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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

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.


> 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.