blk-wbt: make enable_state more accurate

Currently, if user disable wbt through sysfs, 'enable_state' will be
'WBT_STATE_ON_MANUAL', which will be confusing. Add a new state
'WBT_STATE_OFF_MANUAL' to cover that case.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221019121518.3865235-4-yukuai1@huaweicloud.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-wbt.c

@@ -435,8 +435,13 @@ void wbt_set_min_lat(struct request_queue *q, u64 val)
 	struct rq_qos *rqos = wbt_rq_qos(q);
 	if (!rqos)
 		return;
+
 	RQWB(rqos)->min_lat_nsec = val;
-	RQWB(rqos)->enable_state = WBT_STATE_ON_MANUAL;
+	if (val)
+		RQWB(rqos)->enable_state = WBT_STATE_ON_MANUAL;
+	else
+		RQWB(rqos)->enable_state = WBT_STATE_OFF_MANUAL;
+
 	wbt_update_limits(RQWB(rqos));
 }
 

block/blk-wbt.h

@@ -28,13 +28,15 @@ enum {
 };
 
 /*
- * Enable states. Either off, or on by default (done at init time),
- * or on through manual setup in sysfs.
+ * If current state is WBT_STATE_ON/OFF_DEFAULT, it can be covered to any other
+ * state, if current state is WBT_STATE_ON/OFF_MANUAL, it can only be covered
+ * to WBT_STATE_OFF/ON_MANUAL.
  */
 enum {
-	WBT_STATE_ON_DEFAULT	= 1,
-	WBT_STATE_ON_MANUAL	= 2,
-	WBT_STATE_OFF_DEFAULT
+	WBT_STATE_ON_DEFAULT	= 1,	/* on by default */
+	WBT_STATE_ON_MANUAL	= 2,	/* on manually by sysfs */
+	WBT_STATE_OFF_DEFAULT	= 3,	/* off by default */
+	WBT_STATE_OFF_MANUAL	= 4,	/* off manually by sysfs */
 };
 
 struct rq_wb {