Outro

Congratulations! You've completed the book. You've learned how to implement a simple OS kernel from scratch. You've learned about the basic concepts of operating systems, such as booting CPU, context switching, page table, user mode, system call, disk I/O, and file system.

Although it's less than 1000 lines, it must have been quite challenging. This is because you built the core of the core of the core of kernel.

For those who are not satisfied yet and wants to continue with something, here are some next steps:

Add new features

In this book, we implemented the basic features of a kernel. However, there are still many features that can be implemented. For example, it would be interesting to implement the following features:

• A proper memory allocator that allows freeing memory.
• Interrupt handling. Do not busy-wait for disk I/O.
• A full-fledged file system. Implementing ext2 would be a good start.
• Network communication (TCP/IP). It's not hard to implement UDP/IP (TCP is somewhat advanced). Virtio-net is very similar to virtio-blk!

Read other OS implementations

The most recommended next step is to read the implementation of existing OSes. Comparing your implementation with others and learning how others implemented is very educational.

My favorite is RISC-V version of xv6. This is a UNIX-like OS for educational purposes, and it comes with an explanatory book (in English). It's recommended for those who want to learn about UNIX-specific features like fork(2).

Another one is my project Starina, a microkernel-based OS written in Rust. This is still very experimental, but would be interesting for those who want to learn about microkernel architecture and how Rust shines in OS development.

Feedbacks are very welcome!

If you have any questions or feedback, please feel free to ask on GitHub, or send me an email if you prefer. Happy your endless OS programming!