From c958902d4473e6abec41e383d43c28f7ec674a09 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Tue, 23 Nov 2010 16:07:00 +0000
Subject: [PATCH] * Added an option "nixpkgs.system" to specify the system type
 for   which NixOS should be built.  This is useful in NixOS network  
 specifications, because it allows machines in the network to have   different
 types, e.g.,

    {
      machine1 =
        { config, pkgs, ... }:
        { nixpkgs.system = "i686-linux";
          ... other config ...
        };

      machine2 =
        { config, pkgs, ... }:
        { nixpkgs.system = "x86_64-linux";
          ... other config ...
        };
    }

  It can also be useful in distributed NixOS tests.

svn path=/nixos/trunk/; revision=24823
---
 lib/eval-config.nix      |  8 +++++---
 modules/misc/nixpkgs.nix | 11 +++++++++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/lib/eval-config.nix b/lib/eval-config.nix
index 8a7b225e8500..d34a73fd1661 100644
--- a/lib/eval-config.nix
+++ b/lib/eval-config.nix
@@ -11,7 +11,7 @@
 , modules
 }:
 
-let extraArgs_ = extraArgs; pkgs_ = pkgs; in
+let extraArgs_ = extraArgs; pkgs_ = pkgs; system_ = system; in
 
 rec {
 
@@ -39,7 +39,8 @@ rec {
   # Import Nixpkgs, allowing the NixOS option nixpkgs.config to
   # specify the Nixpkgs configuration (e.g., to set package options
   # such as firefox.enableGeckoMediaPlayer, or to apply global
-  # overrides such as changing GCC throughout the system).  This is
+  # overrides such as changing GCC throughout the system), and the
+  # option nixpkgs.system to override the platform type.  This is
   # tricky, because we have to prevent an infinite recursion: "pkgs"
   # is passed as an argument to NixOS modules, but the value of "pkgs"
   # depends on config.nixpkgs.config, which we get from the modules.
@@ -50,12 +51,13 @@ rec {
     then pkgs_
     else import nixpkgs (
       let
+        system = if nixpkgsOptions.system != "" then nixpkgsOptions.system else system_;
         nixpkgsOptions = (import ./eval-config.nix {
           inherit system nixpkgs services extraArgs modules;
           # For efficiency, leave out most NixOS modules; they don't
           # define nixpkgs.config, so it's pointless to evaluate them.
           baseModules = [ ../modules/misc/nixpkgs.nix ];
-          pkgs = import nixpkgs { inherit system; config = {}; };
+          pkgs = import nixpkgs { system = system_; config = {}; };
         }).optionDefinitions.nixpkgs;
       in
       {
diff --git a/modules/misc/nixpkgs.nix b/modules/misc/nixpkgs.nix
index 8173d716d841..d940b32dbd56 100644
--- a/modules/misc/nixpkgs.nix
+++ b/modules/misc/nixpkgs.nix
@@ -13,6 +13,17 @@
       '';
     };
 
+    nixpkgs.system = pkgs.lib.mkOption {
+      default = "";
+      description = ''
+        Specifies the Nix platform type for which NixOS should be built.
+        If unset, it defaults to the platform type of your host system
+        (<literal>${builtins.currentSystem}</literal>).
+        Specifying this option is useful when doing distributed
+        multi-platform deployment, or when building virtual machines.
+      '';
+    };
+
     nixpkgs.platform = pkgs.lib.mkOption {
       default = pkgs.platforms.pc;
       description = ''