[PATCH 1/2] nvme-core: add ctrl state transition debug helper

[Chaitanya Kulkarni <kch@nvidia.com>]

NVMe controller state machine has total 7 states and 13 state transition
arcs. Debugging NVMeOF problems in the field is not straight-froward,
since it involves complex combination of connect/reconnect/kato/timeout
handlers etc scenarios.
We already have a helper in sysfs.c that reads the controller state, but
one has to constantly read the state in order understand the complete
state transition which is very inconvenient.

It is often helpful to know full state transition of controller when
dealing with NVMeOF issues at the time of analyzing the trace.

Add a helper that allows us to decode and print each controller state
transition :-

blktests (master) # dmesg -c | grep nvme_change_ctrl_state
blktests (master) # nvme_trtype=tcp ./check nvme/048
nvme/048 (Test queue count changes on reconnect)             [passed]
    runtime  6.264s  ...  5.240s
blktests (master) # dmesg -c | grep nvme_change_ctrl_state
[17080.988689] nvme nvme0: nvme_change_ctrl_state new -> connecting
[17081.006623] nvme nvme0: nvme_change_ctrl_state connecting -> live
[17081.038313] nvme nvme0: nvme_change_ctrl_state live -> resetting
[17081.040730] nvme nvme0: nvme_change_ctrl_state resetting -> connecting
[17083.056750] nvme nvme0: nvme_change_ctrl_state connecting -> live
[17083.075906] nvme nvme0: nvme_change_ctrl_state live -> resetting
[17083.076112] nvme nvme0: nvme_change_ctrl_state resetting -> connecting
[17085.105270] nvme nvme0: nvme_change_ctrl_state connecting -> live
[17086.126484] nvme nvme0: nvme_change_ctrl_state live -> deleting
[17086.126506] nvme nvme0: nvme_change_ctrl_state deleting -> deleting (no IO)
blktests (master) #

Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
---

 drivers/nvme/host/core.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 20c0c141fcc0..daeb2409f989 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -544,6 +544,21 @@ void nvme_cancel_admin_tagset(struct nvme_ctrl *ctrl)
 }
 EXPORT_SYMBOL_GPL(nvme_cancel_admin_tagset);
 
+static const char *nvme_ctrl_state_str(enum nvme_ctrl_state st)
+{
+	static const char *const str[] = {
+		[NVME_CTRL_NEW]			= "new",
+		[NVME_CTRL_LIVE]		= "live",
+		[NVME_CTRL_RESETTING]		= "resetting",
+		[NVME_CTRL_CONNECTING]		= "connecting",
+		[NVME_CTRL_DELETING]		= "deleting",
+		[NVME_CTRL_DELETING_NOIO]	= "deleting (no IO)",
+		[NVME_CTRL_DEAD]		= "dead",
+	};
+
+	return st < ARRAY_SIZE(str) && str[st] ? str[st] : "unknown state";
+}
+
 bool nvme_change_ctrl_state(struct nvme_ctrl *ctrl,
 		enum nvme_ctrl_state new_state)
 {
@@ -621,6 +636,9 @@ bool nvme_change_ctrl_state(struct nvme_ctrl *ctrl,
 	}
 
 	if (changed) {
+		dev_dbg(ctrl->device, "%s %s -> %s\n", __func__,
+			nvme_ctrl_state_str(old_state),
+			nvme_ctrl_state_str(new_state));
 		WRITE_ONCE(ctrl->state, new_state);
 		wake_up_all(&ctrl->state_wq);
 	}
-- 
2.40.0