From mboxrd@z Thu Jan  1 00:00:00 1970
From: Pekka Enberg <penberg@kernel.org>
Subject: Re: [PATCH 5/5] ioeventfd: Introduce KVM_IOEVENTFD_FLAG_SOCKET
Date: Wed, 13 Jul 2011 14:14:26 +0300
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Cc: "Michael S. Tsirkin" <mst@redhat.com>, kvm@vger.kernel.org,
	Avi Kivity <avi@redhat.com>, Ingo Molnar <mingo@elte.hu>,
	Marcelo Tosatti <mtosatti@redhat.com>
To: Sasha Levin <levinsasha928@gmail.com>
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On Wed, Jul 13, 2011 at 1:56 PM, Pekka Enberg <penberg@kernel.org> wrote:
> On Wed, Jul 13, 2011 at 1:26 PM, Sasha Levin <levinsasha928@gmail.com> wrote:
>> The problem is that if we received a signal during the read notification
>> the write and before receiving the read, we have to go back to
>> userspace.
>>
>> This means that userspace will see same read request twice (once in the
>> socket and once in the MMIO exit).
>
> So the problem is only in ioeventfd_read() if socket_write() succeeds
> but socket_read() fails? If so, can we do the socket_read() somewhere
> else in the code which is able to restart it?
>
> AFAICT, both ioeventfd_read() and ioeventfd_write() should -ENOSUPP if
> socket_write() fails. If socket_write() succeeds, we should return
> -EINTR and teach vcpu_mmio_read() and kernel_pio() to KVM_EXIT_INTR in
> those cases. We'll can just restart the read, no? The only
> complication I can see is that ioeventfd_read() needs to keep track if
> it did the socket_write() already or not.

Maybe struct _ioeventfd could hold a flag that tells ioevenfd_read()
that the write part was already successful?