# SPDX-License-Identifier: GPL-2.0
#
# Copyright (C) 2020 Manuel Bentele <development@manuel-bentele.de>
#

# check if custom Linux kernel build directory was specified
if(NOT KERNEL_BUILD_DIR)
    set(KERNEL_BUILD_DIR "/lib/modules/${CMAKE_SYSTEM_VERSION}/build"
        CACHE PATH "Path to Linux kernel modules to compile against")
endif(NOT KERNEL_BUILD_DIR)

# check if custom Linux kernel output directory was specified
if(NOT KERNEL_INSTALL_DIR)
    set(KERNEL_INSTALL_DIR "/lib/modules/${CMAKE_SYSTEM_VERSION}/extra"
        CACHE PATH "Path to install Linux kernel modules")
endif(NOT KERNEL_INSTALL_DIR)

# find the Linux kernel headers from given KERNEL_BUILD_DIR
find_path(KernelHeaders_INCLUDE_DIR
          NAMES linux/user.h
          PATHS ${KERNEL_BUILD_DIR}/include)

# get Linux kernel headers version
string(REGEX MATCH "[0-9]+\\.[0-9]+\\.[0-9]+" KernelHeaders_VERSION ${KernelHeaders_INCLUDE_DIR})

include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(KernelHeaders
                                  FOUND_VAR KernelHeaders_FOUND
                                  REQUIRED_VARS KernelHeaders_INCLUDE_DIR
                                  VERSION_VAR KernelHeaders_VERSION
                                  FAIL_MESSAGE "Linux kernel headers are not available! Please install them to build kernel modules!")

if(KernelHeaders_FOUND)
    set(KernelHeaders_INCLUDE_DIRS ${KernelHeaders_INCLUDE_DIR}/include
        CACHE PATH "Path to Linux kernel header includes")
endif(KernelHeaders_FOUND)

mark_as_advanced(KernelHeaders_INCLUDE_DIR KernelHeaders_MODULE_INSTALL_DIR)

# print found information
message(VERBOSE "KERNEL_BUILD_DIR: ${KERNEL_BUILD_DIR}")
message(VERBOSE "KERNEL_INSTALL_DIR: ${KERNEL_INSTALL_DIR}")
message(VERBOSE "KernelHeaders_FOUND: ${KernelHeaders_FOUND}")
message(VERBOSE "KernelHeaders_VERSION: ${KernelHeaders_VERSION}")
message(VERBOSE "KernelHeaders_INCLUDE_DIRS: ${KernelHeaders_INCLUDE_DIRS}")