How to build kernel module without full kernel source tree?

Question

I would like to build kernel module without kernel source tree.
Instead that, I specified the kernel header directory only.

This reference link tell me it should be workable :
build kernel module w/o source source tree

But some other reference links tell me should build module with full kernel source tree!

My question is :
1. Shall I build kernel module link with full kernel source tree ?
2. Is it necessary to do a full build under kernel source tree before build my single module ?

Answer 1

1. Not it's not necessary. You need a header files that contains function and types declarations. You also kernel tree with Makefiles and Kconfig but without sources. This kernel tree is needed by kbuild - kernel building system.

2. Absolutely not. You can build a single module without building whole kernel regardless of it's out-of-tree or in-tree module.

Answer 2

No to both questions. You're talking about out-of-tree (or "external") modules.

Here is a tutorial of Building External Modules.

And here is a simple sample of a Makefile.

obj-m += your-module.o
KDIR=/lib/modules/`uname -r`/build
default:
    $(MAKE) -C $(KDIR) M=$(PWD) modules