On 21.10.2023 01:26, Stefano Stabellini wrote: > 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.
Well, I kind of implicitly suggested "no path derived prefixes for private headers", albeit realizing that there's a chance then of guards colliding. I can't think of a good scheme which would fit all goals (no collisions, uniformity, and not unduly long). Jan
