Re: Outline for VHOST_USER_PROTOCOL_F_VDPA

[Marc-André Lureau]

Hi

On Mon, Sep 28, 2020 at 1:25 PM Stefan Hajnoczi <stefanha@redhat.com wrote:
> Where this converges with multi-process QEMU
> --------------------------------------------
> At this point QEMU can run ad-hoc vhost-user backends using existing
> VIRTIO device models. It is possible to go further by creating a
> qemu-dev launcher executable that implements the vhost-user spec's
> "Backend program conventions". This way a minimal device emulator
> executable hosts the device instead of a full system emulator.
>
> The requirements for this are similar to the multi-process QEMU effort,
> which aims to run QEMU devices as separate processes. One of the main
> open questions is how to design build system and Kconfig support for
> building minimal device emulator executables.
>
> In the case of vhost-user-net the qemu-dev-vhost-user-net executable
> would contain virtio-net-device, vhost-user-backend, any netdevs the
> user wishes to include, a QMP monitor, and a vhost-user backend
> command-line interface.
>
> Where does this leave us? QEMU's existing VIRTIO device models can be
> used as vhost-user devices and run in a separate processes from the VMM.
> It's a great way of reusing code and having the flexibility to deploy it
> in the way that makes most sense for the intended use case.
>

My understanding is that this would only be able to expose virtio
devices from external processes. But vfio-user could expose more kinds
of devices, including the virtio devices.

Shouldn't we focus on vfio-user now, as the general out-of-process
device solution?