nixpkgs/nixos/modules/virtualisation/libvirtd.nix
Bjørn Forsman f52f9bf7cd nixos/libvirtd-service: fix for garbage collected emulator paths
libvirtd puts the full path of the emulator binary in the machine config
file. But this path can unfortunately be garbage collected while still
being used by the virtual machine. Then this happens:

Error starting domain: Cannot check QEMU binary /nix/store/z5c2xzk9x0pj6x511w0w4gy9xl5wljxy-qemu-1.5.2-x86-only/bin/qemu-kvm: No such file or directory

Fix by updating the emulator path on each service startup to something
valid (re-scan $PATH).
2013-11-27 23:09:57 +01:00

162 lines
4.9 KiB
Nix

# Systemd services for libvirtd.
{ config, pkgs, ... }:
with pkgs.lib;
let
cfg = config.virtualisation.libvirtd;
configFile = pkgs.writeText "libvirtd.conf" ''
unix_sock_group = "libvirtd"
unix_sock_rw_perms = "0770"
auth_unix_ro = "none"
auth_unix_rw = "none"
${cfg.extraConfig}
'';
in
{
###### interface
options = {
virtualisation.libvirtd.enable =
mkOption {
default = false;
description =
''
This option enables libvirtd, a daemon that manages
virtual machines. Users in the "libvirtd" group can interact with
the daemon (e.g. to start or stop VMs) using the
<command>virsh</command> command line tool, among others.
'';
};
virtualisation.libvirtd.enableKVM =
mkOption {
default = true;
description =
''
This option enables support for QEMU/KVM in libvirtd.
'';
};
virtualisation.libvirtd.extraConfig =
mkOption {
default = "";
description =
''
Extra contents appended to the libvirtd configuration file,
libvirtd.conf.
'';
};
};
###### implementation
config = mkIf cfg.enable {
environment.systemPackages =
[ pkgs.libvirt pkgs.netcat-openbsd ]
++ optional cfg.enableKVM pkgs.qemu_kvm;
boot.kernelModules = [ "tun" ];
systemd.services.libvirtd =
{ description = "Libvirt Virtual Machine Management Daemon";
wantedBy = [ "multi-user.target" ];
after = [ "systemd-udev-settle.service" ];
path =
[ pkgs.bridge_utils pkgs.dmidecode pkgs.dnsmasq
pkgs.ebtables
] ++ optional cfg.enableKVM pkgs.qemu_kvm;
preStart =
''
mkdir -p /var/log/libvirt/qemu -m 755
rm -f /var/run/libvirtd.pid
mkdir -p /var/lib/libvirt
mkdir -p /var/lib/libvirt/dnsmasq
chmod 755 /var/lib/libvirt
chmod 755 /var/lib/libvirt/dnsmasq
# Libvirt unfortunately writes mutable state (such as
# runtime changes to VM, network or filter configurations)
# to /etc. So we can't use environment.etc to make the
# default network and filter definitions available, since
# libvirt will then modify the originals in the Nix store.
# So here we copy them instead. Ugly.
for i in $(cd ${pkgs.libvirt}/etc && echo \
libvirt/qemu/networks/*.xml libvirt/qemu/networks/autostart/*.xml \
libvirt/nwfilter/*.xml );
do
mkdir -p /etc/$(dirname $i) -m 755
cp -fpd ${pkgs.libvirt}/etc/$i /etc/$i
done
# libvirtd puts the full path of the emulator binary in the machine
# config file. But this path can unfortunately be garbage collected
# while still being used by the virtual machine. So update the
# emulator path on each startup to something valid (re-scan $PATH).
for file in /etc/libvirt/qemu/*.xml; do
# get (old) emulator path from config file
emulator=$(grep "^[[:space:]]*<emulator>" "$file" | sed 's,^[[:space:]]*<emulator>\(.*\)</emulator>.*,\1,')
# get a (definitely) working emulator path by re-scanning $PATH
new_emulator=$(command -v $(basename "$emulator"))
# write back
sed -i "s,^[[:space:]]*<emulator>.*, <emulator>$new_emulator</emulator> <!-- WARNING: emulator dirname is auto-updated by the nixos libvirtd module -->," "$file"
done
''; # */
serviceConfig.ExecStart = ''@${pkgs.libvirt}/sbin/libvirtd libvirtd --config "${configFile}" --daemon --verbose'';
serviceConfig.Type = "forking";
serviceConfig.KillMode = "process"; # when stopping, leave the VMs alone
# Wait until libvirtd is ready to accept requests.
postStart =
''
for ((i = 0; i < 60; i++)); do
if ${pkgs.libvirt}/bin/virsh list > /dev/null; then exit 0; fi
sleep 1
done
exit 1 # !!! seems to be ignored
'';
};
jobs."libvirt-guests" =
{ description = "Libvirt Virtual Machines";
wantedBy = [ "multi-user.target" ];
wants = [ "libvirtd.service" ];
after = [ "libvirtd.service" ];
restartIfChanged = false;
path = [ pkgs.gettext pkgs.libvirt pkgs.gawk ];
preStart =
''
mkdir -p /var/lock/subsys -m 755
${pkgs.libvirt}/etc/rc.d/init.d/libvirt-guests start || true
'';
postStop = "${pkgs.libvirt}/etc/rc.d/init.d/libvirt-guests stop";
serviceConfig.Type = "oneshot";
serviceConfig.RemainAfterExit = true;
};
users.extraGroups.libvirtd.gid = config.ids.gids.libvirtd;
};
}