On 5/4/21 4:21 AM, Bart Van Assche wrote:

On 5/3/21 8:03 AM, Hannes Reinecke wrote:

quoted

+/**
+ * scsi_get_internal_cmd - allocate an internal SCSI command
+ * @sdev: SCSI device from which to allocate the command
+ * @op: operation (REQ_OP_SCSI_IN or REQ_OP_SCSI_OUT)
+ * @flags: BLK_MQ_REQ_* flags, e.g. BLK_MQ_REQ_NOWAIT.
+ *
+ * Allocates a SCSI command for internal LLDD use.
+ */
+struct scsi_cmnd *scsi_get_internal_cmd(struct scsi_device *sdev,
+	unsigned int op, blk_mq_req_flags_t flags)
+{
+	struct request *rq;
+	struct scsi_cmnd *scmd;
+
+	WARN_ON_ONCE(((op & REQ_OP_MASK) != REQ_OP_SCSI_IN) &&
+		     ((op & REQ_OP_MASK) != REQ_OP_SCSI_OUT));
+	rq = blk_mq_alloc_request(sdev->request_queue, op, flags);
+	if (IS_ERR(rq))
+		return NULL;
+	scmd = blk_mq_rq_to_pdu(rq);
+	scmd->request = rq;
+	scmd->device = sdev;
+	return scmd;
+}
+EXPORT_SYMBOL_GPL(scsi_get_internal_cmd);

Multiple fields that are initialized by the regular command submission
path are not initialized by the above function, e.g. scmd->tag. Has it
been considered to call scsi_init_command() instead of adding yet
another code path that initializes scmd->request?

Hmm. No, I don't think it's a good idea.
Basic idea is that the SCSI request serves as a container for (non-SCSI) 
management commands, _and_ that they are submitted directly from within 
the driver, ie never ever enter ->queue_rq().
As such we don't need an initialisation vie scsi_init_request(), and it 
would actually be counter-productive as we would be setting up fields 
which we'll never need anyway, and might need to tear down afterwards.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
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