-#ifdef CONFIG_BLK_DEV_VROOT
-extern struct block_device *vroot_get_real_bdev(struct block_device *);
+#if defined(CONFIG_BLK_DEV_VROOT) || defined(CONFIG_BLK_DEV_VROOT_MODULE)
+
+#include <linux/vroot.h>
+#include <linux/kallsyms.h>
+
+static vroot_grb_func *vroot_get_real_bdev = NULL;
+
+static spinlock_t vroot_grb_lock = SPIN_LOCK_UNLOCKED;
+
+int register_vroot_grb(vroot_grb_func *func) {
+ int ret = -EBUSY;
+
+ spin_lock(&vroot_grb_lock);
+ if (!vroot_get_real_bdev) {
+ vroot_get_real_bdev = func;
+ ret = 0;
+ }
+ spin_unlock(&vroot_grb_lock);
+ return ret;
+}
+EXPORT_SYMBOL(register_vroot_grb);
+
+int unregister_vroot_grb(vroot_grb_func *func) {
+ int ret = -EINVAL;
+
+ spin_lock(&vroot_grb_lock);
+ if (vroot_get_real_bdev) {
+ vroot_get_real_bdev = NULL;
+ ret = 0;
+ }
+ spin_unlock(&vroot_grb_lock);
+ return ret;
+}
+EXPORT_SYMBOL(unregister_vroot_grb);
+