nvme: send a rediscover uevent when a persistent discovery controller reconnects

When a discovery controller is disconnected, no AENs will arrive to
notify the host about discovery log change events.

In order to solve this, send a uevent notification when a
persistent discovery controller reconnects. We add a new ctrl
flag NVME_CTRL_STARTED_ONCE that will be set on the first
start, and consecutive calls will find it set, and send the
event to userspace if the controller is a discovery controller.

Upon the event reception, userspace will re-read the discovery
log page and will act upon changes as it sees fit.

Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Daniel Wagner <dwagner@suse.de>
Reviewed-by: James Smart <jsmart2021@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -4815,6 +4815,16 @@ void nvme_start_ctrl(struct nvme_ctrl *ctrl)
 
 	nvme_enable_aen(ctrl);
 
+	/*
+	 * persistent discovery controllers need to send indication to userspace
+	 * to re-read the discovery log page to learn about possible changes
+	 * that were missed. We identify persistent discovery controllers by
+	 * checking that they started once before, hence are reconnecting back.
+	 */
+	if (test_and_set_bit(NVME_CTRL_STARTED_ONCE, &ctrl->flags) &&
+	    nvme_discovery_ctrl(ctrl))
+		nvme_change_uevent(ctrl, "NVME_EVENT=rediscover");
+
 	if (ctrl->queue_count > 1) {
 		nvme_queue_scan(ctrl);
 		nvme_start_queues(ctrl);

drivers/nvme/host/nvme.h

@@ -236,6 +236,7 @@ struct nvme_fault_inject {
 enum nvme_ctrl_flags {
 	NVME_CTRL_FAILFAST_EXPIRED	= 0,
 	NVME_CTRL_ADMIN_Q_STOPPED	= 1,
+	NVME_CTRL_STARTED_ONCE		= 2,
 };
 
 struct nvme_ctrl {