[PATCH 11/24] scsi: add scsi_host_get_reserved_cmd()

[Hannes Reinecke <hare@xxxxxxx>]

Implement a function to allocate a SCSI command from the reserved
tag pool using the host-wide reserved command queue.

Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
---
 drivers/scsi/scsi_lib.c  | 21 +++++++++++++++++++++
 include/scsi/scsi_cmnd.h |  1 +
 2 files changed, 22 insertions(+)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 076459853622..da850bf28065 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1871,6 +1871,27 @@ void scsi_mq_destroy_tags(struct Scsi_Host *shost)
 	blk_mq_free_tag_set(&shost->tag_set);
 }
 
+struct scsi_cmnd *scsi_host_get_reserved_cmd(struct Scsi_Host *shost)
+{
+	struct request *rq;
+	struct scsi_cmnd *scmd;
+
+	if (WARN_ON(!shost->reserved_cmd_q))
+		return NULL;
+
+	rq = blk_mq_alloc_request(shost->reserved_cmd_q,
+				  REQ_OP_DRV_OUT | REQ_NOWAIT,
+				  BLK_MQ_REQ_RESERVED);
+	if (IS_ERR(rq))
+		return NULL;
+	WARN_ON(rq->tag == -1);
+	scmd = blk_mq_rq_to_pdu(rq);
+	scmd->request = rq;
+
+	return scmd;
+}
+EXPORT_SYMBOL_GPL(scsi_host_get_reserved_cmd);
+
 /**
  * scsi_device_from_queue - return sdev associated with a request_queue
  * @q: The request queue to return the sdev from
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index 318f1e729318..4a45704b28fe 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -167,6 +167,7 @@ static inline struct scsi_driver *scsi_cmd_to_driver(struct scsi_cmnd *cmd)
 	return *(struct scsi_driver **)cmd->request->rq_disk->private_data;
 }
 
+struct scsi_cmnd *scsi_host_get_reserved_cmd(struct Scsi_Host *shost);
 extern void scsi_put_command(struct scsi_cmnd *);
 extern void scsi_finish_command(struct scsi_cmnd *cmd);
 
-- 
2.16.4