ANDROID: dm verity fec: add sysfs attribute fec/corrected

Add a sysfs entry that allows user space to determine whether dm-verity
has come across correctable errors on the underlying block device.

Bug: 22655252
Bug: 27928374
Change-Id: I80547a2aa944af2fb9ffde002650482877ade31b
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
(cherry picked from commit 7911fad5f0a2cf5afc2215657219a21e6630e001)
diff --git a/drivers/md/dm-verity-fec.h b/drivers/md/dm-verity-fec.h
index 7fa0298..a22098d 100644
--- a/drivers/md/dm-verity-fec.h
+++ b/drivers/md/dm-verity-fec.h
@@ -12,6 +12,8 @@
 #ifndef DM_VERITY_FEC_H
 #define DM_VERITY_FEC_H
 
+#include "dm.h"
+#include "dm-core.h"
 #include "dm-verity.h"
 #include <linux/rslib.h>
 
@@ -48,6 +50,8 @@
 	mempool_t *extra_pool;	/* mempool for extra buffers */
 	mempool_t *output_pool;	/* mempool for output */
 	struct kmem_cache *cache;	/* cache for buffers */
+	atomic_t corrected;		/* corrected errors */
+	struct dm_kobject_holder kobj_holder;	/* for sysfs attributes */
 };
 
 /* per-bio data */