octox

octox is a Unix-like operating system inspired by xv6-riscv. octox loosely follows the structure and style of xv6, but is implemented in pure Rust.

Everything from kernel, userland, mkfs, to build system is written in safe Rust as much as possible.
There are no dependencies on external crates.
The userland has a library similar to Rust’s std with K&R malloc.
Multi-core support, buddy allocator as kernel-side memory allocator, file system with logging support, etc.

Getting Started

Requirements

Install the rust toolchain to have cargo installed by following this guide.
Install qemu-system-riscv
(option) Install gdb-multiarch

Build and Run

Clone this project & enter: git clone ... && cd octox
Build: cargo build --target riscv64gc-unknown-none-elf.
Run: cargo run --target riscv64gc-unknown-none-elf, then qemu will boot octox. To exit, press Ctrl+a and x.

Play with the Shell

A very simple shell is implemented. In addition to executing commands, you can only do the following things.

Pipe: cat file | head | grep test
Dump processes: Ctrl + P
End of line: Ctrl + D
Redirect output: >, >>

Development

Userland Application

The userland comes with a user library called ulib that is similar to Rust’s std, so you can use it to develop your favorite commands. If you create a bin crate named _command in src/user, the build.rs and mkfs.rs will place a file named command in the file system and make it available for use.

In src/user/Cargo.toml, define a bin crate with the name of the command you want to create with a _ prefix
```
[[bin]]
name = "_rm"
path = "rm.rs"
    
```

userland is also no_std, so don’t forget to add #[no_std]. Use ulib to develop any command you like. Here is an example of the rm command.

#![no_std]
use ulib::{env, fs};

fn main() {
    let mut args = env::args().skip(1).peekable();

    if args.peek().is_none() {
        panic!("Usage: rm files...")
    }
    for arg in args {
        fs::remove_file(arg).unwrap()
    }
}

Then, cargo run --target riscv64gc-unknown-none-elf in the root of octox.

To use Vec and String, etc, do the following:

extern crate alloc;
use alloc::{string::String, vec::Vec};

Kernel

Developing in src/kernel. Here is an example of adding a system call. If you want to add a new system call, you only need to add a definition to the system call table in libkernel, and the userland library will be automatically generated by build.rs.

Add a variant and Syscall Number to enum SysCalls in src/kernel/syscall.rs. Here is Dup2 as an example:

pub enum SysCalls {
    Fork = 1,
    ...,
    Dup2 = 23,
    Invalid = 0,
}

Define the function signature of the system call in the TABLE of SysCalls. Use the enum type Fn to describe the return type(U (Unit), I (Integer), N (never)) and use &str to represent arguments. then, define kernel-side implementation as a method on SysCalls. cfg flag is used to control the compilation target for kernel and the rest. Here is an example of dup2:

impl SysCalls {
    pub const TABLE: [(fn, &'static str); variant_count::<Self>()] = [
        (Fn::N(Self::Invalid), ""),
        (Fn::I(Self::fork), "()"),
        (Fn::N(Self::exit), "(xstatus: i32)"),
        ...,
        (Fn::I(Self::dup2), "(src: usize, dst: usize)"),
    ];
    pub fn dup2() -> Result<usize> {
        #[cfg(not(all(target_os = "none", feature = "kernel")))]
        return Ok(0);
        #[cfg(all(target_os = "none", feature = "kernel"))]
        {
            let p = Cpus::myproc().unwrap().data_mut();
            let src_fd = argraw(0); let dst_fd = argraw(1);
            if src_fd != dst_fd {
                let mut src = p.ofile.get_mut(src_fd).unwrap()
                    .take().unwrap();
                src.clear_cloexec();
                p.ofile.get_mut(dst_fd)
                    .ok_or(FileDescriptorTooLarge)?.replace(src);
            }
            Ok(dst_fd)
        }
    }

With just these steps, the dup2 system call is implemented in both kernel and userland.

License

Licensed under either of

at your option.

Acknowledgments

octox is inspired by xv6-riscv.

I’m also grateful for the bug reports and discussion about the implementation contributed by Takahiro Itazuri and Kuniyuki Iwashima.

Contribution

This is a learning project for me, and I will not be accepting pull requests until I consider the implementation complete. However, discussions and advice are welcome.

o8vm/octox

o8vm

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