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Re: [Qemu-devel] [RFC] block: Removed coroutine ownership assumption

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [RFC] block: Removed coroutine ownership assumption
Date: Mon, 2 Jul 2012 09:50:20 +0100

On Fri, Jun 29, 2012 at 12:51 PM, Peter Crosthwaite
<address@hidden> wrote:
> BTW Yielding is one thing, but the elephant in the room here is
> resumption of the coroutine. When AIO yields my coroutine I i need to
> talk to AIO to get it unyielded (Stefans propsoed edit to my code).
> What happens when tommorow something in QOM, or a device model or  is
> implemented with coros too? how do I know who yielded my routines and
> what API to call re-enter it?

Going back to what Kevin said, the qemu_aio_wait() isn't block layer
specific and there will never be a requirement to call any other magic

QEMU is event-driven and you must pump events.  If you call into
another subsystem, be prepared to pump events so that I/O can make
progress.  It's an assumption that is so central to QEMU architecture
that I don't see it as a problem.

Once the main loop is running then the event loop is taken care of for
you.  But during startup you're in a different environment and need to
pump events yourself.

If we drop bdrv_read()/bdrv_write() this won't change.  You'll have to
call bdrv_co_readv()/bdrv_co_writev() and pump events.


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