Re: [PATCH 2/2] docs/misra: add Rule 5.1

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

> On 26 May 2022, at 10:40, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> 
> On 26.05.2022 03:18, Stefano Stabellini wrote:
>> On Wed, 25 May 2022, Jan Beulich wrote:
>>> On 25.05.2022 02:35, Stefano Stabellini wrote:
>>>> From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
>>>> 
>>>> Add Rule 5.1, with the additional note that the character limit for Xen
>>>> is 63 characters.
>>>> 
>>>> The max length identifiers found by ECLAIR are:
>>>> 
>>>> __mitigate_spectre_bhb_clear_insn_start
>>>> domain_pause_by_systemcontroller_nosync
>>>> 
>>>> Both of them are 40 characters long. A limit of 63 characters work for
>>>> the existing code.
>>> 
>>> I have to admit that it hasn't become clear to me why we want to
>>> permit (if not to say encourage) the use of such long identifiers.
>>> If 40 is the longest we've got, why not limit it to 40 for now
>>> with a goal of further reducing? A 40-char symbol plus some
>>> indentation will already pose problems with 80-char line length.
>> 
>> We can go lower than 63 if we want to. I chose the closest power-of-two
>> length -1 for the NUL terminator. But it doesn't have to be a
>> power-of-two. So we could go with "41" if we want to.
>> 
>> Anyone in favor of that? I am happy with any number between 41 and 63.
> 
> Why 41, not 40? 41 seems yet more arbitrary to me than e.g. 40.
> 
>>> Otoh, as said on the call, I think the public headers want
>>> mentioning explicitly here in some way. Part of them (most or all
>>> of what's under io/) aren't used when building Xen, so won't be
>>> seen by Eclair (aiui). Yet they are a formal part of the code
>>> base, and e.g. ring.h has some pretty long names (albeit still
>>> below 40 chars as it looks). So once we're able to go down to e.g.
>>> 32 for the bulk of the code base, public headers should imo still
>>> be explicitly allowed to use longer identifiers.
>> 
>> Actually I thought about writing something for the public header but I
>> wasn't sure what to write. What about:
>> 
>> - Note: the Xen characters limit for identifiers is 41. Public headers
>> (xen/include/public/) are allowed to retain longer identifiers for
>> backward compatibility.
> 
> Fine with me, except I wonder in how far going forward we actually
> need to play by that limit there. Proper name-spacing is particularly
> important in the public headers, so may warrant a higher limit for
> certain (unusual?) circumstances.

I think we can have a “global” deviation for public headers with an higher
limit but there should still be a limit.

Bertrand

> 
> Jan