How do I add an include path for kernel module makefile

Question

How do I add an include path for kernel module makefile? I want to include "test_kernel.h" in test_module.c. the "test_kernel.h" resides in other directory "inc" I tried in the following solution in my Makefile but it does not work:

obj-m += test_module.o

test_module:
    $(MAKE) -C "$(LINUX_DIR)" -Iinc $(MAKE_OPTS) modules

Answer 1

You should make use of EXTRA_CFLAGS in your Makefile. Try something on these lines:

obj-m += test_module.o
EXTRA_CFLAGS=-I$(PWD)/inc

test_module:
    $(MAKE) -C "$(LINUX_DIR)" $(MAKE_OPTS) modules

See section 3.7 Compilation Flags section here.
Hope this helps!

Answer 2

are you sure you correctly specified the include in your file?

e.g.:

#include "inc/something.h"

instead of

#include <inc/something.h>