Re: [Qemu-devel] [PATCH 2/2] virtio-blk: disable write cache if not negotiated

From: Paolo Bonzini <pbonzini@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: anthony@codemonkey.ws, rusty@rustcorp.com.au,
	qemu-devel@nongnu.org, kvm@vger.kernel.org, mst@redhat.com
Subject: Re: [Qemu-devel] [PATCH 2/2] virtio-blk: disable write cache if not negotiated
Date: Wed, 04 Jul 2012 14:21:19 +0200	[thread overview]
Message-ID: <4FF4353F.8010809@redhat.com> (raw)
In-Reply-To: <4FF417F3.2090400@redhat.com>

Il 04/07/2012 12:16, Kevin Wolf ha scritto:
>> > Yes.  It doesn't override cache=unsafe though.
> When the guest doesn't support flushes, cache=writeback is equivalent to
> cache=unsafe, so if you want the old behaviour back you can switch to
> cache=unsafe without additional risks.
> 
> We don't have a cache=directunsafe, though, so if you want to get the
> old behaviour of cache=none back, you're out of luck. Not sure how
> acceptable this is.

If we want to fix this, let's take the occasion to split the parameters
into cache=on/off (well, we have that already), flush=on/off, and a
device-side wce=on/off.

> Irrespective of this concern I've come to the conclusion that I agree
> and we actually must enforce this for non-unsafe mode, and not doing it
> is a bug.

Thanks!  Is that an Acked-by/Reviewed-by? :)

Paolo