Re: [PATCH v5 01/52] core: Introduce the scsi_cmd_to_rq() function

Hannes Reinecke
2021-08-10T06:15:05Z

On 8/10/21 1:03 AM, Bart Van Assche wrote:
> 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 90da9617d28a..e76278ea1fee 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 *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.
>
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
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