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Date: Mon, 30 Jun 2014 18:18:07 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v1 1/3] block: block: introduce
	bdrv_io_plug() and bdrv_io_unplug()
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To: Ming Lei <ming.lei@canonical.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Peter Maydell <peter.maydell@linaro.org>, Fam Zheng <famz@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

Il 30/06/2014 18:15, Ming Lei ha scritto:
>>> >> +int bdrv_io_unplug(BlockDriverState *bs)
>>> >> +{
>>> >> +    BlockDriver *drv = bs->drv;
>>> >> +    if (drv && drv->bdrv_io_unplug) {
>>> >> +        return drv->bdrv_io_unplug(bs);
>>> >> +    } else if (bs->file) {
>>> >> +        return bdrv_io_unplug(bs->file);
>>> >> +    }
>>> >> +    return 0;
>> >
>> >
>> > I think this should return void (and that's how you use it in patch 3
>> > indeed).  If you fix this you can add my Reviewed-by tag.
> It can be used to trace how many IO are submitted at batch,
> otherwise device can't know this information at all.

Having a return value however suggests that bdrv_io_unplug can fail.  So 
this should be documented.  For now, I'd prefer to keep it simple.

Paolo