nixos-generate-config: Add --no-filesystems flag.

This is to get back the old behavior of nixos-hardware-scan, which
didn't include fileSystems and swapDevices.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

nixos/doc/manual/man-nixos-generate-config.xml

@@ -110,6 +110,14 @@
     </listitem>
   </varlistentry>
 
+  <varlistentry>
+    <term><option>--no-filesystems</option></term>
+    <listitem>
+      <para>Omit everything concerning file system information
+      (which includes swap devices) from the hardware configuration.</para>
+    </listitem>
+  </varlistentry>
+
 </variablelist>
 
 </refsection>

nixos/modules/installer/tools/nixos-generate-config.pl

@@ -23,6 +23,7 @@ sub uniq {
 my $outDir = "/etc/nixos";
 my $rootDir = ""; # = /
 my $force = 0;
+my $noFilesystems = 0;
 
 for (my $n = 0; $n < scalar @ARGV; $n++) {
     my $arg = $ARGV[$n];
@@ -43,6 +44,9 @@ for (my $n = 0; $n < scalar @ARGV; $n++) {
     elsif ($arg eq "--force") {
         $force = 1;
     }
+    elsif ($arg eq "--no-filesystems") {
+        $noFilesystems = 1;
+    }
     else {
         die "$0: unrecognized argument ‘$arg’\n";
     }
@@ -338,6 +342,12 @@ 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);
 # Do not modify this file!  It was generated by ‘nixos-generate-config’
 # and may be overwritten by future invocations.  Please make changes
@@ -350,9 +360,7 @@ write_file($fn, <<EOF);
   boot.initrd.availableKernelModules = [$initrdAvailableKernelModules ];
   boot.kernelModules = [$kernelModules ];
   boot.extraModulePackages = [$modulePackages ];
-
-${fileSystems}  swapDevices = ${\multiLineList("    ", @swapDevices)};
-
+$fsAndSwap
   nix.maxJobs = $cpus;
 ${\join "", (map { "  $_\n" } (uniq @attrs))}}
 EOF