linux-kernel - Re: [Intel-gfx] [PATCH v3] drm: move allocation out of drm_get_format

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Date:   Thu, 10 Nov 2016 13:03:20 +0200
From:   Jani Nikula <jani.nikula@...el.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Eric Engestrom <eric.engestrom@...tec.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Eric Engestrom <eric@...estrom.ch>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <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>,
        Chunming Zhou <David1.Zhou@....com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Sinclair Yeh <syeh@...are.com>,
        Xinliang Liu <z.liuxinliang@...ilicon.com>,
        Xinwei Kong <kong.kongxinwei@...ilicon.com>,
        VMware Graphics <linux-graphics-maintainer@...are.com>,
        Vitaly Prosyak <vitaly.prosyak@....com>,
        Alexandre Demers <alexandre.f.demers@...il.com>,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        Emily Deng <Emily.Deng@....com>,
        Colin Ian King <colin.king@...onical.com>,
        Junwei Zhang <Jerry.Zhang@....com>,
        Michel Dänzer <michel.daenzer@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>
Subject: Re: [Intel-gfx] [PATCH v3] drm: move allocation out of drm_get_format_name()

On Thu, 10 Nov 2016, Laurent Pinchart <laurent.pinchart@...asonboard.com> wrote:
> Hi Jani,
>
> On Thursday 10 Nov 2016 12:30:09 Jani Nikula wrote:
>> On Thu, 10 Nov 2016, Laurent Pinchart wrote:
>> > The issue here is that printk can't format the fourcc as a string by
>> > itself. There's a bunch of places in the kernel where a similar
>> > formatting problem occurs. In a few occasions it has been solved by
>> > extending printk with additional format specifiers (such as for MAC/IP
>> > addresses, GUIDs, various kind of device names, ...). DRM fourccs are
>> > probably too DRM specific to be worth a format specifier, but I wonder
>> > whether we could introduce a new specifier that takes a function pointer
>> > as a formatting helper. Another similarly crazy option would be a format
>> > specifier for strings that would free the passed pointer after printing
>> > it.
>> 
>> I think there are too many non-standard format specifiers already. I
>> can't review the non-standard format strings without looking at
>> Documentation/prink-formats.txt first. The formatting hook would be a
>> generic alternative, but that's more than a little scary from the
>> security standpoint. And what if the hook has to allocate memory? Can't
>> do that in atomic contexts.
>
> There are lots of details to sort out obviously and I don't have an answer to 
> all questions yet. I think it would be worth researching this, as the problem 
> isn't specific to DRM/KMS.

That's easy to agree to; as much as you didn't mean to shoot down the
patch, I didn't mean to shoot down your idea! :)

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center