vduse: Tie vduse mgmtdev and its device

vduse devices are not backed by any real devices such as PCI. Hence it
doesn't have any parent device linked to it.

Kernel driver model in [1] suggests to avoid an empty device
release callback.

Hence tie the mgmtdevice object's life cycle to an allocate dummy struct
device instead of static one.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/core-api/kobject.rst?h=v5.18-rc7#n284

Signed-off-by: Parav Pandit <parav@nvidia.com>
Message-Id: <20220613195223.473966-1-parav@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Xie Yongji <xieyongji@bytedance.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/vdpa/vdpa_user/vduse_dev.c

@@ -1476,16 +1476,12 @@ static char *vduse_devnode(struct device *dev, umode_t *mode)
 	return kasprintf(GFP_KERNEL, "vduse/%s", dev_name(dev));
 }
 
-static void vduse_mgmtdev_release(struct device *dev)
-{
-}
-
-static struct device vduse_mgmtdev = {
-	.init_name = "vduse",
-	.release = vduse_mgmtdev_release,
+struct vduse_mgmt_dev {
+	struct vdpa_mgmt_dev mgmt_dev;
+	struct device dev;
 };
 
-static struct vdpa_mgmt_dev mgmt_dev;
+static struct vduse_mgmt_dev *vduse_mgmt;
 
 static int vduse_dev_init_vdpa(struct vduse_dev *dev, const char *name)
 {
@@ -1510,7 +1506,7 @@ static int vduse_dev_init_vdpa(struct vduse_dev *dev, const char *name)
 	}
 	set_dma_ops(&vdev->vdpa.dev, &vduse_dev_dma_ops);
 	vdev->vdpa.dma_dev = &vdev->vdpa.dev;
-	vdev->vdpa.mdev = &mgmt_dev;
+	vdev->vdpa.mdev = &vduse_mgmt->mgmt_dev;
 
 	return 0;
 }
@@ -1556,34 +1552,52 @@ static struct virtio_device_id id_table[] = {
 	{ 0 },
 };
 
-static struct vdpa_mgmt_dev mgmt_dev = {
-	.device = &vduse_mgmtdev,
-	.id_table = id_table,
-	.ops = &vdpa_dev_mgmtdev_ops,
-};
+static void vduse_mgmtdev_release(struct device *dev)
+{
+	struct vduse_mgmt_dev *mgmt_dev;
+
+	mgmt_dev = container_of(dev, struct vduse_mgmt_dev, dev);
+	kfree(mgmt_dev);
+}
 
 static int vduse_mgmtdev_init(void)
 {
 	int ret;
 
-	ret = device_register(&vduse_mgmtdev);
-	if (ret)
+	vduse_mgmt = kzalloc(sizeof(*vduse_mgmt), GFP_KERNEL);
+	if (!vduse_mgmt)
+		return -ENOMEM;
+
+	ret = dev_set_name(&vduse_mgmt->dev, "vduse");
+	if (ret) {
+		kfree(vduse_mgmt);
 		return ret;
+	}
 
-	ret = vdpa_mgmtdev_register(&mgmt_dev);
+	vduse_mgmt->dev.release = vduse_mgmtdev_release;
+
+	ret = device_register(&vduse_mgmt->dev);
 	if (ret)
-		goto err;
+		goto dev_reg_err;
 
-	return 0;
-err:
-	device_unregister(&vduse_mgmtdev);
+	vduse_mgmt->mgmt_dev.id_table = id_table;
+	vduse_mgmt->mgmt_dev.ops = &vdpa_dev_mgmtdev_ops;
+	vduse_mgmt->mgmt_dev.device = &vduse_mgmt->dev;
+	ret = vdpa_mgmtdev_register(&vduse_mgmt->mgmt_dev);
+	if (ret)
+		device_unregister(&vduse_mgmt->dev);
+
+	return ret;
+
+dev_reg_err:
+	put_device(&vduse_mgmt->dev);
 	return ret;
 }
 
 static void vduse_mgmtdev_exit(void)
 {
-	vdpa_mgmtdev_unregister(&mgmt_dev);
-	device_unregister(&vduse_mgmtdev);
+	vdpa_mgmtdev_unregister(&vduse_mgmt->mgmt_dev);
+	device_unregister(&vduse_mgmt->dev);
 }
 
 static int vduse_init(void)