virtio-md-pci: Support unplug requests for compatible devices

Let's support unplug requests for virtio-md-pci devices that provide
a unplug_request_check() callback.

We'll wire that up for virtio-mem-pci next.

Message-ID: <20230711153445.514112-6-david@redhat.com>
Tested-by: Mario Casquero <mcasquer@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>

hw/virtio/virtio-md-pci.c

@@ -69,8 +69,42 @@ void virtio_md_pci_plug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp)
 void virtio_md_pci_unplug_request(VirtIOMDPCI *vmd, MachineState *ms,
                                   Error **errp)
 {
-    /* We don't support hot unplug of virtio based memory devices */
-    error_setg(errp, "virtio based memory devices cannot be unplugged.");
+    VirtIOMDPCIClass *vmdc = VIRTIO_MD_PCI_GET_CLASS(vmd);
+    DeviceState *dev = DEVICE(vmd);
+    HotplugHandler *bus_handler = qdev_get_bus_hotplug_handler(dev);
+    HotplugHandlerClass *hdc;
+    Error *local_err = NULL;
+
+    if (!vmdc->unplug_request_check) {
+        error_setg(errp, "this virtio based memory devices cannot be unplugged");
+        return;
+    }
+
+    if (!bus_handler) {
+        error_setg(errp, "hotunplug of virtio based memory devices not"
+                   "supported on this bus");
+        return;
+    }
+
+    vmdc->unplug_request_check(vmd, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    /*
+     * Forward the async request or turn it into a sync request (handling it
+     * like qdev_unplug()).
+     */
+    hdc = HOTPLUG_HANDLER_GET_CLASS(bus_handler);
+    if (hdc->unplug_request) {
+        hotplug_handler_unplug_request(bus_handler, dev, &local_err);
+    } else {
+        virtio_md_pci_unplug(vmd, ms, &local_err);
+        if (!local_err) {
+            object_unparent(OBJECT(dev));
+        }
+    }
 }
 
 void virtio_md_pci_unplug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp)

include/hw/virtio/virtio-md-pci.h

@@ -26,6 +26,9 @@ OBJECT_DECLARE_TYPE(VirtIOMDPCI, VirtIOMDPCIClass, VIRTIO_MD_PCI)
 struct VirtIOMDPCIClass {
     /* private */
     VirtioPCIClass parent;
+
+    /* public */
+    void (*unplug_request_check)(VirtIOMDPCI *vmd, Error **errp);
 };
 
 struct VirtIOMDPCI {