The document discusses libvirt's support for libxl, detailing its tools, stable API for virtualization management, and wide hypervisor support. It explains the architecture of libvirt including the differences between legacy xen and libxl drivers, along with migration instructions from xend to libxl. The document also highlights planned improvements and calls for contributions to enhance the libxl driver.

1. Libvirt support for libxl
Jim Fehlig
jfehlig@suse.com

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Why libvirt?
• The tools!
‒ virt-manager, virt-viewer, installers, monitoring, IaaS, ...
‒ http://libvirt.org/apps.html
• Stable API for managing virutalization on a host
‒ Storage, network interfaces, networks, host devices,
hypervisors, and virtual machines
• Stable XML config format for managed entities
‒ Extensible
‒ Simple APIs

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Why libvirt?
• Insulate users from changes in underlying
components
• Secure migration protocols
• Integration with other subsystems used in the
virtualization ecosystem
• Wide hypervisor support
‒ Xen, KVM/QEMU, LXC, ESX, Hyper-V, XenServer, VirtualBox,
bhyve, UML, ...

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libvirt Architecture
stateful stateless
remote ESX hyperv
RPC
libvirtd
VMware Hyper-V
Client (virsh)
libvirt.so
xen
qemu lxc storage network
xend libxl

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Hypervisor driver
• Accessed via hypervisor+protocol URI
‒ xen+ssh://host, qemu+tls://host
‒ xen:///, xen:///system, qemu:///system
• 202 functions in virDriver struct (src/driver.h)
‒ qemu: 192 functions
‒ Legacy xen: 91 functions
‒ libxl: 91 functions
‒ lxc: 86 functions
‒ esx: 73 functions
‒ hyperv: 31 functions
• src/<hypervisor>/<hypervisor>_driver.c

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Legacy Xen driver
• Uber-driver that uses xend, xenstore, xm, and
hypercalls
• Requires and primarily uses xend
• Became a stateful driver in libvirt 1.0.5, but state
maintained in xend
• I repeat: state is maintained in xend

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libxl Xen driver
• Introduced in libvirt 0,9.0
• Supports Xen >= 4.2 (best to have latest 4.x.y)
• Accessed with same Xen URI
• All existing domain configuration should just work
• Will not load if legacy Xen driver is loaded (xend is
running)
• Stateful driver, state maintained in libvirt
• I repeat: state is maintained in libvirt
• Note: don't mix and match libxl apps

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Migrating libvirt from xend to libxl
• Export domain config
virsh dumpxml > dom.xml
• Update Xen and libvirt
• Import domain config
virsh define dom.xml
• Alternatively
‒ virsh domxml-from-native <native-config> > dom.xml
‒ virsh define dom.xml

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Planned Improvements
• Support for xl config format
‒ domxml-{to,from}-native
• LockManager integration
• Snapshots
• Spice
• Unit tests
• <your feature>

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Help Wanted!
• SPoF with only one maintainer of upstream Xen
drivers
• Need more libxl APIs
• Need more functions implemented in the libxl driver
• Please consider libvirt when adding APIs to libxl
git://libvirt.org/libvirt.git
http://libvirt.org/hacking.html

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Questions?