qdev: Add Error parameter to hide_device() callbacks

hide_device() is used for virtio-net failover, where the standby virtio
device delays creation of the primary device. It only makes sense to
have a single primary device for each standby device. Adding a second
one should result in an error instead of hiding it and never using it
afterwards.

Prepare for this by adding an Error parameter to the hide_device()
callback where virtio-net is informed about adding a primary device.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20211008133442.141332-12-kwolf@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Peter Krempa <pkrempa@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

hw/core/qdev.c

@@ -211,14 +211,17 @@ void device_listener_unregister(DeviceListener *listener)
     QTAILQ_REMOVE(&device_listeners, listener, link);
 }
 
-bool qdev_should_hide_device(QemuOpts *opts)
+bool qdev_should_hide_device(QemuOpts *opts, Error **errp)
 {
+    ERRP_GUARD();
     DeviceListener *listener;
 
     QTAILQ_FOREACH(listener, &device_listeners, link) {
         if (listener->hide_device) {
-            if (listener->hide_device(listener, opts)) {
+            if (listener->hide_device(listener, opts, errp)) {
                 return true;
+            } else if (*errp) {
+                return false;
             }
         }
     }

hw/net/virtio-net.c

@@ -3304,7 +3304,7 @@ static void virtio_net_migration_state_notifier(Notifier *notifier, void *data)
 }
 
 static bool failover_hide_primary_device(DeviceListener *listener,
-                                         QemuOpts *device_opts)
+                                         QemuOpts *device_opts, Error **errp)
 {
     VirtIONet *n = container_of(listener, VirtIONet, primary_listener);
     const char *standby_id;

include/hw/qdev-core.h

@@ -201,8 +201,12 @@ struct DeviceListener {
      * informs qdev if a device should be visible or hidden.  We can
      * hide a failover device depending for example on the device
      * opts.
+     *
+     * On errors, it returns false and errp is set. Device creation
+     * should fail in this case.
      */
-    bool (*hide_device)(DeviceListener *listener, QemuOpts *device_opts);
+    bool (*hide_device)(DeviceListener *listener, QemuOpts *device_opts,
+                        Error **errp);
     QTAILQ_ENTRY(DeviceListener) link;
 };
 
@@ -837,7 +841,7 @@ void device_listener_unregister(DeviceListener *listener);
  * When a device is added via qdev_device_add() this will be called,
  * and return if the device should be added now or not.
  */
-bool qdev_should_hide_device(QemuOpts *opts);
+bool qdev_should_hide_device(QemuOpts *opts, Error **errp);
 
 typedef enum MachineInitPhase {
     /* current_machine is NULL.  */

softmmu/qdev-monitor.c

@@ -626,6 +626,7 @@ const char *qdev_set_id(DeviceState *dev, char *id, Error **errp)
 
 DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
 {
+    ERRP_GUARD();
     DeviceClass *dc;
     const char *driver, *path;
     DeviceState *dev = NULL;
@@ -669,11 +670,13 @@ DeviceState *qdev_device_add(QemuOpts *opts, Error **errp)
             error_setg(errp, "Device with failover_pair_id don't have id");
             return NULL;
         }
-        if (qdev_should_hide_device(opts)) {
+        if (qdev_should_hide_device(opts, errp)) {
             if (bus && !qbus_is_hotpluggable(bus)) {
                 error_setg(errp, QERR_BUS_NO_HOTPLUG, bus->name);
             }
             return NULL;
+        } else if (*errp) {
+            return NULL;
         }
     }