udev string ID_SERIAL_SHORT might not be available

[NiklasNeugebauer]

The new USB Camera Module uses udev strings to assign a unique id to each camera.
For that it currently combines ID_VENDOR_ID, ID_MODEL_ID and ID_SERIAL_SHORT.

We have seen one instance of a camera not providing ID_SERIAL_SHORT.

Note: ID_SERIAL does not come directly from the USB device descriptor, but is constructed from multiple strings like we do. It might be a better fit if it is always available.

[NiklasNeugebauer]

An indirect issue here is that this camera will not have a unique identifier, which should be guaranteed.
Its ID_SERIAL is HD_USB_Camera_HD_USB_Camera.

$ udevadm info -q all -n dump:

P: /devices/platform/3610000.xhci/usb1/1-2/1-2.1/1-2.1:1.0/video4linux/video1
N: video1
L: 0
S: v4l/by-path/platform-3610000.xhci-usb-0:2.1:1.0-video-index1
S: v4l/by-id/usb-HD_USB_Camera_HD_USB_Camera-video-index1
E: DEVPATH=/devices/platform/3610000.xhci/usb1/1-2/1-2.1/1-2.1:1.0/video4linux/video1
E: DEVNAME=/dev/video1
E: MAJOR=81
E: MINOR=1
E: SUBSYSTEM=video4linux
E: USEC_INITIALIZED=12827015
E: ID_V4L_VERSION=2
E: ID_V4L_PRODUCT=HD USB Camera: HD USB Camera
E: ID_V4L_CAPABILITIES=:
E: ID_VENDOR=HD_USB_Camera
E: ID_VENDOR_ENC=HD\x20USB\x20Camera
E: ID_VENDOR_ID=32e4
E: ID_MODEL=HD_USB_Camera
E: ID_MODEL_ENC=HD\x20USB\x20Camera
E: ID_MODEL_ID=9230
E: ID_REVISION=0100
E: ID_SERIAL=HD_USB_Camera_HD_USB_Camera
E: ID_TYPE=video
E: ID_BUS=usb
E: ID_USB_INTERFACES=:0e0100:0e0200:
E: ID_USB_INTERFACE_NUM=00
E: ID_USB_DRIVER=uvcvideo
E: ID_PATH=platform-3610000.xhci-usb-0:2.1:1.0
E: ID_PATH_TAG=platform-3610000_xhci-usb-0_2_1_1_0
E: ID_FOR_SEAT=video4linux-platform-3610000_xhci-usb-0_2_1_1_0
E: COLORD_DEVICE=1
E: COLORD_KIND=camera
E: DEVLINKS=/dev/v4l/by-path/platform-3610000.xhci-usb-0:2.1:1.0-video-index1 /dev/v4l/by-id/usb-HD_USB_Camera_HD_USB_Camera-video-index1
E: TAGS=:uaccess:seat:

[rodja]

Maybe we could fallback to DEVNAME or DEVPATH if ID_SERIAL_SHORT is not available. That would still allow us to identify different cameras and only lose the ability to freely chose the usb port.