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nixpkgs/modules/virtualisation/qemu-vm.nix

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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 =
if config.networking.hostName == ""
then "noname"
else config.networking.hostName;
options = {
virtualisation.memorySize =
mkOption {
default = 384;
description =
''
Memory size (M) of virtual machine.
'';
};
virtualisation.diskSize =
mkOption {
default = 512;
description =
''
Disk 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.
'';
};
virtualisation.pathsInNixDB =
mkOption {
default = [];
description =
''
The list of paths whose closure is registered in the Nix
database in the VM. All other paths in the host Nix store
appear in the guest Nix store as well, but are considered
garbage (because they are not registered in the Nix
database in the guest).
'';
};
virtualisation.vlans =
mkOption {
default = [ 1 ];
example = [ 1 2 ];
description =
''
Virtual networks to which the VM is connected. Each
number <replaceable>N</replaceable> in this list causes
the VM to have a virtual Ethernet interface attached to a
separate virtual network on which it will be assigned IP
address
<literal>192.168.<replaceable>N</replaceable>.<replaceable>M</replaceable></literal>,
where <replaceable>M</replaceable> is the index of this VM
in the list of VMs.
'';
};
virtualisation.writableStore =
mkOption {
default = false;
description =
''
If enabled, the Nix store in the VM is made writable by
layering a unionfs-fuse/tmpfs filesystem on top of the host's Nix
store.
'';
};
networking.primaryIPAddress =
mkOption {
default = "";
internal = true;
description = "Primary IP address used in /etc/hosts.";
};
virtualisation.qemu.options =
mkOption {
default = [];
example = [ "-vga std" ];
description = "Options passed to QEMU.";
};
virtualisation.useBootLoader =
mkOption {
default = false;
description =
''
If enabled, the virtual machine will be booted using the
regular boot loader (i.e., GRUB 1 or 2). This allows
testing of the boot loader. If
disabled (the default), the VM directly boots the NixOS
kernel and initial ramdisk, bypassing the boot loader
altogether.
'';
};
};
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 =
''
#! ${pkgs.stdenv.shell}
NIX_DISK_IMAGE=$(readlink -f ''${NIX_DISK_IMAGE:-${config.virtualisation.diskImage}})
if ! test -e "$NIX_DISK_IMAGE"; then
${pkgs.qemu_kvm}/bin/qemu-img create -f qcow2 "$NIX_DISK_IMAGE" \
${toString config.virtualisation.diskSize}M || exit 1
fi
# Start Samba (which wants to put its socket and config files in TMPDIR).
if [ -z "$TMPDIR" -o -z "$USE_TMPDIR" ]; then
TMPDIR=$(mktemp -d nix-vm-smbd.XXXXXXXXXX --tmpdir)
fi
cd $TMPDIR
mkdir -p $TMPDIR/xchg
EXTRA_SAMBA_CONF="
[shared]
force user = $WHO
path = ''${SHARED_DIR:-$TMPDIR/xchg}
read only = no
guest ok = yes
"
${pkgs.vmTools.startSamba}
# Start QEMU.
# "-boot menu=on" is there, because I don't know how to make qemu boot from 2nd hd.
exec ${pkgs.qemu_kvm}/bin/qemu-kvm \
-name ${vmName} \
-m ${toString config.virtualisation.memorySize} \
${optionalString (pkgs.stdenv.system == "x86_64-linux") "-cpu kvm64"} \
-net nic,vlan=0,model=virtio \
-chardev socket,id=samba,path=./samba \
-net user,vlan=0,guestfwd=tcp:10.0.2.4:445-chardev:samba''${QEMU_NET_OPTS:+,$QEMU_NET_OPTS} \
${if cfg.useBootLoader then ''
-drive index=0,id=drive1,file=$NIX_DISK_IMAGE,if=virtio,cache=writeback,werror=report \
-drive index=1,id=drive2,file=${bootDisk}/disk.img,if=virtio,readonly \
-boot menu=on
'' else ''
-drive file=$NIX_DISK_IMAGE,if=virtio,cache=writeback,werror=report \
-kernel ${config.system.build.toplevel}/kernel \
-initrd ${config.system.build.toplevel}/initrd \
-append "$(cat ${config.system.build.toplevel}/kernel-params) init=${config.system.build.toplevel}/init regInfo=${regInfo} ${kernelConsole} $QEMU_KERNEL_PARAMS" \
''} \
${qemuGraphics} \
${toString config.virtualisation.qemu.options} \
$QEMU_OPTS
'';
regInfo = pkgs.runCommand "reginfo"
{ exportReferencesGraph =
map (x: [("closure-" + baseNameOf x) x]) config.virtualisation.pathsInNixDB;
buildInputs = [ pkgs.perl ];
preferLocalBuild = true;
}
''
printRegistration=1 perl ${pkgs.pathsFromGraph} closure-* > $out
'';
# Generate a hard disk image containing a /boot partition and GRUB
# in the MBR. Used when the `useBootLoader' option is set.
bootDisk =
pkgs.vmTools.runInLinuxVM (
pkgs.runCommand "nixos-boot-disk"
{ preVM =
''
mkdir $out
diskImage=$out/disk.img
${pkgs.vmTools.kvm}/bin/qemu-img create -f qcow2 $diskImage "32M"
'';
buildInputs = [ pkgs.utillinux ];
}
''
# Create a single /boot partition.
${pkgs.parted}/sbin/parted /dev/vda mklabel msdos
${pkgs.parted}/sbin/parted /dev/vda -- mkpart primary ext2 1M -1s
. /sys/class/block/vda1/uevent
mknod /dev/vda1 b $MAJOR $MINOR
. /sys/class/block/vda/uevent
${pkgs.e2fsprogs}/sbin/mkfs.ext4 -L boot /dev/vda1
${pkgs.e2fsprogs}/sbin/tune2fs -c 0 -i 0 /dev/vda1
# Mount /boot.
mkdir /boot
mount /dev/vda1 /boot
# This is needed for GRUB 0.97, which doesn't know about virtio devices.
mkdir /boot/grub
echo '(hd0) /dev/vda' > /boot/grub/device.map
# Install GRUB and generate the GRUB boot menu.
touch /etc/NIXOS
mkdir -p /nix/var/nix/profiles
${config.system.build.toplevel}/bin/switch-to-configuration boot
umount /boot
''
);
in
{
require = [ options ../profiles/qemu-guest.nix ];
boot.loader.grub.device = mkOverride 50 "/dev/vda";
# 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" "nls_utf8" "hmac" "md4" "ecb" "des_generic" ];
boot.initrd.supportedFilesystems = optional cfg.writableStore "unionfs-fuse";
boot.initrd.extraUtilsCommands =
''
# We need mke2fs in the initrd.
cp ${pkgs.e2fsprogs}/sbin/mke2fs $out/bin
'';
boot.initrd.postDeviceCommands =
''
# Set up networking. Needed for CIFS mounting.
ip link set eth0 up
ip addr add 10.0.2.15/24 dev eth0
# If the disk image appears to be empty, run mke2fs to
# initialise.
FSTYPE=$(blkid -o value -s TYPE /dev/vda || true)
if test -z "$FSTYPE"; then
mke2fs -t ext4 /dev/vda
fi
'';
boot.initrd.postMountCommands =
''
# Mark this as a NixOS machinex.
mkdir -p $targetRoot/etc
echo -n > $targetRoot/etc/NIXOS
# Fix the permissions on /tmp.
chmod 1777 $targetRoot/tmp
mkdir -p $targetRoot/boot
mount -o remount,ro $targetRoot/nix/store
${optionalString cfg.writableStore ''
mkdir -p /unionfs-chroot/ro-store
mount --rbind $targetRoot/nix/store /unionfs-chroot/ro-store
mkdir /unionfs-chroot/rw-store
mount -t tmpfs -o "mode=755" none /unionfs-chroot/rw-store
unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot,max_files=32768,hide_meta_files /rw-store=RW:/ro-store=RO $targetRoot/nix/store
''}
'';
# After booting, register the closure of the paths in
# `virtualisation.pathsInNixDB' in the Nix database in the VM. This
# allows Nix operations to work in the VM. The path to the
# registration file is passed through the kernel command line to
# allow `system.build.toplevel' to be included. (If we had a direct
# reference to ${regInfo} here, then we would get a cyclic
# dependency.)
boot.postBootCommands =
''
if [[ "$(cat /proc/cmdline)" =~ regInfo=([^ ]*) ]]; then
${config.environment.nix}/bin/nix-store --load-db < ''${BASH_REMATCH[1]}
fi
'';
virtualisation.pathsInNixDB = [ config.system.build.toplevel ];
virtualisation.qemu.options = [ "-vga std" "-usbdevice tablet" ];
# 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 10
{ "/".device = "/dev/vda";
"/nix/store" =
{ device = "//10.0.2.4/store";
fsType = "cifs";
options = "guest,sec=none,noperm,noacl";
};
"/tmp/xchg" =
{ device = "//10.0.2.4/xchg";
fsType = "cifs";
options = "guest,sec=none,noperm,noacl";
neededForBoot = true;
};
"/tmp/shared" =
{ device = "//10.0.2.4/shared";
fsType = "cifs";
options = "guest,sec=none,noperm,noacl";
neededForBoot = true;
};
} // optionalAttrs cfg.useBootLoader
{ "/boot" =
{ device = "/dev/disk/by-label/boot";
fsType = "ext4";
options = "ro";
noCheck = true; # fsck fails on a r/o filesystem
};
};
swapDevices = mkOverride 50 [ ];
# Starting DHCP brings down eth0, which kills the connection to the
# host filesystem and thus deadlocks the system.
networking.useDHCP = false;
networking.defaultGateway = mkOverride 200 "10.0.2.2";
networking.nameservers = [ "10.0.2.3" ];
networking.interfaces = singleton
{ name = "eth0";
ipAddress = "10.0.2.15";
prefixLength = 24;
};
# Don't run ntpd in the guest. It should get the correct time from KVM.
services.ntp.enable = false;
system.build.vm = pkgs.runCommand "nixos-vm" { preferLocalBuild = true; }
''
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 [ "vesa" ];
services.xserver.defaultDepth = mkOverride 50 0;
services.xserver.resolutions = mkOverride 50 [ { x = 1024; y = 768; } ];
services.xserver.monitorSection =
''
# Set a higher refresh rate so that resolutions > 800x600 work.
HorizSync 30-140
VertRefresh 50-160
'';
# Wireless won't work in the VM.
networking.wireless.enable = mkOverride 50 false;
system.requiredKernelConfig = with config.lib.kernelConfig;
[ (isEnabled "VIRTIO_BLK")
(isEnabled "VIRTIO_PCI")
(isEnabled "VIRTIO_NET")
(isEnabled "EXT4_FS")
(isEnabled "CIFS")
(isYes "BLK_DEV")
(isYes "PCI")
(isYes "EXPERIMENTAL")
(isYes "NETDEVICES")
(isYes "NET_CORE")
(isYes "INET")
(isYes "NETWORK_FILESYSTEMS")
] ++ optional (!cfg.graphics) [
(isYes "SERIAL_8250_CONSOLE")
(isYes "SERIAL_8250")
];
}