nvme: send uevent on connection up

When connectivity with a controller is lost, the driver will keep
trying to reconnect once every 10 sec. When connection is restored,
user-space apps need to be informed so that they can take proper
action. For example, TP8010 introduces the DIM PDU, which is used to
register with a discovery controller (DC). The DIM PDU is sent from
user-space.  The DIM PDU must be sent every time a connection is
established with a DC. Therefore, the kernel must tell user-space apps
when connection is restored so that registration can happen.

The uevent sent is a "change" uevent with environmental data
set to: "NVME_EVENT=connected".
Signed-off-by: Martin Belanger <martin.belanger@dell.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: John Meneghini <jmeneghi@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -4262,6 +4262,13 @@ static int nvme_class_uevent(struct device *dev, struct kobj_uevent_env *env)
 	return ret;
 }
 
+static void nvme_change_uevent(struct nvme_ctrl *ctrl, char *envdata)
+{
+	char *envp[2] = { envdata, NULL };
+
+	kobject_uevent_env(&ctrl->device->kobj, KOBJ_CHANGE, envp);
+}
+
 static void nvme_aen_uevent(struct nvme_ctrl *ctrl)
 {
 	char *envp[2] = { NULL, NULL };
@@ -4429,6 +4436,8 @@ void nvme_start_ctrl(struct nvme_ctrl *ctrl)
 		nvme_queue_scan(ctrl);
 		nvme_start_queues(ctrl);
 	}
+
+	nvme_change_uevent(ctrl, "NVME_EVENT=connected");
 }
 EXPORT_SYMBOL_GPL(nvme_start_ctrl);