Subject: Re: RFC [patch 00/34] PID Virtualization Overview
From: Dave Hansen <haveblue@us.ibm.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Suleiman Souhlal <ssouhlal@FreeBSD.org>, Serge Hallyn <serue@us.ibm.com>,
       linux-kernel@vger.kernel.org, Hubertus Franke <frankeh@watson.ibm.com>,
       Cedric Le Goater <clg@fr.ibm.com>
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Date: Wed, 18 Jan 2006 11:01:52 -0800
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On Tue, 2006-01-17 at 18:29 +0000, Alan Cox wrote:
> On Maw, 2006-01-17 at 10:12 -0800, Dave Hansen wrote:
> > You do assign new pids, at least as far as the kernel is concerned.
> > However, any processes that continue to run would get confused if their
> > pid changed.  You have to make sure that the tasks have a _consistent_
> > view of which process is which pid.
> 
> Don't reassign the pid at all. Keep task->container and do the job
> explicitly. Most task searches for a pid are abstracted already and most
> users of ->pid who try and use it for comparing two tasks for equality
> or for keeping a task reference are already terminally racey and want
> fixing anyway.

Other than searches, there appear to be quite a number of drivers an
subsystems that like to print out pids.  I can't find any cases yet
where these are integral to functionality, but I wonder what approach we
should take.  Should we deprecate printk'ing of pids?  Make a special
function or % modifier to turn a task_struct into something printable?

A function would run into issues of having buffers in which to print the
output.  But, we'd be able to do things like:

	sprintf(buffer, "%d:%d", tsk->container, tsk->pid);

-- Dave

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