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Re: [Qemu-block] [PATCH v4 3/3] aio: Introduce aio-epoll.c

From: Stefan Hajnoczi
Subject: Re: [Qemu-block] [PATCH v4 3/3] aio: Introduce aio-epoll.c
Date: Mon, 2 Nov 2015 13:19:16 +0000
User-agent: Mutt/1.5.24 (2015-08-30)

On Mon, Nov 02, 2015 at 10:32:54AM +0800, Fam Zheng wrote:
> On Fri, 10/30 10:07, Stefan Hajnoczi wrote:
> > On Fri, Oct 30, 2015 at 12:06:29PM +0800, Fam Zheng wrote:
> > > To comply with aio_{disable,enable}_external, we always use ppoll when
> > > aio_external_disabled() is true.
> > 
> > All file descriptors are added to the epoll fd.  Does that mean epoll
> > will report the same fds again after we come out of
> > ppoll()/aio_external_disabled()?
> > 
> > The two constraints to think about:
> > 1. Ideally there should be no duplicated events.
> > 2. There absolutely cannot be any missed events.
> > 
> I'm not sure I understood your question. The file descriptors added to epollfd
> are always in sync with ppoll, so there is no difference between calling
> epoll_wait and ppoll. When we come out of aio_external_disabled(), the same 
> set
> of fds will be polled, but the events got by ppoll should already be handled.
> What am I missing?

I'm asking about duplicated events.  The epoll fd monitors the same set
of fds as ppoll().  When we come out of aio_external_disabled() will
epoll fd see the old events that have already been handled by ppoll()?


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