From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cornelia Huck Subject: Re: [Qemu-devel] [PATCH RFC 05/11] virtio: introduce legacy virtio devices Date: Mon, 3 Nov 2014 12:44:59 +0100 Message-ID: <20141103124459.553cb103.cornelia.huck@de.ibm.com> References: <1412692807-12398-1-git-send-email-cornelia.huck@de.ibm.com> <1412692807-12398-6-git-send-email-cornelia.huck@de.ibm.com> <20141028164018.29d73d9f@bahia.local> <20141030190201.41e8940d.cornelia.huck@de.ibm.com> <20141030232950.00ee96e4@bahia.local> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: virtualization@lists.linux-foundation.org, qemu-devel@nongnu.org, kvm@vger.kernel.org, rusty@rustcorp.com.au, thuth@linux.vnet.ibm.com To: Greg Kurz Return-path: Received: from e06smtp14.uk.ibm.com ([195.75.94.110]:56102 "EHLO e06smtp14.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751081AbaKCLpJ (ORCPT ); Mon, 3 Nov 2014 06:45:09 -0500 Received: from /spool/local by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 3 Nov 2014 11:45:08 -0000 Received: from b06cxnps3075.portsmouth.uk.ibm.com (d06relay10.portsmouth.uk.ibm.com [9.149.109.195]) by d06dlp03.portsmouth.uk.ibm.com (Postfix) with ESMTP id C126D1B0804B for ; Mon, 3 Nov 2014 11:45:10 +0000 (GMT) Received: from d06av02.portsmouth.uk.ibm.com (d06av02.portsmouth.uk.ibm.com [9.149.37.228]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id sA3Bj5kG14614962 for ; Mon, 3 Nov 2014 11:45:05 GMT Received: from d06av02.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av02.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id sA3Bj34r012185 for ; Mon, 3 Nov 2014 04:45:05 -0700 In-Reply-To: <20141030232950.00ee96e4@bahia.local> Sender: kvm-owner@vger.kernel.org List-ID: On Thu, 30 Oct 2014 23:29:50 +0100 Greg Kurz wrote: > On Thu, 30 Oct 2014 19:02:01 +0100 > Cornelia Huck wrote: > > > On Tue, 28 Oct 2014 16:40:18 +0100 > > Greg Kurz wrote: > > > > > On Tue, 7 Oct 2014 16:40:01 +0200 > > > Cornelia Huck wrote: > > > > > > > Introduce a helper function to indicate whether a virtio device is > > > > operating in legacy or virtio standard mode. > > > > > > > > It may be used to make decisions about the endianess of virtio accesses > > > > and other virtio-1 specific changes, enabling us to support transitional > > > > devices. > > > > > > > > Reviewed-by: Thomas Huth > > > > Signed-off-by: Cornelia Huck > > > > --- > > > > hw/virtio/virtio.c | 6 +++++- > > > > include/hw/virtio/virtio-access.h | 4 ++++ > > > > include/hw/virtio/virtio.h | 13 +++++++++++-- > > > > 3 files changed, 20 insertions(+), 3 deletions(-) > > > > > > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > > > > index 7aaa953..e6ae3a0 100644 > > > > --- a/hw/virtio/virtio.c > > > > +++ b/hw/virtio/virtio.c > > > > @@ -883,7 +883,11 @@ static bool virtio_device_endian_needed(void *opaque) > > > > VirtIODevice *vdev = opaque; > > > > > > > > assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN); > > > > - return vdev->device_endian != virtio_default_endian(); > > > > + if (virtio_device_is_legacy(vdev)) { > > > > + return vdev->device_endian != virtio_default_endian(); > > > > + } > > > > + /* Devices conforming to VIRTIO 1.0 or later are always LE. */ > > > > + return vdev->device_endian != VIRTIO_DEVICE_ENDIAN_LITTLE; > > > > } > > > > > > > > > > Shouldn't we have some code doing the following somewhere ? > > > > > > if (!virtio_device_is_legacy(vdev)) { > > > vdev->device_endian = VIRTIO_DEVICE_ENDIAN_LITTLE; > > > } > > > > > > also, since virtio-1 is LE only, do we expect device_endian to > > > be different from VIRTIO_DEVICE_ENDIAN_LITTLE ? > > > > device_endian should not depend on whether the device is legacy or not. > > virtio_is_big_endian always returns false for virtio-1 devices, though. > > Sorry, I had missed the virtio_is_big_endian() change: it that makes > device_endian a legacy virtio only matter. > So why would we care to migrate the endian subsection when we have a > virtio-1 device ? Shouldn't virtio_device_endian_needed() return false > for virtio-1 ? Indeeed, we can just leave device_endian at the default value for virtio-1 devices.