hw/virtio/vhost-user: don't suppress F_CONFIG when supported

Previously we would silently suppress VHOST_USER_PROTOCOL_F_CONFIG
during the protocol negotiation if the QEMU stub hadn't implemented
the vhost_dev_config_notifier. However this isn't the only way we can
handle config messages, the existing vdc->get/set_config can do this
as well.

Lightly re-factor the code to check for both potential methods and
instead of silently squashing the feature error out. It is unlikely
that a vhost-user backend expecting to handle CONFIG messages will
behave correctly if they never get sent.

Fixes: 1c3e5a2617 ("vhost-user: back SET/GET_CONFIG requests with a protocol feature")
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

Message-Id: <20220321153037.3622127-13-alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h
index e44a41b..6e0e8a7 100644
--- a/include/hw/virtio/vhost-user.h
+++ b/include/hw/virtio/vhost-user.h
@@ -22,6 +22,7 @@ typedef struct VhostUserState {
     CharBackend *chr;
     VhostUserHostNotifier notifier[VIRTIO_QUEUE_MAX];
     int memory_slots;
+    bool supports_config;
 } VhostUserState;
 
 bool vhost_user_init(VhostUserState *user, CharBackend *chr, Error **errp);