linux-kernel - Re: [PATCH 3/3] eventfd: add internal reference counting to fix notifier race conditions

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Message-ID: <alpine.DEB.1.10.0906221146210.10952@makko.or.mcafeemobile.com>
Date:	Mon, 22 Jun 2009 11:51:42 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
cc:	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	avi@...hat.com, paulmck@...ux.vnet.ibm.com,
	Ingo Molnar <mingo@...e.hu>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 3/3] eventfd: add internal reference counting to fix
 notifier race conditions

On Mon, 22 Jun 2009, Michael S. Tsirkin wrote:

> On Mon, Jun 22, 2009 at 11:03:22AM -0700, Davide Libenzi wrote:
> > In your case of kernel-to-kernel scenario, why would you need eventfd at 
> > all, if userspace role in that model is simply to create it?
> 
> That's not 100% true. We have a mode where userspace is the producer
> and/or consumer (migration mode) and we switch between that and
> direct kernel-to-kernel communication.

Then you'd need to ask yourself how to handle your complex case inside the 
KVM code, so that other eventfd users are not affected by the extra fat 
needed to handle your scenarios. Thing that seem to be continuosly tried.
A file* based kernel-to-kernel interface is rather wrong IMO.



- Davide


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