udev – Rules for Seemingly Indistinguishable Devices

udevvideo

I'm trying to use udev to automatically set up symlinks to an Intel RealSense D415. This is because I use several cameras on the machine and need to be able to reliably refer to them via a filename (that doesn't change on reboot).

The RealSense D415 creates three video devices in /dev. I'm having no problem setting up symlinks for the first two, but as far as I can see the first and third devices are identical apart from the KERNEL and KERNELS attributes which are liable to change if another camera is plugged in first.

How can I use a udev rule to differentiate between these?

Output for sudo udevadm info -ap /devices/pci0000:00/0000:00:14.0/usb2/2-1/2-1:1.0/video4linux/video0:

  looking at device '/devices/pci0000:00/0000:00:14.0/usb2/2-1/2-1:1.0/video4linux/video0':
    KERNEL=="video0"
    SUBSYSTEM=="video4linux"
    DRIVER==""
    ATTR{dev_debug}=="0"
    ATTR{index}=="0"
    ATTR{name}=="Intel(R) RealSense(TM) 415: Int"

  looking at parent device '/devices/pci0000:00/0000:00:14.0/usb2/2-1/2-1:1.0':
    KERNELS=="2-1:1.0"
    SUBSYSTEMS=="usb"
    DRIVERS=="uvcvideo"
    ATTRS{authorized}=="1"
    ATTRS{bAlternateSetting}==" 0"
    ATTRS{bInterfaceClass}=="0e"
    ATTRS{bInterfaceNumber}=="00"
    ATTRS{bInterfaceProtocol}=="00"
    ATTRS{bInterfaceSubClass}=="01"
    ATTRS{bNumEndpoints}=="01"
    ATTRS{iad_bFirstInterface}=="00"
    ATTRS{iad_bFunctionClass}=="0e"
    ATTRS{iad_bFunctionProtocol}=="00"
    ATTRS{iad_bFunctionSubClass}=="03"
    ATTRS{iad_bInterfaceCount}=="03"
    ATTRS{interface}=="Intel(R) RealSense(TM) 415 Depth"
    ATTRS{supports_autosuspend}=="1"

  looking at parent device '/devices/pci0000:00/0000:00:14.0/usb2/2-1':
    KERNELS=="2-1"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{authorized}=="1"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bDeviceClass}=="ef"
    ATTRS{bDeviceProtocol}=="01"
    ATTRS{bDeviceSubClass}=="02"
    ATTRS{bMaxPacketSize0}=="9"
    ATTRS{bMaxPower}=="440mA"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bNumInterfaces}==" 5"
    ATTRS{bcdDevice}=="508f"
    ATTRS{bmAttributes}=="c0"
    ATTRS{busnum}=="2"
    ATTRS{configuration}==""
    ATTRS{devnum}=="2"
    ATTRS{devpath}=="1"
    ATTRS{idProduct}=="0ad3"
    ATTRS{idVendor}=="8086"
    ATTRS{ltm_capable}=="no"
    ATTRS{manufacturer}=="Intel(R) RealSense(TM) 415"
    ATTRS{maxchild}=="0"
    ATTRS{product}=="Intel(R) RealSense(TM) 415"
    ATTRS{quirks}=="0x0"
    ATTRS{removable}=="removable"
    ATTRS{serial}=="736613021813"
    ATTRS{speed}=="5000"
    ATTRS{urbnum}=="56"
    ATTRS{version}==" 3.10"

  looking at parent device '/devices/pci0000:00/0000:00:14.0/usb2':
    KERNELS=="usb2"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{authorized}=="1"
    ATTRS{authorized_default}=="1"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bDeviceClass}=="09"
    ATTRS{bDeviceProtocol}=="03"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bMaxPacketSize0}=="9"
    ATTRS{bMaxPower}=="0mA"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bNumInterfaces}==" 1"
    ATTRS{bcdDevice}=="0415"
    ATTRS{bmAttributes}=="e0"
    ATTRS{busnum}=="2"
    ATTRS{configuration}==""
    ATTRS{devnum}=="1"
    ATTRS{devpath}=="0"
    ATTRS{idProduct}=="0003"
    ATTRS{idVendor}=="1d6b"
    ATTRS{interface_authorized_default}=="1"
    ATTRS{ltm_capable}=="yes"
    ATTRS{manufacturer}=="Linux 4.15.0-36-generic xhci-hcd"
    ATTRS{maxchild}=="10"
    ATTRS{product}=="xHCI Host Controller"
    ATTRS{quirks}=="0x0"
    ATTRS{removable}=="unknown"
    ATTRS{serial}=="0000:00:14.0"
    ATTRS{speed}=="5000"
    ATTRS{urbnum}=="101"
    ATTRS{version}==" 3.00"

  looking at parent device '/devices/pci0000:00/0000:00:14.0':
    KERNELS=="0000:00:14.0"
    SUBSYSTEMS=="pci"
    DRIVERS=="xhci_hcd"
    ATTRS{broken_parity_status}=="0"
    ATTRS{class}=="0x0c0330"
    ATTRS{consistent_dma_mask_bits}=="64"
    ATTRS{d3cold_allowed}=="1"
    ATTRS{dbc}=="disabled"
    ATTRS{device}=="0xa2af"
    ATTRS{dma_mask_bits}=="64"
    ATTRS{driver_override}=="(null)"
    ATTRS{enable}=="1"
    ATTRS{irq}=="123"
    ATTRS{local_cpulist}=="0-3"
    ATTRS{local_cpus}=="f"
    ATTRS{msi_bus}=="1"
    ATTRS{numa_node}=="-1"
    ATTRS{revision}=="0x00"
    ATTRS{subsystem_device}=="0x310c"
    ATTRS{subsystem_vendor}=="0x17aa"
    ATTRS{vendor}=="0x8086"

  looking at parent device '/devices/pci0000:00':
    KERNELS=="pci0000:00"
    SUBSYSTEMS==""
    DRIVERS==""

Output for sudo udevadm info -ap /devices/pci0000:00/0000:00:14.0/usb2/2-1/2-1:1.3/video4linux/video2:

  looking at device '/devices/pci0000:00/0000:00:14.0/usb2/2-1/2-1:1.3/video4linux/video2':
    KERNEL=="video2"
    SUBSYSTEM=="video4linux"
    DRIVER==""
    ATTR{dev_debug}=="0"
    ATTR{index}=="0"
    ATTR{name}=="Intel(R) RealSense(TM) 415: Int"

  looking at parent device '/devices/pci0000:00/0000:00:14.0/usb2/2-1/2-1:1.3':
    KERNELS=="2-1:1.3"
    SUBSYSTEMS=="usb"
    DRIVERS=="uvcvideo"
    ATTRS{authorized}=="1"
    ATTRS{bAlternateSetting}==" 0"
    ATTRS{bInterfaceClass}=="0e"
    ATTRS{bInterfaceNumber}=="03"
    ATTRS{bInterfaceProtocol}=="00"
    ATTRS{bInterfaceSubClass}=="01"
    ATTRS{bNumEndpoints}=="00"
    ATTRS{iad_bFirstInterface}=="03"
    ATTRS{iad_bFunctionClass}=="0e"
    ATTRS{iad_bFunctionProtocol}=="00"
    ATTRS{iad_bFunctionSubClass}=="03"
    ATTRS{iad_bInterfaceCount}=="02"
    ATTRS{interface}=="Intel(R) RealSense(TM) 415 RGB"
    ATTRS{supports_autosuspend}=="1"

  looking at parent device '/devices/pci0000:00/0000:00:14.0/usb2/2-1':
    KERNELS=="2-1"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{authorized}=="1"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bDeviceClass}=="ef"
    ATTRS{bDeviceProtocol}=="01"
    ATTRS{bDeviceSubClass}=="02"
    ATTRS{bMaxPacketSize0}=="9"
    ATTRS{bMaxPower}=="440mA"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bNumInterfaces}==" 5"
    ATTRS{bcdDevice}=="508f"
    ATTRS{bmAttributes}=="c0"
    ATTRS{busnum}=="2"
    ATTRS{configuration}==""
    ATTRS{devnum}=="2"
    ATTRS{devpath}=="1"
    ATTRS{idProduct}=="0ad3"
    ATTRS{idVendor}=="8086"
    ATTRS{ltm_capable}=="no"
    ATTRS{manufacturer}=="Intel(R) RealSense(TM) 415"
    ATTRS{maxchild}=="0"
    ATTRS{product}=="Intel(R) RealSense(TM) 415"
    ATTRS{quirks}=="0x0"
    ATTRS{removable}=="removable"
    ATTRS{serial}=="736613021813"
    ATTRS{speed}=="5000"
    ATTRS{urbnum}=="56"
    ATTRS{version}==" 3.10"

  looking at parent device '/devices/pci0000:00/0000:00:14.0/usb2':
    KERNELS=="usb2"
    SUBSYSTEMS=="usb"
    DRIVERS=="usb"
    ATTRS{authorized}=="1"
    ATTRS{authorized_default}=="1"
    ATTRS{avoid_reset_quirk}=="0"
    ATTRS{bConfigurationValue}=="1"
    ATTRS{bDeviceClass}=="09"
    ATTRS{bDeviceProtocol}=="03"
    ATTRS{bDeviceSubClass}=="00"
    ATTRS{bMaxPacketSize0}=="9"
    ATTRS{bMaxPower}=="0mA"
    ATTRS{bNumConfigurations}=="1"
    ATTRS{bNumInterfaces}==" 1"
    ATTRS{bcdDevice}=="0415"
    ATTRS{bmAttributes}=="e0"
    ATTRS{busnum}=="2"
    ATTRS{configuration}==""
    ATTRS{devnum}=="1"
    ATTRS{devpath}=="0"
    ATTRS{idProduct}=="0003"
    ATTRS{idVendor}=="1d6b"
    ATTRS{interface_authorized_default}=="1"
    ATTRS{ltm_capable}=="yes"
    ATTRS{manufacturer}=="Linux 4.15.0-36-generic xhci-hcd"
    ATTRS{maxchild}=="10"
    ATTRS{product}=="xHCI Host Controller"
    ATTRS{quirks}=="0x0"
    ATTRS{removable}=="unknown"
    ATTRS{serial}=="0000:00:14.0"
    ATTRS{speed}=="5000"
    ATTRS{urbnum}=="101"
    ATTRS{version}==" 3.00"

  looking at parent device '/devices/pci0000:00/0000:00:14.0':
    KERNELS=="0000:00:14.0"
    SUBSYSTEMS=="pci"
    DRIVERS=="xhci_hcd"
    ATTRS{broken_parity_status}=="0"
    ATTRS{class}=="0x0c0330"
    ATTRS{consistent_dma_mask_bits}=="64"
    ATTRS{d3cold_allowed}=="1"
    ATTRS{dbc}=="disabled"
    ATTRS{device}=="0xa2af"
    ATTRS{dma_mask_bits}=="64"
    ATTRS{driver_override}=="(null)"
    ATTRS{enable}=="1"
    ATTRS{irq}=="123"
    ATTRS{local_cpulist}=="0-3"
    ATTRS{local_cpus}=="f"
    ATTRS{msi_bus}=="1"
    ATTRS{numa_node}=="-1"
    ATTRS{revision}=="0x00"
    ATTRS{subsystem_device}=="0x310c"
    ATTRS{subsystem_vendor}=="0x17aa"
    ATTRS{vendor}=="0x8086"

  looking at parent device '/devices/pci0000:00':
    KERNELS=="pci0000:00"
    SUBSYSTEMS==""
    DRIVERS==""

Best Answer

There seems to be one distinguishing factor here:

ATTRS{interface}=="Intel(R) RealSense(TM) 415 Depth"

vs.

ATTRS{interface}=="Intel(R) RealSense(TM) 415 RGB"

And to tell multiple cameras apart, you'll probably need this one:

ATTRS{serial}=="736613021813"

The udev(7) man page says:

If multiple keys that match a parent device are specified in a single rule, all these keys must match at one and the same parent device.

The attribute that makes the interfaces distinguishable is in the parent block, and the attribute that makes the cameras distinguishable is in the grandparent block. So, you'll have to use multiple rule lines.

For each camera, there should be a group of rules like this:

SUBSYSTEM=="video4linux", ATTRS{serial}!="736613021813", GOTO="not_first_camera"
SUBSYSTEM=="video4linux", KERNEL=="video*", ATTRS{interface}=="Intel(R) RealSense(TM) 415 Depth", SYMLINK+="cam1_depth"
SUBSYSTEM=="video4linux", KERNEL=="video*", ATTRS{interface}=="Intel(R) RealSense(TM) 415 RGB", SYMLINK+="cam1_rgb"
LABEL="not_first_camera"

The first rule bypasses the two following rules if the camera serial number does not match. In this way, between the first rule and the LABEL associated with it, we can be sure of the identity of the camera we're talking about and can concentrate on telling the interfaces apart.

Each block should have an unique LABEL= line and a GOTO= statement that matches the unique label. Of course you can name the SYMLINKs as you wish.

Related Solutions

List all udev rules (e.g. for a device)

If you use:

udevadm monitor

you get an entry for each action taken by KERNEL and UDEV. Typically add, change, remove. If you include the --property option:

udevadm monitor --property

You will get a listing of what properties are used.

As one can test udev rules with udevadm:

udevadm test $(udevadm info -q path -n <device>)

one could test out something as this:

udevadm test $(udevadm info -q path -n <device>) 2>&1 | \
sed -n 's/.* \(\/[^ ]*\)\.rules:\([0-9]\+\)/\1.rules \2/p' | \
while read -r f n; do printf "%03d:%-50s " $n "$f"; sed -n ${n}p $f; done

but not sure how reliable this is. Anyhow, using e.g. video1 for <device> that could yield something like:

031:/lib/udev/rules.d/50-udev-default.rules            SUBSYSTEM=="video4linux", GROUP="video"
007:/lib/udev/rules.d/60-persistent-v4l.rules          IMPORT{program}="v4l_id $devnode"
009:/lib/udev/rules.d/60-persistent-v4l.rules          SUBSYSTEMS=="usb", IMPORT{builtin}="usb_id"
010:/lib/udev/rules.d/60-persistent-v4l.rules          KERNEL=="video*", ENV{ID_SERIAL}=="?*", SYMLINK+="v4l/by-id/$env{ID_BUS}-$env{ID_SERIAL}-video-index$attr{index}"
016:/lib/udev/rules.d/60-persistent-v4l.rules          IMPORT{builtin}="path_id"
017:/lib/udev/rules.d/60-persistent-v4l.rules          ENV{ID_PATH}=="?*", KERNEL=="video*|vbi*", SYMLINK+="v4l/by-path/$env{ID_PATH}-video-index$attr{index}"
015:/lib/udev/rules.d/73-seat-late.rules               TAG=="uaccess", ENV{MAJOR}!="", RUN{builtin}+="uaccess"
006:/etc/udev/rules.d/83-webcam.rules                  KERNEL=="video[0-9]", SUBSYSTEMS=="usb", ATTRS{idVendor}=="0c45", SYMLINK+="video-webcam1"

But guess looking at the test as a whole is better. Also note the message:

This program is for debugging only, it does not run any program specified by a RUN key. It may show incorrect results, because some values may be different, or not available at a simulation run.

You can also set

udev_log="debug"

in udev.conf and restart udev (reload udev) to get a somewhat more verbose output.

Raspberry Pi Ubuntu Mate – Persistent Names for Physical USB Ports

I found a solution. The following rules assign a symbolic link to the corresponding usb ports for the given device. You could probably get rid of the idVendor and idProduct terms.

SUBSYSTEM=="tty", KERNELS=="1-1.2", ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", SYMLINK+="rplidar1"
SUBSYSTEM=="tty", KERNELS=="1-1.3", ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", SYMLINK+="rplidar2"

Best Answer

Related Solutions

List all udev rules (e.g. for a device)

Raspberry Pi Ubuntu Mate – Persistent Names for Physical USB Ports

Related Question