[Xen-devel] QEMU upstreaming: status and todo

[Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>]

Hi all,
I would like to spent few words to let people know the current status of
the Qemu upstreaming work and what is still missing.

Anthony Perard sent the 8th version of his "Xen device model support"
patch series to qemu-devel and he has already received an ack from
Alexander Graf. We are currently waiting for another review by Anthony
Liguori but we are positive the series is close to be accepted in its
current form.

Once the series is upstream we can start using upstream Qemu to do Xen
development, however before we can actually use it as default device
model we need to fill some gaps.
In fact some things are still missing compared to qemu-xen, the
followings in particular: 

- VGA dirty bits optimization
This is a performance optimization for the emulated VGA card, Anthony
Perard is already working on it.

- switch to SeaBios
Qemu uses SeaBios, that has several advantages on RomBios, one of them
is that SeaBios is actually maintained.
It makes sense to switch from the old Qemu and the old bios to a new
Qemu and a new bios at the same time in order to reduce the
compatibility pains to users.

- stubdom support
The "Xen device model support" patch series lacks stubdom support.
This is mainly a matter of compiling upstream Qemu against MiniOS,
the problem is that MiniOS is not exactly posix compliant so we'll need
to make some changes.

- pci passthrough
The patch series also lacks pci passthrough support.
The current pci passthrough code in qemu-xen is rather large and doesn't
integrate very well with the rest of Qemu so it is non-trivial to
upstream. 

- QMP support in libxl
upstream Qemu supports an RPC protocol called QMP that is JSON based.
We need to be able to use it to issue commands to Qemu, replacing the
current mechanism based on xenstore. For example this would be needed by
pci passthrough to send the "plug" and "unplug" commands to Qemu.


Ideally we'll be able to complete these tasks by the end of the Xen 4.2
release cycle so that we can have the new Qemu as default device model
by then.

Cheers,

Stefano

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