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pv-runtime: Don't rewrite /nix/store/... to /run/host/nix/store/...

Simon McVittie requested to merge wip/nixos into master
  • runtime: Comment why the /app special case exists

  • pv-runtime: Don't rewrite /nix/store/... to /run/host/nix/store/...

    We must expose /nix in the sandbox as /nix, not /run/host/nix, because hard-coding paths below /nix is ubiquitous on NixOS. There's already a special case in wrap.c to mount /nix read-only.

    This resolves a regression that occurred when we switched to a runtime structure that relies on PRESSURE_VESSEL_COPY_RUNTIME.

    Resolves: https://github.com/ValveSoftware/steam-runtime/issues/431

  • runtime: Assume /etc is visible in the provider namespace

    If the realpath() of an OS file is below /etc, each of our code paths ends up with it visible below /run/host/etc, /run/parent/etc or /run/gfx/etc, as appropriate.

  • runtime: Adjust fallback behaviour when taking files from provider

    Previously, we assumed that if OS files on the provider are in a location that is not /usr or a related directory, for example if the OS has /lib/ld-linux.so.2 -> /some/odd/path/i386/ld.so, then they will appear below the same path_in_container_ns as /usr, for example /run/host/some/odd/path/i386/ld.so. However, nothing sets this up for directories other than /usr, /lib*, /bin, /sbin and /etc, so it's a bad assumption.

    A previous commit handled /etc by redirecting it to /run/host/etc, /run/parent/etc or /run/gfx/etc as appropriate, so we don't need to worry about that here.

    For the rest, assume that if they appear in the container at all, they'll appear at a path that matches their location in the provider. For the common case where provider = host, which is the only one where we really need to support non-FHS layouts, this means that users can work around lack of explicit support for a particular non-FHS directory with something like PRESSURE_VESSEL_FILESYSTEMS_RO=/some/odd/path.

    In particular, if we didn't have explicit support for /nix, NixOS users would have been able to use that workaround to get it mounted.

Edited by Simon McVittie

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