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

[Fam Zheng <famz@redhat.com>]

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?

Fam