Add fastfail to SCSI

This is the preliminary version with no error indications or
control over the types of failures.

drivers/scsi/scsi_error.c

@@ -1285,7 +1285,12 @@ int scsi_decide_disposition(struct scsi_cmnd *scmd)
 
       maybe_retry:
 
-	if ((++scmd->retries) < scmd->allowed) {
+	/* we requeue for retry because the error was retryable, and
+	 * the request was not marked fast fail.  Note that above,
+	 * even if the request is marked fast fail, we still requeue
+	 * for queue congestion conditions (QUEUE_FULL or BUSY) */
+	if ((++scmd->retries) < scmd->allowed 
+	    && !blk_noretry_request(scmd->request)) {
 		return NEEDS_RETRY;
 	} else {
 		/*

drivers/scsi/scsi_lib.c

@@ -502,15 +502,23 @@ static struct scsi_cmnd *scsi_end_request(struct scsi_cmnd *cmd, int uptodate,
 	 * to queue the remainder of them.
 	 */
 	if (end_that_request_first(req, uptodate, sectors)) {
-		if (requeue) {
+		int leftover = req->hard_nr_sectors - sectors;
+
+		/* kill remainder if no retrys */
+		if (!uptodate && blk_noretry_request(req))
+			end_that_request_first(req, 0, leftover);
+		else {
+			if (requeue)
 				/*
-			 * Bleah.  Leftovers again.  Stick the leftovers in
-			 * the front of the queue, and goose the queue again.
+				 * Bleah.  Leftovers again.  Stick the
+				 * leftovers in the front of the
+				 * queue, and goose the queue again.
 				 */
 				scsi_requeue_command(q, cmd);
-		}
+
 			return cmd;
 		}
+	}
 
 	add_disk_randomness(req->rq_disk);