nvmet: add async event tracing support

This adds a new tracepoint for the target to trace async event. This is
helpful in debugging and comparing host and target side async events
especially when host is connected to different targets on different
machines and now that we rely on userspace components to generate AEN. 
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/core.c

@@ -151,6 +151,7 @@ static void nvmet_async_events_process(struct nvmet_ctrl *ctrl, u16 status)
 		kfree(aen);
 
 		mutex_unlock(&ctrl->lock);
+		trace_nvmet_async_event(ctrl, req->cqe->result.u32);
 		nvmet_req_complete(req, status);
 	}
 }

drivers/nvme/target/trace.h

@@ -130,6 +130,34 @@ TRACE_EVENT(nvmet_req_complete,
 
 );
 
+#define aer_name(aer) { aer, #aer }
+
+TRACE_EVENT(nvmet_async_event,
+	TP_PROTO(struct nvmet_ctrl *ctrl, __le32 result),
+	TP_ARGS(ctrl, result),
+	TP_STRUCT__entry(
+		__field(int, ctrl_id)
+		__field(u32, result)
+	),
+	TP_fast_assign(
+		__entry->ctrl_id = ctrl->cntlid;
+		__entry->result = (le32_to_cpu(result) & 0xff00) >> 8;
+	),
+	TP_printk("nvmet%d: NVME_AEN=%#08x [%s]",
+		__entry->ctrl_id, __entry->result,
+		__print_symbolic(__entry->result,
+		aer_name(NVME_AER_NOTICE_NS_CHANGED),
+		aer_name(NVME_AER_NOTICE_ANA),
+		aer_name(NVME_AER_NOTICE_FW_ACT_STARTING),
+		aer_name(NVME_AER_NOTICE_DISC_CHANGED),
+		aer_name(NVME_AER_ERROR),
+		aer_name(NVME_AER_SMART),
+		aer_name(NVME_AER_CSS),
+		aer_name(NVME_AER_VS))
+	)
+);
+#undef aer_name
+
 #endif /* _TRACE_NVMET_H */
 
 #undef TRACE_INCLUDE_PATH