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

From: Julien Grall <julien@xen.org>
To: Jan Beulich <jbeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Julien Grall <jgrall@amazon.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [PATCH 03/17] xen/mm: Move the MM types in a separate header
Date: Sat, 28 Mar 2020 10:15:10 +0000	[thread overview]
Message-ID: <04cc7785-176d-87d0-8966-214ab0986e45@xen.org> (raw)
In-Reply-To: <e2396098-1c65-835c-533f-dfc0cfe3fa0e@suse.com>

Hi Jan,

On 26/03/2020 09:02, Jan Beulich wrote:
> 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@xen.org wrote:
>>>> From: Julien Grall <jgrall@amazon.com>
>>>>
>>>> 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"?

I will rename the file to mm-typesafe.h.

Cheers,

-- 
Julien Grall