linux-kernel - Re: [KVM PATCH v4 2/2] kvm: add support for irqfd via eventfd-notification interface

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Date:	Wed, 6 May 2009 18:34:52 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Gregory Haskins <ghaskins@...ell.com>
cc:	viro@...IV.linux.org.uk, kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	avi@...hat.com
Subject: Re: [KVM PATCH v4 2/2] kvm: add support for irqfd via eventfd-notification
 interface

On Wed, 6 May 2009, Gregory Haskins wrote:

> I think we are ok in this regard (at least in v5) without the callback. 
> kvm holds irqfd, which holds eventfd.  In a normal situation, we will
> have eventfd with 2 references.  If userspace closes the eventfd, it
> will drop 1 of the 2 eventfd file references, but the object should
> remain intact as long as kvm still holds it as well.  When the kvm-fd is
> released, we will then decouple from the eventfd->wqh and drop the last
> fput(), officially freeing it.
> 
> Likewise, if kvm is closed before the eventfd, we will simply decouple
> from the wqh and fput(eventfd), leaving the last reference held by
> userspace until it closes as well.
> 
> Let me know if you see any holes in that.

Looks OK, modulo my knowledge of KVM internals.


- Davide


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