Re: [XEN PATCH v2 00/10] address violations of MISRA C:2012 Directive 4.10

[Stefano Stabellini <stefano.stabellini@xxxxxxx>]

On Fri, 20 Oct 2023, Jan Beulich wrote:
> On 19.10.2023 18:19, Stefano Stabellini wrote:
> > On Thu, 19 Oct 2023, Jan Beulich wrote:
> >> On 19.10.2023 02:44, Stefano Stabellini wrote:
> >>> On Wed, 18 Oct 2023, Jan Beulich wrote:
> >>>> On 18.10.2023 02:48, Stefano Stabellini wrote:
> >>>>> On Mon, 16 Oct 2023, Jan Beulich wrote:
> >>>>>> On 29.09.2023 00:24, Stefano Stabellini wrote:
> >>>>>>> If it is not a MISRA requirement, then I think we should go for the 
> >>>>>>> path
> >>>>>>> of least resistance and try to make the smallest amount of changes
> >>>>>>> overall, which seems to be:
> >>>>>>
> >>>>>> ... "least resistance" won't gain us much, as hardly any guards don't
> >>>>>> start with an underscore.
> >>>>>>
> >>>>>>> - for xen/include/blah.h, __BLAH_H__
> >>>>>>> - for xen/arch/arm/asm/include/blah.h, __ASM_ARM_BLAH_H__
> >>>>>>> - for xen/arch/x86/asm/include/blah.h, it is far less consistent, 
> >>>>>>> maybe __ASM_X86_BLAH_H__ ?
> >>>>>>
> >>>>>> There are no headers in xen/include/. For (e.g.) xen/include/xen/ we
> >>>>>> may go with XEN_BLAH_H; whether ASM prefixes are needed I'm not sure;
> >>>>>> we could go with just ARM_BLAH_H and X86_BLAH_H?
> >>>>>>
> >>>>>> The primary question though is (imo) how to deal with private headers,
> >>>>>> such that the risk of name collisions is as small as possible.
> >>>>>
> >>>>> Looking at concrete examples under xen/include/xen:
> >>>>> xen/include/xen/mm.h __XEN_MM_H__
> >>>>> xen/include/xen/dm.h __XEN_DM_H__
> >>>>> xen/include/xen/hypfs.h __XEN_HYPFS_H__
> >>>>>
> >>>>> So I think we should do for consistency:
> >>>>> xen/include/xen/blah.h __XEN_BLAH_H__
> >>>>>
> >>>>> Even if we know the leading underscore are undesirable, in this case I
> >>>>> would prefer consistency.
> >>>>
> >>>> I'm kind of okay with that. FTAOD - here and below you mean to make this
> >>>> one explicit first exception from the "no new leading underscores" goal,
> >>>> for newly added headers?
> >>>
> >>> Yes. The reason is for consistency with the existing header files.
> >>>
> >>>
> >>>>> On the other hand looking at ARM examples:
> >>>>> xen/arch/arm/include/asm/traps.h __ASM_ARM_TRAPS__
> >>>>> xen/arch/arm/include/asm/time.h __ARM_TIME_H__
> >>>>> xen/arch/arm/include/asm/sysregs.h __ASM_ARM_SYSREGS_H
> >>>>> xen/arch/arm/include/asm/io.h _ASM_IO_H
> >>>>>
> >>>>> And also looking at x86 examples:
> >>>>> xen/arch/x86/include/asm/paging.h _XEN_PAGING_H
> >>>>> xen/arch/x86/include/asm/p2m.h _XEN_ASM_X86_P2M_H
> >>>>> xen/arch/x86/include/asm/io.h _ASM_IO_H
> >>>>>
> >>>>> Thet are very inconsistent.
> >>>>>
> >>>>>
> >>>>> So for ARM and X86 headers I think we are free to pick anything we want,
> >>>>> including your suggested ARM_BLAH_H and X86_BLAH_H. Those are fine by
> >>>>> me.
> >>>>
> >>>> To be honest, I'd prefer a global underlying pattern, i.e. if common
> >>>> headers are "fine" to use leading underscores for guards, arch header
> >>>> should, too.
> >>>
> >>> I am OK with that too. We could go with:
> >>> __ASM_ARM_BLAH_H__
> >>> __ASM_X86_BLAH_H__
> >>>
> >>> I used "ASM" to make it easier to differentiate with the private headers
> >>> below. Also the version without "ASM" would work but it would only
> >>> differ with the private headers in terms of leading underscores. I
> >>> thought that also having "ASM" would help readability and help avoid
> >>> confusion.
> >>>
> >>>
> >>>>> For private headers such as:
> >>>>> xen/arch/arm/vuart.h __ARCH_ARM_VUART_H__
> >>>>> xen/arch/arm/decode.h __ARCH_ARM_DECODE_H_
> >>>>> xen/arch/x86/mm/p2m.h __ARCH_MM_P2M_H__
> >>>>> xen/arch/x86/hvm/viridian/private.h X86_HVM_VIRIDIAN_PRIVATE_H
> >>>>>
> >>>>> More similar but still inconsistent. I would go with ARCH_ARM_BLAH_H and
> >>>>> ARCH_X86_BLAH_H for new headers.
> >>>>
> >>>> I'm afraid I don't like this, as deeper paths would lead to unwieldy
> >>>> guard names. If we continue to use double-underscore prefixed names
> >>>> in common and arch headers, why don't we demand no leading underscores
> >>>> and no path-derived prefixes in private headers? That'll avoid any
> >>>> collisions between the two groups.
> >>>
> >>> OK, so for private headers:
> >>>
> >>> ARM_BLAH_H
> >>> X86_BLAH_H
> >>>
> >>> What that work for you?
> >>
> >> What are the ARM_ and X86_ prefixes supposed to indicate here? Or to ask
> >> differently, how would you see e.g. common/decompress.h's guard named?
> > 
> > I meant that:
> > 
> > xen/arch/arm/blah.h would use ARM_BLAH_H
> > xen/arch/x86/blah.h would use X86_BLAH_H
> > 
> > You have a good question on something like xen/common/decompress.h and
> > xen/common/event_channel.h.  What do you think about:
> > 
> > COMMON_BLAH_H, so specifically COMMON_DECOMPRESS_H
> > 
> > otherwise:
> > 
> > XEN_BLAH_H, so specifically XEN_DECOMPRESS_H
> > 
> > I prefer COMMON_BLAH_H but I think both versions are OK.
> 
> IOW you disagree with my earlier "... and no path-derived prefixes",
> and you prefer e.g. DRIVERS_PASSTHROUGH_VTD_DMAR_H as a consequence?
> FTAOD my earlier suggestion was simply based on the observation that
> the deeper the location of a header in the tree, the more unwieldy
> its guard name would end up being if path prefixes were to be used.

I don't have a strong opinion on "path-derived prefixes". I prefer
consistency and easy-to-figure-out guidelines over shortness.

The advantage of a path-derived prefix is that it is trivial to figure
out at first glance. If we can come up with another system that is also
easy then fine. Do you have a suggestion? If so, sorry I missed it.