Add kexec support

You can now do a fast reboot (bypassing the BIOS, which may take
several minutes on servers) by running ‘systemctl kexec’.

Unfortunately the QEMU test for this is unreliable due to a QEMU bug
(it randomly crashes with a message like ‘Guest moved used index from
8 to 0’), so it's commented out.

doc/manual/running.xml

@@ -101,9 +101,25 @@ doing:
 $ shutdown
 </screen>
 
-This is equivalent to running <command>systemctl poweroff</command>.
-Likewise, <command>reboot</command> (a.k.a. <command>systemctl
-reboot</command>) will reboot the system.</para>
+This is equivalent to running <command>systemctl
+poweroff</command>.</para>
+
+<para>To reboot the system, run
+
+<screen>
+$ reboot
+</screen>
+
+which is equivalent to <command>systemctl reboot</command>.
+Alternatively, you can quickly reboot the system using
+<literal>kexec</literal>, which bypasses the BIOS by directly loading
+the new kernel into memory:
+
+<screen>
+$ systemctl kexec
+</screen>
+
+</para>
 
 <para>The machine can be suspended to RAM (if supported) using
 <command>systemctl suspend</command>, and suspended to disk using

lib/test-driver/Machine.pm

@@ -232,9 +232,9 @@ sub connect {
 
         $self->start;
 
-        local $SIG{ALRM} = sub { die "timed out waiting for the guest to connect\n"; };
+        local $SIG{ALRM} = sub { die "timed out waiting for the VM to connect\n"; };
         alarm 300;
-        readline $self->{socket} or die;
+        readline $self->{socket} or die "the VM quit before connecting\n";
         alarm 0;
         
         $self->log("connected to guest root shell");

modules/module-list.nix

@@ -235,6 +235,7 @@
   ./system/activation/activation-script.nix
   ./system/activation/top-level.nix
   ./system/boot/kernel.nix
+  ./system/boot/kexec.nix
   ./system/boot/loader/efi-boot-stub/efi-boot-stub.nix
   ./system/boot/loader/efi.nix
   ./system/boot/loader/generations-dir/generations-dir.nix

modules/system/boot/kexec.nix

@@ -0,0 +1,21 @@
+{ config, pkgs, ... }:
+
+{
+  environment.systemPackages = [ pkgs.kexectools ];
+
+  systemd.services."prepare-kexec" =
+    { description = "Preparation for kexec";
+      wantedBy = [ "kexec.target" ];
+      before = [ "systemd-kexec.service" ];
+      unitConfig.DefaultDependencies = false;
+      serviceConfig.Type = "oneshot";
+      path = [ pkgs.kexectools ];
+      script =
+        ''
+          p=$(readlink -f /nix/var/nix/profiles/system)
+          if ! [ -d $p ]; then exit 1; fi
+          exec kexec --load $p/kernel --initrd=$p/initrd --append="$(cat $p/kernel-params) init=$p/init"
+        '';
+    };
+
+}

modules/system/boot/systemd.nix

@@ -129,6 +129,7 @@ let
       "umount.target"
       "final.target"
       "kexec.target"
+      "systemd-kexec.service"
 
       # Password entry.
       "systemd-ask-password-console.path"

tests/default.nix

@@ -10,6 +10,7 @@ with import ../lib/testing.nix { inherit system minimal; };
   installer = makeTests (import ./installer.nix);
   ipv6 = makeTest (import ./ipv6.nix);
   kde4 = makeTest (import ./kde4.nix);
+  #kexec = makeTest (import ./kexec.nix);
   login = makeTest (import ./login.nix {});
   latestKernel.login = makeTest (import ./login.nix ({ config, pkgs, ... }: { boot.kernelPackages = pkgs.linuxPackages_latest; }));
   misc = makeTest (import ./misc.nix);

tests/kexec.nix

@@ -0,0 +1,18 @@
+# Test whether fast reboots via kexec work.
+
+{ pkgs, ... }:
+
+{
+
+  machine = { config, pkgs, ... }:
+    { virtualisation.vlans = [ ]; };
+
+  testScript =
+    ''
+      $machine->waitForUnit("multi-user.target");
+      $machine->execute("systemctl kexec &");
+      $machine->{connected} = 0;
+      $machine->waitForUnit("multi-user.target");
+    '';
+
+}