[PATCH 1/2] scsi: core: Add support for reserved tags

[Bart Van Assche <bvanassche@acm.org>]

Allow SCSI LLDs to allocate reserved tags by passing the BLK_MQ_REQ_RESERVED
flag to blk_get_request().

Cc: Hannes Reinecke <hare@suse.de>
Cc: John Garry <john.garry@huawei.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/scsi_lib.c  | 4 +++-
 include/scsi/scsi_host.h | 9 ++++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index d0b7c6dc74f8..1cbade5fe990 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1917,6 +1917,7 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
 {
 	unsigned int cmd_size, sgl_size;
 	struct blk_mq_tag_set *tag_set = &shost->tag_set;
+	unsigned int reserved_tags = shost->hostt->reserved_tags;
 
 	sgl_size = max_t(unsigned int, sizeof(struct scatterlist),
 				scsi_mq_inline_sgl_size(shost));
@@ -1932,7 +1933,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
 		tag_set->ops = &scsi_mq_ops_no_commit;
 	tag_set->nr_hw_queues = shost->nr_hw_queues ? : 1;
 	tag_set->nr_maps = shost->nr_maps ? : 1;
-	tag_set->queue_depth = shost->can_queue;
+	tag_set->queue_depth = shost->can_queue + reserved_tags;
+	tag_set->reserved_tags = reserved_tags;
 	tag_set->cmd_size = cmd_size;
 	tag_set->numa_node = NUMA_NO_NODE;
 	tag_set->flags = BLK_MQ_F_SHOULD_MERGE;
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 97cdad14de56..5502fcb306db 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -367,10 +367,17 @@ struct scsi_host_template {
 	/*
 	 * This determines if we will use a non-interrupt driven
 	 * or an interrupt driven scheme.  It is set to the maximum number
-	 * of simultaneous commands a single hw queue in HBA will accept.
+	 * of simultaneous commands a single hw queue in HBA will accept. Does
+	 * not include @reserved_tags.
 	 */
 	int can_queue;
 
+	/*
+	 * Number of tags to reserve. A reserved tag can be allocated by passing
+	 * the BLK_MQ_REQ_RESERVED flag to blk_get_request().
+	 */
+	unsigned reserved_tags;
+
 	/*
 	 * In many instances, especially where disconnect / reconnect are
 	 * supported, our host also has an ID on the SCSI bus.  If this is