Re: vfork implementation...

[Gleb Natapov <gleb@minantech.com>]

On Wed, Jun 14, 2006 at 03:33:27PM +0530, Abu M. Muttalib wrote:
> I meant, its NOT ALLOWED, still program is ABLE to do so.. hence the
> wordings..
> 
The only thing a process ALLOWED to do after vfork() is exec(), but it is
ABLE to do whatever it wants to do. I am not ALLOWED to drive while drunk,
but I am ABLE to.


> ~Abu.
> 
> -----Original Message-----
> From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org]On
> Behalf Of Gleb Natapov
> Sent: Wednesday, June 14, 2006 3:16 PM
> To: Abu M. Muttalib
> Cc: linux-mm@kvack.org
> Subject: Re: vfork implementation...
> 
> 
> On Wed, Jun 14, 2006 at 03:11:58PM +0530, Abu M. Muttalib wrote:
> > Hi,
> >
> > This mail is intended for Robert Love, I hope I can find him on the list.
> >
> > Please refer to Pg 24 of chapter 2 of Linux Kernel Development.
> >
> > As mentioned in the description of vfork call, it is said that child is
> not
> > allowed to write to the address space, but in the following example its
> not
> > so. The child is able to write to the process address space. This program
> > was tested with Linux Kernel 2.6.9. Why is it so?
> >
> Not allowed and not able are two different things.
> 
> > fork.c
> > --------------------------------------------------------------------------
> --
> > ---------------------------------------
> > #include <stdio.h>
> >
> > unsigned char *glob_var = NULL;
> >
> > void main()
> > {
> > 	int pid = -8,i;
> > 	pid = vfork();
> >
> > 	if(pid < 0)
> > 		printf("\n FORK ERROR \n");
> >
> > 	if(pid == 0)
> > 	{
> > 		unsigned char * local_var = NULL;
> > 		local_var = (unsigned char *)malloc(5);
> > 		strcpy(local_var,"ABCD");
> > 		glob_var = local_var;
> > 		printf("\nCHILD :Value of glob_var is  %X local_var is %X glob_var is %c
> > \n",glob_var,local_var,*glob_var);
> > 		for(i=0;i<4;i++)
> > 		{
> > 			printf("\n CHAR is %c \n",glob_var[i]);
> > 		}
> > 		printf("\nCHILD1 :Value of glob_var is %X %c\n",glob_var,*(glob_var));
> > 	}
> >
> > 	if(pid > 0)
> > 	{
> > 		printf("\nParent : Value of glob_var is  %X %c\n",glob_var,*(glob_var));
> > 		free(glob_var);
> > 		printf("\nParent : Value of glob_var is %X %c\n",glob_var,*(glob_var));
> > 		exit(0);
> > 	}
> > }
> > --------------------------------------------------------------------------
> --
> > ---------------------------------------
> >
> > Regards,
> > Abu.
> >
> > --
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> 
> --
> 			Gleb.
> 
> --
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--
			Gleb.

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