virtio-bus: Plug devices after features are negotiated

Currently, devices are plugged before features are negotiated.
If the backend doesn't support VIRTIO_F_VERSION_1, the transport
needs to rewind some settings.

This is the case for CCW, for which a post_plugged callback had
been introduced, where max_rev field is just updated if
VIRTIO_F_VERSION_1 is not supported by the backend.
For PCI, implementing post_plugged would be much more
complicated, so it needs to know whether the backend supports
VIRTIO_F_VERSION_1 at plug time.

Currently, nothing is done for PCI. Modern capabilities get
exposed to the guest even if VIRTIO_F_VERSION_1 is not supported
by the backend, which confuses the guest.

This patch replaces existing post_plugged solution with an
approach that fits with both transports.
Features negotiation is performed before ->device_plugged() call.
A pre_plugged callback is introduced so that the transports can
set their supported features.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: qemu-stable@nongnu.org
Tested-by: Cornelia Huck <cornelia.huck@de.ibm.com> [ccw]
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>

1 files changed, 15 insertions, 15 deletions

diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
index 96789569a7..9f3f386964 100644
--- a/hw/s390x/virtio-ccw.c
+++ b/hw/s390x/virtio-ccw.c
@@ -1261,6 +1261,16 @@ static int virtio_ccw_load_config(DeviceState *d, QEMUFile *f)
     return 0;
 }
 
+static void virtio_ccw_pre_plugged(DeviceState *d, Error **errp)
+{
+   VirtioCcwDevice *dev = VIRTIO_CCW_DEVICE(d);
+   VirtIODevice *vdev = virtio_bus_get_device(&dev->bus);
+
+    if (dev->max_rev >= 1) {
+        virtio_add_feature(&vdev->host_features, VIRTIO_F_VERSION_1);
+    }
+}
+
 /* This is called by virtio-bus just after the device is plugged. */
 static void virtio_ccw_device_plugged(DeviceState *d, Error **errp)
 {
@@ -1270,6 +1280,10 @@ static void virtio_ccw_device_plugged(DeviceState *d, Error **errp)
     SubchDev *sch = ccw_dev->sch;
     int n = virtio_get_num_queues(vdev);
 
+    if (!virtio_has_feature(vdev->host_features, VIRTIO_F_VERSION_1)) {
+        dev->max_rev = 0;
+    }
+
     if (virtio_get_num_queues(vdev) > VIRTIO_CCW_QUEUE_MAX) {
         error_setg(errp, "The number of virtqueues %d "
                    "exceeds ccw limit %d", n,
@@ -1283,25 +1297,11 @@ static void virtio_ccw_device_plugged(DeviceState *d, Error **errp)
 
     sch->id.cu_model = virtio_bus_get_vdev_id(&dev->bus);
 
-    if (dev->max_rev >= 1) {
-        virtio_add_feature(&vdev->host_features, VIRTIO_F_VERSION_1);
-    }
 
     css_generate_sch_crws(sch->cssid, sch->ssid, sch->schid,
                           d->hotplugged, 1);
 }
 
-static void virtio_ccw_post_plugged(DeviceState *d, Error **errp)
-{
-   VirtioCcwDevice *dev = VIRTIO_CCW_DEVICE(d);
-   VirtIODevice *vdev = virtio_bus_get_device(&dev->bus);
-
-   if (!virtio_host_has_feature(vdev, VIRTIO_F_VERSION_1)) {
-        /* A backend didn't support modern virtio. */
-       dev->max_rev = 0;
-   }
-}
-
 static void virtio_ccw_device_unplugged(DeviceState *d)
 {
     VirtioCcwDevice *dev = VIRTIO_CCW_DEVICE(d);
@@ -1593,8 +1593,8 @@ static void virtio_ccw_bus_class_init(ObjectClass *klass, void *data)
     k->load_queue = virtio_ccw_load_queue;
     k->save_config = virtio_ccw_save_config;
     k->load_config = virtio_ccw_load_config;
+    k->pre_plugged = virtio_ccw_pre_plugged;
     k->device_plugged = virtio_ccw_device_plugged;
-    k->post_plugged = virtio_ccw_post_plugged;
     k->device_unplugged = virtio_ccw_device_unplugged;
     k->ioeventfd_started = virtio_ccw_ioeventfd_started;
     k->ioeventfd_set_started = virtio_ccw_ioeventfd_set_started;