From: Yu Kuai <yukuai3@huawei.com>

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 if it's disabled.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reported-and-tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
---
 block/blk-sysfs.c | 6 +++++-
 block/blk-wbt.c   | 8 ++++++++
 block/blk-wbt.h   | 5 +++++
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e71b3b43927c..5a6950b4ff69 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,
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index 9cac54569ff1..1852ef223c68 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -422,6 +422,14 @@ 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 ||
+	       RQWB(rqos)->enable_state == WBT_STATE_OFF_MANUAL;
+}
+
 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 7fe98638fff5..e3ea6e7e2900 100644
--- a/block/blk-wbt.h
+++ b/block/blk-wbt.h
@@ -96,6 +96,7 @@ 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);
 
@@ -127,6 +128,10 @@ static inline u64 wbt_default_latency_nsec(struct request_queue *q)
 {
 	return 0;
 }
+static inline bool wbt_disabled(struct request_queue *q)
+{
+	return true;
+}
 
 #endif /* CONFIG_BLK_WBT */
 
-- 
2.31.1

>  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);

	if (wbt_disabled(q))
		return sprintf(page, "0\n");
	return sprintf(page, "%llu\n", div_u64(wbt_get_min_lat(q), 1000));

but otherwise the patch looks fine:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Hi,

在 2022/10/18 23:49, Christoph Hellwig 写道:
>>   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);
> 
> 	if (wbt_disabled(q))
> 		return sprintf(page, "0\n");
> 	return sprintf(page, "%llu\n", div_u64(wbt_get_min_lat(q), 1000));
> 
> but otherwise the patch looks fine:
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> .
> 

Thanks for the review, I'll send a new version.

Kuai