how about:

cmakeFlags = ["-DCMAKE_INSTALL_RUNDIR=/run"];

instead?

That does not seem to work. @CMAKE_INSTALL_FULL_SHAREDSTATEDIR@ still gets substituted by the store path (e.g. /nix/store/vaxhll3n336v6rlh8ql2jqalq1hpykxw-rdma-core-16.1/com/rxe) when I set CMAKE_INSTALL_RUNDIR=/run. The cmake doc says that this should be substituted as PREFIX/com
(https://cmake.org/cmake/help/v3.8/module/GNUInstallDirs.html). Is there another way to override SHAREDSTATEDIR through cmake? I don't see it in the docs.

This is strange, when looking at this code: https://github.com/linux-rdma/rdma-core/blob/master/CMakeLists.txt#L93

overriding CMAKE_INSTALL_RUNDIR with an absolute path as part of cmake flags should just work.

OK I see. I guess the problem is a different one here. The script uses SHAREDSTATEDIR, which ends up being PREFIX/com (this seems to be an odd choice to me). If it would use CMAKE_INSTALL_RUNDIR, then I guess your suggestions should work.

The reason I need to patch that is the following: rxe_cfg lets one choice if the config should be made persistent or not. Even when I select -n (no persistent) it still performs touch on the config file (which fails on a location in the nix store). From a nixos perspective the persistent choice should be made through a module. That's why I chose to set this path to /run.

Sorry I mixed up variables -DCMAKE_INSTALL_SHAREDSTATEDIR=/var/lib should do the trick. So you would recommend /run instead?

Unless it would breaks the module, I would keep it as the developer intended it. In future sharedstatedir might be use somewhere else also.

Also people might want to use it on non-nixos system - does this makes sense?

Yes it does make sense. /var/lib is a good choice. Just checked your commit, it works. Thanks!