null_blk: multi queue aware block test driver

A driver that simply completes IO it receives, it does no
transfers. Written to fascilitate testing of the blk-mq code.
It supports various module options to use either bio queueing,
rq queueing, or mq mode.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index e07a5fd..4682546 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -15,6 +15,9 @@
 
 if BLK_DEV
 
+config BLK_DEV_NULL_BLK
+	tristate "Null test block driver"
+
 config BLK_DEV_FD
 	tristate "Normal floppy disk support"
 	depends on ARCH_MAY_HAVE_PC_FDC