Re: [Xen-devel] [PATCH v3 for-next 0/4] xen: Convert __page_to_mfn and _mfn_to_page to use typesafe MFN

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Jan,

On 06/11/17 11:37, Jan Beulich wrote:
> > > > On 01.11.17 at 15:03, <julien.grall@xxxxxxxxxx> wrote:
> > Most of the users of page_to_mfn and mfn_to_page are either overriding
> > the macros to make them work with mfn_t or use mfn_x/_mfn becaue the rest
> > of the function use mfn_t.
> >
> > So I think it is time to make __page_to_mfn and __mfn_to_page using typesafe
> > MFN.
> I have to admit that I still find the overall goal confusing: Afaict
> the double-underscore-prefixed versions exist only to allow
> easily overriding the non-prefixed ones. Hence the first and
> foremost goal ought to be to convert everyone to using the
> non-prefixed versions. Files wanting to avoid the typed forms
> could then continue to use / be switched to the prefixed ones.
>
> What you're doing here is producing a mess: The prefixed
> versions should never have been touched in the first place.
> And iirc this was discussed before, with the suggestion to use
> overrides (for the non-prefixed versions) to limit overall patch
> size.
At the end of the discussion in the previous version, you were happy 
with the modification done here (see [1]).
Overall, I think this is an improvement compare to what we have today. 
Because we enforce the use of MFN typesafe by default. The developer 
would have to override the helpers if he wants to to use the 
non-typesafe version.
With your suggestion here, you would just keep the override around even 
when they are not necessary. They will have to be dropped at some point, 
so why not now?
Cheers,

[1] 
https://lists.xenproject.org/archives/html/xen-devel/2017-10/msg00986.html
> Jan
--
Julien Grall

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