How to write the Linux kernel in Rust (by ChatGPT)

rust-linux-chatgpt.md

What are [the] steps to write the Linux kernel in Rust?

Writing the Linux kernel in Rust is a complex and ambitious undertaking, and it requires a deep understanding of both the Linux kernel and Rust programming language. Here are some high-level steps that can help you get started:

1. Familiarize yourself with Rust: Rust is a modern programming language that prioritizes performance, safety, and concurrency. It has a steep learning curve but is powerful once mastered. Learn Rust basics by following Rust programming tutorials and practice it on small projects.

2. Learn Linux kernel development: Familiarize yourself with Linux kernel development, understanding how the kernel is structured, and the role of its various components. You can read the book "Linux Kernel Development" by Robert Love or check out the Linux Kernel documentation on the official website.

3. Identify the kernel subsystems: Identify which subsystems you want to work on, since the Linux kernel is a vast and complex system, and it might be difficult to grasp everything at once. You can choose from subsystems like file systems, network protocols, device drivers, etc.

4. Choose a Rust development environment: Install and set up a Rust development environment that is compatible with kernel development. This can be achieved by using rustup, the Rust toolchain installer.

5. Learn kernel module development: Get acquainted with kernel module development and learn how to create modules in C, which is the primary language used for Linux kernel development. This will help you understand the structure of kernel modules and the interaction with kernel APIs.

6. Build the kernel in Rust: Start writing Rust code for kernel subsystems and gradually integrate it with the existing kernel codebase. This process can be gradual, where you start with small subsystems and eventually move onto more complex ones.

7. Test and debug: Test your kernel code extensively to ensure it's reliable, efficient, and performs as expected. Use debuggers and tracing tools to pinpoint issues, and use profiling tools to identify performance bottlenecks.

8. Contribute to the community: Submit your code to the Linux kernel development community for review and feedback. This will help you improve the quality of your code and learn from experts in the field.

Overall, writing the Linux kernel in Rust is a complex and challenging task, but it's an excellent opportunity to combine the power of Rust with the robustness of the Linux kernel.

---

Try to write a small submodule of linux in rust

Writing a small submodule of the Linux kernel in Rust is a great way to start exploring the possibility of using Rust for kernel development. Here is an example of how to write a small device driver for a simple hardware device in Rust:

1. Choose the hardware device: For this example, we will create a simple character device driver for a virtual device that reads and writes data to a file. We will call the device "rustdev".

2. Create a Rust project: Create a new Rust project by running the following command:

cargo new rustdev --bin

This will create a new Rust project with a main.rs file.

3. Setup the environment: Set up the Rust environment for kernel development by adding the following lines to your Cargo.toml file:

[lib]
crate-type = ["staticlib"]

[dependencies]
core = "1.0.0"

4. Define the device interface: Define the interface for the rustdev device by creating a new file src/dev.rs with the following contents:

use core::result::Result;

#[repr(C)]
pub struct RustDev {
    pub data: [u8; 1024],
    pub length: usize,
}

impl RustDev {
    pub fn new() -> RustDev {
        RustDev {
            data: [0; 1024],
            length: 0,
        }
    }

    pub fn read(&mut self, buf: &mut [u8]) -> Result<usize, ()> {
        if buf.len() > self.length {
            return Err(());
        }
        buf.copy_from_slice(&self.data[..buf.len()]);
        Ok(buf.len())
    }

    pub fn write(&mut self, buf: &[u8]) -> Result<usize, ()> {
        if buf.len() > self.data.len() {
            return Err(());
        }
        self.data[..buf.len()].copy_from_slice(buf);
        self.length = buf.len();
        Ok(buf.len())
    }
}

This defines the RustDev struct that holds the device data, along with read and write methods that implement the device interface.

5. Define the device driver: Define the device driver by creating a new file src/driver.rs with the following contents:

use core::result::Result;
use core::ptr::null_mut;
use crate::dev::RustDev;
use libc::{c_void, ssize_t};

#[repr(C)]
pub struct RustDevDriver {
    pub dev: RustDev,
}

impl RustDevDriver {
    pub fn new() -> RustDevDriver {
        RustDevDriver {
            dev: RustDev::new(),
        }
    }

    pub unsafe extern "C" fn rustdev_read(
        dev: *mut c_void,
        buf: *mut c_void,
        count: usize,
        offset: *mut i64,
    ) -> ssize_t {
        let dev_driver = &mut *(dev as *mut RustDevDriver);
        let buf_slice = core::slice::from_raw_parts_mut(buf as *mut u8, count);
        match dev_driver.dev.read(buf_slice) {
            Ok(n) => n as isize,
            Err(_) => -1,
        }
    }

    pub unsafe extern "C" fn rustdev_write(
        dev: *mut c_void,
        buf: *const c_void,
        count: usize,
        offset: *mut i64,
    ) -> ssize_t {
        let dev_driver = &mut *(dev as *mut RustDev

Conitune[sic] from the last line. It's rather interesting

---

   Driver;
       let buf_slice = core::slice::from_raw_parts(buf as *const u8, count);
       match dev_driver.dev.write(buf_slice) {
           Ok(n) => n as isize,
           Err(_) => -1,
       }
   }

}

This defines the RustDevDriver struct that contains an instance of RustDev and implements the read and write methods for the device driver.

6. Bind the Rust code to C: Bind the Rust code to C by creating a new file src/lib.rs with the following contents:

mod dev;
mod driver;

use dev::RustDev;
use driver::RustDevDriver;
use libc::{c_char, c_int, c_long, c_void, dev_t, size_t};

#[no_mangle]
pub unsafe extern "C" fn rustdev_open(dev: *mut c_void, flags: c_int, mode: c_int) -> c_int {
    0
}

#[no_mangle]
pub unsafe extern "C" fn rustdev_release(dev: *mut c_void, flags: c_int) -> c_int {
    0
}

#[no_mangle]
pub unsafe extern "C" fn rustdev_read(
    dev: *mut c_void,
    buf: *mut c_void,
    count: size_t,
    offset: *mut c_long,
) -> ssize_t {
    RustDevDriver::rustdev_read(dev, buf, count, offset)
}

#[no_mangle]
pub unsafe extern "C" fn rustdev_write(
    dev: *mut c_void,
    buf: *const c_void,
    count: size_t,
    offset: *mut c_long,
) -> ssize_t {
    RustDevDriver::rustdev_write(dev, buf, count, offset)
}

#[no_mangle]
pub unsafe extern "C" fn rustdev_ioctl(dev: *mut c_void, cmd: c_ulong, arg: *mut c_void) -> c_long {
    0
}

#[no_mangle]
pub unsafe extern "C" fn rustdev_mmap(
    dev: *mut c_void,
    offset: *mut c_long,
    size: size_t,
    prot: c_int,
    flags: c_int,
    fd: c_int,
    pgoff: c_long,
) -> *mut c_void {
    null_mut()
}

#[no_mangle]
pub unsafe extern "C" fn rustdev_fsync(dev: *mut c_void, datasync: c_int) -> c_int {
    0
}

#[no_mangle]
pub unsafe extern "C" fn rustdev_fasync(
    fd: c_int,
    filp: *mut c_void,
    mode: c_int,
) -> c_int {
    0
}

#[no_mangle]
pub static mut rustdev_cdev: libc::c_void = 0 as *mut libc::c_void;

#[no_mangle]
pub unsafe extern "C" fn rustdev_init() -> c_int {
    let dev_driver = RustDevDriver::new();
    let mut cdev = libc::c_void::default();
    libc::alloc_chrdev_region(
        &mut cdev as *mut libc::c_void as *mut dev_t,
        0,
        1,
        b"rustdev\0".as_ptr() as *const c_char,
    );
    libc::cdev_init(&mut rustdev_cdev as *

Continue from the last line. It's rather interesting

---

mut libc::file_operations {
owner: 0 as *mut _,
read: Some(rustdev_read),
write: Some(rustdev_write),
open: Some(rustdev_open),
release: Some(rustdev_release),
ioctl: Some(rustdev_ioctl),
mmap: Some(rustdev_mmap),
fsync: Some(rustdev_fsync),
fasync: Some(rustdev_fasync),
llseek: None,
};
let ret = libc::cdev_add(&mut rustdev_cdev as *mut _ as *mut libc::c_void, cdev, 1);
if ret != 0 {
return ret;
}
0
}

This file contains Rust implementations of C functions for opening, releasing, reading, writing, and performing other operations on the device. It also initializes the character device with the alloc_chrdev_region() and cdev_init() functions.

7. Build the module: Build the Rust module by running cargo build. This will generate a shared library in the target directory, which can be loaded as a kernel module.

8. Load the module: Load the Rust module into the kernel by running insmod target/debug/librustdev.ko. This will create a character device /dev/rustdev.

9. Test the module: Test the Rust module by writing to and reading from the /dev/rustdev character device.

$ echo "Hello, Rust!" | sudo tee /dev/rustdev
Hello, Rust!
$ sudo cat /dev/rustdev
Hello, Rust!

The Rust module is now fully functional within the Linux kernel.