bcache: A block layer cache

Does writethrough and writeback caching, handles unclean shutdown, and
has a bunch of other nifty features motivated by real world usage.

See the wiki at http://bcache.evilpiepirate.org for more.

Signed-off-by: Kent Overstreet <koverstreet@google.com>
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index 4d8d90b..3bfc8f1 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -174,6 +174,8 @@
 
 	  In unsure, say N.
 
+source "drivers/md/bcache/Kconfig"
+
 config BLK_DEV_DM
 	tristate "Device mapper support"
 	---help---