From: Bart Van Assche <bvanassche@acm.org>
Date: Mon, 9 Aug 2021 16:03:04 -0700
Subject: scsi: core: Introduce the scsi_cmd_to_rq() function
Patch-mainline: v5.15-rc1
Git-commit: 51f3a478892873337c54068d1185bcd797000a52
References: bsc#1190576

The 'request' member of struct scsi_cmnd is superfluous. The struct request
and struct scsi_cmnd data structures are adjacent and hence the request
pointer can be derived easily from a scsi_cmnd pointer. Introduce a helper
function that performs that conversion in a type-safe way. This patch is
the first step towards removing the request member from struct
scsi_cmnd. Making that change has the following advantages:

 - This is a performance optimization since adding an offset to a pointer
   takes less time than dereferencing a pointer.

 - struct scsi_cmnd becomes smaller.

Link: https://lore.kernel.org/r/20210809230355.8186-2-bvanassche@acm.org
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 include/scsi/scsi_cmnd.h |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -148,6 +148,12 @@ struct scsi_cmnd {
 	unsigned char tag;	/* SCSI-II queued command tag */
 };
 
+/* Variant of blk_mq_rq_from_pdu() that verifies the type of its argument. */
+static inline struct request *scsi_cmd_to_rq(struct scsi_cmnd *scmd)
+{
+	return blk_mq_rq_from_pdu(scmd);
+}
+
 /*
  * Return the driver private allocation behind the command.
  * Only works if cmd_size is set in the host template.