Re: [Libusb-devel] Find specific USB device based on udev info

[Alan S. <st...@ro...>]

On Thu, 30 Jun 2011, Michael Bauer wrote:

> Hi there,
> 
> i think i am missing somethin obvious here, but i've looked into this topic for several days now without a solution. I hope you can give me some hint :-)
> 
> I want to make a tool which can be invoked by an udev rule to configure certain USB devices after they are plugged in. Problem is that i need to find the link between the information available through udev and the information availble from libusb to access the device through libusb.
> 
> This is what i get from udev:
> E:DEVPATH=/devices/pci0000:00/0000:00:02.1/usb1/1-1/1-1.4/1-1.4.3/1-1.4.3:1.0/input/input7/event7

This devpath is the pointer to the input device, not the USB device.  
The path you want is just:

	/devices/pci0000:00/0000:00:02.1/usb1/1-1/1-1.4/1-1.4.3/

> E: MAJOR=13
> E: MINOR=71
> E: DEVNAME=/dev/input/event7
> E: SUBSYSTEM=input
> E: ID_INPUT=1
> E: ID_INPUT_JOYSTICK=1
> E: ID_VENDOR=Logitech
> E: ID_VENDOR_ENC=Logitech
> E: ID_VENDOR_ID=046d
> E: ID_MODEL=Logitech_Driving_Force
> E: ID_MODEL_ENC=Logitech\x20Driving\x20Force
> E: ID_MODEL_ID=c294
> E: ID_REVISION=1106
> E: ID_SERIAL=Logitech_Logitech_Driving_Force
> E: ID_TYPE=hid
> E: ID_BUS=usb
> E: ID_USB_INTERFACES=:030000:
> E: ID_USB_INTERFACE_NUM=00
> E: ID_USB_DRIVER=usbhid
> E: ID_PATH=pci-0000:00:02.1-usb-0:1.4.3:1.0
> E: DEVLINKS=/dev/input/by-id/usb-Logitech_Logitech_Driving_Force-event-joystick /dev/input/by-path/pci-0000:00:02.1-usb-0:1.4.3:1.0-event-joystick /dev/input/DF
> 
> I want to also support multiple connected devices, so ideally i would do the following:
> 1. Pass the DEVPATH of the connected device into my tool
> 2. use libUSB to get access to the device based on the DEVPATH or DEVNAME (maybe double-check that the correct device is found by comparing VENDOR_ID and MODEL_ID)
> 3. do some stuff with device
> 
> Problem is: The DEVPATH/DEVNAME seems unavailable in libusb interface, so i did not find any way to make sure that i open the correct device. I only found "libusb_get_bus_number" and "libusb_get_device_address", but the information i get here is not matching anything i would get from udev...
> 
> So i am pretty  much stuck - Do you have any suggestion how i could do this?

If you look in the 
/sys/devices/pci0000:00/0000:00:02.1/usb1/1-1/1-1.4/1-1.4.3/ directory, 
you'll find files named "busnum" and "devnum".  They contain the bus 
number and device address values you can pass to libusb.

Alan Stern