Windows PV Drivers Incubation Project Proposal

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Windows PV Drivers Project Proposal


  • Project Lead: Paul Durrant - Paul is Windows subsystem architect for XenServer and has authored the majority of the driver code.
  • Project Sponsor: Matt Wilson - Matt is Xen Project AB member representing Amazon
  • Project Mentor: Lars Kurth - Lars is the Community Manager for and has agreed to act as the project’s Mentor.


ParaVirtualization aware (PV) device drivers are an important part of HVM guests running under Xen. Citrix has provided a set of PV driver for Windows since the inception of XenServer. These drivers have evolved over the years and recently the full set has been made open source with a BSD license and are therefore available to the community to modify and build. Paul Durrant gave a talk at the 2013 Xen Developer Summit in Edinburgh (see to introduce the drivers. This proposal is intended to be a logical next step to that initial offering to the community.

Relevance to Xen and its Community

The drivers have a dependency on Xen as they are ParaVirtualization aware. They are not tied in any way to Citrix commercial Xen offerings; they are designed to function on any build of Xen since 3.4. They encompass high performance network and storage frontends and enable functionality such as memory ballooning, and clean shutdown or reboot via the xl toolstack. They are well tested and supported, since they are crucial to Citrix products, and are of benefit to anyone wishing to run Windows (i386 or x86_64) as a guest under Xen.

Current Status

Recent builds of the drivers are currently being tested by Citrix and Amazon using the Microsoft HCK and Citrix will be providing logo-signed builds of the drivers in future commercial Xen offerings. Amazon are evaluating the drivers and may ship them in future AMIs. Citrix may also provide logo-signed drivers via Microsoft's Windows Update mechanism, making them widely available to anyone running Windows under Xen (not just XenServer) without the need for them to build the drivers themselves. Any other organization is also free to do the same by registering a top level PV device with the Xen community (see pci-device-reservations.txt) and logo-signing their driver builds.


The aim of making the Windows PV Drivers an incubated project is to raise their profile to members of the Xen community other than Citrix and Amazon and hopefully gain more developer interest and contribution. The driver set provide APIs to fundamental Xen subsystems such as grant tables, event channels and xenstore and therefore provide a basis for further frontends, e.g. HID (keyboard and mouse), PV audio and possibly framebuffer. Current maintainers of the driver repositories are all employed by Citrix but by becoming an incubated project we hope gain maintainers from the community as we build interest. We hope we can work with the maintainers of the GPLPV Windows Drivers to standardize Windows PV drivers for the Xen project.

Required Infrastructure


As a Xen Project sub-project we would wish the driver repositories to be hosted on xenbits, but mirrored to GitHub to allow use of the the GitHub workflow. It makes sense to maintain a separate repository for each driver as: Each driver is separately installable with no compile-time linkage to any other driver. Some headers may be imported from one repository to another to facilitate run-time discovery of interfaces provided by one driver and consumed by another, but it is desirable that this is an explicit step to move from one version of an interface to another. A continuous integration server project can be created for each repository such that the only a modified driver is re-built, rather than the entire set.

The set of drivers (and hence repositories) is currently:

  • XENBUS: Bus driver binding to the top-level PCI device (and providing most of the interfaces to Xen)
  • XENVIF: Network class driver (hosting the code necessary to drive the netif ring protocol)
  • XENNET: Network device driver (client of the class driver, provides VIFs to Windows network stack)
  • XENVBD: Storage class driver (hosting the code necessary to drive the blkif ring protocol)
  • XENIFACE: Interface driver (providing user-space access to xenstore)

Build and Test

We request build infrastructure to make new builds of driver repositories immediately available for use by community members. This includes:

  • A build machine (physical or virtual), possibly part of the Xen Project test framework, running Jenkins or some such continuous integration server to monitor the repositories
  • A license for Microsoft Visual Studio (~ $1000)
  • Storage, either on the build machine or elsewhere, to act as a public facing symbol server for the convenience of developers
Approval Status
  • The Advisory Board agreed to fund a Visual Studio license and two vendors in the community offered VM's to host the build environment.
  • Discussed proposal on the list
  • Vote on community approval was open until Jun 17 and has been approved



  • Project name: Windows PV Drivers Subproject
  • Repository namespace on xenbits: pvdrivers/win/*.git
  • Mailing list namespace:
  • Workflow: as Xen Project Hypervisor - no use of GitHub, but list based


Pictogram voting comment 15px.png Action Lars: Minor text changes as per [1]
Pictogram voting comment 15px.png Action Lars: Verify whether due diligence on licenses and build has been performed Citrix has run a license check and made some code modifications to ensure all files are under a BSD License
Pictogram voting comment 15px.png Action Lars: Verify whether code builds from existing public repositories
Pictogram voting comment 15px.png Action Paul: Nominate initial set of maintainers and committers and communicate to Lars
Pictogram voting comment 15px.png Action Paul: Confirm workflow with team
Pictogram voting comment 15px.png Action Lars: Request creation of mailing list
Pictogram voting comment 15px.png Action Lars: Infrastructure: confirm with Rackspace whether we can use one extra VM for build and test Rackspace is happy to do this
Pictogram voting comment 15px.png Action Paul: Contact Ian Jackson to set up pvdrivers/win/ on and migrate code
Pictogram voting comment 15px.png Action Paul: Work with Ian Jackson to set up build VM : inform Antony Messerly from Rackspace
Pictogram voting comment 15px.png Action Lars: Create portal on and and update
Pictogram voting comment 15px.png Action Paul: Notify developers on xen-devel of newly created infrastructure and list
Pictogram voting comment 15px.png Action Lars: Work with Sarah and Paul on launch communication