Message-ID: <4A265FBD.3080108@novell.com>
Date: Wed, 03 Jun 2009 07:34:21 -0400
From: Gregory Haskins <ghaskins@novell.com>
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To: "Michael S. Tsirkin" <mst@redhat.com>
CC: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, avi@redhat.com,
       davidel@xmailserver.org, paulmck@linux.vnet.ibm.com
Subject: Re: [KVM-RFC PATCH 0/2] irqfd: use POLLHUP notification for close()
References: <20090602151135.29746.91320.stgit@dev.haskins.net> <20090602160434.GA6827@redhat.com> <4A254FD7.5090302@novell.com> <20090602162021.GB6827@redhat.com> <4A255484.6060401@novell.com> <20090602165949.GD6827@redhat.com> <4A256431.2080101@novell.com> <20090603063956.GA8134@redhat.com>
In-Reply-To: <20090603063956.GA8134@redhat.com>
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Michael S. Tsirkin wrote:
> On Tue, Jun 02, 2009 at 01:41:05PM -0400, Gregory Haskins wrote:
>  =20
>>> And having close not clean up the state unless you do an ioctl first =
is
>>> very messy IMO - I don't think you'll find any such examples in kerne=
l.
>>>
>>>  =20
>>>      =20
>> I agree, and that is why I am advocating this POLLHUP solution.  It wa=
s
>> only this other way to begin with because the technology didn't exist
>> until Davide showed me the light.
>>
>> Problem with your request is that I already looked into what is
>> essentially a bi-directional reference problem (for a different reason=
)
>> when I started the POLLHUP series.  Its messy to do this in a way that=

>> doesn't negatively impact the fast path (introducing locking, etc) or
>> make my head explode making sure it doesn't race.  Afaict, we would ne=
ed
>> to solve this problem to do what you are proposing (patches welcome).
>>
>> If this hybrid decoupled-deassign + unified-close is indeed an importa=
nt
>> feature set, I suggest that we still consider this POLLHUP series for
>> inclusion, and then someone can re-introduce DEASSIGN support in the
>> future as a CAP bit extension.  That way we at least get the desirable=

>> close() properties that we both seem in favor of, and get this advance=
d
>> use case when we need it (and can figure out the locking design).
>>
>>    =20
>
> FWIW, I took a look and yes, it is non-trivial.
> I concur, we can always add the deassign ioctl later.
>
>
>
>  =20

Sounds good, Michael.  Thanks!

-Greg


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