Message-ID: <20260203212110.GE11369@killaraus>
Date: Tue, 3 Feb 2026 23:21:10 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: Sakari Ailus <sakari.ailus@...ux.intel.com>,
	linux-media@...r.kernel.org, jani.nikula@...ux.intel.com,
	anisse@...ier.eu, oleksandr@...alenko.name,
	linux-integrity@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Hans Verkuil <hverkuil@...nel.org>,
	Jacopo Mondi <jacopo.mondi@...asonboard.com>,
	Ricardo Ribalda <ribalda@...omium.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2] media: Virtual camera driver

On Tue, Feb 03, 2026 at 11:11:19PM +0200, Jarkko Sakkinen wrote:
> On Tue, Feb 03, 2026 at 10:57:42PM +0200, Laurent Pinchart wrote:
> > On Tue, Feb 03, 2026 at 03:36:59AM +0200, Jarkko Sakkinen wrote:
> > > On Tue, Feb 03, 2026 at 02:10:15AM +0200, Jarkko Sakkinen wrote:
> > > > On Tue, Feb 03, 2026 at 12:50:06AM +0200, Sakari Ailus wrote:
> > > > > On Mon, Feb 02, 2026 at 10:44:21PM +0200, Jarkko Sakkinen wrote:
> > > > > > Already a quick Google survey backs strongly that OOT drivers (e.g.,
> > > > > > v4l2loopback) are the defacto solution for streaming phone cameras in
> > > > > > video conference calls, which puts confidential discussions at risk.
> > > > > 
> > > > > As I think it was pointed out in review comments for v1, the reason behind
> > > > > using v4l2loopback is the use of a downstream driver, which itself is a
> > > > > source of a security risk. If I understand correctly, supporting this
> > > > > (proprietary/downstream vendor drivers) would be the main use case this
> > > > > driver serves? Should this downstream driver be upstreamed to alleviate the
> > > > > security risks, the need for v4l2loopback or similar drivers presumably
> > > > > disappears.
> > > > 
> > > > My goal is not to proactively support proprietary drivers, and I don't
> > > > know how to measure such incentive or risk, when it comes to video
> > > > drivers.
> > > > 
> > > > And besides there is e.g. FUSE.
> > > > 
> > > > > Another of the downsides of such proprietary/downstream solutions is they
> > > > > can never be properly integrated into the Linux ecosystem so functionality
> > > > > will remain spotty (limited to specific systems and specific releases of
> > > > > specific distributions) at best.
> > > > > 
> > > > > In other words, this driver appears to be orthogonal to solving either of
> > > > > the above two problems the proprietary/downstream solutions have.
> > > > > 
> > > > > From the Open Source libcamera based camera software stack point of view
> > > > > there doesn't seem to be a need for v4l2loopback or another similar driver.
> > > > > The two main reasons for this is that (1) there's no need for glueing
> > > > > something separate together like this and (2) V4L2 isn't a great
> > > > > application interface for cameras -- use libcamera or Pipewire instead.
> > > > 
> > > > While I get this argument isolated, it does not match the observed
> > > > reality, and does not provide tools to address the core issue. I
> > > > will be in my grave before I've fixed the world like you are
> > > > suggesting :-)
> > 
> > I really hope we'll provide a solution much faster than that :-)
> > 
> > > > Like, first off, where would I use libcamera or Pipewire? There's
> > > > no well-defined target other than kernel in this problem.
> > 
> > PipeWire is becoming the de facto media server on desktop systems, for
> > both audio and video. It has been shipped by distributions for a while
> > for audio, and is the core component that allows screen capture (and
> > therefore screen sharing in video conferencing) on Wayland-based
> > systems. For video, PipeWire support has most notably been integrated in
> > WebRTC, used by both Firefox and Chrome. The number of applications
> > using PipeWire is growing, OBS has recently received support for
> > PipeWire sources for instance. If you need to use it in an application
> > that requires a V4L2 capture device, the pw-v4l2 script emulates the
> > V4L2 API to provide a quick stopgap measure until applications get
> > native PipeWire support.
> > 
> > libcamera solves an orthogonal problem, which is control of raw camera
> > sensors and ISPs typically found in mobile and embedded devices, and now
> > increasingly in laptops as well (Intel IPU3, IPU4, IPU6 and IPU7).
> > Applications typically don't use libcamera directly, but interface it
> > with GStreamer (libcamerasrc element) or PipeWire (which has native
> > libcamera support).
> > 
> > While I understand that libcamera and PipeWire may be quite new for a
> > large number of users, the ecosystem is moving in that direction, and
> > both projects are very active.
> 
> Thanks for the information and I take this into account when/if considering
> any updates.  The response is so informative that I need to purge this a
> bit (thank you for that) :-) This does not disregard your response but
> personally I'm not have huge a fan of LD_PRELOAD style compatibility
> wrappers.

I'm not either as it can only provide best-effort compatibility, but it
has proven to be useful. For instance, we successfully tested the
libcamera LD_PRELOAD v4l2-compat.so with Firefox before support for
PipeWire was ready in WebRTC, providing a way to use ISPs in video
conferencing as a stopgap measure. It's all about helping the ecosystem
with the transition, and not intended as a long-term solution.

-- 
Regards,

Laurent Pinchart

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