linux-kernel - Re: [PATCH] drm: move allocation out of drm_get_format_name()

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Message-ID: <8af873a2-31a9-1146-289d-35d2e48edffa@amd.com>
Date:   Sun, 6 Nov 2016 10:47:25 +0100
From:   Christian König <christian.koenig@....com>
To:     Rob Clark <robdclark@...il.com>, Eric Engestrom <eric@...estrom.ch>
CC:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "Wei Yongjun" <yongjun_wei@...ndmicro.com.cn>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Flora Cui <Flora.Cui@....com>,
        Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
        Tom St Denis <tom.stdenis@....com>,
        "Thomas Hellstrom" <thellstrom@...are.com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Xinliang Liu <z.liuxinliang@...ilicon.com>,
        VMware Graphics <linux-graphics-maintainer@...are.com>,
        Vitaly Prosyak <vitaly.prosyak@....com>,
        Alexandre Demers <alexandre.f.demers@...il.com>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Emily Deng <Emily.Deng@....com>,
        Ken Wang <Qingqing.Wang@....com>,
        Junwei Zhang <Jerry.Zhang@....com>,
        Michel Dänzer <michel.daenzer@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alex Deucher <alexander.deucher@....com>,
        Colin Ian King <colin.king@...onical.com>
Subject: Re: [PATCH] drm: move allocation out of drm_get_format_name()

Am 05.11.2016 um 17:49 schrieb Rob Clark:
> On Sat, Nov 5, 2016 at 12:38 PM, Eric Engestrom <eric@...estrom.ch> wrote:
>> On Saturday, 2016-11-05 13:11:36 +0100, Christian König wrote:
>>> Am 05.11.2016 um 02:33 schrieb Eric Engestrom:
>>>> +typedef char drm_format_name_buf[32];
>>> Please don't use a typedef for this, just define the maximum size of
>>> characters the function might write somewhere.
>>>
>>> See the kernel coding style as well:
>>>> In general, a pointer, or a struct that has elements that can reasonably
>>>> be directly accessed should **never** be a typedef.
>> I would normally agree as I tend to hate typedefs ($DAYJOB {ab,mis}uses
>> them way too much), and your way was what I wrote at first, but Rob Clark's
>> typedef idea makes it much harder for someone to allocate a buffer of
>> the wrong size, which IMO is good thing here.
> IMHO I would make a small test program to verify this actually helps
> the compiler catch problems.  And if it does, I would stick with it.
> The coding-style should be guidelines, not something that supersedes
> common sense / practicality.

Well completely agree that we should be able to question the coding 
style rules, but when we do it we discuss this on a the mailing list 
first and then start to use it in code. Not the other way around.

>
> That is my $0.02 anyways.. if others vehemently disagree and want to
> dogmatically stick to the coding-style guidelines, ok then.  OTOH, if
> this approach doesn't help the compiler catch issues, then it isn't
> worth it.

Yeah, exactly that's the point. If I'm not completely mistaken the 
compiler won't issue a warning here if you pass an array with the wrong 
size.

I think you need something like "struct drm_format_name_buf { char 
str[32]; };" to trigger this.

Apart from that is this function really called so often that using 
kasprintf() is a problem here? Or is there another motivation behind the 
change?

Regards,
Christian.

>
> BR,
> -R
>
>> I can rewrite the typedef out if you think it's better.
>>
>> Cheers,
>>    Eric
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@...ts.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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