Re: VHOST_USER_PROTOCOL_F_VDPA

[Stefan Hajnoczi]

On Thu, Sep 10, 2020 at 10:55:00AM +0200, Maxime Coquelin wrote:
> I understand the need and like the idea.

If no one plans to work on this within the next 6 months it could be an
internship project since the Outreachy December-March round is coming
up.

The time requirement is typically ~5 hours per week from the mentor.

Jason, Maxime, Cindy, Michael: Are you interested in mentoring this
project idea?

Internships focus mostly implementing existing designs since the intern
doesn't have enough background knowledge or time to design some of this
complexity from scratch.

As a starting point, the vhost-user protocol can be extended with all
the vDPA messages. Redundant vhost-user messages from the existing
protocol can be dropped/deprecated (i.e. device-specific messages that
were introduced to work around the lack of the VIRTIO device lifecycle).

Fully embracing the vDPA/VIRTIO lifecycle eliminates the need for
per-type QEMU devices (vhost-user-net, vhost-user-blk, etc). Instead
per-transport devices are needed (-device vdpa-user-{pci,ccw,mmio}).
This means new device types can be added later without writing all the
boilerplate -device vhost-user-foo-{pci,ccw,mmio} code!

The internship could focus on implementing -device vdpa-user-pci and a
libvdpa-user test/example. The vhost-user spec changes should probably
be agreed by the community beforehand so the intern doesn't need to
worry about the protocol design (there's plenty of implementation work
to do!).

This is one way to break this down into an internship project, but there
are other approaches. Maybe you prefer to extend vhost-user more
gradually (e.g. no -device vdpa-user-pci and the existing per-type
device approach is continued) while still adding the vDPA protocol
messages...

Anyway, if you'd like to mentor this project in Outreachy December-March
please add a project idea to the QEMU wiki:
https://wiki.qemu.org/Outreachy_2020_DecemberMarch

Stefan

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