Tutorial 4: Linux Kernel Character Device Drivers

This tutorial was more about understanding concepts than hands-on, focusing on character device drivers in the Linux kernel. It introduced key concepts like major and minor device numbers, file operations (open, read, write, release), and how these drivers interact with user space through special files in /dev.

Character devices and driver structure

I learned how character devices manage sequential data transfer (for example, serial ports or keyboards) and how the kernel maps these devices using major and minor numbers. The tutorial also explained how drivers implement file operations to handle system calls for these devices, and how they connect these operations to the device using cdev structures.

Writing and testing a simple driver

After understanding the theory, I worked through an example character driver that allocated a buffer in kernel space and implemented basic file operations. The process involved:

• Adding the driver to kbuild (Kconfig and Makefile).
• Enabling it via menuconfig.
• Rebuilding the kernel and installing the module in the VM.
• Using modprobe, mknod, and simple C programs to test read and write operations.

Issues faced

Although the tutorial was mostly conceptual, the practical steps turned out to be the most challenging so far. During the kernel build, I got stuck with many unexpected config prompts, and later, my VM wouldn’t mount properly. I suspect I misconfigured some directories related to the VM filesystem running commands from previous tutorials.

I had to backtrack, redo parts of the setup from earlier tutorials, and, with help from the course monitors, finally got the VM working again.

Key takeaways

• Gained a deeper understanding of character device drivers and how they map to /dev files.
• Experienced real issues with kernel configuration and VM management, which helped reinforce the importance of having a solid environment setup.

📚 You can follow the full tutorial here