QEMU

qemu advent calendar, powered by Nix flakes

https://www.qemu-advent-calendar.org/2020/

Running QEMU images

To run one of the images, you'll need nix installed with flakes.

Then

" nix run github:idrisr/qemu-advent#day<day number>
nix run github:idrisr/qemu-advent#day01

replace <day-number> with one of the supported images. Note, not all images are included as part of this flake. To see which ones are available, run

nix flake show github:idrisr/qemu-advent

lessons learned

• use patches
• use prior nixpkgs for deprecated things
• download shas make things feel safer
• use nix expression language to simplify
• share nix flakes to allow easy reproduction of issue
• autoconf is a beast, but makes things easier
• read derivation expressions to find the tweak you need. often via overrides
• use nix develop to debug and trial run
• grep nixpkgs to find examples
• nixos discourse and nix irc is a friendly place
• get good (better) with bash as it's a strong prereq for going deeper
• watch out for shebangs. theyll blow up your build.
• even nix develop --ignore-environment --command bash --norc is not a pure sandbox
• beware false positives. i had qemu running as a service on my machine
  • without that it was broken
  • see makewrapper?
• string escaping between nix and bash is treacherous
• always stay aware of what's happening with $PATH. that's the whole game
• you can know nothing about a project and its language ecosystem
  • and still make a package for it
• to get command line helpers, write yet another package
• use --set PATH to get purity, instead of --prefix
• be prepared to patch makefiles, bash scripts, and configs
• there's a sub-rosa haskell-like layer
  • the functions for manipulating lists, attrsets, strings, etc
  • rarely used, but powerful
  • useful when merging attrsets with custom logic