Re: [Xen-devel] [PATCH v9 5/7] memory: add check_get_page_from_gfn() as a wrapper...

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.09.18 at 10:54, <Paul.Durrant@xxxxxxxxxx> wrote:
>>  -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: 19 September 2018 09:34
>> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
>> Cc: Julien Grall <julien.grall@xxxxxxx>; Andrew Cooper
>> <Andrew.Cooper3@xxxxxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxx>; Ian
>> Jackson <Ian.Jackson@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Stefano
>> Stabellini <sstabellini@xxxxxxxxxx>; xen-devel <xen-
>> devel@xxxxxxxxxxxxxxxxxxxx>; Konrad Rzeszutek Wilk
>> <konrad.wilk@xxxxxxxxxx>; Tim (Xen.org) <tim@xxxxxxx>
>> Subject: RE: [Xen-devel] [PATCH v9 5/7] memory: add
>> check_get_page_from_gfn() as a wrapper...
>> 
>> >>> On 19.09.18 at 09:56, <Paul.Durrant@xxxxxxxxxx> wrote:
>> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> >> Sent: 19 September 2018 07:03
>> >>
>> >> >>> On 18.09.18 at 18:37, <Paul.Durrant@xxxxxxxxxx> wrote:
>> >> > Moving to p2m-common won't work. The function declaration involves a
>> >> > p2m_type_t argument and that enum is defined in the arm and x86
>> specific
>> >> > headers. I propose therefore to leave this patch as-is.
>> >>
>> >> Leaving the duplication in place is just the last resort imo. Does
>> >> xen/mm.h
>> >> not work either?
>> >
>> > No, it won't. It has to be something *after* the definition of the
>> > p2m_type_t enum. I could, as Julien suggested, move the inclusion of
>> > p2m-common after that point, but it would mean the header guards would
>> cease
>> > to DTRT of course. I'm not sure whether C will allow me to forward
>> declare
>> > the enum (not something I've tried) but I could give that a go. Any
>> other
>> > suggestions?
>> 
>> I'm afraid I don't understand your concern wrt include guards. Each header
>> has its own. I'm actually surprised the current inclusion point is at the
>> top
>> of the file, rather than after at least the basic type definitions each
>> arch
>> has to supply.
>> 
> 
> Ok, if we include p2m-common in the middle of p2m, and then add stuff 
> dependent on the declaration of p2m_type_t, what happens when a source module 
> explicitly includes p2m-common prior to p2m?

This is not supposed to happen, as this header is supposed to only be
included from the per-arch p2m.h; we should put an #error there. I
see there's exactly one violation of this (drivers/vpci/header.c). But
your series can go in as is; I'll try to remember to clean this up.

Jan



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