[PATCH RFC V2 4/5] scsi: Add template flag 'host_tagset'

[John Garry]

From: Hannes Reinecke <hare@xxxxxxxx>

Add a host template flag 'host_tagset' so hostwide tagset can be
shared on multiple reply queues after the SCSI device's reply queue
is converted to blk-mq hw queue.

Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
Signed-off-by: John Garry <john.garry@xxxxxxxxxx>
---
 drivers/scsi/scsi_lib.c  | 2 ++
 include/scsi/scsi_host.h | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 5447738906ac..97c9352f2d16 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1901,6 +1901,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
 	shost->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
 	shost->tag_set.flags |=
 		BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
+	if (shost->hostt->host_tagset)
+		shost->tag_set.flags |= BLK_MQ_F_TAG_HCTX_SHARED;
 	shost->tag_set.driver_data = shost;
 
 	return blk_mq_alloc_tag_set(&shost->tag_set);
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 31e0d6ca1eba..08299aeb822d 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -442,6 +442,9 @@ struct scsi_host_template {
 	/* True if the low-level driver supports blk-mq only */
 	unsigned force_blk_mq:1;
 
+	/* True if the host uses host-wide tagspace */
+	unsigned host_tagset:1;
+
 	/*
 	 * Countdown for host blocking with no commands outstanding.
 	 */
-- 
2.17.1