nixpkgs/modules/virtualisation/qemu-vm.nix
Lluís Batlle i Rossell 79073c7b3d Adding a virtualisation option: run qemu without graphics.
svn path=/nixos/trunk/; revision=18978
2009-12-15 18:49:34 +00:00

179 lines
5.6 KiB
Nix

# This module creates a virtual machine from the NixOS configuration.
# Building the `config.system.build.vm' attribute gives you a command
# that starts a KVM/QEMU VM running the NixOS configuration defined in
# `config'. The Nix store is shared read-only with the host, which
# makes (re)building VMs very efficient. However, it also means you
# can't reconfigure the guest inside the guest - you need to rebuild
# the VM in the host. On the other hand, the root filesystem is a
# read/writable disk image persistent across VM reboots.
{ config, pkgs, ... }:
with pkgs.lib;
let
vmName = config.networking.hostName;
options = {
virtualisation.memorySize =
mkOption {
default = 384;
description =
''
Memory size (M) of virtual machine.
'';
};
virtualisation.diskImage =
mkOption {
default = "./${vmName}.qcow2";
description =
''
Path to the disk image containing the root filesystem.
The image will be created on startup if it does not
exist.
'';
};
virtualisation.graphics =
mkOption {
default = true;
description =
''
Whether to run qemu with a graphics window, or access
the guest computer serial port through the host tty.
'';
};
};
cfg = config.virtualisation;
qemuGraphics = if (cfg.graphics) then "" else "-nographic";
kernelConsole = if (cfg.graphics) then "" else "console=ttyS0";
ttys = [ "tty1" "tty2" "tty3" "tty4" "tty5" "tty6" ];
# Shell script to start the VM.
startVM =
''
#! ${pkgs.stdenv.shell}
export PATH=${pkgs.samba}/sbin:$PATH
NIX_DISK_IMAGE=''${NIX_DISK_IMAGE:-${config.virtualisation.diskImage}}
if ! test -e "$NIX_DISK_IMAGE"; then
${pkgs.qemu_kvm}/bin/qemu-img create -f qcow2 "$NIX_DISK_IMAGE" 512M || exit 1
fi
# -no-kvm-irqchip is needed to prevent the CIFS mount from
# hanging the VM on x86_64.
exec ${pkgs.qemu_kvm}/bin/qemu-system-x86_64 -m ${toString config.virtualisation.memorySize} \
-no-kvm-irqchip \
-net nic,model=virtio -net user -smb / \
-drive file=$NIX_DISK_IMAGE,if=virtio,boot=on \
-kernel ${config.system.build.toplevel}/kernel \
-initrd ${config.system.build.toplevel}/initrd \
${qemuGraphics} \
$QEMU_OPTS \
-append "$(cat ${config.system.build.toplevel}/kernel-params) init=${config.system.build.bootStage2} systemConfig=${config.system.build.toplevel} ${kernelConsole} $QEMU_KERNEL_PARAMS"
'';
in
{
require = options;
# All the modules the initrd needs to mount the host filesystem via
# CIFS. Also use paravirtualised network and block devices for
# performance.
boot.initrd.availableKernelModules =
[ "cifs" "virtio_net" "virtio_pci" "virtio_blk" "virtio_balloon" "nls_utf8" ];
boot.initrd.extraUtilsCommands =
''
# We need mke2fs in the initrd.
cp ${pkgs.e2fsprogs}/sbin/mke2fs $out/bin
'';
boot.initrd.postDeviceCommands =
''
# Set up networking. Needed for CIFS mounting.
ipconfig 10.0.2.15:::::eth0:none
# If the disk image appears to be empty (fstype "unknown";
# hacky!!!), run mke2fs to initialise.
eval $(fstype /dev/vda)
if test "$FSTYPE" = unknown; then
mke2fs -t ext3 /dev/vda
fi
'';
# Mount the host filesystem via CIFS, and bind-mount the Nix store
# of the host into our own filesystem. We use mkOverride to allow
# this module to be applied to "normal" NixOS system configuration,
# where the regular value for the `fileSystems' attribute should be
# disregarded for the purpose of building a VM test image (since
# those filesystems don't exist in the VM).
fileSystems = mkOverride 50 {}
[ { mountPoint = "/";
device = "/dev/vda";
}
{ mountPoint = "/hostfs";
device = "//10.0.2.4/qemu";
fsType = "cifs";
options = "guest,username=nobody,noperm";
neededForBoot = true;
}
{ mountPoint = "/nix/store";
device = "/hostfs/nix/store";
options = "bind";
neededForBoot = true;
}
# Mount the host's Nix database. This allows read-only Nix
# operations in the guest to work properly.
{ mountPoint = "/nix/var/nix/db";
device = "/hostfs/nix/var/nix/db";
options = "bind";
}
];
# Starting DHCP brings down eth0, which kills the connection to the
# host filesystem and thus deadlocks the system.
networking.useDHCP = false;
networking.defaultGateway = "10.0.2.2";
networking.nameservers = [ "10.0.2.3" ];
networking.interfaces = singleton
{ name = "eth0";
ipAddress = "10.0.2.15";
};
system.build.vm = pkgs.runCommand "nixos-vm" {}
''
ensureDir $out/bin
ln -s ${config.system.build.toplevel} $out/system
ln -s ${pkgs.writeScript "run-nixos-vm" startVM} $out/bin/run-${vmName}-vm
'';
# sendfile() is currently broken over CIFS, so fix it here for all
# configurations that use Apache.
services.httpd.extraConfig =
''
EnableSendFile Off
'';
# When building a regular system configuration, override whatever
# video driver the host uses.
services.xserver.videoDriver = mkOverride 50 {} null;
services.xserver.videoDrivers = mkOverride 50 {} [ "cirrus" "vesa" ];
services.xserver.defaultDepth = mkOverride 50 {} 0;
services.xserver.resolutions = mkOverride 50 {} [];
services.mingetty.ttys = ttys ++ optional (!cfg.graphics) "ttyS0";
# Wireless won't work in the VM.
networking.enableWLAN = mkOverride 50 {} false;
}