linux-kernel - Re: [PATCH] pid: change task

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Date:	Thu, 23 Jan 2014 14:24:03 -0500
From:	Richard Guy Briggs <rgb@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	akpm@...ux-foundation.org, Peter Zijlstra <peterz@...radead.org>,
	linux-audit@...hat.com, linux-kernel@...r.kernel.org,
	Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH] pid: change task_struct::pid to read-only

On 13/12/22, Oleg Nesterov wrote:
> On 12/20, Peter Zijlstra wrote:
> >
> > On Fri, Dec 20, 2013 at 08:01:57PM +0100, Oleg Nesterov wrote:
> > > The only problem is that
> > >
> > > 	#define ASSIGN_CONST(l, r)      (*(typeof(r) *)&(l) = (r))
> > >
> > > obviously can't work in this case ;) We need something more clever.
> >
> > Hmm indeed, C++ has both the const_cast<>() thingy and the template
> > system is powerful enough to actually implement const_cast<>() inside
> > the language.
> 
> So, how about
> 
> 	#define CONST_CAST(type, lval)	\
> 		(*({					\
> 			(void)((type *)0 == &(lval));	\
> 			(type *)&(lval);		\
> 		}))					\
> 
> de_thread/copy_process can do
> 
> 	CONST_CAST(pid_t, tsk->pid) = leader->pid;
> 
> and if "type" is wrong we have a warning.

Cool.  This works very nicely.  Thanks for the ideas Oleg!

> Oleg.

- RGB

--
Richard Guy Briggs <rbriggs@...hat.com>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
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