Re: [Xen-devel] [PATCH 03/17] xen/mm: Move the MM types in a separate header

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.03.2020 19:09, Julien Grall wrote:
> Hi Jan,
> 
> On 25/03/2020 15:00, Jan Beulich wrote:
>> On 22.03.2020 17:14, julien@xxxxxxx wrote:
>>> From: Julien Grall <jgrall@xxxxxxxxxx>
>>>
>>> It is getting incredibly difficult to use typesafe GFN/MFN/PFN in the
>>> headers because of circular dependency. For instance, asm-x86/page.h
>>> cannot include xen/mm.h.
>>>
>>> In order to convert more code to use typesafe, the types are now moved
>>> in a separate header that requires only a few dependencies.
>>
>> We definitely need to do this, so thanks for investing the
>> time. I think though that we want to settle up front (and
>> perhaps record in a comment in the new header) what is or
>> is not suitable to go into the new header. After all you're
>> moving not just type definitions, but also simple helper
>> functions.
> 
> I am expecting headers to use the typesafe helpers (such mfn_add)
> in the long term. So I would like the new header to contain the
> type definitions and any wrappers that would turn 'generic'
> operations safe.
> 
> I am not entirely sure yet how to formalize the rules in the
> header. Any ideas?

Well, if the header was just for the typesafe types, it could be
renamed (to e.g. mm-typesafe.h) and be left without any respective
comment. The issue I've mentioned arises if, with its currently
suggested name, further types get added. In such a case perhaps it
could be "type definitions and their immediate accessors,
involving no other non-trivial types"?

Jan