Re: [PATCH V2 09/23] xen/dm: Make x86's DM feature common

[Jan Beulich <jbeulich@xxxxxxxx>]

On 15.10.2020 18:44, Oleksandr Tyshchenko wrote:
> From: Julien Grall <julien.grall@xxxxxxx>
> 
> As a lot of x86 code can be re-used on Arm later on, this patch
> splits devicemodel support into common and arch specific parts.
> 
> The common DM feature is supposed to be built with IOREQ_SERVER
> option enabled (as well as the IOREQ feature), which is selected
> for x86's config HVM for now.

Did you consider doing it the other way around? It would seem
more natural to have the top level dm-op handling arch-specific
and call into e.g. ioreq_server_dm_op() for otherwise unhandled
ops, just like e.g. do_domctl() calls into iommu_do_domctl()
(indirectly via arch_do_domctl()). I ask because in the long
run I expect the ioreq server sub-ops to only be a small part
of the overall set of dm-ops; already now it's 7 out of 18 if
I got the counting right.

This would then also leave compat_dm_op() in x86 code.

But yes, there are also downsides with this alternative.

Jan