(count = 0; count < 10; ++count, --p) printf("%x
", *p);
printf("\n{%d}i : %d (%X)\n", pid, i, &i);
}
return 0;
}
Look at it closely, and match it with the output. Who
can explain that to me ?
Did you try to compile this? Here are the results of my efforts:
gcc -std=c99 -W -Wall -pedantic -ansi Test.c
Test.c:29: warning: format '%X' expects type 'unsigned int', but argument
3 has type 'int *'
Test.c:37: warning: implicit declaration of function 'fork'
Test.c:46: warning: format '%X' expects type 'unsigned int', but argument
3 has type 'int *'
Test.c:50: warning: format '%X' expects type 'unsigned int', but argument
4 has type 'int *'
Test.c:51: warning: implicit declaration of function 'wait'
Test.c:52: warning: format '%X' expects type 'unsigned int', but argument
4 has type 'int *'
Test.c:60: warning: format '%X' expects type 'unsigned int', but argument
4 has type 'int *'
Hints:
*) man scanf / `p' conversion specifier, and the need to cast it to (void *)
*) header inclusion
Regards,
Suman.
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