On 04/05/2021 07:12, Hannes Reinecke wrote:
On 5/4/21 4:21 AM, Bart Van Assche wrote:
On 5/3/21 8:03 AM, Hannes Reinecke wrote:
+/**
+ * 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.
I will note that we also bypass the queue budgeting in
blk_mq_ops.{get,put}_budget. I figure that is not an issue...
BTW, any chance of a new version?
Thanks,
John
