QEMU Upstream

How to build QEMU with Xen

Nowadays, xen-unstable will clone and build a qemu git tree from xenbits. (It is qemu-stable-1.0 today). But you can follow this guide to build the upstream unstable qemu git tree.

You can add this to your "xen-unstable.git/.config" file, so xen-unstable will clone and build the upstream tree.

 QEMU_UPSTREAM_URL = git://git.qemu.org/qemu.git
 QEMU_UPSTREAM_REVISION = master

Then, add "device_model_version = 'qemu-xen'" in your vm config file to use this new qemu.

Or build qemu out of the xen-unstable dir:

Get the source

• Get Xen source (version 4.2 aka xen-unstable development version)
• Get QEMU upstream source from:
  • git://git.qemu.org/qemu.git

Build it!

• Build Xen
  • make xen tools, if it fail see bellow.
• Build QEMU upstream with Xen
  • ./configure --enable-xen --target-list=i386-softmmu --extra-cflags="-I$path_to_xen_source/tools/include -I$path_to_xen_source/tools/libxc -I$path_to_xen_source/tools/xenstore" --extra-ldflags="-L$path_to_xen_source/tools/libxc -L$path_to_xen_source/tools/xenstore"
  • make

Troubleshooting compilation errors: If you get an error from configure like "ERROR: User requested feature xen ERROR: configure was not able to find it" then see this: http://xen.1045712.n5.nabble.com/Upstream-Qemu-With-Xen-configuration-problem-td4561779.html , ie. you need to point the paths for "configure" to xen source directory, not to xen dist directory.

Run it!

Either:

• With the latest xen-unstable tree, use:
  • device_model_version = 'qemu-xen'
  • device_model_override = '/root/work/qemu/_build/i386-softmmu/qemu-system-i386'

Now xl will always try run qemu upstream with seabios, so build xen with seabios.

• For troubleshooting device_model on older Xen related errors (Xen specific options -domain-name, -vcpus, etc) see: http://xen.1045712.n5.nabble.com/Upstream-QEMU-not-working-with-Xen-unstable-lacks-option-definitions-td4372252.html

Use with SeaBIOS

SeaBIOS support is now fully integrated into the Xen build system (in xen-unstable and xen-4.2 onwards) and is always used when using device_model_version = "qemu-xen".

If you want to build a version of SeaBIOS other than the default then you can override SEABIOS_UPSTREAM_URL and/or SEABIOS_UPSTREAM_TAG via .config. For reference the upstream SeaBIOS repository is [[1]].

New features

VirtIO

It's the PV drivers from KVM world. To use it for network, just use 'virtio-net' as a model:

 vif = [ 'model=virtio-net' ]

You will need those kernel modules to use a VirtIO device

 virtio_mmio virtio_pci virtio_net

SPICE / QXL

SPICE is another remote-display protocol and QXL is a PV framebuffer which uses the best of the SPICE capabilities. To activate SPICE you can add this in the VM config file (this works only with xl).

 spice=1
 spicehost='0.0.0.0'
 spiceport=6000
 spicedisable_ticketing=1

If you wish to use QXL as well you have to add:

 device_model_args_hvm = [ '-vga', 'qxl' ]
 videoram = 128

QXL does not currently work under Xen due to some limitation. (check [this email] for more information.)

Difference with qemu-xen-traditional

Missing feature from the good old qemu-dm

Currently, there is few missing feature that not supported by QEMU upstream, but the work is ongoing.

• dirty log: This is needed to migrate a guest. Patches have been posted to both QEMU and libxl, but are not applied yet.
• VGA passthrough: Sometime (all the time?), simple PCI passthrough does not works for graphics card. The few things that are done in qemu-dm are not yet upstreamed.

New feature from QEMU upstream

There are some benefits from upstreaming the support of Xen to QEMU. We can now use:

• VirtIO, as an alternative to Xen PV drivers
• SPICE, as a remote-display protocol instead of the old VNC.
• different kind of file format for a disc.
• the ability to connect several times to the VNC server.
• ...