linux-kernel - Re: [PATCH 19/20] Changes to show virtual ids to user

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Date:	Tue, 14 Aug 2007 13:12:02 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	xemul@...nvz.org
Cc:	devel@...nvz.org, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, oleg@...sign.ru, sukadev@...ibm.com
Subject: Re: [PATCH 19/20] Changes to show virtual ids to user

On Fri, 10 Aug 2007 15:48:28 +0400
xemul@...nvz.org wrote:

> This is the largest patch in the set. Make all (I hope) the places where
> the pid is shown to or get from user operate on the virtual pids.
> 
> The idea is:
>  - all in-kernel data structures must store either struct pid itself
>    or the pid's global nr, obtained with pid_nr() call;
>  - when seeking the task from kernel code with the stored id one
>    should use find_task_by_pid() call that works with global pids;
>  - when showing pid's numerical value to the user the virtual one
>    should be used, but however when one shows task's pid outside this
>    task's namespace the global one is to be used;
>  - when getting the pid from userspace one need to consider this as
>    the virtual one and use appropriate task/pid-searching functions.
> 
> ...
>
> -	si.si_pid = current->pid;
> +	si.si_pid = task_pid_vnr(current);

This is going to be an ongoing maintenance problem: people will sneak
new references to current->pid into the tree and nobody will notice.

It'd be best to rename task_struct.pid to something else to catch such
problems and to force people to use the right accessors.  Is that feasible?

Generally this is a tactic which should be used whenever things like this
are virtualised.
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