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Date: Thu, 28 May 2015 18:46:16 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v6 01/13] block: Add op blocker type
 "device IO"
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org, armbru@redhat.com, jcody@redhat.com, qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, amit.shah@redhat.com

On Thu, 05/28 10:23, Paolo Bonzini wrote:
> 
> 
> On 28/05/2015 04:49, Fam Zheng wrote:
> > 
> > On a second thought, although in this series, we only need to modify
> > virtio-{scsi,blk}, Wen pointed out that mirror job also wants this during
> > completion (because bdrv_swap is in a BH after the job coroutine returns).
> 
> Mirror needs to pause/resume the source.  It doesn't need to handle
> pause/resume of the target, does it?
> 
> > So, in order for the solution to be general, and complete, this nofitier list
> > approach relies on the listening devices to do the right thing, which requires
> > modifying all of them, and is harder to maintain.
> 
> Isn't it only devices that use aio_set_event_notifier for their ioeventfd?

I think it's only the case for qmp_transaction, mirror job needs all block
devices to implement pause: mirror_run guarantees source and target in sync
when it returns; but bdrv_swap is deferred to a main loop bottom half -  what
if there is a guest write to source in between?

Fam