Welcome to the Poplar Book, which serves as the main source of documentation for Poplar. The Book aims to be both a 10,000-meter overview of Poplar for the interested observer, and a definitive reference for the inner workings of the kernel and userspace.
Please note that this book (like the rest of the OS!) is still very early in development and not at all complete. If anything is unclear, please file an issue!
This book is not always up to date, and needs to document a lot more to be very useful. If you have questions not covered by the book, please don't hesitate to contact me through other channels and I'll do my best to answer them. I aim to keep this book up to date, but I do not have enough time to make that a reality at the moment - sorry.
At heart, Poplar is a microkernel written in the Rust programming language. Poplar becomes an "OS" when it's combined with other packages such as drivers, filesystems and user applications.
Poplar is designed to be a modern microkernel, supporting a minimal system call interface and first-class support for message-passing-based IPC between userspace processes. Versatile message-passing allows Poplar to move much more out of the kernel than traditionally possible. For example, the kernel has no concept of a filesystem or of files - instead, the VFS and all filesystems are implemented entirely in userspace, and files are read and written to by passing messages.
While Poplar's design is in theory language-agnostic, the implementation is very tied to Rust. Rust is a systems programming language with a rich type system and a novel ownership model that guarantees
memory and thread safety in safe code. This qualification is important, as Poplar uses a lot of
unsafe code out of necessity - it's important to understand that the use of Rust does not in any way
mean that Poplar is automatically bug-free.
However, Rust makes you think a lot more about how to make your programs safe, which is exactly the sort of code we want to be writing for a kernel. This focus on safety, as well as good ergonomics features and performance, makes Rust perfect for OS-level code.