[PATCH] add request prep functions to SCSI

This patch adds request prep functions to the mid-layer.  At the moment, its a single request prep function for all of SCSI.  I've altered the logic in scsi_request_fn so that we now do early preparation (this should improve throughput slightly in the untagged case with only a single command block).

The prep function also cannot drop the queue lock, so the calling assumptions for scsi_init_io and the upper layer driver init_commands have changed to be that the lock is now held and they cannot drop it.  I think this means that we have no callers of scsi_init_io that aren't atomic, so perhaps I can just take the if out.

I've hammered this in my usual set up, but other testers would be welcome.

James

drivers/scsi/scsi.c

@@ -226,6 +226,8 @@ void  scsi_initialize_queue(Scsi_Device * SDpnt, struct Scsi_Host * SHpnt)
 
 	if (!SHpnt->use_clustering)
 		clear_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
+
+        blk_queue_prep_rq(q, scsi_prep_fn);
 }
 
 #ifdef MODULE

drivers/scsi/scsi.h

@@ -455,6 +455,7 @@ extern int scsi_insert_special_cmd(Scsi_Cmnd * SCpnt, int);
 extern void scsi_io_completion(Scsi_Cmnd * SCpnt, int good_sectors,
 			       int block_sectors);
 extern void scsi_queue_next_request(request_queue_t * q, Scsi_Cmnd * SCpnt);
+extern int scsi_prep_fn(struct request_queue *q, struct request *req);
 extern void scsi_request_fn(request_queue_t * q);
 extern int scsi_starvation_completion(Scsi_Device * SDpnt);