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Date: Fri, 22 Aug 2014 12:10:35 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC PATCH 1/9] block: Add bdrv_aio_cancel_async
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To: Fam Zheng <famz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

Il 22/08/2014 11:37, Fam Zheng ha scritto:
> Exactly. I'd rather not change the contract then.
> 
> Alternatively, we may add a refcnt field to BlockDriverAioCB and grab one before
> calling .cancel, so the qemu_aio_release will not free it.

Yes, and I don't exclude that sooner or later we'll have to add
reference counts to AIOCB anyway.  However, reference counting is not
_that_ cheap so for now I'd rather see other solutions explored.

The problem is implementing cancel_sync in terms of cancel.  The
simplest solution, for now, is to make bdrv_aio_cancel_async return
false if the callback is not implemented, and fall back to synchronous
cancellation.

Paolo