Re: [RFC PATCH v2] media: Virtual camera driver

[Jarkko Sakkinen <jarkko@kernel.org>]

On Tue, Feb 03, 2026 at 10:57:42PM +0200, Laurent Pinchart wrote:
> Hello Jarkko,
> 
> 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.

BR, Jarkko