This project contains a subset of the example modules introduced throughout the Linux Device Drivers 3rd edition text. LDD3 examples are meant to be compatible with Linux Kernel v2.6. This project uses kernel v5.19. Modernized sources for the modules found in Chapters 1-12 are provided.

Included with the project is a set of Docker containers that can be used to

• Build a custom initramfs
• Configure and build the Linux kernel
• Build out-of-tree kernel modules

The containers create the initramfs and kernel bzImage that can be handed off to the QEMU emulator. From within the emulator, we can load/unload our custom modules and experiment with LDD3's in memory "devices" from the safety of a sandboxed environment.

This project includes the linux-next branch for kernel v5.19 as a submodule. There's a lot of code and a lot of git history that comes along with the linux-next submodule. To speed up the checkout process and save space on your PC, you may want to follow these steps when cloning the repo:

$ git clone [email protected]:ivan-guerra/linux_device_drivers.git
$ cd linux_device_drivers
$ git submodule init
$ git submodule update --depth 1

You can change the argument to --depth to include however much history you like or remove it completey for the full history.

To build and run the examples, you will need Docker and QEMU installed on your host PC. The steps that follow were run on a Fedora 36 PC with Docker v20.10 and QEMU v6.2 installed.

All scripts referenced below can be found under scripts/.

To build the kernel, modules, and initramfs:

$ ./build.sh

To run the kernel with the init ram disk:

$ ./run.sh

Once the virtual machine boots, you can find the example modules under the /modules/ directory. Many of the modules include a MODNAME_load and corresponding MODNAME_unload script. You can run these scripts to load/unload the modules or you can do so directly yourself using the userland tools provided (i.e., insmod, rmmod, mknod, etc.).

It can sometimes be useful to run an interactive debugger against your module to diagnose issues. This project includes support for GDB debug of kernel code and modules.

You will first need to compile a kernel with debug info, kgdb debug support, and more. You can find the details of which config parameters are required by reading this Star Lab's article. When you're ready, run the build.sh script and configure/build the kernel and all modules.

The run.sh script includes GDB debug support. To launch your kernel in debug mode:

$ ./run.sh -g

From a seperate terminal, you can connect gdb to your live kernel and begin stepping through code. Note, $LINUX_OBJ_DIR below refers to the directory containing the Linux kernel objects produced by the build. These should always be under /path/to/linux_device_drivers/bin/obj.

$ cd $LINUX_OBJ_DIR
$ gdb vmlinux
(gdb) target remote localhost:1234

At this point, you can set breakpoints, step through code, etc. Be wary, there are quite a few differences between using GDB to debug the kernel versus a userland app. It's worth taking the time to read some articles to understand what those differences are.

The authors and publishers have made the text and source code for these examples publicly avilable. Here are the links to the source material I used:

• Linux Device Drivers 3rd Edition
• Original Example Files