Re: [PATCH for-4.16 2/2] xen: Report grant table v1/v2 capabilities to the toolstack

[Jan Beulich <jbeulich@suse.com>]

On 30.10.2021 13:20, Roger Pau Monné wrote:
> On Fri, Oct 29, 2021 at 06:38:13PM +0100, Andrew Cooper wrote:
>> In order to let the toolstack be able to set the gnttab version on a
>> per-domain basis, it needs to know which ABIs Xen supports.  Introduce
>> XEN_SYSCTL_PHYSCAP_gnttab_v{1,2} for the purpose, and plumb in down into
>> userspace.
> 
> I did consider exposing the versions supported together with
> max_{grant,maptrack}_frames using a new grant-table dedicated sysctl,
> but maybe it's fine to expose the version as a physcap and fetch the
> other two separately?
> 
> I certainly didn't look much into this, maybe it's pointless to expose
> max_{grant,maptrack}_frames. I think the toolstack will need to be
> able to fetch grant related limits on a per-domain basis like we plan
> to do with the grant version in order to assert the destination host
> supports the current limit applied to the domain.

I think the other two are a better fit to expose via hypfs (alongside
the version). And indeed they are being exposed there already, just
not the version (which would imo belong there for completeness, not
to replace the exposure as a physcap here).

Jan