Btrfs: add config option to enable btrfs integrity check

Added the BTRFS_FS_CHECK_INTEGRITY option to Kconfig. It depends on
BTRFS_FS.
Signed-off-by: NStefan Behrens <sbehrens@giantdisaster.de>

fs/btrfs/Kconfig

@@ -31,3 +31,22 @@ config BTRFS_FS_POSIX_ACL
 	  Linux website <http://acl.bestbits.at/>.
 
 	  If you don't know what Access Control Lists are, say N
+
+config BTRFS_FS_CHECK_INTEGRITY
+	bool "Btrfs with integrity check tool compiled in (DANGEROUS)"
+	depends on BTRFS_FS
+	help
+	  Adds code that examines all block write requests (including
+	  writes of the super block). The goal is to verify that the
+	  state of the filesystem on disk is always consistent, i.e.,
+	  after a power-loss or kernel panic event the filesystem is
+	  in a consistent state.
+
+	  If the integrity check tool is included and activated in
+	  the mount options, plenty of kernel memory is used, and
+	  plenty of additional CPU cycles are spent. Enabling this
+	  functionality is not intended for normal use.
+
+	  In most cases, unless you are a btrfs developer who needs
+	  to verify the integrity of (super)-block write requests
+	  during the run of a regression test, say N