block/rnbd-clt: Generate kobject_uevent when the rnbd device state changes

When an RTRS session state changes, the transport layer generates an event
to RNBD. Then RNBD will change the state of the RNBD client device
accordingly.

This commit add kobject_uevent when the RNBD device state changes. With
this udev rules can be configured to react accordingly.
Signed-off-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
Link: https://lore.kernel.org/r/20210419073722.15351-17-gi-oh.kim@ionos.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/rnbd/rnbd-clt-sysfs.c

@@ -490,6 +490,7 @@ static int rnbd_clt_add_dev_kobj(struct rnbd_clt_dev *dev)
 			      ret);
 		kobject_put(&dev->kobj);
 	}
+	kobject_uevent(gd_kobj, KOBJ_ONLINE);
 
 	return ret;
 }

drivers/block/rnbd/rnbd-clt.c

@@ -110,6 +110,7 @@ static int rnbd_clt_change_capacity(struct rnbd_clt_dev *dev,
 static int process_msg_open_rsp(struct rnbd_clt_dev *dev,
 				struct rnbd_msg_open_rsp *rsp)
 {
+	struct kobject *gd_kobj;
 	int err = 0;
 
 	mutex_lock(&dev->lock);
@@ -128,6 +129,8 @@ static int process_msg_open_rsp(struct rnbd_clt_dev *dev,
 		 */
 		if (dev->nsectors != nsectors)
 			rnbd_clt_change_capacity(dev, nsectors);
+		gd_kobj = &disk_to_dev(dev->gd)->kobj;
+		kobject_uevent(gd_kobj, KOBJ_ONLINE);
 		rnbd_clt_info(dev, "Device online, device remapped successfully\n");
 	}
 	err = rnbd_clt_set_dev_attr(dev, rsp);
@@ -649,14 +652,18 @@ static int send_msg_sess_info(struct rnbd_clt_session *sess, enum wait_type wait
 static void set_dev_states_to_disconnected(struct rnbd_clt_session *sess)
 {
 	struct rnbd_clt_dev *dev;
+	struct kobject *gd_kobj;
 
 	mutex_lock(&sess->lock);
 	list_for_each_entry(dev, &sess->devs_list, list) {
 		rnbd_clt_err(dev, "Device disconnected.\n");
 
 		mutex_lock(&dev->lock);
-		if (dev->dev_state == DEV_STATE_MAPPED)
+		if (dev->dev_state == DEV_STATE_MAPPED) {
 			dev->dev_state = DEV_STATE_MAPPED_DISCONNECTED;
+			gd_kobj = &disk_to_dev(dev->gd)->kobj;
+			kobject_uevent(gd_kobj, KOBJ_OFFLINE);
+		}
 		mutex_unlock(&dev->lock);
 	}
 	mutex_unlock(&sess->lock);