linux-kernel - Re: [PATCH] docs: deprecated.rst: Add note to the use of struct

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Date:   Thu, 4 Jun 2020 14:33:47 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: Re: [PATCH] docs: deprecated.rst: Add note to the use of
 struct_size() helper

On Thu, Jun 04, 2020 at 04:19:03PM -0500, Gustavo A. R. Silva wrote:
> On Thu, Jun 04, 2020 at 01:25:26PM -0700, Kees Cook wrote:
> > On Thu, Jun 04, 2020 at 01:21:23PM -0500, Gustavo A. R. Silva wrote:
> > > Yeah. My reasoning for is that it will take a while --at least one 
> > > development cycle more-- to completely get rid of all the 0/1-arrays.
> > 
> > Right -- but we need a place to point people when we tell them "please
> > don't use 0-byte and 1-byte arrays", and the deprecated.rst is the place
> > for that.
> > 
> > Having it in deprecated.rst once they're all gone only serves to explain
> > why various compiler flags are enabled, etc. But while they're being
> > removed, it serves as a single place to document the issue (as in, much
> > of the flex-array patch commit log "boilerplate" can actually be
> > repeated in deprecated.rst.
> > 
> > > But I think we can add this note while I continue working on the flexible-array
> > > conversions. Once that work is complete, I can go back and update the
> > > documentation. :)
> > > 
> > > What do you think?
> > 
> > I think we need to document it at the beginning of the work (and I
> > should have asked for this earlier). So let's just add a new section on
> > dynamic array usage, etc. It can include a note about struct_size() as
> > an example for why 1-byte arrays are so weird. :)
> > 
> 
> Got ya. :)
> 
> One last thing... I was thinking on adding such section (dynamic array
> usage) to coding-style.rst, explaining how to use struct_size() and
> transform the different open-coded versions we currently have in the
> kernel, e.g. I have seen people use offsetof() --and sometimes open-coded
> versions of sizeof_field()-- and its open-coded version to do arithmetic
> in allocator arguments.

Yeah, that sounds good to me!

-Kees

> 
> Thanks
> --
> Gustavo
> 

-- 
Kees Cook