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/Makefile b/drivers/block/Makefile
index ca07399..03b3b4a 100644
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -41,6 +41,7 @@
 obj-$(CONFIG_BLK_DEV_PCIESSD_MTIP32XX)	+= mtip32xx/
 
 obj-$(CONFIG_BLK_DEV_RSXX) += rsxx/
+obj-$(CONFIG_BLK_DEV_NULL_BLK)	+= null_blk.o
 
 nvme-y		:= nvme-core.o nvme-scsi.o
 swim_mod-y	:= swim.o swim_asm.o