linux-kernel - Re: [PATCH][next] mei: Avoid the use of one-element arrays

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Date:   Tue, 14 Jul 2020 15:13:24 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     "Winkler, Tomas" <tomas.winkler@...el.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][next] mei: Avoid the use of one-element arrays

On Tue, Jul 14, 2020 at 07:57:51PM +0000, Winkler, Tomas wrote:
> > 
> > On Tue, Jul 14, 2020 at 05:54:32PM +0000, Winkler, Tomas wrote:
> > > >
> > > > There is a regular need in the kernel to provide a way to declare
> > > > having a dynamically sized set of trailing elements in a structure.
> > > > Kernel code should always use “flexible array members”[1] for these
> > > > cases or, as in this particular case, replace the one-element array
> > > > with a simple value type u8 reserved once this is just a placeholder
> > > > for alignment. The older style of one-element or zero-length arrays
> > should no longer be used[2].
> > > >
> > > > Also, while there, use the preferred form for passing a size of a struct.
> > > > The alternative form where struct name is spelled out hurts
> > > > readability and introduces an opportunity for a bug when the
> > > > variable type is changed but the corresponding sizeof that is passed as
> > argument is not.
> > > >
> > > > [1] https://en.wikipedia.org/wiki/Flexible_array_member
> > > > [2] https://github.com/KSPP/linux/issues/79
> > > >
> > > > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> > > I'm okay with the patch but in this case the description is a bit off.
> > > In this case there was no intention for a flexible arrays its just a reserved
> > field.
> > >
> > 
> > The reserved field is actually mentioned in the description:
> > 
> > "... or, as in this particular case, replace the one-element array with a simple
> > value type u8 reserved once this is just a placeholder for alignment."
> 
> Right, but it looks not connected to overall context, it looks like not very clean reuse of a commit message.
> I would say that this reserved[1] rather had confused the detection scripts you are using for the  cleanup you are doing. 
> Again, I'm okay with the patch, but if you can  reword the commit message it would be even more okay.
> 

Yep; I've come up with a more concise text for these sorts of cases:

"One-element arrays are being deprecated[1]. Replace the one-element
array with a simple value type u8 reserved, once this is just a
placeholder for alignment.

[1] https://github.com/KSPP/linux/issues/79"

I'll send v2 with the text above, shortly.

Thanks for the feedback.
--
Gustavo