.. role:: since =============================== libxl hypervisor driver for Xen =============================== .. contents:: The libvirt libxl driver provides the ability to manage virtual machines on any Xen release from 4.6.0 onwards. Project Links ------------- - The `Xen `__ hypervisor on Linux and Solaris hosts Deployment pre-requisites ------------------------- The libvirt libxl driver uses Xen's libxl API, also known as libxenlight, to implement libvirt's hypervisor driver functionality. libxl provides a consolidated interface for managing a Xen host and its virtual machines, unlike old versions of Xen where applications often had to communicate with xend, xenstored, and the hypervisor itself via hypercalls. With libxl the only pre-requisit is a properly installed Xen host with the libxl toolstack running in a service domain (often Domain-0). Connections to libxl driver --------------------------- The libvirt libxl driver is a single-instance privileged driver, with a driver name of 'xen'. Some example connection URIs for the libxl driver are: :: xen:///system (local access, direct) xen+unix:///system (local access, via daemon) xen://example.com/system (remote access, TLS/x509) xen+tcp://example.com/system (remote access, SASl/Kerberos) xen+ssh://root@example.com/system (remote access, SSH tunnelled) Location of configuration files ------------------------------- The libxl driver comes with sane default values. However, during its initialization it reads a configuration file which offers system administrator to override some of that default. The file is located under ``/etc/libvirt/libxl.conf`` Import and export of libvirt domain XML configs ----------------------------------------------- The libxl driver currently supports three native config formats. The first, known as ``xen-xm``, is the original Xen virtual machine config format used by the legacy xm/xend toolstack. The second, known as ``xen-sxpr``, is also one of the original formats that was used by xend's legacy HTTP RPC service ( :since:`removed in 5.6.0` ) The third format is ``xen-xl``, which is the virtual machine config format supported by modern Xen. The ``xen-xl`` format is described in the xl.cfg(5) man page. Converting from XM config files to domain XML ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The ``virsh domxml-from-native`` provides a way to convert an existing set of xl, xm, or sxpr config files to libvirt Domain XML, which can then be used by libvirt. :: $ virsh -c xen:///system domxml-from-native xen-xm rhel5.cfg rhel5pv 8f07fe28-753f-2729-d76d-bdbd892f949a 2560000 307200 4 /usr/bin/pygrub linux destroy restart restart Converting from domain XML to XM config files ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The ``virsh domxml-to-native`` provides a way to convert a guest description using libvirt Domain XML into xl, xm, or sxpr config format. :: $ virsh -c xen:///system domxml-to-native xen-xm rhel5pv.xml name = "rhel5pv" uuid = "8f07fe28-753f-2729-d76d-bdbd892f949a" maxmem = 2500 memory = 300 vcpus = 4 bootloader = "/usr/bin/pygrub" kernel = "/var/lib/xen/boot_kernel.0YK-cS" ramdisk = "/var/lib/xen/boot_ramdisk.vWgrxK" extra = "ro root=/dev/VolGroup00/LogVol00 rhgb quiet" on_poweroff = "destroy" on_reboot = "restart" on_crash = "restart" sdl = 0 vnc = 1 vncunused = 1 vnclisten = "0.0.0.0" disk = [ "tap:aio:/var/lib/xen/images/rhel5pv.img,xvda,w", "tap:qcow:/root/qcow1-xen.img,xvdd,w" ] vif = [ "mac=00:16:3e:60:36:ba,bridge=virbr0,script=vif-bridge,vifname=vif5.0" ] Pass-through of arbitrary command-line arguments to the qemu device model ------------------------------------------------------------------------- :since:`Since 6.7.0`, the Xen driver supports passing arbitrary command-line arguments to the qemu device model used by Xen with the ```` element under ``domain``. In order to use command-line pass-through, an XML namespace request must be issued that pulls in ``http://libvirt.org/schemas/domain/xen/1.0``. With the namespace in place, it is then possible to add ````\ sub-elements to ```` describing each argument passed to the device model when starting the domain. The following example illustrates passing arguments to the QEMU device model that define a floppy drive, which Xen does not support through its public APIs: :: ... Example domain XML config ------------------------- Below are some example XML configurations for Xen guest domains. For full details of the available options, consult the `domain XML format `__ guide. Paravirtualized guest bootloader ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Using a bootloader allows a paravirtualized guest to be booted using a kernel stored inside its virtual disk image :: fc8 /usr/bin/pygrub linux 131072 1