Re: [Xen-devel] [PATCH v4 12/16] xen/mm: Switch common/memory.c to use typesafe MFN

["Jan Beulich" <jbeulich@xxxxxxxx>]

>>> Julien Grall <julien.grall@xxxxxxx> 03/11/18 8:44 PM >>>
>On 03/09/2018 05:33 PM, Wei Liu wrote:
>> On Mon, Mar 05, 2018 at 07:41:54AM -0700, Jan Beulich wrote:
>>>>>> On 05.03.18 at 15:18, <julien.grall@xxxxxxx> wrote:
>>>> Also, do you have an opinion on Wei's suggestion:
>>>>
>>>> "What I meant was to make copy_{to,from}_guest* type-safe. I just feel it
>>>> a bit strange you only created a wrapper for this file. I wonder why.
>>>>
>>>> Note I'm just asking question. That's not necessarily a good idea to
>>>> turn them all in the end."
>>>
>>> Well, I didn't really understand what he's after (in the context of
>>> this series) - copy_{to,from}_guest() don't take or return MFNs or
>>> GFNs.
>>>
>> 
>> Fundamentally Julien's patch is to wrap around an existing API for this
>> one file only. Why is this file special? Why not just make that class of
>> APIs do what he wants?
>> 
>> But that is going to be intrusive and a bit counter-intuitive.
>
>I have quickly looked at it. The major problem I can see is it is not 
>possible to generically define for any typesafe. Indeed, TYPE_SAFE(...) 
>cannot define new macro and, AFAICT, it is not feasible to define static 
>inline for copy_* helpers.
>
>So we would need to introduce macros for each typesafe by hand. I can 
>move copy_mfn_to_guest in xen/mm.h if people think it could be useful.

First of all - how often do we copy in/out individual MFNs? Not in many places,
I think. Hence I'm afraid I continue to not see the value of such a construct,
especially not as a wider-than-file-scope one.

Jan


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