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scsi: core: Introduce the scsi_cmd_to_rq() function 

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>
This commit is contained in:
Bart Van Assche 2021-08-09 16:03:04 -07:00 committed by Martin K. Petersen
parent 10163cee1f
commit 51f3a47889
1 changed files with 6 additions and 0 deletions
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6
include/scsi/scsi_cmnd.h
View File

@ -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 *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.