Re: [Qemu-devel] [PATCH] vhost-user: sync backend features

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jul 29, 2015 at 08:43:47PM +0300, Marcel Apfelbaum wrote:
> On 07/29/2015 08:20 PM, Michael S. Tsirkin wrote:
> >On Wed, Jul 29, 2015 at 08:11:58PM +0300, Marcel Apfelbaum wrote:
> >>Complete vhost-user negotiation by syncing the features
> >>supported by the backend.
> >>
> >>Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
> >>---
> >>  To be used on top of:
> >>  [PATCH 0/4] vhost-user: protocol updates
> >>  https://lists.gnu.org/archive/html/qemu-devel/2015-07/msg03842.html
> >>
> >>  Currently the vhost-user supported features are not evaluated.
> >>  The way I see it, and please correct me, the best way to do
> >>  this is to:
> >>   1. get the backend features on vhost init
> >>   2. Instead of simply copying them during features ack,
> >>      check that that all backend features are supported by current QEMU
> >>   3. All other code should remain the same.
> >>
> >>   Thanks,
> >>   Marcel
> >>
> >>  hw/net/vhost_net.c     | 3 ++-
> >>  hw/virtio/vhost-user.c | 4 ++--
> >>  2 files changed, 4 insertions(+), 3 deletions(-)
> >>
> >>diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> >>index c864237..1ea5866 100644
> >>--- a/hw/net/vhost_net.c
> >>+++ b/hw/net/vhost_net.c
> >>@@ -118,7 +118,8 @@ uint64_t vhost_net_get_features(struct vhost_net *net, uint64_t features)
> >>
> >>  void vhost_net_ack_features(struct vhost_net *net, uint64_t features)
> >>  {
> >>-    net->dev.acked_features = net->dev.backend_features;
> >>+    vhost_ack_features(&net->dev, vhost_net_get_feature_bits(net),
> >>+                       net->dev.backend_features);
> >>      vhost_ack_features(&net->dev, vhost_net_get_feature_bits(net), features);
> >
> >So you ack it twice?
> Not really, first call to vhost_ack_features acks the net->dev.backend_features,
> the second one acks the guest features.
> 
> The first call replaces the previous assignment that assumes that all backend features are
> supported by QEMU.
> 
> Thanks,
> Marcel

I think it's cleaner to whitelist backend features QEMU supports.
I thought we did this, will look again.

> 
> >
> >>  }
> >>
> >>diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> >>index c4428a1..077457b 100644
> >>--- a/hw/virtio/vhost-user.c
> >>+++ b/hw/virtio/vhost-user.c
> >>@@ -358,9 +358,9 @@ static int vhost_user_init(struct vhost_dev *dev, void *opaque)
> >>          return err;
> >>      }
> >>
> >>-    if (__virtio_has_feature(msg.u64, VHOST_USER_F_PROTOCOL_FEATURES)) {
> >>-        dev->backend_features |= 1ULL << VHOST_USER_F_PROTOCOL_FEATURES;
> >>+    dev->backend_features = msg.u64;
> >>
> >>+    if (__virtio_has_feature(msg.u64, VHOST_USER_F_PROTOCOL_FEATURES)) {
> >>          msg.request = VHOST_USER_GET_PROTOCOL_FEATURES;
> >>          msg.flags = VHOST_USER_VERSION;
> >>          msg.size = 0;
> >>--
> >>2.1.0