From: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>

Use virtio_get_config_size() rather than sizeof(struct
virtio_snd_config) for the config_size in the vhost-user-snd frontend.
The frontend shall rely on device features for the size of the device
configuration space. The presence of `controls` in the config space
depends on VIRTIO_SND_F_CTLS according to the specification (v1.3):
`
5.14.4 Device Configuration Layout
...

controls
(driver-read-only) indicates a total number of all available control
elements if VIRTIO_SND_F_CTLS has been negotiated.
`
This fixes an issue introduced by commit ab0c7fb2 ("linux-headers:
update to current kvm/next") in which the optional field `controls` is
added to the virtio_snd_config structure. This breaks vhost-user-device
backends that do not implement the `controls` field.

Fixes: ab0c7fb22b ("linux-headers: update to current kvm/next")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2805
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Matias Ezequiel Vara Larsen <mvaralar@redhat.com>
Message-Id: <20250217131255.829892-1-mvaralar@redhat.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Dorinda Bassey <dbassey@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/virtio/vhost-user-snd.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-user-snd.c b/hw/virtio/vhost-user-snd.c
index 8610370af8..b414c75c06 100644
--- a/hw/virtio/vhost-user-snd.c
+++ b/hw/virtio/vhost-user-snd.c
@@ -16,6 +16,18 @@
 #include "standard-headers/linux/virtio_ids.h"
 #include "standard-headers/linux/virtio_snd.h"
 
+static const VirtIOFeature feature_sizes[] = {
+    {.flags = 1ULL << VIRTIO_SND_F_CTLS,
+    .end = endof(struct virtio_snd_config, controls)},
+    {}
+};
+
+static const VirtIOConfigSizeParams cfg_size_params = {
+    .min_size = endof(struct virtio_snd_config, chmaps),
+    .max_size = sizeof(struct virtio_snd_config),
+    .feature_sizes = feature_sizes
+};
+
 static const VMStateDescription vu_snd_vmstate = {
     .name = "vhost-user-snd",
     .unmigratable = 1,
@@ -23,16 +35,20 @@ static const VMStateDescription vu_snd_vmstate = {
 
 static const Property vsnd_properties[] = {
     DEFINE_PROP_CHR("chardev", VHostUserBase, chardev),
+    DEFINE_PROP_BIT64("controls", VHostUserBase,
+                      parent_obj.host_features, VIRTIO_SND_F_CTLS, false),
 };
 
 static void vu_snd_base_realize(DeviceState *dev, Error **errp)
 {
     VHostUserBase *vub = VHOST_USER_BASE(dev);
     VHostUserBaseClass *vubs = VHOST_USER_BASE_GET_CLASS(dev);
+    VirtIODevice *vdev = &vub->parent_obj;
 
     vub->virtio_id = VIRTIO_ID_SOUND;
     vub->num_vqs = 4;
-    vub->config_size = sizeof(struct virtio_snd_config);
+    vub->config_size = virtio_get_config_size(&cfg_size_params,
+                                              vdev->host_features);
     vub->vq_size = 64;
 
     vubs->parent_realize(dev, errp);
-- 
MST