Re: [Intel-gfx] [PATCH v3] drm: move allocation out of drm_get_format_name()

From: Jani Nikula <jani.nikula@intel.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: dri-devel <dri-devel@lists.freedesktop.org>,
	"Wei Yongjun" <yongjun_wei@trendmicro.com.cn>,
	"Daniel Vetter" <daniel.vetter@intel.com>,
	"Flora Cui" <Flora.Cui@amd.com>,
	"Gustavo Padovan" <gustavo.padovan@collabora.co.uk>,
	"Tom St Denis" <tom.stdenis@amd.com>,
	"Thomas Hellstrom" <thellstrom@vmware.com>,
	"Laurent Pinchart" <laurent.pinchart+renesas@ideasonboard.com>,
	"Xinliang Liu" <z.liuxinliang@hisilicon.com>,
	"VMware Graphics" <linux-graphics-maintainer@vmware.com>,
	"Vitaly Prosyak" <vitaly.prosyak@amd.com>,
	"Alexandre Demers" <alexandre.f.demers@gmail.com>,
	intel-gfx <intel-gfx@lists.freedesktop.org>,
	"Eric Engestrom" <eric@engestrom.ch>,
	"Emily Deng" <Emily.Deng@amd.com>,
	"Junwei Zhang" <Jerry.Zhang@amd.com>,
	"Michel Dänzer" <michel.daenzer@amd.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Alex Deucher" <alexander.deucher@amd.com>,
	"Colin Ian King" <colin.king@can>
Subject: Re: [Intel-gfx] [PATCH v3] drm: move allocation out of drm_get_format_name()
Date: Thu, 10 Nov 2016 13:03:20 +0200	[thread overview]
Message-ID: <87pom3egw7.fsf@intel.com> (raw)
In-Reply-To: <1577179.SKedfdZVPT@avalon>

On Thu, 10 Nov 2016, Laurent Pinchart <laurent.pinchart@ideasonboard.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
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