linux-kernel - Re: [RFC][PATCH 8/8] check files for checkpointability

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Message-ID: <20090302112247.76bb3662@thinkcentre.lan>
Date:	Mon, 2 Mar 2009 11:22:47 -0600
From:	Nathan Lynch <ntl@...ox.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	containers <containers@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	hch@...radead.org, Ingo Molnar <mingo@...e.hu>,
	Alexey Dobriyan <adobriyan@...il.com>
Subject: Re: [RFC][PATCH 8/8] check files for checkpointability

On Mon, 02 Mar 2009 08:27:31 -0800
Dave Hansen <dave@...ux.vnet.ibm.com> wrote:

> On Mon, 2009-03-02 at 09:59 -0600, Nathan Lynch wrote:
> > On Mon, 2 Mar 2009 07:37:54 -0600
> > "Serge E. Hallyn" <serue@...ibm.com> wrote:
> > > So on a practical note, Ingo's scheme appears to be paying off.
> > > In order for any program's files_struct to be checkpointable
> > > right now, it must be statically compiled, else ld.so (I assume)
> > > looks up /proc/$$/status.  So since proc is not checkpointable,
> > > the result is irreversibly non-checkpointable.
> > > 
> > > So...  does it make sense to mark proc as checkpointable?  Do we
> > > reasonably assume that the same procfile will be available at
> > > restart?
> > 
> > With respect to /proc/$x/* where $x is the pid the restarted task
> > wants, is that not a chicken-and-egg problem?
> 
> Do you mean that we have to go look into /proc to figure out which
> task we want before we can checkpoint it?  That makes the process
> *doing* the checkpoint uncheckpointable, but no the process being
> examined.

No.. I mean what if a process 1234 does

f = fopen("/proc/1234/stat", "r");

and is then checkpointed.  Can that path be resolved during restart,
before pid 1234 is alive?
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