[PATCH RFC v3 02/41] scsi: add scsi_{get,put}_reserved_cmd()

[Hannes Reinecke <hare@xxxxxxx>]

Add helper functions to retrieve SCSI commands from the reserved
tag pool.

Signed-off-by: Hannes Reinecke <hare@xxxxxxxx>
---
 drivers/scsi/scsi_lib.c    | 35 +++++++++++++++++++++++++++++++++++
 include/scsi/scsi_device.h |  3 +++
 2 files changed, 38 insertions(+)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 5358f553f526..d0972744ea7f 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1901,6 +1901,41 @@ void scsi_mq_destroy_tags(struct Scsi_Host *shost)
 	blk_mq_free_tag_set(&shost->tag_set);
 }
 
+/**
+ * scsi_get_reserved_cmd - allocate a SCSI command from reserved tags
+ * @sdev: SCSI device from which to allocate the command
+ * @data_direction: Data direction for the allocated command
+ */
+struct scsi_cmnd *scsi_get_reserved_cmd(struct scsi_device *sdev,
+					int data_direction)
+{
+	struct request *rq;
+	struct scsi_cmnd *scmd;
+
+	rq = blk_mq_alloc_request(sdev->request_queue,
+				  data_direction == DMA_TO_DEVICE ?
+				  REQ_OP_SCSI_OUT : REQ_OP_SCSI_IN | REQ_NOWAIT,
+				  BLK_MQ_REQ_RESERVED);
+	if (IS_ERR(rq))
+		return NULL;
+	scmd = blk_mq_rq_to_pdu(rq);
+	scmd->request = rq;
+	return scmd;
+}
+EXPORT_SYMBOL_GPL(scsi_get_reserved_cmd);
+
+/**
+ * scsi_put_reserved_cmd - free a SCSI command allocated from reserved tags
+ * @scmd: SCSI command to be freed
+ */
+void scsi_put_reserved_cmd(struct scsi_cmnd *scmd)
+{
+	struct request *rq = blk_mq_rq_from_pdu(scmd);
+
+	blk_mq_free_request(rq);
+}
+EXPORT_SYMBOL_GPL(scsi_put_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_device.h b/include/scsi/scsi_device.h
index c3cba2aaf934..e74c7e671aa0 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -457,6 +457,9 @@ static inline int scsi_execute_req(struct scsi_device *sdev,
 	return scsi_execute(sdev, cmd, data_direction, buffer,
 		bufflen, NULL, sshdr, timeout, retries,  0, 0, resid);
 }
+struct scsi_cmnd *scsi_get_reserved_cmd(struct scsi_device *sdev,
+					int data_direction);
+void scsi_put_reserved_cmd(struct scsi_cmnd *scmd);
 extern void sdev_disable_disk_events(struct scsi_device *sdev);
 extern void sdev_enable_disk_events(struct scsi_device *sdev);
 extern int scsi_vpd_lun_id(struct scsi_device *, char *, size_t);
-- 
2.16.4