374 lines
12 KiB
Nix
374 lines
12 KiB
Nix
# This module creates a virtual machine from the NixOS configuration.
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# Building the `config.system.build.vm' attribute gives you a command
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# that starts a KVM/QEMU VM running the NixOS configuration defined in
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# `config'. The Nix store is shared read-only with the host, which
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# makes (re)building VMs very efficient. However, it also means you
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# can't reconfigure the guest inside the guest - you need to rebuild
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# the VM in the host. On the other hand, the root filesystem is a
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# read/writable disk image persistent across VM reboots.
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{ config, pkgs, ... }:
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with pkgs.lib;
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let
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vmName = config.networking.hostName;
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options = {
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virtualisation.memorySize =
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mkOption {
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default = 384;
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description =
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''
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Memory size (M) of virtual machine.
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'';
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};
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virtualisation.diskSize =
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mkOption {
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default = 512;
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description =
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''
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Disk size (M) of virtual machine.
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'';
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};
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virtualisation.diskImage =
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mkOption {
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default = "./${vmName}.qcow2";
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description =
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''
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Path to the disk image containing the root filesystem.
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The image will be created on startup if it does not
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exist.
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'';
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};
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virtualisation.graphics =
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mkOption {
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default = true;
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description =
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''
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Whether to run QEMU with a graphics window, or access
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the guest computer serial port through the host tty.
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'';
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};
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virtualisation.pathsInNixDB =
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mkOption {
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default = [];
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description =
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''
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The list of paths whose closure is registered in the Nix
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database in the VM. All other paths in the host Nix store
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appear in the guest Nix store as well, but are considered
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garbage (because they are not registered in the Nix
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database in the guest).
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'';
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};
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virtualisation.vlans =
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mkOption {
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default = [ 1 ];
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example = [ 1 2 ];
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description =
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''
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Virtual networks to which the VM is connected. Each
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number <replaceable>N</replaceable> in this list causes
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the VM to have a virtual Ethernet interface attached to a
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separate virtual network on which it will be assigned IP
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address
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<literal>192.168.<replaceable>N</replaceable>.<replaceable>M</replaceable></literal>,
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where <replaceable>M</replaceable> is the index of this VM
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in the list of VMs.
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'';
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};
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virtualisation.writableStore =
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mkOption {
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default = false;
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description =
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''
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If enabled, the Nix store in the VM is made writable by
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layering an AUFS/tmpfs filesystem on top of the host's Nix
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store.
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'';
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};
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networking.primaryIPAddress =
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mkOption {
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default = "";
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internal = true;
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description = "Primary IP address used in /etc/hosts.";
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};
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virtualisation.qemu.options =
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mkOption {
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default = "";
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example = "-vga std";
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description = "Options passed to QEMU.";
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};
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virtualisation.useBootLoader =
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mkOption {
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default = false;
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description =
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''
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If enabled, the virtual machine will be booted using the
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regular boot loader (i.e., GRUB 1 or 2). This allows
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testing of the boot loader. If
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disabled (the default), the VM directly boots the NixOS
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kernel and initial ramdisk, bypassing the boot loader
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altogether.
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'';
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};
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};
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cfg = config.virtualisation;
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qemuGraphics = if cfg.graphics then "" else "-nographic";
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kernelConsole = if cfg.graphics then "" else "console=ttyS0";
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ttys = [ "tty1" "tty2" "tty3" "tty4" "tty5" "tty6" ];
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# Shell script to start the VM.
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startVM =
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''
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#! ${pkgs.stdenv.shell}
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NIX_DISK_IMAGE=$(readlink -f ''${NIX_DISK_IMAGE:-${config.virtualisation.diskImage}})
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if ! test -e "$NIX_DISK_IMAGE"; then
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${pkgs.qemu_kvm}/bin/qemu-img create -f qcow2 "$NIX_DISK_IMAGE" \
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${toString config.virtualisation.diskSize}M || exit 1
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fi
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# Start Samba (which wants to put its socket and config files in TMPDIR).
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if [ -z "$TMPDIR" -o -z "$USE_TMPDIR" ]; then
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TMPDIR=$(mktemp -d nix-vm-smbd.XXXXXXXXXX --tmpdir)
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fi
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cd $TMPDIR
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${pkgs.vmTools.startSamba}
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# Start QEMU.
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exec ${pkgs.qemu_kvm}/bin/qemu-system-x86_64 \
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-name ${vmName} \
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-m ${toString config.virtualisation.memorySize} \
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-net nic,vlan=0,model=virtio \
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-chardev socket,id=samba,path=./samba \
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-net user,vlan=0,guestfwd=tcp:10.0.2.4:445-chardev:samba''${QEMU_NET_OPTS:+,$QEMU_NET_OPTS} \
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${if cfg.useBootLoader then ''
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-drive index=0,file=$NIX_DISK_IMAGE,if=virtio,cache=writeback,werror=report \
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-drive index=1,file=${bootDisk}/disk.img,if=virtio,boot=on \
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'' else ''
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-drive file=$NIX_DISK_IMAGE,if=virtio,boot=on,cache=writeback,werror=report \
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-kernel ${config.system.build.toplevel}/kernel \
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-initrd ${config.system.build.toplevel}/initrd \
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-append "$(cat ${config.system.build.toplevel}/kernel-params) init=${config.system.build.toplevel}/init regInfo=${regInfo} ${kernelConsole} $QEMU_KERNEL_PARAMS" \
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''} \
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${qemuGraphics} \
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$QEMU_OPTS \
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${config.virtualisation.qemu.options}
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'';
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regInfo = pkgs.runCommand "reginfo"
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{ exportReferencesGraph =
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map (x: [("closure-" + baseNameOf x) x]) config.virtualisation.pathsInNixDB;
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buildInputs = [ pkgs.perl ];
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}
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''
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printRegistration=1 perl ${pkgs.pathsFromGraph} closure-* > $out
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'';
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# Generate a hard disk image containing a /boot partition and GRUB
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# in the MBR. Used when the `useBootLoader' option is set.
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bootDisk =
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pkgs.vmTools.runInLinuxVM (
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pkgs.runCommand "nixos-boot-disk"
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{ preVM =
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''
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mkdir $out
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diskImage=$out/disk.img
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${pkgs.vmTools.kvm}/bin/qemu-img create -f qcow2 $diskImage "32M"
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'';
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buildInputs = [ pkgs.utillinux ];
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}
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''
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# Create a single /boot partition.
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${pkgs.parted}/sbin/parted /dev/vda mklabel msdos
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${pkgs.parted}/sbin/parted /dev/vda -- mkpart primary ext2 1M -1s
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. /sys/class/block/vda1/uevent
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mknod /dev/vda1 b $MAJOR $MINOR
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. /sys/class/block/vda/uevent
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${pkgs.e2fsprogs}/sbin/mkfs.ext3 -L boot /dev/vda1
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${pkgs.e2fsprogs}/sbin/tune2fs -c 0 -i 0 /dev/vda1
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# Mount /boot.
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mkdir /boot
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mount /dev/vda1 /boot
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# This is needed for GRUB 0.97, which doesn't know about virtio devices.
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mkdir /boot/grub
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echo '(hd0) /dev/vda' > /boot/grub/device.map
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# Install GRUB and generate the GRUB boot menu.
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touch /etc/NIXOS
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mkdir -p /nix/var/nix/profiles
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${config.system.build.toplevel}/bin/switch-to-configuration boot
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umount /boot
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''
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);
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in
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{
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require = options;
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boot.loader.grub.device = mkOverride 50 "/dev/vda";
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# All the modules the initrd needs to mount the host filesystem via
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# CIFS. Also use paravirtualised network and block devices for
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# performance.
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boot.initrd.availableKernelModules =
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[ "cifs" "virtio_net" "virtio_pci" "virtio_blk" "virtio_balloon" "nls_utf8" ]
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++ optional cfg.writableStore [ "aufs" ];
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boot.extraModulePackages =
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optional cfg.writableStore config.boot.kernelPackages.aufs2;
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boot.initrd.extraUtilsCommands =
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''
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# We need mke2fs in the initrd.
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cp ${pkgs.e2fsprogs}/sbin/mke2fs $out/bin
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# And `ifconfig'.
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cp ${pkgs.nettools}/sbin/ifconfig $out/bin
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'';
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boot.initrd.postDeviceCommands =
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''
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# Set up networking. Needed for CIFS mounting.
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ifconfig eth0 up 10.0.2.15
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# If the disk image appears to be empty, run mke2fs to
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# initialise.
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FSTYPE=$(blkid -o value -s TYPE /dev/vda || true)
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if test -z "$FSTYPE"; then
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mke2fs -t ext3 /dev/vda
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fi
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'';
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boot.initrd.postMountCommands =
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''
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mkdir -p $targetRoot/boot
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mount -o remount,ro $targetRoot/nix/store
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${optionalString cfg.writableStore ''
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mkdir /mnt-store-tmpfs
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mount -t tmpfs -o "mode=755" none /mnt-store-tmpfs
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mount -t aufs -o dirs=/mnt-store-tmpfs=rw:$targetRoot/nix/store=rr none $targetRoot/nix/store
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''}
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'';
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# After booting, register the closure of the paths in
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# `virtualisation.pathsInNixDB' in the Nix database in the VM. This
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# allows Nix operations to work in the VM. The path to the
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# registration file is passed through the kernel command line to
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# allow `system.build.toplevel' to be included. (If we had a direct
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# reference to ${regInfo} here, then we would get a cyclic
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# dependency.)
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boot.postBootCommands =
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''
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( source /proc/cmdline
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if [ -n "$regInfo" ]; then
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${config.environment.nix}/bin/nix-store --load-db < $regInfo
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fi
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)
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'';
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virtualisation.pathsInNixDB = [ config.system.build.toplevel ];
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# Mount the host filesystem via CIFS, and bind-mount the Nix store
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# of the host into our own filesystem. We use mkOverride to allow
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# this module to be applied to "normal" NixOS system configuration,
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# where the regular value for the `fileSystems' attribute should be
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# disregarded for the purpose of building a VM test image (since
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# those filesystems don't exist in the VM).
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fileSystems = mkOverride 50 (
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[ { mountPoint = "/";
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device = "/dev/vda";
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}
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{ mountPoint = "/hostfs";
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device = "//10.0.2.4/qemu";
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fsType = "cifs";
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options = "guest,sec=none,noperm,noacl";
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neededForBoot = true;
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}
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{ mountPoint = "/nix/store";
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device = "/hostfs/nix/store";
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fsType = "none";
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options = "bind";
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neededForBoot = true;
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}
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] ++ optional cfg.useBootLoader
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{ mountPoint = "/boot";
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device = "/dev/disk/by-label/boot";
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fsType = "ext3";
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options = "ro";
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noCheck = true; # fsck fails on a r/o filesystem
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});
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swapDevices = mkOverride 50 [ ];
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# Starting DHCP brings down eth0, which kills the connection to the
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# host filesystem and thus deadlocks the system.
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networking.useDHCP = false;
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networking.defaultGateway = mkOverride 200 "10.0.2.2";
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networking.nameservers = [ "10.0.2.3" ];
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networking.interfaces = singleton
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{ name = "eth0";
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ipAddress = "10.0.2.15";
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};
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# Don't run ntpd in the guest. It should get the correct time from KVM.
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services.ntp.enable = false;
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system.build.vm = pkgs.runCommand "nixos-vm" {}
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''
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ensureDir $out/bin
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ln -s ${config.system.build.toplevel} $out/system
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ln -s ${pkgs.writeScript "run-nixos-vm" startVM} $out/bin/run-${vmName}-vm
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'';
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# sendfile() is currently broken over CIFS, so fix it here for all
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# configurations that use Apache.
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services.httpd.extraConfig =
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''
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EnableSendFile Off
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'';
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# When building a regular system configuration, override whatever
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# video driver the host uses.
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services.xserver.videoDriver = mkOverride 50 null;
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services.xserver.videoDrivers = mkOverride 50 [ "cirrus" "vesa" ];
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services.xserver.defaultDepth = mkOverride 50 0;
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services.xserver.monitorSection =
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''
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# Set a higher refresh rate so that resolutions > 800x600 work.
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HorizSync 30-140
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VertRefresh 50-160
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'';
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services.mingetty.ttys = ttys ++ optional (!cfg.graphics) "ttyS0";
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# Wireless won't work in the VM.
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networking.enableWLAN = mkOverride 50 false;
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}
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