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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Mon, 12 Oct 2015 16:27:06 +0200
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Subject: Re: [Qemu-devel] [PATCH v2 05/12] block: Introduce "drained
	begin/end" API
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To: Fam Zheng <famz@redhat.com>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, qemu-block@nongnu.org



On 12/10/2015 13:50, Fam Zheng wrote:
> +void bdrv_drained_begin(BlockDriverState *bs)
> +{
> +    if (bs->quiesce_counter++) {
> +        return;
> +    }
> +    aio_disable_external(bdrv_get_aio_context(bs));
> +    bdrv_drain(bs);
> +}

I think bdrv_drain should be called unconditionally, i.e. before the
"if".  This should also solve Kevin's doubt about new allocating write
request reenabling the timer: any write request from the drained section
happens normally, until you get a nested drain request and then the
callback completes the requests.

Paolo