virtio: allow per-device-class legacy features

Legacy features are those that transitional devices only
expose on the legacy interface.
Allow different ones per device class.

Cc: qemu-stable@nongnu.org # dependency for the next patch
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NCornelia Huck <cornelia.huck@de.ibm.com>
(cherry picked from commit 9b706dbb)

Conflicts:
	hw/virtio/virtio.c

* drop context dep on ff4c07df
* resolv func dep on ff4c07df creating vdc variable in
  virtio_device_class_init()
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

hw/s390x/virtio-ccw.c

@@ -330,6 +330,8 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
         if (!ccw.cda) {
             ret = -EFAULT;
         } else {
+            VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev);
+
             features.index = address_space_ldub(&address_space_memory,
                                                 ccw.cda
                                                 + sizeof(features.features),
@@ -339,7 +341,7 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
                 if (dev->revision >= 1) {
                     /* Don't offer legacy features for modern devices. */
                     features.features = (uint32_t)
-                        (vdev->host_features & ~VIRTIO_LEGACY_FEATURES);
+                        (vdev->host_features & ~vdc->legacy_features);
                 } else {
                     features.features = (uint32_t)vdev->host_features;
                 }

hw/virtio/virtio-pci.c

@@ -1192,7 +1192,9 @@ static uint64_t virtio_pci_common_read(void *opaque, hwaddr addr,
         break;
     case VIRTIO_PCI_COMMON_DF:
         if (proxy->dfselect <= 1) {
-            val = (vdev->host_features & ~VIRTIO_LEGACY_FEATURES) >>
+            VirtioDeviceClass *vdc = VIRTIO_DEVICE_GET_CLASS(vdev);
+
+            val = (vdev->host_features & ~vdc->legacy_features) >>
                 (32 * proxy->dfselect);
         }
         break;

hw/virtio/virtio.c

@@ -1966,12 +1966,15 @@ static Property virtio_properties[] = {
 static void virtio_device_class_init(ObjectClass *klass, void *data)
 {
     /* Set the default value here. */
+    VirtioDeviceClass *vdc = VIRTIO_DEVICE_CLASS(klass);
     DeviceClass *dc = DEVICE_CLASS(klass);
 
     dc->realize = virtio_device_realize;
     dc->unrealize = virtio_device_unrealize;
     dc->bus_type = TYPE_VIRTIO_BUS;
     dc->props = virtio_properties;
+
+    vdc->legacy_features |= VIRTIO_LEGACY_FEATURES;
 }
 
 static const TypeInfo virtio_device_info = {

include/hw/virtio/virtio.h

@@ -112,6 +112,11 @@ typedef struct VirtioDeviceClass {
     void (*set_config)(VirtIODevice *vdev, const uint8_t *config);
     void (*reset)(VirtIODevice *vdev);
     void (*set_status)(VirtIODevice *vdev, uint8_t val);
+    /* For transitional devices, this is a bitmap of features
+     * that are only exposed on the legacy interface but not
+     * the modern one.
+     */
+    uint64_t legacy_features;
     /* Test and clear event pending status.
      * Should be called after unmask to avoid losing events.
      * If backend does not support masking,