* A module for building KVM/QEMU virtual machines from a NixOS

configuration.  No virtual disk image is generated; the VM shares a
  Nix store with the host.  This makes it very fast to build new VMs.

svn path=/nixos/branches/modular-nixos/; revision=15999
This commit is contained in:
Eelco Dolstra 2009-06-18 16:16:12 +00:00
parent e08e7aedbc
commit 8179e5213f

View File

@ -0,0 +1,61 @@
# 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, ...}:
{
# 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"];
fileSystems =
[ { mountPoint = "/";
device = "/dev/vda";
}
];
# Mount the host filesystem and bind-mount its Nix store into our
# own root FS.
boot.initrd.postMountCommands =
''
ipconfig 10.0.2.15:::::eth0:none
mkdir /hostfs
${pkgs.vmTools.mountCifs}/bin/mount.cifs //10.0.2.4/qemu /hostfs -o guest,username=nobody
mkdir -p $targetRoot/nix/store
mount --bind /hostfs/nix/store $targetRoot/nix/store
'';
# 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
ln -s ${config.system.build.system} $out/system
ensureDir $out/bin
cat > $out/bin/run-nixos-vm <<EOF
#! ${pkgs.stdenv.shell}
export PATH=${pkgs.samba}/sbin:\$PATH
${pkgs.kvm}/bin/qemu-system-x86_64 \
-net nic,model=virtio -net user -smb / \
-drive file=\$diskImage,if=virtio,boot=on \
-kernel ${config.system.build.system}/kernel \
-initrd ${config.system.build.system}/initrd \
-append "\$(cat ${config.system.build.system}/kernel-params) init=${config.system.build.bootStage2} systemConfig=${config.system.build.system}"
EOF
chmod u+x $out/bin/run-nixos-vm
'';
}