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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Thu, 30 Nov 2017 17:04:40 +0100
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Subject: Re: [Qemu-devel] [PATCH RFC 0/9] block: Rewrite block drain
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To: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, jcody@redhat.com, Max Reitz <mreitz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>

On 30/11/2017 16:10, Kevin Wolf wrote:
>> Yes, I agree, but that (using CoMutex around graph change) requires
>> everything, especially the defer_to_main_loop_bh, runs in a coroutine
>> context, which is exactly what I mean by "introducing 'ubiquitous
>> coroutines'", because currently we don't have them.
> Is it hard to do, though? Instead of using a BH to switch to the main
> loop and outside of coroutine context, you could use aio_co_schedule()
> and yield, which would leave you in the main loop, but still in
> coroutine context.

Not that I think of, but just aio_co_schedule wouldn't work, because
"the coroutine must have yielded unless ctx is the context in which the
coroutine is running (i.e. the value of qemu_get_current_aio_context()
from the coroutine itself)".

So you'd have to use a bottom half that calls aio_co_schedule.  But that
would work.

Paolo

> Would this have any bad side effects I'm not aware of?