[PATCH v6 3/4] scsi: core: Make fair tag sharing configurable via sysfs

[Bart Van Assche <bvanassche@xxxxxxx>]

Add a sysfs attribute to SCSI hosts for configuring fair tag sharing.

Cc: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Keith Busch <kbusch@xxxxxxxxxx>
Cc: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
Cc: Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>
Cc: Ed Tsai <ed.tsai@xxxxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
 drivers/scsi/scsi_sysfs.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 24f6eefb6803..58f0aba50566 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -403,6 +403,35 @@ show_nr_hw_queues(struct device *dev, struct device_attribute *attr, char *buf)
 }
 static DEVICE_ATTR(nr_hw_queues, S_IRUGO, show_nr_hw_queues, NULL);
 
+static ssize_t show_fair_sharing(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct Scsi_Host *shost = class_to_shost(dev);
+	struct blk_mq_tag_set *tag_set = &shost->tag_set;
+
+	return sysfs_emit(buf, "%d\n",
+		!(tag_set->flags & BLK_MQ_F_DISABLE_FAIR_TAG_SHARING));
+}
+
+static ssize_t store_fair_sharing(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t count)
+{
+	struct Scsi_Host *shost = class_to_shost(dev);
+	struct blk_mq_tag_set *tag_set = &shost->tag_set;
+	bool enable;
+	int res;
+
+	res = kstrtobool(buf, &enable);
+	if (res < 0)
+		return res;
+	blk_mq_update_fair_sharing(tag_set, enable);
+
+	return count;
+}
+
+static DEVICE_ATTR(fair_sharing, 0644, show_fair_sharing, store_fair_sharing);
+
 static struct attribute *scsi_sysfs_shost_attrs[] = {
 	&dev_attr_use_blk_mq.attr,
 	&dev_attr_unique_id.attr,
@@ -421,6 +450,7 @@ static struct attribute *scsi_sysfs_shost_attrs[] = {
 	&dev_attr_host_reset.attr,
 	&dev_attr_eh_deadline.attr,
 	&dev_attr_nr_hw_queues.attr,
+	&dev_attr_fair_sharing.attr,
 	NULL
 };