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Re: [XEN PATCH v6] CODING_STYLE: Add a section on header guards naming conventions


  • To: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 12 Sep 2024 17:05:10 +0200
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  • Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Alessandro Zucchelli <alessandro.zucchelli@xxxxxxxxxxx>, consulting@xxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 12 Sep 2024 15:05:15 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 12.09.2024 17:03, Frediano Ziglio wrote:
> On Thu, Sep 12, 2024 at 3:35 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> On 12.09.2024 03:13, Stefano Stabellini wrote:
>>> On Tue, 10 Sep 2024, Jan Beulich wrote:
>>>> On 10.09.2024 06:57, Stefano Stabellini wrote:
>>>>> On Mon, 9 Sep 2024, Jan Beulich wrote:
>>>>>> On 05.09.2024 17:48, Alessandro Zucchelli wrote:
>>>>>>> This section explains which format should be followed by header
>>>>>>> inclusion guards via a drop-down list of rules.
>>>>>>>
>>>>>>> No functional change.
>>>>>>>
>>>>>>> Signed-off-by: Alessandro Zucchelli <alessandro.zucchelli@xxxxxxxxxxx>
>>>>>>>
>>>>>>> ---
>>>>>>> Changes in v6:
>>>>>>> - edit inclusion guards naming conventions, including more details
>>>>>>
>>>>>> Yet I'm afraid that from my pov we're still not there. Specifically ...
>>>>>>
>>>>>>> --- a/CODING_STYLE
>>>>>>> +++ b/CODING_STYLE
>>>>>>> @@ -159,6 +159,34 @@ Emacs local variables
>>>>>>>  A comment block containing local variables for emacs is permitted at
>>>>>>>  the end of files.  It should be:
>>>>>>>
>>>>>>> +Header inclusion guards
>>>>>>> +-----------------------
>>>>>>> +
>>>>>>> +Unless otherwise specified, all header files should include proper
>>>>>>> +guards to prevent multiple inclusions. The following naming conventions
>>>>>>> +apply:
>>>>>>
>>>>>> ... reading this, I can't derive ...
>>>>>>
>>>>>>> +- 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
>>>>>>
>>>>>> ... the absence of an equivalent of the arch/ part of the path. As per
>>>>>> my recollection we agreed on that shortening, but it needs spelling out
>>>>>> in the textual description. Such that it is possible to derived what to
>>>>>> uses as a name for, say, a header under common/, crypto/, or drivers/
>>>>>> (or anywhere else of course). Specifically with the further examples ...
>>>>>
>>>>> Are you asking for something like this?
>>>>>
>>>>> Omit the word "arch" from the filepath.
>>>>>
>>>>> If you prefer an alternative wording please suggest the text.
>>>>>
>>>>>
>>>>>>> +- asm-generic headers: ASM_GENERIC__<filename>_H
>>>>>>> +    - include/asm-generic/something.h -> ASM_GENERIC__SOMETHING_H
>>>>>>> +
>>>>>>> +- arch-specific headers: ASM__<architecture>__<subdir>__<filename>_H
>>>>>>> +    - arch/x86/include/asm/something.h -> ASM__X86__SOMETHING_H
>>>>>>
>>>>>> ... here and ...
>>>>>
>>>>> Suggested text:
>>>>>
>>>>> Omit the words "arch" and "include/asm" from the filepath, ASM is also
>>>>> prefixed.
>>>>>
>>>>>
>>>>>>> +- Xen headers: XEN__<filename>_H
>>>>>>> +    - include/xen/something.h -> XEN__SOMETHING_H
>>>>>>
>>>>>> ... here, where more than just one path component is omitted, deriving
>>>>>> what's meant can end up ambiguous. Yet ambiguity is what we absolutely
>>>>>> want to avoid, to preempt later discussions on any such naming.
>>>>>
>>>>> Suggested text:
>>>>>
>>>>> Omit the words "include/xen" from the filepath, XEN is always prefixed.
>>>>>
>>>>> Please suggest a specific alternative if you prefer
>>>>
>>>> Looks like I still didn't get across my point: The verbal description
>>>> that's ahead of all of the examples should be complete enough to describe
>>>> the whole set of rules, in sufficiently abstract terms. Then the examples
>>>> will be easy to prove as fitting those rules, and it will be easy to
>>>> derive the naming for further identifiers. IOW - no, I'm not asking for
>>>> the examples to be further commented, but for the naming rules to be
>>>> _fully_ spelled out.
>>>
>>>
>>> Hi Jan, we have gone back and forth on this a few times, but neither
>>> Alessandro nor I fully understand your perspective. To help streamline
>>> the process and save time for everyone, I suggest you provide an example
>>> of the rules written in the style you believe is appropriate. Once you
>>> set the initial direction, Alessandro and I can continue and complete
>>> the rest in that preferred style.
>>
>> If you really expect me to do so (hence effectively me becoming the one
>> to make the proposal, which I never meant to), it'll have to wait until
>> I'm back from the GNU Tools Cauldron and the PTO I'm taking immediately
>> afterwards.
>>
>> Jan
>>
>>> On a related note, I have encountered formal specifications that use less
>>> formal language than this simple code style and naming convention
>>> adjustment. I feel we might be over-engineering this, and in my opinion,
>>> the current version is sufficient. Any additional time spent on this
>>> could be better used addressing MISRA violations that pose real safety
>>> risks for Xen users.
> 
> Why not just following the simple rule?
> If file is arch/arm/arm64/lib/something.h have a
> ARCH__ARM__ARM64__LIB__SOMETHING_H guard, if file is
> arch/x86/lib/something.h have a ARCH__X86__LIB__SOMETHING_H guard.

We've been there before: Identifiers get overly long this way.

Jan



 


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