nixpkgs/modules/virtualisation/qemu-vm.nix
Eelco Dolstra da77a6437f * qemu-vm.nix: automatically create and initialise the disk image if
it doesn't already exist.  Also set up some ad hoc port forwarding
  from the host to the guest.

svn path=/nixos/branches/modular-nixos/; revision=16012
2009-06-19 15:19:56 +00:00

117 lines
3.5 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, ...}:
let
options = {
virtualisation.diskImage =
pkgs.lib.mkOption {
default = "./${config.networking.hostName}.qcow2";
description =
''
Path to the disk image containing the root filesystem.
The image will be created on startup if it does not
exist.
'';
};
};
# 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
${pkgs.kvm}/bin/qemu-img create -f qcow2 "$NIX_DISK_IMAGE" 512M || exit 1
fi
${pkgs.kvm}/bin/qemu-system-x86_64 \
-net nic,model=virtio -net user -smb / \
-drive file=$NIX_DISK_IMAGE,if=virtio,boot=on \
-kernel ${config.system.build.system}/kernel \
-initrd ${config.system.build.system}/initrd \
-redir tcp:8080::80 \
-redir tcp:8022::22 \
-append "$(cat ${config.system.build.system}/kernel-params) init=${config.system.build.bootStage2} systemConfig=${config.system.build.system}"
'';
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.extraKernelModules =
["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.
fileSystems =
[ { mountPoint = "/";
device = "/dev/vda";
}
{ mountPoint = "/hostfs";
device = "//10.0.2.4/qemu";
fsType = "cifs";
options = "guest,username=nobody";
neededForBoot = true;
}
{ mountPoint = "/nix/store";
device = "/hostfs/nix/store";
options = "bind";
neededForBoot = true;
}
];
# Starting DHCP brings down eth0, which kills the connection to the
# host filesystem and thus deadlocks the system.
networking.useDHCP = false;
system.build.vm = pkgs.runCommand "nixos-vm" {}
''
ensureDir $out/bin
ln -s ${config.system.build.system} $out/system
ln -s ${pkgs.writeScript "run-nixos-vm" startVM} $out/bin/run-nixos-vm
'';
# sendfile() is currently broken over CIFS, so fix it here for all
# configurations that use Apache.
services.httpd.extraConfig = "EnableSendFile Off";
}