rename kernel_module to kernel_modules, start README mass factorings

packages/kernel_modules/make-host.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+
+# We can almost do everything from the Makefile itself by using default values for
+#
+#    LINUX_DIR ?= "/lib/modules/$(uname -r)/build"
+#    BR2_EXTERNAL_KERNEL_MODULES_PATH="$(pwd)"
+#
+# The problem with that is that if you define those variables in your environment,
+# the build breaks, so this is more portable.
+#
+# Trying to add `-i` to overcome incompatible modules will fail,
+# because any build failure prevents the generation of all `.mod.c` files.
+
+j="$(($(nproc) - 2))"
+while getopts j: OPT; do
+  case "$OPT" in
+    'j')
+      j="$OPTARG"
+    ;;
+  esac
+done
+shift $(($OPTIND - 1))
+make -j "$j" KERNEL_MODULES_PATH="$(pwd)" LINUX_DIR="/lib/modules/$(uname -r)/build" "$@"
+make -C user/ -j "$j" "$@"