nvme: add new reconnecting controller state

The nvme fabric (RDMA, FC, etc...) can introduce port, link or node
failures that may require a reconnect to re-establish the connection.

Add a new reconnecting state that will initially be used by the RDMA
driver.
Reviewed-by: NJay Freyensee <james.p.freyensee@intel.com>
Reviewed-by: NSagi Grimberg <sagi@grimberg.me>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NSteve Wise <swise@opengridcomputing.com>
Tested-by: NSteve Wise <swise@opengridcomputing.com>
Signed-off-by: NJens Axboe <axboe@fb.com>

drivers/nvme/host/core.c

@@ -88,6 +88,7 @@ bool nvme_change_ctrl_state(struct nvme_ctrl *ctrl,
 		switch (old_state) {
 		case NVME_CTRL_NEW:
 		case NVME_CTRL_RESETTING:
+		case NVME_CTRL_RECONNECTING:
 			changed = true;
 			/* FALLTHRU */
 		default:
@@ -97,6 +98,16 @@ bool nvme_change_ctrl_state(struct nvme_ctrl *ctrl,
 	case NVME_CTRL_RESETTING:
 		switch (old_state) {
 		case NVME_CTRL_NEW:
+		case NVME_CTRL_LIVE:
+		case NVME_CTRL_RECONNECTING:
+			changed = true;
+			/* FALLTHRU */
+		default:
+			break;
+		}
+		break;
+	case NVME_CTRL_RECONNECTING:
+		switch (old_state) {
 		case NVME_CTRL_LIVE:
 			changed = true;
 			/* FALLTHRU */
@@ -108,6 +119,7 @@ bool nvme_change_ctrl_state(struct nvme_ctrl *ctrl,
 		switch (old_state) {
 		case NVME_CTRL_LIVE:
 		case NVME_CTRL_RESETTING:
+		case NVME_CTRL_RECONNECTING:
 			changed = true;
 			/* FALLTHRU */
 		default:

drivers/nvme/host/nvme.h

@@ -74,6 +74,7 @@ enum nvme_ctrl_state {
 	NVME_CTRL_NEW,
 	NVME_CTRL_LIVE,
 	NVME_CTRL_RESETTING,
+	NVME_CTRL_RECONNECTING,
 	NVME_CTRL_DELETING,
 	NVME_CTRL_DEAD,
 };