Explaining the current Steam Package build

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This article should give insight about how steam is currently packaged and how and why it works like this. It also discusses what the problems are in packaging it and how we can approach solving them.

Description of the package

Steam is distributed as a .deb file, for now only as an i686 package (the amd64 package only has documentation). When unpacked, it has a script called steam that in ubuntu (their target distro) would go to /usr/bin. When run for the first time, this script copies some files to the user's home, which include another script that is the ultimate responsible for launching the steam binary, which is also in $HOME.

Nix problems and constraints

  • We don't have /bin/bash and many scripts point there. Similarly for /usr/bin/python, for some functionality.
  • We don't have the dynamic loader in /lib
  • The steam.sh script in $HOME could not be patched last I tried, as it is checked and rewritten by steam
  • The steam binary cannot be patched, it's also checked

Approaches

chroot

This is the current approach, documented here: http://sandervanderburg.blogspot.nl/2013/09/composing-fhs-compatible-chroot.html

  • Pros:
    • it would allow us to have binaries in the expected paths without disrupting the system
    • Steam itself, as well as Valve games and perhaps others like to checksum their executables, so patching does not work
  • Cons: performance?

Link bash to /bin and glibc/lib to /lib and be happy

  • Pros: easy, works
  • Cons: not very nix-compliant

Workaround the scripts and launch steam directly

  • Pros: not so hard
  • Cons: this only solves the part concerned with running steam. What about the games? We can patch some of them, but at least Team Fortress is checked and rewritten if modified

This is the approach that I (page) took in my GitHub branch: https://github.com/cpages/nixpkgs/tree/steam

Intercept Steam's calls with LD_PRELOAD or the like

  • Pros: more robust
  • Cons: difficult to achieve and may be broken by changes in the binary

aszlig started working in this in his branch: https://github.com/aszlig/nixpkgs/tree/steam

But what about the games?

You can install any of the games normally, but they will fail to start. From this step on, you're in the unsupported realm. Some games can be patchelfed: 

patchelf --set-interpreter /path/to/ld.so game_binary (you can get the path to an x86 ld.so looking at the steam script in the store, for me /nix/store/xh0q23rgqbjfrh3zfv4jyxvcvjnxqh64-glibc-2.15.0/lib/ld-linux.so.2)

You might also need patching some scripts. That all depends on each one. You can then press play from steam and if you're lucky that'll be it!

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