# 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, lib, pkgs, options, ... }:
with lib;
let
qemu-common = import ../../lib/qemu-common.nix { inherit lib pkgs; };
cfg = config.virtualisation;
opt = options.virtualisation;
qemu = cfg.qemu.package;
consoles = lib.concatMapStringsSep " " (c: "console=${c}") cfg.qemu.consoles;
driveOpts = { ... }: {
options = {
file = mkOption {
type = types.str;
description = lib.mdDoc "The file image used for this drive.";
};
driveExtraOpts = mkOption {
type = types.attrsOf types.str;
default = {};
description = lib.mdDoc "Extra options passed to drive flag.";
};
deviceExtraOpts = mkOption {
type = types.attrsOf types.str;
default = {};
description = lib.mdDoc "Extra options passed to device flag.";
};
name = mkOption {
type = types.nullOr types.str;
default = null;
description =
lib.mdDoc "A name for the drive. Must be unique in the drives list. Not passed to qemu.";
};
};
};
driveCmdline = idx: { file, driveExtraOpts, deviceExtraOpts, ... }:
let
drvId = "drive${toString idx}";
mkKeyValue = generators.mkKeyValueDefault {} "=";
mkOpts = opts: concatStringsSep "," (mapAttrsToList mkKeyValue opts);
driveOpts = mkOpts (driveExtraOpts // {
index = idx;
id = drvId;
"if" = "none";
inherit file;
});
deviceOpts = mkOpts (deviceExtraOpts // {
drive = drvId;
});
device =
if cfg.qemu.diskInterface == "scsi" then
"-device lsi53c895a -device scsi-hd,${deviceOpts}"
else
"-device virtio-blk-pci,${deviceOpts}";
in
"-drive ${driveOpts} ${device}";
drivesCmdLine = drives: concatStringsSep "\\\n " (imap1 driveCmdline drives);
# Creates a device name from a 1-based a numerical index, e.g.
# * `driveDeviceName 1` -> `/dev/vda`
# * `driveDeviceName 2` -> `/dev/vdb`
driveDeviceName = idx:
let letter = elemAt lowerChars (idx - 1);
in if cfg.qemu.diskInterface == "scsi" then
"/dev/sd${letter}"
else
"/dev/vd${letter}";
lookupDriveDeviceName = driveName: driveList:
(findSingle (drive: drive.name == driveName)
(throw "Drive ${driveName} not found")
(throw "Multiple drives named ${driveName}") driveList).device;
addDeviceNames =
imap1 (idx: drive: drive // { device = driveDeviceName idx; });
# Shell script to start the VM.
startVM =
''
#! ${cfg.host.pkgs.runtimeShell}
export PATH=${makeBinPath [ cfg.host.pkgs.coreutils ]}''${PATH:+:}$PATH
set -e
NIX_DISK_IMAGE=$(readlink -f "''${NIX_DISK_IMAGE:-${toString config.virtualisation.diskImage}}") || test -z "$NIX_DISK_IMAGE"
if test -n "$NIX_DISK_IMAGE" && ! test -e "$NIX_DISK_IMAGE"; then
${qemu}/bin/qemu-img create -f qcow2 "$NIX_DISK_IMAGE" \
${toString config.virtualisation.diskSize}M
fi
# Create a directory for storing temporary data of the running VM.
if [ -z "$TMPDIR" ] || [ -z "$USE_TMPDIR" ]; then
TMPDIR=$(mktemp -d nix-vm.XXXXXXXXXX --tmpdir)
fi
${lib.optionalString (cfg.useNixStoreImage)
(if cfg.writableStore
then ''
# Create a writable copy/snapshot of the store image.
${qemu}/bin/qemu-img create -f qcow2 -F qcow2 -b ${storeImage}/nixos.qcow2 "$TMPDIR"/store.img
''
else ''
(
cd ${builtins