cmake_minimum_required(VERSION 3.13)

project(pico_rng_driver LANGUAGES C)
set(CMAKE_C_STANDARD 11)
set(CMAKE_CXX_STANDARD 17)

# Find kernel headers
execute_process(
        COMMAND uname -r
        OUTPUT_VARIABLE KERNEL_RELEASE
        OUTPUT_STRIP_TRAILING_WHITESPACE
)

# Find the headers
find_path(KERNELHEADERS_DIR
        include/linux/user.h
        PATHS /usr/src/linux-headers-${KERNEL_RELEASE}
        )

message(STATUS "Kernel release: ${KERNEL_RELEASE}")
message(STATUS "Kernel headers: ${KERNELHEADERS_DIR}")

if (KERNELHEADERS_DIR)
    set(KERNELHEADERS_INCLUDE_DIRS
            ${KERNELHEADERS_DIR}/include
            ${KERNELHEADERS_DIR}/arch/x86/include
            CACHE PATH "Kernel headers include dirs"
            )
    set(KERNELHEADERS_FOUND 1 CACHE STRING "Set to 1 if kernel headers were found")
else (KERNELHEADERS_DIR)
    set(KERNELHEADERS_FOUND 0 CACHE STRING "Set to 1 if kernel headers were found")
endif (KERNELHEADERS_DIR)

mark_as_advanced(KERNELHEADERS_FOUND)

include_directories(${KERNELHEADERS_INCLUDE_DIRS})

set(DRIVER_FILE pico_rng.ko)
set(KBUILD_CMD $(MAKE) -C ${KERNELHEADERS_DIR} modules M=${CMAKE_CURRENT_BINARY_DIR} src=${CMAKE_CURRENT_SOURCE_DIR})
#FILE(WRITE ${CMAKE_CURRENT_SOURCE_DIR}/Kbuild "obj-m := pico_rng.o")

add_custom_command(OUTPUT ${DRIVER_FILE}
        COMMAND ${KBUILD_CMD}
        WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
        DEPENDS pico_rng.c VERBATIM)

add_custom_target(pico_rng_driver ALL DEPENDS ${DRIVER_FILE})