lkm_template

A generic project template for developing Linux Kernel Modules (LKMs), specifically enabling out of source tree builds. I'm a beginner with LKMs so I don't really know what I'm doing but this works for me so far, but there may be errors or bad design decisions.

There is a c_cpp_properties.json file for configuring intellisense in vscode, which should just work - provided the linux source code can be found at toolchain/linux and the raspberrypi/tools repository can be found at toolchain/tools (if not, just change the include paths and compiler path in the json file to reflect the actual locations, or make use of symlinks).

Compilation

(Both steps should be run in the project root directory)

./configure

This will discover all .c and .h files in src, and symlink them (preserving directory structure) into newly created target/src.

It will also create a Makefile at target/Makefile that can be used to compile the project in-tree in the target directory.

The Makefile will compile 1 module, named after the basename of the project root directory (e.g. if your project directory is ~/projects/gpio_drv then the module will be called gpio_drv). All the source (.c) files in src will be used to compile the module.

The configure.sh script will need to be re-run whenever a new file is added. To remove old files in target/src, just run make clean and reconfigure and compile.

make KERNEL=<path_to_kernel_src> CROSS=<path_to_raspberrypi/tools>/arm-bcm2708/arm-linux-gnueabihf/bin/arm-linux-gnueabihf-

Where <path_to_kernel_src> is the path to the source code of linux of the version that you want to build against, and <path_to_raspberrypi/tools> is the path to where you've cloned https://github.com/raspberrypi/tools.

E.g. make KERNEL=toolchain/linux CROSS=toolchain/tools/arm-bcm2708/arm-linux-gnueabihf/bin/arm-linux-gnueabihf-

This will invoke the compilation process to produce a kernel module (.ko) file in target, which is then copied into the project root directory.

Running the module on the pi

Also provided is a script, rpiz_exec.sh, which can be used to transfer the module onto the raspberry pi at ~/mods and put you in a SSH session in that directory, intended so you can then manually do whatever to the module.

./rpiz_exec.sh <pi_username>@<pi_ip_addr>

This will connect to the SSH daemon/service running on the pi and transfer the module, and then drop you into a shell (this will require entering the password for SSH twice unless a different authentication mechanism is set up).

Cleanup

Simply run make clean, which just deletes the .ko file and target directory.