From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49241) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YsATG-0001F1-8J for qemu-devel@nongnu.org; Tue, 12 May 2015 09:43:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YsATB-0003ok-4w for qemu-devel@nongnu.org; Tue, 12 May 2015 09:43:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46500) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YsATA-0003oV-VJ for qemu-devel@nongnu.org; Tue, 12 May 2015 09:43:37 -0400 Date: Tue, 12 May 2015 15:34:47 +0200 From: "Michael S. Tsirkin" Message-ID: <20150512153150-mutt-send-email-mst@redhat.com> References: <20150506120729.8607.23404.stgit@bahia.huguette.org> <20150506120737.8607.30158.stgit@bahia.huguette.org> <20150512151453.42880d6c.cornelia.huck@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150512151453.42880d6c.cornelia.huck@de.ibm.com> Subject: Re: [Qemu-devel] [PATCH RFC 1/7] virtio: relax feature check List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Cornelia Huck Cc: Jason Wang , virtualization@lists.linux-foundation.org, qemu-devel@nongnu.org, Stefan Hajnoczi On Tue, May 12, 2015 at 03:14:53PM +0200, Cornelia Huck wrote: > On Wed, 06 May 2015 14:07:37 +0200 > Greg Kurz wrote: > > > Unlike with add and clear, there is no valid reason to abort when checking > > for a feature. It makes more sense to return false (i.e. the feature bit > > isn't set). This is exactly what __virtio_has_feature() does if fbit >= 32. > > > > This allows to introduce code that is aware about new 64-bit features like > > VIRTIO_F_VERSION_1, even if they are still not implemented. > > > > Signed-off-by: Greg Kurz > > --- > > include/hw/virtio/virtio.h | 1 - > > 1 file changed, 1 deletion(-) > > > > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h > > index d95f8b6..6ef70f1 100644 > > --- a/include/hw/virtio/virtio.h > > +++ b/include/hw/virtio/virtio.h > > @@ -233,7 +233,6 @@ static inline void virtio_clear_feature(uint32_t *features, unsigned int fbit) > > > > static inline bool __virtio_has_feature(uint32_t features, unsigned int fbit) > > { > > - assert(fbit < 32); > > return !!(features & (1 << fbit)); > > } > > > > > > > > I must say I'm not very comfortable with knowingly passing out-of-rage > values to this function. > > Can we perhaps apply at least the feature-bit-size extending patches > prior to your patchset, if the remainder of the virtio-1 patchset still > takes some time? So the feature-bit-size extending patches currently don't support migration correctly, that's why they are not merged. What I think we need to do for this is move host_features out from transports into core virtio device. Then we can simply check host features >31 and skip migrating low guest features is none set. Thoughts? Any takers? -- MST