[PATCH 01/50] core: Introduce the blk_req() function

Bart Van Assche
2021-05-14T21:34:12Z

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.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
include/scsi/scsi_cmnd.h | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index fed024f4c02a..f5825be7ee76 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -146,6 +146,12 @@ struct scsi_cmnd {
unsigned int extra_len; /* length of alignment and padding */
};

+/* Variant of blk_mq_rq_from_pdu() that verifies the type of its argument. */
+static inline struct request *blk_req(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.