[PATCH -next 1/3] wbt: don't show valid wbt_lat_usec in sysfs while wbt is disabled

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

Currently, if wbt is initialized and then disabled by
wbt_disable_default(), sysfs will still show valid wbt_lat_usec, which
will confuse users that wbt is still enabled.

This patch shows wbt_lat_usec as zero and forbid to set it while wbt
is disabled.

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
Reported-and-tested-by: Holger Hoffstätte <holger@xxxxxxxxxxxxxxxxxxxxxx>
---
 block/blk-sysfs.c | 9 ++++++++-
 block/blk-wbt.c   | 7 +++++++
 block/blk-wbt.h   | 1 +
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e1f009aba6fd..1955bb6a284d 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -467,10 +467,14 @@ static ssize_t queue_io_timeout_store(struct request_queue *q, const char *page,
 
 static ssize_t queue_wb_lat_show(struct request_queue *q, char *page)
 {
+	u64 lat;
+
 	if (!wbt_rq_qos(q))
 		return -EINVAL;
 
-	return sprintf(page, "%llu\n", div_u64(wbt_get_min_lat(q), 1000));
+	lat = wbt_disabled(q) ? 0 : div_u64(wbt_get_min_lat(q), 1000);
+
+	return sprintf(page, "%llu\n", lat);
 }
 
 static ssize_t queue_wb_lat_store(struct request_queue *q, const char *page,
@@ -493,6 +497,9 @@ static ssize_t queue_wb_lat_store(struct request_queue *q, const char *page,
 			return ret;
 	}
 
+	if (wbt_disabled(q))
+		return -EINVAL;
+
 	if (val == -1)
 		val = wbt_default_latency_nsec(q);
 	else if (val >= 0)
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index a9982000b667..68851c2c02d2 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -422,6 +422,13 @@ static void wbt_update_limits(struct rq_wb *rwb)
 	rwb_wake_all(rwb);
 }
 
+bool wbt_disabled(struct request_queue *q)
+{
+	struct rq_qos *rqos = wbt_rq_qos(q);
+
+	return !rqos || RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT;
+}
+
 u64 wbt_get_min_lat(struct request_queue *q)
 {
 	struct rq_qos *rqos = wbt_rq_qos(q);
diff --git a/block/blk-wbt.h b/block/blk-wbt.h
index 7e44eccc676d..018d3a14cc30 100644
--- a/block/blk-wbt.h
+++ b/block/blk-wbt.h
@@ -94,6 +94,7 @@ void wbt_enable_default(struct request_queue *);
 
 u64 wbt_get_min_lat(struct request_queue *q);
 void wbt_set_min_lat(struct request_queue *q, u64 val);
+bool wbt_disabled(struct request_queue *);
 
 void wbt_set_write_cache(struct request_queue *, bool);
 
-- 
2.31.1