Re: vfork implementation...

[Gleb Natapov <gleb@minantech.com>]

On Wed, Jun 14, 2006 at 03:47:07PM +0530, Abu M. Muttalib wrote:
> HI,
> 
> Should the wording be interpreted as "should not write"?
> 
Yes. After vfork() a child and a parent share an address space. Whatever a child
does to memory is visible in a parent.

> ~Abu.
> 
> -----Original Message-----
> From: Gleb Natapov [mailto:gleb@minantech.com]
> Sent: Wednesday, June 14, 2006 3:37 PM
> To: Abu M. Muttalib
> Cc: linux-mm@kvack.org
> Subject: Re: vfork implementation...
> 
> 
> 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.
> > >
> > > --
> > > To unsubscribe, send a message with 'unsubscribe linux-mm' in
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> >
> > --
> > 			Gleb.
> >
> > --
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> 
> --
> 			Gleb.

--
			Gleb.

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