[PATCH v3 06/21] hw/virtio: incorporate backend features in features

["Alex Bennée" <alex.bennee@linaro.org>]

There are some extra bits used over a vhost-user connection which are
hidden from the device itself. We need to set them here to ensure we
enable things like the protocol extensions.

Currently net/vhost-user.c has it's own inscrutable way of persisting
this data but it really should live in the core vhost_user code.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 hw/virtio/vhost-user.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 55fce18480..a96a586ebf 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -1461,7 +1461,14 @@ static int vhost_user_set_features(struct vhost_dev *dev,
      */
     bool log_enabled = features & (0x1ULL << VHOST_F_LOG_ALL);
 
-    return vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES, features,
+    /*
+     * We need to include any extra backend only feature bits that
+     * might be needed by our device. Currently this includes the
+     * VHOST_USER_F_PROTOCOL_FEATURES bit for enabling protocol
+     * features.
+     */
+    return vhost_user_set_u64(dev, VHOST_USER_SET_FEATURES,
+                              features | dev->backend_features,
                               log_enabled);
 }
 
-- 
2.30.2