Control: tags -1 + upstream Hello
Am 18.10.21 um 08:20 schrieb Joseph Carter:
Package: udev
Version: 249.5-1
Severity: normal
Many webcams new use more than the standard /dev/videoN device to
control them through e.g. uvcdynctrl. For example, here is my Logitech
C930e, which is a pretty common example on Debian:
```
tjcarter@aki:~$ uvcdynctrl -l
Listing available devices:
video0 Logitech Webcam C930e
Media controller device: /dev/media0
ERROR: Unable to open media controller device '/dev/media0': Permission denied
(Error: 13)
ERROR: Unable to list device entities: Invalid device or device cannot be
opened. (Code: 5)
video1 Logitech Webcam C930e
Media controller device /dev/media1 doesn't exist
ERROR: Unable to list device entities: Invalid device or device cannot be
opened. (Code: 5)
```
Okay, I have no idea why there are two /dev/video entries there since
only the first one actually is a video device. Either way, you can see
that there's an error accessing /dev/media0, which is definitely
provided by the camera:
```
tjcarter@aki:~$ ls -l /dev/media*
crw-rw----+ 1 root video 239, 0 Oct 17 11:01 /dev/media0
tjcarter@aki:~$ cat /sys/dev/char/239\:0/model
Logitech Webcam C930e
```
I should have access to this as a console user, but I don't. Searching
online, I found this file, named 65-media-uaccess.rules which is
supposedly part of systemd … but not on my system it isn't!
Where exactly did you find this information? My online searches turn up nothing
Do you have a reference? Looking at the systemd/udev git repo, it never shipped a file named 65-media-uaccess.rules afaics
```
# SPDX-License-Identifier: LGPL-2.1+
#
# This file is part of systemd.
#
# systemd is free software; you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 2.1 of the License, or
# (at your option) any later version.
ACTION=="remove", GOTO="media_uaccess_end"
ENV{MAJOR}=="", GOTO="media_uaccess_end"
# Newer Webcams, frame grabber, TV cards
SUBSYSTEM=="media", TAG+="uaccess"
LABEL="media_uaccess_end"
```
Sure enough, adding it to the system fixes the permission error:
```
tjcarter@aki:~$ uvcdynctrl -l
Listing available devices:
video0 Logitech Webcam C930e
Media controller device: /dev/media0
Entity 1: Logitech Webcam C930e. Type: 65537, Revision: 0, Flags: 1,
Group-id: 0, Pads: 1, Links: 0
Device node
Entity: 1, Pad 0, Flags: 1
video1 Logitech Webcam C930e
Media controller device /dev/media1 doesn't exist
ERROR: Unable to list device entities: Invalid device or device cannot be
opened. (Code: 5)
tjcarter@aki:~$ uvcdynctrl -c
Listing available controls for device video0:
Brightness
Contrast
Saturation
White Balance Temperature, Auto
Gain
Power Line Frequency
White Balance Temperature
Sharpness
Backlight Compensation
Exposure, Auto
Exposure (Absolute)
Exposure, Auto Priority
Pan (Absolute)
Tilt (Absolute)
Focus (absolute)
Focus, Auto
Zoom, Absolute
LED1 Mode
LED1 Frequency
tjcarter@aki:~$ uvcdynctrl -g "Zoom, Absolute"
100
tjcarter@aki:~$ uvcdynctrl -s "Zoom, Absolute" 150
tjcarter@aki:~$ uvcdynctrl -g "Zoom, Absolute"
150
```
(This by the way zooms the camera in to have a tighter focus on me and
less my kitchen behind me.)
On some cameras (my IPEVO document camera for example) access to the
associated /dev/mediaN device is required to put the camera into a mode
offering (compressed) high-resolution AND high-framerate mode. The
aforementioned IPEVO can do 4k at 30fps, but Cheese and OBS are unable
to set that mode without access to the media controller.
Is there a reason the tag for the media subsystem is not found on Debian
systems? It seems currently or previously it was intended by systemd's
devs that console users have access to it. Can or should it be made that
way by default on Debian systems?
Looking at /lib/udev/rules.d/50-udev-default.rules, I see a static group permission for those types of devices:
SUBSYSTEM=="media", GROUP="video"So I assume if you are in group video, you should have access to those devices.
In don't find anything in /lib/udev/rules.d/70-uaccess.rules related to those types of devices. I'm not sure, if this intentional or not.
Can you please raise this upstream at https://github.com/systemd/systemd/issues/newI'm not really familiar with those types of devices to assess whether it's safe to ship such a rule which set the uaccess tag or not.
And if so, it should definitely be addressed upstream not via a downstream patch/change.
Regards, Michael
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