virtio-pci: Send qapi events when the virtio-mem size changes

Let's register the notifier and trigger the qapi event with the right
device id.

MEMORY_DEVICE_SIZE_CHANGE is similar to BALLOON_CHANGE, however on a
memory device level.

Don't unregister the notifier (we neither have finalize() nor unrealize()
for VirtIOPCIProxy, so it's not that simple to do it) - both devices are
expected to vanish at the same time.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20200626072248.78761-18-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio-mem-pci.c

@@ -14,6 +14,7 @@
 #include "virtio-mem-pci.h"
 #include "hw/mem/memory-device.h"
 #include "qapi/error.h"
+#include "qapi/qapi-events-misc.h"
 
 static void virtio_mem_pci_realize(VirtIOPCIProxy *vpci_dev, Error **errp)
 {
@@ -74,6 +75,21 @@ static void virtio_mem_pci_fill_device_info(const MemoryDeviceState *md,
     info->type = MEMORY_DEVICE_INFO_KIND_VIRTIO_MEM;
 }
 
+static void virtio_mem_pci_size_change_notify(Notifier *notifier, void *data)
+{
+    VirtIOMEMPCI *pci_mem = container_of(notifier, VirtIOMEMPCI,
+                                         size_change_notifier);
+    DeviceState *dev = DEVICE(pci_mem);
+    const uint64_t * const size_p = data;
+    const char *id = NULL;
+
+    if (dev->id) {
+        id = g_strdup(dev->id);
+    }
+
+    qapi_event_send_memory_device_size_change(!!id, id, *size_p);
+}
+
 static void virtio_mem_pci_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
@@ -98,9 +114,21 @@ static void virtio_mem_pci_class_init(ObjectClass *klass, void *data)
 static void virtio_mem_pci_instance_init(Object *obj)
 {
     VirtIOMEMPCI *dev = VIRTIO_MEM_PCI(obj);
+    VirtIOMEMClass *vmc;
+    VirtIOMEM *vmem;
 
     virtio_instance_init_common(obj, &dev->vdev, sizeof(dev->vdev),
                                 TYPE_VIRTIO_MEM);
+
+    dev->size_change_notifier.notify = virtio_mem_pci_size_change_notify;
+    vmem = VIRTIO_MEM(&dev->vdev);
+    vmc = VIRTIO_MEM_GET_CLASS(vmem);
+    /*
+     * We never remove the notifier again, as we expect both devices to
+     * disappear at the same time.
+     */
+    vmc->add_size_change_notifier(vmem, &dev->size_change_notifier);
+
     object_property_add_alias(obj, VIRTIO_MEM_BLOCK_SIZE_PROP,
                               OBJECT(&dev->vdev), VIRTIO_MEM_BLOCK_SIZE_PROP);
     object_property_add_alias(obj, VIRTIO_MEM_SIZE_PROP, OBJECT(&dev->vdev),

hw/virtio/virtio-mem-pci.h

@@ -28,6 +28,7 @@ typedef struct VirtIOMEMPCI VirtIOMEMPCI;
 struct VirtIOMEMPCI {
     VirtIOPCIProxy parent_obj;
     VirtIOMEM vdev;
+    Notifier size_change_notifier;
 };
 
 #endif /* QEMU_VIRTIO_MEM_PCI_H */

monitor/monitor.c

@@ -235,6 +235,7 @@ static MonitorQAPIEventConf monitor_qapi_event_conf[QAPI_EVENT__MAX] = {
     [QAPI_EVENT_QUORUM_REPORT_BAD] = { 1000 * SCALE_MS },
     [QAPI_EVENT_QUORUM_FAILURE]    = { 1000 * SCALE_MS },
     [QAPI_EVENT_VSERPORT_CHANGE]   = { 1000 * SCALE_MS },
+    [QAPI_EVENT_MEMORY_DEVICE_SIZE_CHANGE] = { 1000 * SCALE_MS },
 };
 
 /*

qapi/misc.json

@@ -1434,6 +1434,31 @@
 ##
 { 'command': 'query-memory-devices', 'returns': ['MemoryDeviceInfo'] }
 
+##
+# @MEMORY_DEVICE_SIZE_CHANGE:
+#
+# Emitted when the size of a memory device changes. Only emitted for memory
+# devices that can actually change the size (e.g., virtio-mem due to guest
+# action).
+#
+# @id: device's ID
+# @size: the new size of memory that the device provides
+#
+# Note: this event is rate-limited.
+#
+# Since: 5.1
+#
+# Example:
+#
+# <- { "event": "MEMORY_DEVICE_SIZE_CHANGE",
+#      "data": { "id": "vm0", "size": 1073741824},
+#      "timestamp": { "seconds": 1588168529, "microseconds": 201316 } }
+#
+##
+{ 'event': 'MEMORY_DEVICE_SIZE_CHANGE',
+  'data': { '*id': 'str', 'size': 'size' } }
+
+
 ##
 # @MEM_UNPLUG_ERROR:
 #