linux-kernel - Re: [KVM-RFC PATCH 0/2] irqfd: use POLLHUP notification for close()

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Date:	Tue, 02 Jun 2009 12:14:15 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, avi@...hat.com,
	davidel@...ilserver.org, paulmck@...ux.vnet.ibm.com
Subject: Re: [KVM-RFC PATCH 0/2] irqfd: use POLLHUP notification for close()

Michael S. Tsirkin wrote:
> On Tue, Jun 02, 2009 at 11:15:28AM -0400, Gregory Haskins wrote:
>   
>> (Applies to kvm.git/master:25deed73)
>>
>> Please see the header for 2/2 for a description.  This patch series has
>> been fully tested and appears to be working correctly.  I have it as an RFC
>> for now because it needs Davide's official submission/SOB for patch 1/2, and
>> it should get some eyeballs/acks on my SRCU usage before going in.
>>
>> I will submit the updated irqfd userspace which eschews the deassign() verb
>> since we can now just use the close(fd) method alone.  I will also address
>> the userspace review comments from Avi.
>>     
>
>
> We are not killing the deassign though, do we?
>   

Yes, it is not needed any more now that we have proper
release-notification from eventfd.

> It's good to have that option e.g. for when we pass
> the fd to another process.
>   

Passing the fd to another app should up the underlying file reference
count.  If the producer app wants to "deassign" it simply calls
close(fd) (as opposed to today where it calls DEASSIGN+close), but the
reference count will allow the consuming app to leave the eventfd's file
open.  Or am I misunderstanding you?

-Greg



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