v4.19.13 snapshot.
diff --git a/include/linux/initrd.h b/include/linux/initrd.h
new file mode 100644
index 0000000..84b4230
--- /dev/null
+++ b/include/linux/initrd.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#define INITRD_MINOR 250 /* shouldn't collide with /dev/ram* too soon ... */
+
+/* 1 = load ramdisk, 0 = don't load */
+extern int rd_doload;
+
+/* 1 = prompt for ramdisk, 0 = don't prompt */
+extern int rd_prompt;
+
+/* starting block # of image */
+extern int rd_image_start;
+
+/* size of a single RAM disk */
+extern unsigned long rd_size;
+
+/* 1 if it is not an error if initrd_start < memory_start */
+extern int initrd_below_start_ok;
+
+/* free_initrd_mem always gets called with the next two as arguments.. */
+extern unsigned long initrd_start, initrd_end;
+extern void free_initrd_mem(unsigned long, unsigned long);
+
+extern unsigned int real_root_dev;