From f182fdf6ed3acf820a5f619eda9bffee1ecd1c46 Mon Sep 17 00:00:00 2001
From: aszlig <aszlig@redmoonstudios.org>
Date: Wed, 23 Oct 2013 16:42:34 +0200
Subject: [PATCH] nixos-generate-config: Add --show-hardware-config.

So, we get the old behaviour of nixos-hardware-scane if we run the
following command:

nixos-generate-config --no-filesystems --show-hardware-config

This allows to use scripts in order to fetch NixOS specific hardware
information, without the need to duplicate code elsewhere.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
---
 .../doc/manual/man-nixos-generate-config.xml  |  9 ++++
 .../installer/tools/nixos-generate-config.pl  | 49 +++++++++++--------
 2 files changed, 38 insertions(+), 20 deletions(-)

diff --git a/nixos/doc/manual/man-nixos-generate-config.xml b/nixos/doc/manual/man-nixos-generate-config.xml
index 0771753f6893..e4fba4a40a97 100644
--- a/nixos/doc/manual/man-nixos-generate-config.xml
+++ b/nixos/doc/manual/man-nixos-generate-config.xml
@@ -118,6 +118,15 @@
     </listitem>
   </varlistentry>
 
+  <varlistentry>
+    <term><option>--show-hardware-config</option></term>
+    <listitem>
+      <para>Don't generate <filename>configuration.nix</filename> or
+      <filename>hardware-configuration.nix</filename> and print the
+      hardware configuration to stdout only.</para>
+    </listitem>
+  </varlistentry>
+
 </variablelist>
 
 </refsection>
diff --git a/nixos/modules/installer/tools/nixos-generate-config.pl b/nixos/modules/installer/tools/nixos-generate-config.pl
index a4d224108061..c6ac72e113be 100644
--- a/nixos/modules/installer/tools/nixos-generate-config.pl
+++ b/nixos/modules/installer/tools/nixos-generate-config.pl
@@ -24,6 +24,7 @@ my $outDir = "/etc/nixos";
 my $rootDir = ""; # = /
 my $force = 0;
 my $noFilesystems = 0;
+my $showHardwareConfig = 0;
 
 for (my $n = 0; $n < scalar @ARGV; $n++) {
     my $arg = $ARGV[$n];
@@ -47,6 +48,9 @@ for (my $n = 0; $n < scalar @ARGV; $n++) {
     elsif ($arg eq "--no-filesystems") {
         $noFilesystems = 1;
     }
+    elsif ($arg eq "--show-hardware-config") {
+        $showHardwareConfig = 1;
+    }
     else {
         die "$0: unrecognized argument ‘$arg’\n";
     }
@@ -336,19 +340,13 @@ my $initrdAvailableKernelModules = toNixExpr(uniq @initrdAvailableKernelModules)
 my $kernelModules = toNixExpr(uniq @kernelModules);
 my $modulePackages = toNixExpr(uniq @modulePackages);
 
-$outDir = "$rootDir$outDir";
-
-my $fn = "$outDir/hardware-configuration.nix";
-print STDERR "writing $fn...\n";
-mkpath($outDir, 0, 0755);
-
 my $fsAndSwap = "";
 if (!$noFilesystems) {
     $fsAndSwap = "\n${fileSystems}  ";
     $fsAndSwap .= "swapDevices =" . multiLineList("    ", @swapDevices) . ";\n";
 }
 
-write_file($fn, <<EOF);
+my $hwConfig = <<EOF;
 # Do not modify this file!  It was generated by ‘nixos-generate-config’
 # and may be overwritten by future invocations.  Please make changes
 # to /etc/nixos/configuration.nix instead.
@@ -366,14 +364,24 @@ ${\join "", (map { "  $_\n" } (uniq @attrs))}}
 EOF
 
 
-# Generate a basic configuration.nix, unless one already exists.
-$fn = "$outDir/configuration.nix";
-if ($force || ! -e $fn) {
-    print STDERR "writing $fn...\n";
+if ($showHardwareConfig) {
+    print STDOUT $hwConfig;
+} else {
+    $outDir = "$rootDir$outDir";
 
-    my $bootloaderConfig;
-    if (-e "/sys/firmware/efi/efivars") {
-        $bootLoaderConfig = <<EOF;
+    my $fn = "$outDir/hardware-configuration.nix";
+    print STDERR "writing $fn...\n";
+    mkpath($outDir, 0, 0755);
+    write_file($fn, $hwConfig);
+
+    # Generate a basic configuration.nix, unless one already exists.
+    $fn = "$outDir/configuration.nix";
+    if ($force || ! -e $fn) {
+        print STDERR "writing $fn...\n";
+
+        my $bootloaderConfig;
+        if (-e "/sys/firmware/efi/efivars") {
+            $bootLoaderConfig = <<EOF;
   # Use the gummiboot efi boot loader.
   boot.loader.grub.enable = false;
   boot.loader.gummiboot.enable = true;
@@ -382,17 +390,17 @@ if ($force || ! -e $fn) {
   # EFI booting requires kernel >= 3.10
   boot.kernelPackages = pkgs.linuxPackages_3_10;
 EOF
-    } else {
-        $bootLoaderConfig = <<EOF;
+        } else {
+            $bootLoaderConfig = <<EOF;
   # Use the GRUB 2 boot loader.
   boot.loader.grub.enable = true;
   boot.loader.grub.version = 2;
   # Define on which hard drive you want to install Grub.
   # boot.loader.grub.device = "/dev/sda";
 EOF
-    }
+        }
 
-    write_file($fn, <<EOF);
+        write_file($fn, <<EOF);
 # Edit this configuration file to define what should be installed on
 # your system.  Help is available in the configuration.nix(5) man page
 # and in the NixOS manual (accessible by running ‘nixos-help’).
@@ -453,8 +461,9 @@ $bootLoaderConfig
   # services.xserver.desktopManager.kde4.enable = true;
 }
 EOF
-} else {
-    print STDERR "warning: not overwriting existing $fn\n";
+    } else {
+        print STDERR "warning: not overwriting existing $fn\n";
+    }
 }
 
 # workaround for a bug in substituteAll