linux-kernel - Re: [PATCH] media: videobuf2: forbid create_bufs/remove

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Message-ID: <84133573-986d-4cc8-8147-246f0da34640@samsung.com>
Date: Mon, 20 Oct 2025 09:34:08 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Benjamin Gaignard <benjamin.gaignard@...labora.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Tomasz Figa <tfiga@...omium.org>, Mauro Carvalho Chehab
	<mchehab@...nel.org>, Guennadi Liakhovetski <g.liakhovetski@....de>, Hans
	Verkuil <hverkuil@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH] media: videobuf2: forbid create_bufs/remove_bufs when
 legacy fileio is active

On 20.10.2025 09:11, Benjamin Gaignard wrote:
>
> Le 16/10/2025 à 13:11, Marek Szyprowski a écrit :
>> create_bufs and remove_bufs ioctl calls manipulate queue internal buffer
>> list, potentially overwriting some pointers used by the legacy fileio
>> access mode. Simply forbid those calls when fileio is active to protect
>> internal queue state between subsequent read/write calls.
>
> Hi Marek,
>
> I may be wrong but using fileio API and create/remove API at the same 
> time
> sound incorrect from application point of view, right ? If that not the
> case maybe we should also add a test in v4l2-compliance.

Definitely that's incorrect and v4l2-core must forbid such calls. The 
standard reqbufs/qbuf/dqbuf API is also forbidden. Extending 
v4l2-compliance tools is probably a good idea. I also wonder if its a 
good time to add a kernel option to completely disable legacy fileio 
access mode, as it is not really needed for most of the systems nowadays.

 > ...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland