Re: [RFC PATCH 17/17] CODING_STYLE: Add a section on header guards naming conventions

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 18 Jul 2024, Jan Beulich wrote:
> On 18.07.2024 01:02, Stefano Stabellini wrote:
> > On Wed, 17 Jul 2024, Jan Beulich wrote:
> >> On 17.07.2024 02:20, Stefano Stabellini wrote:
> >>> On Tue, 16 Jul 2024, Jan Beulich wrote:
> >>>> On 16.07.2024 02:43, Stefano Stabellini wrote:
> >>>>> On Mon, 15 Jul 2024, Jan Beulich wrote:
> >>>>>> On 13.07.2024 00:38, Stefano Stabellini wrote:
> >>>>>>> On Wed, 3 Jul 2024, Jan Beulich wrote:
> >>>>>>>> I further have to note that, as indicated during the earlier 
> >>>>>>>> discussion,
> >>>>>>>> I still cannot see how occasional ambiguity is going to be dealt 
> >>>>>>>> with.
> >>>>>>>> IOW from the rules above two different headers could still end up 
> >>>>>>>> with
> >>>>>>>> the same guard identifier.
> >>>>>>>
> >>>>>>> Maybe something like this?
> >>>>>>>
> >>>>>>> "In the event of naming collisions, exceptions to the coding style may
> >>>>>>> be made at the discretion of the contributor and maintainers."
> >>>>>>
> >>>>>> Hmm, maybe I wasn't clear enough then. My take is that the scheme 
> >>>>>> should
> >>>>>> simply not allow for possible collisions. Neither the contributor nor 
> >>>>>> the
> >>>>>> reviewer may spot such a collision, and it may therefore take until the
> >>>>>> first full scan that one is actually noticed. Which I consider too late
> >>>>>> in the process, even if we already were at the point where commits were
> >>>>>> checked pre-push.
> >>>>>
> >>>>> Looking at the proposal, copy/pasted here for convenience:
> >>>>>
> >>>>> - private headers -> <dir>_<filename>_H
> >>>>> - asm-generic headers -> ASM_GENERIC_<filename>_H
> >>>>>     - #ifndef ASM_GENERIC_X86_PERCPU_H
> >>>>>       #define ASM_GENERIC_X86_PERCPU_H
> >>>>>       //...
> >>>>>       #endif /* ASM_GENERIC_X86_PERCPU_H */
> >>>>> - arch/<architecture>/include/asm/<subdir>/<filename>.h -> 
> >>>>> ASM_<architecture>_<subdir>_<filename>_H
> >>>>>     - #ifndef ASM_X86_DOMAIN_H
> >>>>>       #define ASM_X86_DOMAIN_H
> >>>>>       //...
> >>>>>       #endif /* ASM_X86_DOMAIN_H */
> >>>>> - xen/include/xen/<filename>.h -> XEN_<filename>_H
> >>>>> - xen/include/xen/<subdir>/<filename>.h -> XEN_<subdir>_<filename>_H
> >>>>>
> >>>>>
> >>>>> The only possibility for collision that I can see is from the first
> >>>>> point:
> >>>>>
> >>>>> - private headers -> <dir>_<filename>_H
> >>>>
> >>>> I don't think this is the only possibility of collisions. The 
> >>>> <subdir>_<filename>
> >>>> parts can similarly cause problems if either of the two involved names 
> >>>> contains
> >>>> e.g. a dash (which would need converting to an underscore) or an 
> >>>> underscore. To
> >>>> avoid this, the name separators (slashes in the actual file names) there 
> >>>> may need
> >>>> representing by double underscores.
> >>>
> >>> I am OK with you two underscores as name separator (slashes in the
> >>> actual file names). Would you do it for all levels like this?
> >>>
> >>> - arch/arm/arm64/lib/something.h -> ARM__ARM64__LIB__SOMETHING_H
> >>> - arch/arm/arm32/lib/something.h -> ARM__ARM32__LIB__SOMETHING_H
> >>> - arch/x86/lib/something.h -> X86__LIB__SOMETHING_H
> >>>
> >>>
> >>> I think it is better than the below:
> >>>
> >>> - arch/arm/arm64/lib/something.h -> ARM_ARM64__LIB__SOMETHING_H
> >>> - arch/arm/arm32/lib/something.h -> ARM_ARM32__LIB__SOMETHING_H
> >>> - arch/x86/lib/something.h -> X86_LIB__SOMETHING_H
> >>
> >> Hmm, maybe it's indeed better to do it entirely uniformly then.
> > 
> > 
> > Do we have agreement on the naming convention then? 
> > 
> > 
> > - private headers -> <dir>__<filename>__H
> >     - arch/arm/arm64/lib/something.h -> ARM__ARM64__LIB__SOMETHING_H
> >     - arch/arm/arm32/lib/something.h -> ARM__ARM32__LIB__SOMETHING_H
> >     - arch/x86/lib/something.h -> X86__LIB__SOMETHING_H
> > 
> > - asm-generic headers -> ASM_GENERIC_<filename>_H
> >     - include/asm-generic/percpu.h -> ASM_GENERIC_X86_PERCPU_H
> > 
> > - arch/<architecture>/include/asm/<subdir>/<filename>.h -> 
> > ASM_<architecture>_<subdir>_<filename>_H
> >     - arch/x86/include/asm/domain.h -> ASM_X86_DOMAIN_H
> > 
> > - include/xen -> XEN_<filename>_H
> >     - include/xen/percpu.h -> XEN_PERCPU_H
> > 
> > 
> > Or do you prefer the double underscore __  in all cases?
> 
> It's not so much prefer, but a requirement if we want to be future proof.
> Even for ASM_GENERIC_* that'll be needed, as your outline above simply
> doesn't mention the (future) case of there being subdir-s there (see how
> Linux already has some). Imo the question doesn't even arise for XEN_*,
> as xen/ has subdir-s already.

OK. So it becomes:

- private headers -> <dir>__<filename>_H
    - arch/arm/arm64/lib/something.h -> ARM__ARM64__LIB__SOMETHING_H
    - arch/arm/arm32/lib/something.h -> ARM__ARM32__LIB__SOMETHING_H
    - arch/x86/lib/something.h -> X86__LIB__SOMETHING_H

- asm-generic headers -> ASM_GENERIC__<filename>_H
    - include/asm-generic/percpu.h -> ASM_GENERIC__X86__PERCPU_H

- arch/<architecture>/include/asm/<subdir>/<filename>.h -> 
ASM__<architecture>__<subdir>__<filename>_H
    - arch/x86/include/asm/domain.h -> ASM__X86__DOMAIN_H

- include/xen -> XEN__<filename>_H
    - include/xen/percpu.h -> XEN__PERCPU_H

If we have found agreement then Alessandro could send an update