[PATCH v2 16/19] virtio-mem: Allow notifiers for size changes

[David Hildenbrand <david@redhat.com>]

We want to send qapi events in case the size of a virtio-mem device
changes. This allows upper layers to always know how much memory is
actually currently consumed via a virtio-mem device.

Unfortuantely, we have to report the id of our proxy device. Let's provide
an easy way for our proxy device to register, so it can send the qapi
events. Piggy-backing on the notifier infrastructure (although we'll
only ever have one notifier registered) seems to be an easy way.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/virtio/virtio-mem.c         | 21 ++++++++++++++++++++-
 include/hw/virtio/virtio-mem.h |  5 +++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index a7b5a02dac..11c500960c 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -177,6 +177,7 @@ static int virtio_mem_state_change_request(VirtIOMEM *vmem, uint64_t gpa,
     } else {
         vmem->size -= size;
     }
+    notifier_list_notify(&vmem->size_change_notifiers, &vmem->size);
     return VIRTIO_MEM_RESP_ACK;
 }
 
@@ -232,7 +233,10 @@ static int virtio_mem_unplug_all(VirtIOMEM *vmem)
         return -EBUSY;
     }
     bitmap_clear(vmem->bitmap, 0, vmem->bitmap_size);
-    vmem->size = 0;
+    if (vmem->size) {
+        vmem->size = 0;
+        notifier_list_notify(&vmem->size_change_notifiers, &vmem->size);
+    }
 
     virtio_mem_resize_usable_region(vmem, vmem->requested_size, true);
     return 0;
@@ -553,6 +557,18 @@ static MemoryRegion *virtio_mem_get_memory_region(VirtIOMEM *vmem, Error **errp)
     return &vmem->memdev->mr;
 }
 
+static void virtio_mem_add_size_change_notifier(VirtIOMEM *vmem,
+                                                Notifier *notifier)
+{
+    notifier_list_add(&vmem->size_change_notifiers, notifier);
+}
+
+static void virtio_mem_remove_size_change_notifier(VirtIOMEM *vmem,
+                                                   Notifier *notifier)
+{
+    notifier_remove(notifier);
+}
+
 static void virtio_mem_get_size(Object *obj, Visitor *v, const char *name,
                                 void *opaque, Error **errp)
 {
@@ -664,6 +680,7 @@ static void virtio_mem_instance_init(Object *obj)
     VirtIOMEM *vmem = VIRTIO_MEM(obj);
 
     vmem->block_size = VIRTIO_MEM_MIN_BLOCK_SIZE;
+    notifier_list_init(&vmem->size_change_notifiers);
 
     object_property_add(obj, VIRTIO_MEM_SIZE_PROP, "size", virtio_mem_get_size,
                         NULL, NULL, NULL);
@@ -701,6 +718,8 @@ static void virtio_mem_class_init(ObjectClass *klass, void *data)
 
     vmc->fill_device_info = virtio_mem_fill_device_info;
     vmc->get_memory_region = virtio_mem_get_memory_region;
+    vmc->add_size_change_notifier = virtio_mem_add_size_change_notifier;
+    vmc->remove_size_change_notifier = virtio_mem_remove_size_change_notifier;
 }
 
 static const TypeInfo virtio_mem_info = {
diff --git a/include/hw/virtio/virtio-mem.h b/include/hw/virtio/virtio-mem.h
index 26b90e8f3e..408a6ede50 100644
--- a/include/hw/virtio/virtio-mem.h
+++ b/include/hw/virtio/virtio-mem.h
@@ -64,6 +64,9 @@ typedef struct VirtIOMEM {
 
     /* block size and alignment */
     uint32_t block_size;
+
+    /* notifiers to notify when "size" changes */
+    NotifierList size_change_notifiers;
 } VirtIOMEM;
 
 typedef struct VirtIOMEMClass {
@@ -73,6 +76,8 @@ typedef struct VirtIOMEMClass {
     /* public */
     void (*fill_device_info)(const VirtIOMEM *vmen, VirtioMEMDeviceInfo *vi);
     MemoryRegion *(*get_memory_region)(VirtIOMEM *vmem, Error **errp);
+    void (*add_size_change_notifier)(VirtIOMEM *vmem, Notifier *notifier);
+    void (*remove_size_change_notifier)(VirtIOMEM *vmem, Notifier *notifier);
 } VirtIOMEMClass;
 
 #endif
-- 
2.25.4