monitor: Rate-limit MEMORY_DEVICE_SIZE_CHANGE qapi events per device

We want to rate-limit MEMORY_DEVICE_SIZE_CHANGE events per device,
otherwise we can lose some events for devices. We can now use the
qom-path to reliably map an event to a device and make rate-limiting
device-aware.

This was noticed by starting a VM with two virtio-mem devices that each
have a requested size > 0. The Linux guest will initialize both devices
in parallel, resulting in losing MEMORY_DEVICE_SIZE_CHANGE events for
one of the devices.

Fixes: 722a3c783e ("virtio-pci: Send qapi events when the virtio-mem size changes")
Suggested-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210929162445.64060-4-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

monitor/monitor.c

@@ -474,6 +474,10 @@ static unsigned int qapi_event_throttle_hash(const void *key)
         hash += g_str_hash(qdict_get_str(evstate->data, "node-name"));
     }
 
+    if (evstate->event == QAPI_EVENT_MEMORY_DEVICE_SIZE_CHANGE) {
+        hash += g_str_hash(qdict_get_str(evstate->data, "qom-path"));
+    }
+
     return hash;
 }
 
@@ -496,6 +500,11 @@ static gboolean qapi_event_throttle_equal(const void *a, const void *b)
                        qdict_get_str(evb->data, "node-name"));
     }
 
+    if (eva->event == QAPI_EVENT_MEMORY_DEVICE_SIZE_CHANGE) {
+        return !strcmp(qdict_get_str(eva->data, "qom-path"),
+                       qdict_get_str(evb->data, "qom-path"));
+    }
+
     return TRUE;
 }