[PATCH] loop inefficiency fix

Patch from Hugh Dickins <hugh@veritas.com>

The loop driver's loop over elements of bi_io_vec is in lo_send and
lo_receive: iterating that same transfer bi_vcnt times at the level above is,
er, excessive.  (And no need to increment bi_idx here.)

drivers/block/loop.c

@@ -350,15 +350,10 @@ static int do_bio_filebacked(struct loop_device *lo, struct bio *bio)
 	int ret;
 
 	pos = ((loff_t) bio->bi_sector << 9) + lo->lo_offset;
-
-	do {
-		if (bio_rw(bio) == WRITE)
-			ret = lo_send(lo, bio, lo->lo_blocksize, pos);
-		else
-			ret = lo_receive(lo, bio, lo->lo_blocksize, pos);
-
-	} while (++bio->bi_idx < bio->bi_vcnt);
-
+	if (bio_rw(bio) == WRITE)
+		ret = lo_send(lo, bio, lo->lo_blocksize, pos);
+	else
+		ret = lo_receive(lo, bio, lo->lo_blocksize, pos);
 	return ret;
 }