Re: [Qemu-block] [PATCH 1/4] block: Use drained section in bdrv_set_aio_context

[Paolo Bonzini]

On 16/03/2016 11:10, Fam Zheng wrote:
> An empty begin/end pair is almost the same as a bare bdrv_drain except
> the aio_poll inside is wrapped by
> aio_disable_external/aio_enable_external.
> 
> This is safer, and is the only way to achieve quiescence in this
> aio_poll(), because bdrv_drained_begin/end pair cannot span across
> context detach/attach options, so it's not possible to do by the caller.

I'm still not sure about this patch.

When starting dataplane, the ioeventfd is registered with iohandler.c so
bdrv_drained_begin/end is not necessary.

Likewise when stopping dataplane bdrv_set_aio_context is called after
the thread has been stopped and thus the ioeventfd is not registered
anymore as an external client.

Paolo