recitations

VM/Kernel Workflow

Before we get into the heavier assignments in this course, you should invest sometime into setting up a workflow and develop good coding habits.

Why Use a VM?

• Hypervisor: Software responsible for managing VMs (e.g. creation, deletion, resource allocation). In this class, we use VMware.
• Host machine: The hardware running the hypervisor (e.g. your personal laptop)
• Virtual machine (VM): A computer system created by the hypervisor that shares resources with the host machine. In this class, we virtualize Debian 11 (a flavor of Linux). VMs adhere to sandbox properties:
  • Isolate the work you’ll be doing from the rest of the system
  • Be able to take snapshots of your development environment so that if it does get corrupted, you can revert to a clean state

  Working on a VM can be preferable to working on your host machine (i.e. “bare-metal”). You can virtualize other operating systems to test your applications. You can work on potentially buggy/dangerous code without compromising your host machine.

• Snapshot: A feature most hypervisors support. Capture the current running state of the VM, stores it, and then allows you to revert to that state sometime later. You should snapshot your VM before executing something that can compromise the system.

In this class, we will often be “hacking” the Linux kernel and attempting to boot into those hacked kernels. We need to use VMs since not all of us have a Linux host machine. Even if we did, we wouldn’t want to ruin our host machines with our potentially buggy kernels.

VM Setup/Workflow

We’ve already written a series of guides for working on your VM.

First and foremost, you should have a Debian VM installed already (see Debian VM Setup for a guide on how to do this).

Working on your VM

You have more options than simply working on the VM’s graphical interface, which often feels clunky.

The most common workflow involves SSHing into your VM, which we’ve written a guide for. This is a good option if you want to conserve processing power on your host machine and disable the VM’s graphical interface.

Alternatively, you can setup an IDE to SSH into your VM. One option is using Visual Studio Code, which we’ve written up some notes (below) on how to use. This is a nice alternative to command-line editors like vim/emacs if you’re not familiar with them.

Additional Tools

If you do decide to work in a command-line environment, here are some tools we’ve used to streamline our workflow:

• bat: A better version of cat (installation)
• grep: Pattern-match files (learn how to effectively use regexs to improve search results). Even better, ripgrep.
• Reverse-i search: Efficiently search through bash history instead of retyping long commands.
• tmux: Terminal multiplexer. (e.g. open 2 panes for vim, 1 for dmesg, 1 for running commands).

Kernel Workflow

Editor enhancements

Before getting into hw4/supermom, please read through one of our kernel developer workflow guides. These explain how to set up either vim or VSCode for kernel development.

• Vim workflow: Here, we offer a bunch of cool vim additions/tricks to help you develop more efficiently while working on the kernel assignments. Note that this guide is only relevant if you intend to work on the command-line using vim. One notable mention here is cscope. This is a kernel-source navigator that works directly in your terminal/vim session. This is far more powerful than using grep to look for a symbol definition/use in the source-tree.
• VSCode workflow: In this guide, we explain how to configure autocomplete, formatting, and various other features for working on the kernel while using VSCode. VSCode is a very powerful editor, and being able to take advantage of its functionality will make your life much easier.

Web Tools

If you don’t want to use cscope, there’s an popular online kernel-source navigator: bootlin. Note that kernel version matters when you’re navigating code – be sure you select the correct version.

Like bootlin, you can look for symbols in the kernel-source and look for instances of where they are defined and used. However, bootlin doesn’t index all symbols, so you might have better luck searching with cscope.