Linux – How to map /sys/bus/usb/devices to /dev/video*

deviceslinuxsysfsusbvideo

I am using a library (librealsense) that only outputs the bus and port number as such (9.1). It uses libusb internally. The issue is from this identifier in libusb I want to know what physical device it belongs to in /dev/video0. For instance, 9.1 -> /dev/video0 and 7.2 -> /dev/video2 when two cameras are plugged in in ports 9.1 and 7.2.

Is this possible? How do I acquire what devices paths belong to a bus and port? Any partial answer would be helpful.

Best Answer

Answering so I can close this question full credit to @ridgy and @dirkt for their help. With the command:

udevadm info -n video0 -q path

Or similarly with ls -l /sys/class/video4linux/, a path of the form /devices/pci0000:00/0000:00:10.0/usb7/7-2/7-2:1.0/video4linux/video0 can be found. That in combination with the listing of the video devices using either ls /dev/video* or v4l2-ctl --list-devices allows a map between the usb port and video device to be created.

Related Solutions

Video Devices – Manipulating /dev/video

For sure. Here are two suggestions:

Behind the scenes CLI. Use V4L2VD to create a virtual video device such as /dev/videoVirt1 and pipe through mplayer for the effects. Even some similar examples in the notes.
Use a fat desktop program such as webcamstudio to create the pipes and do your skype/broadcast wonders - still with mplayer for the ascii effect

Good Luck!

How creation of new USB device file in /dev/bus/usb/001/ directory work

The devices in /dev/bus/usb/XXX/YYY follow naming policies in the kernel as noted Gilles in the comments. XXX is the bus number which is quite stable, but YYY changes every time the USB device gets enumerated (when a device just got inserted or reset). This cannot be changed and you shouldn't have to change this either.

If you need to change permissions on the device (for example, to make an unprivileged userspace USB driver possible for testing purposes), then you could make a udev rule. An example where I use udev to control the permissions such that adb is able to connect to the device:

# /etc/udev/rules.d/42-usb-permissions.rules
SUBSYSTEM!="usb", GOTO="end_skip_usb"

# CWM 6.0.4.3 in recovery mode
ATTRS{idVendor}=="18d1", ATTRS{idProduct}=="d001", GROUP="peter"

# CM 10.2 with MTP disabled
ATTRS{idVendor}=="18d1", ATTRS{idProduct}=="d002", GROUP="peter"

ATTRS{idVendor}=="148f", ATTRS{idProduct}=="5372", GROUP="peter"

LABEL="end_skip_usb"

Best Answer

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Video Devices – Manipulating /dev/video

How creation of new USB device file in /dev/bus/usb/001/ directory work

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