v4.19.13 snapshot.
diff --git a/include/linux/adfs_fs.h b/include/linux/adfs_fs.h
new file mode 100644
index 0000000..4836e38
--- /dev/null
+++ b/include/linux/adfs_fs.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ADFS_FS_H
+#define _ADFS_FS_H
+
+#include <uapi/linux/adfs_fs.h>
+
+/*
+ * Calculate the boot block checksum on an ADFS drive. Note that this will
+ * appear to be correct if the sector contains all zeros, so also check that
+ * the disk size is non-zero!!!
+ */
+static inline int adfs_checkbblk(unsigned char *ptr)
+{
+ unsigned int result = 0;
+ unsigned char *p = ptr + 511;
+
+ do {
+ result = (result & 0xff) + (result >> 8);
+ result = result + *--p;
+ } while (p != ptr);
+
+ return (result & 0xff) != ptr[511];
+}
+#endif