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

• Apache License, Version 2.0
• MIT license

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.