netdev - Re: [PATCH][next] zd1211rw/zd_usb.h: Replace zero-length array with flexible-array member

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Message-ID: <48ff1333-0a14-36d8-9565-a7f13a06c974@embeddedor.com>
Date:   Tue, 10 Mar 2020 16:52:55 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Kalle Valo <kvalo@...eaurora.org>
Cc:     Joe Perches <joe@...ches.com>, Daniel Drake <dsd@...too.org>,
        Ulrich Kunitz <kune@...ne-taler.de>,
        "David S. Miller" <davem@...emloft.net>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jes.Sorensen@...il.com
Subject: Re: [PATCH][next] zd1211rw/zd_usb.h: Replace zero-length array with
 flexible-array member



On 3/10/20 8:56 AM, Kalle Valo wrote:
> + jes
> 
> "Gustavo A. R. Silva" <gustavo@...eddedor.com> writes:
> 
>> Hi,
>>
>> On 3/5/20 10:10, Kalle Valo wrote:
>>> Joe Perches <joe@...ches.com> writes:
>>>
>>>> On Thu, 2020-03-05 at 16:50 +0200, Kalle Valo wrote:
>>>>> "Gustavo A. R. Silva" <gustavo@...eddedor.com> writes:
>>>> []
>>>>>>  drivers/net/wireless/zydas/zd1211rw/zd_usb.h | 8 ++++----
>>>>>>  1 file changed, 4 insertions(+), 4 deletions(-)
>>>>>
>>>>> "zd1211rw: " is enough, no need to have the filename in the title.
>>>
>>>>> But I asked this already in an earlier patch, who prefers this format?
>>>>> It already got opposition so I'm not sure what to do.
>>>>
>>>> I think it doesn't matter.
>>>>
>>>> Trivial inconsistencies in patch subject and word choice
>>>> don't have much overall impact.
>>>
>>> I wrote in a confusing way, my question above was about the actual patch
>>> and not the the title. For example, Jes didn't like this style change:
>>>
>>> https://patchwork.kernel.org/patch/11402315/
>>>
>>
>> It doesn't seem that that comment adds a lot to the conversation. The only
>> thing that it says is literally "fix the compiler". By the way, more than
>> a hundred patches have already been applied to linux-next[1] and he seems
>> to be the only person that has commented such a thing.
> 
> But I also asked who prefers this format in that thread, you should not
> ignore questions from two maintainers (me and Jes).
> 

I'm sorry. I thought the changelog text had already the proper information.
In the changelog text I'm quoting the GCC documentation below:

"The preferred mechanism to declare variable-length types like struct line
above is the ISO C99 flexible array member..." [1]

I'm also including a link to the following KSPP open issue:

https://github.com/KSPP/linux/issues/21

The issue above mentions the following:

"Both cases (0-byte and 1-byte arrays) pose confusion for things like sizeof(),
CONFIG_FORTIFY_SOURCE."

sizeof(flexible-array-member) triggers a warning because flexible array members have
incomplete type[1]. There are some instances of code in which the sizeof operator
is being incorrectly/erroneously applied to zero-length arrays and the result is zero.
Such instances may be hiding some bugs. So, the idea is also to get completely rid
of those sorts of issues.

Should I update the changelog in some way so it is a bit more informative?

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html

Thanks
--
Gustavo

>> Qemu guys are adopting this format, too[2][3].
>>
>> On the other hand, the changelog text explains the reasons why we are
>> implementing this change all across the kernel tree. :)
>>
>> [1]
>> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/?qt=grep&q=flexible-array
>> [2] https://lists.nongnu.org/archive/html/qemu-s390x/2020-03/msg00019.html
>> [3] https://lists.nongnu.org/archive/html/qemu-s390x/2020-03/msg00020.html
> 
> TBH I was leaning more on Jes side on this, but I guess these patches
> are ok if they are so widely accepted. Unless anyone objects?
>