Buildroot QEMU works. Nuff said.

README.md

@@ -1,9 +1,32 @@
 # Linux Kernel Module Cheat
 
+Run one command, get into QEMU Buildroot BusyBox with several minimal Linux kernel module examples. Tested in Ubuntu 14.04.
+
+Usage:
+
+    ./run
+
+First build will take a while (GCC, Linux kernel).
+
+QEMU opens up, and you can run:
+
+    root
+    insmod /hello.ko
+    insmod /hello2.ko
+    rmmod hello
+    rmmod hello2
+
+Each module comes from a C file under `kernel_module/package/kernel_module/src/`.
+
+The Linux kernel version can be found with:
+
+    grep BR2_LINUX_KERNEL_VERSION buildroot/.config
+
 1.  [Introduction](introduction.md)
 1.  [Build](build.md)
 1.  [kmod](kmod.md)
 1.  Examples
     1.  [Host](host/)
     1.  Buildroot
-        1. [hello](hello.c)
+        1. [hello](kernel_module/package/kernel_module/src/hello.c)
+        1. [hello2](kernel_module/package/kernel_module/src/hello2.c)

kernel_module/Config.in

@@ -0,0 +1 @@
+source "$BR2_EXTERNAL_KERNEL_MODULE_PATH/package/kernel_module/Config.in"

kernel_module/external.desc

@@ -0,0 +1 @@
+name: KERNEL_MODULE

kernel_module/external.mk

@@ -0,0 +1 @@
+include $(sort $(wildcard $(BR2_EXTERNAL_KERNEL_MODULE_PATH)/package/*/*.mk))

kernel_module/package/kernel_module/Config.in

@@ -0,0 +1,5 @@
+config BR2_PACKAGE_KERNEL_MODULE
+	bool "kernel_module"
+    depends on BR2_LINUX_KERNEL
+	help
+	  Linux Kernel Module Cheat.

kernel_module/package/kernel_module/kernel_module.mk

@@ -0,0 +1,20 @@
+################################################################################
+#
+# kernel_module
+#
+################################################################################
+
+KERNEL_MODULE_VERSION = 1.0
+KERNEL_MODULE_SITE = $(BR2_EXTERNAL_KERNEL_MODULE_PATH)/package/kernel_module/src
+KERNEL_MODULE_SITE_METHOD = local
+
+define KERNEL_MODULE_BUILD_CMDS
+	$(MAKE) -C '$(@D)' LINUX_DIR='$(LINUX_DIR)' PWD='$(@D)' CC='$(TARGET_CC)' LD='$(TARGET_LD)'
+endef
+
+define KERNEL_MODULE_INSTALL_TARGET_CMDS
+	$(INSTALL) -D -m 0755 $(@D)/*.ko '$(TARGET_DIR)'
+endef
+
+$(eval $(kernel-module))
+$(eval $(generic-package))

kernel_module/package/kernel_module/src/Makefile

@@ -0,0 +1,10 @@
+obj-m += hello.o hello2.o
+ccflags-y := -Wno-declaration-after-statement -std=gnu99
+
+.PHONY: all clean
+
+all:
+	$(MAKE) -C '$(LINUX_DIR)' M='$(PWD)' modules
+
+clean:
+	$(MAKE) -C '$(LINUX_DIR)' M='$(PWD)' clean

kernel_module/package/kernel_module/src/hello.c

@@ -0,0 +1,17 @@
+/*
+Hello world module.
+*/
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+
+int init_module(void)
+{
+	printk(KERN_INFO "hello init\n");
+	return 0;
+}
+
+void cleanup_module(void)
+{
+	printk(KERN_INFO "hello cleanup\n");
+}

kernel_module/package/kernel_module/src/hello2.c

@@ -0,0 +1,19 @@
+/*
+Hello world module 2.
+
+Mostly to check that our build infrastructure can handle more than one module!
+*/
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+
+int init_module(void)
+{
+	printk(KERN_INFO "hello2 init\n");
+	return 0;
+}
+
+void cleanup_module(void)
+{
+	printk(KERN_INFO "hello2 cleanup\n");
+}

run

@@ -1,10 +1,8 @@
 #!/usr/bin/env bash
 set -e
 cd buildroot
-make BR2_EXTERNAL="$(pwd)/.." qemu_x86_64_defconfig
-echo '
-BR2_TOOLCHAIN_EXTERNAL=y
-BR2_PACKAGE_KERNEL_MODULE=y
-' >> .config
-make BR2_JLEVEL="$(($(nproc) - 2))"
+make BR2_EXTERNAL="$(pwd)/../kernel_module" qemu_x86_64_defconfig
+echo 'BR2_PACKAGE_KERNEL_MODULE=y' >> .config
+# kernel_module-reconfigure rebuilds the modules if they were modified.
+env -u LD_LIBRARY_PATH make BR2_JLEVEL="$(($(nproc) - 2))" kernel_module-reconfigure all
 qemu-system-x86_64 -M pc -kernel output/images/bzImage -drive file=output/images/rootfs.ext2,if=virtio,format=raw -append root=/dev/vda -net nic,model=virtio -net user