29027fd1e1
Using pkgs.lib on the spine of module evaluation is problematic because the pkgs argument depends on the result of module evaluation. To prevent an infinite recursion, pkgs and some of the modules are evaluated twice, which is inefficient. Using ‘with lib’ prevents this problem.
421 lines
14 KiB
Nix
421 lines
14 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, lib, pkgs, ... }:
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with lib;
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let
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vmName =
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if config.networking.hostName == ""
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then "noname"
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else config.networking.hostName;
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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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# Create a directory for exchanging data with the VM.
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if [ -z "$TMPDIR" -o -z "$USE_TMPDIR" ]; then
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TMPDIR=$(mktemp -d nix-vm.XXXXXXXXXX --tmpdir)
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fi
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cd $TMPDIR
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mkdir -p $TMPDIR/xchg
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idx=2
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extraDisks=""
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${flip concatMapStrings cfg.emptyDiskImages (size: ''
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${pkgs.qemu_kvm}/bin/qemu-img create -f raw "empty$idx" "${toString size}M"
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extraDisks="$extraDisks -drive index=$idx,file=$(pwd)/empty$idx,if=virtio,werror=report"
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idx=$((idx + 1))
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'')}
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# Start QEMU.
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# "-boot menu=on" is there, because I don't know how to make qemu boot from 2nd hd.
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exec ${pkgs.qemu_kvm}/bin/qemu-kvm \
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-name ${vmName} \
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-m ${toString config.virtualisation.memorySize} \
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${optionalString (pkgs.stdenv.system == "x86_64-linux") "-cpu kvm64"} \
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-net nic,vlan=0,model=virtio \
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-net user,vlan=0''${QEMU_NET_OPTS:+,$QEMU_NET_OPTS} \
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-virtfs local,path=/nix/store,security_model=none,mount_tag=store \
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-virtfs local,path=$TMPDIR/xchg,security_model=none,mount_tag=xchg \
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-virtfs local,path=''${SHARED_DIR:-$TMPDIR/xchg},security_model=none,mount_tag=shared \
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${if cfg.useBootLoader then ''
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-drive index=0,id=drive1,file=$NIX_DISK_IMAGE,if=virtio,cache=writeback,werror=report \
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-drive index=1,id=drive2,file=${bootDisk}/disk.img,if=virtio,readonly \
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-boot menu=on
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'' else ''
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-drive file=$NIX_DISK_IMAGE,if=virtio,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} $QEMU_KERNEL_PARAMS" \
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''} \
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$extraDisks \
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${qemuGraphics} \
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${toString config.virtualisation.qemu.options} \
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$QEMU_OPTS
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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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preferLocalBuild = true;
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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.qemu_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.ext4 -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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imports = [ ../profiles/qemu-guest.nix ];
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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.emptyDiskImages =
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mkOption {
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default = [];
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type = types.listOf types.int;
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description =
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''
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Additional disk images to provide to the VM, the value is a list of
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sizes in megabytes the empty disk should be.
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These disks are writeable by the VM and will be thrown away
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afterwards.
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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 a unionfs-fuse/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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virtualisation.writableStoreUseTmpfs =
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mkOption {
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default = true;
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description =
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''
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Use a tmpfs for the writable store instead of writing to the VM's
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own filesystem.
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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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config = {
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boot.loader.grub.device = mkVMOverride "/dev/vda";
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boot.initrd.supportedFilesystems = optional cfg.writableStore "unionfs-fuse";
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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 $out/bin
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'';
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boot.initrd.postDeviceCommands =
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''
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# If the disk image appears to be empty, run mke2fs to
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# initialise.
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FSTYPE=$(blkid -o value -s TYPE /dev/vda || true)
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if test -z "$FSTYPE"; then
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mke2fs -t ext4 /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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# Mark this as a NixOS machine.
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mkdir -p $targetRoot/etc
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echo -n > $targetRoot/etc/NIXOS
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# Fix the permissions on /tmp.
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chmod 1777 $targetRoot/tmp
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mkdir -p $targetRoot/boot
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${optionalString cfg.writableStore ''
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mkdir -p /unionfs-chroot/ro-store
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mount --rbind $targetRoot/nix/store /unionfs-chroot/ro-store
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mkdir /unionfs-chroot/rw-store
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${if cfg.writableStoreUseTmpfs then ''
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mount -t tmpfs -o "mode=755" none /unionfs-chroot/rw-store
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'' else ''
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mkdir $targetRoot/.nix-rw-store
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mount --bind $targetRoot/.nix-rw-store /unionfs-chroot/rw-store
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''}
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unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot,max_files=32768,hide_meta_files /rw-store=RW:/ro-store=RO $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 ${regInfo} here, then we would get a cyclic
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# dependency.)
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boot.postBootCommands =
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''
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if [[ "$(cat /proc/cmdline)" =~ regInfo=([^ ]*) ]]; then
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${config.nix.package}/bin/nix-store --load-db < ''${BASH_REMATCH[1]}
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fi
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'';
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virtualisation.pathsInNixDB = [ config.system.build.toplevel ];
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virtualisation.qemu.options = [ "-vga std" "-usbdevice tablet" ];
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# Mount the host filesystem via 9P, and bind-mount the Nix store
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# of the host into our own filesystem. We use mkVMOverride to
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# allow this module to be applied to "normal" NixOS system
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# configuration, where the regular value for the `fileSystems'
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# attribute should be disregarded for the purpose of building a VM
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# test image (since those filesystems don't exist in the VM).
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fileSystems = mkVMOverride
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{ "/".device = "/dev/vda";
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"/nix/store" =
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{ device = "store";
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fsType = "9p";
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options = "trans=virtio,version=9p2000.L,msize=1048576,cache=loose";
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};
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"/tmp/xchg" =
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{ device = "xchg";
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fsType = "9p";
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options = "trans=virtio,version=9p2000.L,msize=1048576,cache=loose";
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neededForBoot = true;
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};
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"/tmp/shared" =
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{ device = "shared";
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fsType = "9p";
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options = "trans=virtio,version=9p2000.L,msize=1048576";
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neededForBoot = true;
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};
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} // optionalAttrs cfg.useBootLoader
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{ "/boot" =
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{ device = "/dev/disk/by-label/boot";
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fsType = "ext4";
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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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};
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swapDevices = mkVMOverride [ ];
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boot.initrd.luks.devices = mkVMOverride [];
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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" { preferLocalBuild = true; }
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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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# When building a regular system configuration, override whatever
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# video driver the host uses.
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hardware.opengl.videoDrivers = mkVMOverride [ "vesa" ];
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services.xserver.defaultDepth = mkVMOverride 0;
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services.xserver.resolutions = mkVMOverride [ { x = 1024; y = 768; } ];
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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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# Wireless won't work in the VM.
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networking.wireless.enable = mkVMOverride false;
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system.requiredKernelConfig = with config.lib.kernelConfig;
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[ (isEnabled "VIRTIO_BLK")
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(isEnabled "VIRTIO_PCI")
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(isEnabled "VIRTIO_NET")
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(isEnabled "EXT4_FS")
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(isYes "BLK_DEV")
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(isYes "PCI")
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(isYes "EXPERIMENTAL")
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(isYes "NETDEVICES")
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(isYes "NET_CORE")
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(isYes "INET")
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(isYes "NETWORK_FILESYSTEMS")
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] ++ optional (!cfg.graphics) [
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(isYes "SERIAL_8250_CONSOLE")
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(isYes "SERIAL_8250")
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];
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};
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}
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