From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:45311)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <peter.maydell@linaro.org>) id 1Yk7bi-0002CE-6O
	for qemu-devel@nongnu.org; Mon, 20 Apr 2015 05:03:15 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <peter.maydell@linaro.org>) id 1Yk7bc-0003Br-5V
	for qemu-devel@nongnu.org; Mon, 20 Apr 2015 05:03:10 -0400
Received: from mail-ig0-f176.google.com ([209.85.213.176]:35532)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <peter.maydell@linaro.org>) id 1Yk7bc-0003Bn-0q
	for qemu-devel@nongnu.org; Mon, 20 Apr 2015 05:03:04 -0400
Received: by igbyr2 with SMTP id yr2so53941488igb.0
	for <qemu-devel@nongnu.org>; Mon, 20 Apr 2015 02:03:03 -0700 (PDT)
MIME-Version: 1.0
In-Reply-To: <20150420105411.75944c6d.cornelia.huck@de.ibm.com>
References: <1429272826-4145-1-git-send-email-shannon.zhao@linaro.org>
	<20150417154335.7fa224ce.cornelia.huck@de.ibm.com>
	<CAFEAcA8b-WBSDNvb5bhGSuwF9ojjG8R2MrnSHautPa-CgTY2_Q@mail.gmail.com>
	<20150420105411.75944c6d.cornelia.huck@de.ibm.com>
From: Peter Maydell <peter.maydell@linaro.org>
Date: Mon, 20 Apr 2015 10:02:43 +0100
Message-ID: <CAFEAcA-=czVyp_X6AkK3yzCCuAOwBOJjLXiLXNiUkW6ZbF26CQ@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [Qemu-devel] [PATCH 0/4] virtio: Move host features to backends
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>, "Huangpeng (Peter)" <peter.huangpeng@huawei.com>, QEMU Developers <qemu-devel@nongnu.org>, Shannon Zhao <shannon.zhao@linaro.org>, Shannon Zhao <zhaoshenglong@huawei.com>, Paolo Bonzini <pbonzini@redhat.com>, Christoffer Dall <christoffer.dall@linaro.org>

On 20 April 2015 at 09:54, Cornelia Huck <cornelia.huck@de.ibm.com> wrote:
> The reason why blk is ok is that it adds the feature bits in its
> ->get_features() callback. net expects the feature bits already present
> and removes not supported ones and therefore requires
> statically-defined bits somewhere.
>
> If we move the feature bits to virtio-net and virtio-scsi, it should
> work for virtio-mmio - but the feature bit propagation from the device
> into the transport becomes a bit useless.
>
> Could net and scsi add the feature bits dynamically in their
> ->get_features() callback instead? This should work for virtio-mmio as
> well afaics.

I think this is what Shannon's v2 patchset just posted does -- could
you check that it doesn't break s390 by accident?

> In the end, we should probably end up with the same mechanism for all
> device types.

Definitely agreed. I suspect we just missed the net and scsi devices
because getting this wrong doesn't make virtio-mmio totally unusable...

thanks
-- PMM