On 21.09.2022 16:03, Marek Marczykowski-Górecki wrote:
> Some sparse notes from the design session:
>
> Passing backend domid ideas:
> - via xenstore: good - can be done now; bad - requires xenstore even if
> only virtio devices are used
> - extend generic part of virtio spec: takes time, but otherwise
> preferred
>
> New "config" virtio device - for configuring backends
>
> Hotplug:
> - ACPI (for HVM at least)
> - xenstore
>
>
> ACTION: Start the virtio spec change.
>
> In the meantime, use xenstore(?)
>
> qemu parameters are device-specific - adding backend id needs to be done for
> every device type - both at qemu side, and libxl side
>
> Device endpoint ID are currently allocated by qemu - for driver domains that
> needs to be moved to the toolstack, to reserve space for devices running in
> other backends.
Thanks for the separate notes, which are certainly helpful on top of
the ones I took. Plus I'll admit I was struggling some with typing and
listening at the same time, so I surely missed pieces (besides
likely also having screwed up here and there). Corrections and alike
appreciated ...
Jürgen - working: frontend/backend but no connecting
- prototype using device tree
- generic solution needed
- ACPI (on x86 at least)? DT (dynamic)? Xenstore?
- for frontends: limited but generic xs entries (central driver)
Marek - Isn't there a virtio mechansim for figuring domid?
Jürgen - would need extending virtio, also for hotplug
- ACPI (for hotplug) not an option for PV guests
George - concerns regarding the use of Xenstore
- at least for static configs it would be nice to do without
Jürgen - option: new virtio device type for passing config information
Marek - Use PCI IDs or alike?
Jürgen - potentially risky going forward (compatibility-wise)
- (excurse to some KVM side aspects, which might also need e.g. such
a config device for certain purposes)
George - Is there a config device already which we could extend?
Jürgen - No, new type needed.
Roger - vPCI usable (for its config space)?
Jürgen - needs extending the virtio spec, preferably for all devices to
represent data consistently (which may take long)
Roger - Use VPD?
Jürgen - still in (global) config space, hence needs specifying
George - Transitory alternative until virtio spec was updated?
Jürgen - backend (ad ioreq server) params perhaps best over Xenstore
- if PV, ioreq server would need hooking up (if to be used)
George - PV requiring Xenstore?
Jürgen - alternatives are (in theory) possible
- Result: Aim at virtio spec change plus introduce config device
- Intermediate: Xenstore?
Anthony - Prototype?
Jürgen - xl/libxl changes needed in addition
George - 1) dom0-only + all grants (global), 2) xenstore (which would
want to continue to work, once 3) config device is there)
Anthony - allocation of PCI IDs currently in qemu, want to move to tools
Marek - How to launch backend in drvdom?
Jürgen - one config device per backend domain
Jan
