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Subject: Re: [PATCH][RFC] kernel.h: provide array iterator
To:     Joe Perches <joe@perches.com>,
        Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
        linux-kernel@vger.kernel.org
Cc:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        linux-media@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Kees Cook <keescook@chromium.org>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Ian Abbott <abbotti@mev.co.uk>
References: <1521108052-26861-1-git-send-email-kieran.bingham@ideasonboard.com>
 <b6af11b9-d697-59ec-6acc-80f0657a3e11@prevas.dk>
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From:   Kieran Bingham <kieran.bingham@ideasonboard.com>
Organization: Ideas on Board
Message-ID: <5f027b5c-7419-d4f2-53a7-28805baa7193@ideasonboard.com>
Date:   Sat, 17 Mar 2018 11:12:01 +0100
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Hi Joe,

On 16/03/18 19:45, Joe Perches wrote:
> On Fri, 2018-03-16 at 16:27 +0100, Rasmus Villemoes wrote:
>> On 2018-03-15 11:00, Kieran Bingham wrote:
>>> Simplify array iteration with a helper to iterate each entry in an array.
>>> Utilise the existing ARRAY_SIZE macro to identify the length of the array
>>> and pointer arithmetic to process each item as a for loop.
> 
> I recall getting negative feedback on a similar proposal
> a decade ago:
> 
> https://lkml.org/lkml/2007/2/13/25

Thanks for the reference. I didn't know about this.

Your suggestion at https://lkml.org/lkml/2007/2/13/25 looks remarkably similar
to my implementation though :-D  (Perhaps even a bit neater, I may have to
incorporate some of your suggestion)


> Not sure this is different.
> 

I count three disagreements in that series. But I'm sure I have more positive
responses already... (Though no 'official Acks' yet ...)

How many ACKs do I need for this to be accepted ? or do the past-nack's have
full veto?

I still believe the use of an iterator in my case [0] makes *absolute sense*
(thus it must make sense elsewhere)

I'm not suggesting a full tree conversion here (though that has been suggested
earlier in the thread) but the ability to add a convenience macro in a common
location, so that it can be used when desired.

In my instance, I have an array of structures which I want to iterate. I believe
this make my code more readable. I have already had another vote to say that
they thought the same.

I'm certain that throughout the media tree there are a lot of use cases where
arrays of structures define types which must be searched where this macro could
also make sense.

Do I need to start a poll to determine if this is a worthy pursuit? or am I to
give up and stop in my tracks (I'm a bit too tenacious usually to give up - so
someone 'high up' better make a clear statement saying ... just give up...
otherwise I likely won't)

Either way - I intend to add an equivalent macro to the UVC driver [1][2]
(because as I said - I believe it makes sense), and I have the support of the
maintainer there, so It seems a shame to have to duplicate the implementation in
other use cases where this would make the code more friendly.


/me awaits a NACK-FULL-STOP, or now fears if I'm about to be the cause of a
flame war :-S

[0]
https://git.kernel.org/pub/scm/linux/kernel/git/kbingham/rcar.git/commit/?h=kernel/array-iterator

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/kbingham/rcar.git/commit/?h=kernel/array-iterator&id=3dece696e5b19d79c94f88c9df77482542d49a75

[2]
https://git.kernel.org/pub/scm/linux/kernel/git/kbingham/rcar.git/commit/?h=kernel/array-iterator&id=a31a5424a6577e14d46ce24ef0eff35de3e089bc

--
Kieran