virt_to_phys: fix multiple read size

build-buildroot: add --make-args

README.adoc

@@ -10989,10 +10989,43 @@ This directory has the following structure:
 
 ==== include directory
 
-link:include/[] contains headers that are shared acros both kernel modules and userland structures.
+link:include/[] contains headers that are shared across both kernel modules and userland structures.
 
 They contain data structs and magic constant for kernel to userland communication.
 
+==== userland directory
+
+Userland test programs.
+
+It is possible to build and run those examples directly on your host:
+
+....
+cd userland
+make
+....
+
+For usage in the guest, build with:
+
+....
+./build-userland
+....
+
+Source: link:build-userland[].
+
+This makes them visible immediately on the 9P mount `/mnt/9p/out_root_overlay`.
+
+In order to place them in the root filesystem image itself, you must also run:
+
+....
+./build-buildroot
+....
+
+To force rebuild all examples, pass the `-B` option to `make`:
+
+....
+./build-buildroot --make-args=-B
+....
+
 ==== packages directory
 
 Every directory inside it is a Buildroot package.