Subject: Re: [RFC v7][PATCH 2/9] General infrastructure for
	checkpoint	restart
From: Matt Helsley <matthltc@us.ibm.com>
To: Oren Laadan <orenl@cs.columbia.edu>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>,
       Andrew Morton <akpm@linux-foundation.org>, linux-api@vger.kernel.org,
       containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, tglx@linutronix.de, viro@zeniv.linux.org.uk,
       hpa@zytor.com, mingo@elte.hu, torvalds@linux-foundation.org,
       Peter Chubb <peterc@gelato.unsw.edu.au>
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Date: Mon, 27 Oct 2008 13:51:45 -0700
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On Mon, 2008-10-27 at 13:11 -0400, Oren Laadan wrote:
> Dave Hansen wrote:
> > On Mon, 2008-10-27 at 07:03 -0400, Oren Laadan wrote:
> >>> In our implementation, we simply refused to checkpoint setid
> >> programs.
> >>
> >> True. And this works very well for HPC applications.
> >>
> >> However, it doesn't work so well for server applications, for
> >> instance.
> >>
> >> Also, you could use file system snapshotting to ensure that the file
> >> system view does not change, and still face the same issue.
> >>
> >> So I'm perfectly ok with deferring this discussion to a later time :)
> > 
> > Oren, is this a good place to stick a process_deny_checkpoint()?  Both
> > so we refuse to checkpoint, and document this as something that has to
> > be addressed later?
> 
> why refuse to checkpoint ?

	If most setuid programs hold privileged resources for extended periods
of time after dropping privileges then it seems like a good idea to
refuse to checkpoint. Restart of those programs would be quite
unreliable unless/until we find a nice solution.

> if I'm root, and I want to checkpoint, and later restart, my sshd server
> (assuming we support listening sockets) - then why not ?
> we can just let it be, and have the restart fail (if it isn't root that
> does the restart); perhaps add something like warn_checkpoint() (similar
> to deny, but only warns) ?

	How will folks not specializing in checkpoint/restart know when to use
this as opposed to deny?

	Instead, how about a flag to sys_checkpoint() -- DO_RISKY_CHECKPOINT --
which checkpoints despite !may_checkpoint?

Cheers,
	-Matt Helsley

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