Re: [PATCH v2 05/20] scsi: core: Add support for internal commands

[John Garry <john.garry@huawei.com>]

On 19/11/2021 19:57, Bart Van Assche wrote:
> +/**
> + * scsi_get_internal_cmd - Allocate an internal SCSI command
> + * @q: request queue from which to allocate the command. This request queue may
> + *	but does not have to be associated with a SCSI device. This request
> + *	queue must be associated with a SCSI tag set. See also
> + *	scsi_mq_setup_tags().
> + * @data_direction: Data direction for the allocated command.
> + * @flags: Zero or more BLK_MQ_REQ_* flags.
> + *
> + * Allocates a request for driver-internal use. The tag of the returned SCSI
> + * command is guaranteed to be unique.
> + */
> +struct scsi_cmnd *scsi_get_internal_cmd(struct request_queue *q,
> +					enum dma_data_direction data_direction,
> +					blk_mq_req_flags_t flags)

I'd pass the Scsi_Host or scsi_device rather than a request q, so maybe:

struct scsi_cmnd *scsi_get_internal_cmd(struct scsi_device *sdev, ..)
struct scsi_cmnd *scsi_host_get_internal_cmd(struct Scsi_Host *shost, ..)

> +{
> +	unsigned int opf = REQ_INTERNAL;
> +	struct request *rq;
> +
> +	opf |= data_direction == DMA_TO_DEVICE ? REQ_OP_DRV_OUT : REQ_OP_DRV_IN;
> +	rq = blk_mq_alloc_request(q, opf, flags);
> +	if (IS_ERR(rq))
> +		return ERR_CAST(rq);

I think that Christoph suggested elsewhere that we should poison all the 
scsi_cmnd

> +	return blk_mq_rq_to_pdu(rq);
> +}
> +EXPORT_SYMBOL_GPL(scsi_get_internal_cmd);