lo?c tourlonias [off-list ref] writes:

Hi everybody,

In my project I have an USB composite device (a LTE modem) which use
USB to communicate with the processor. This device has several
interface to communicate but I do not use all of them. In particular,
it loads cdc_ether device which I don't use and I have an undesired
ethXX which interferes with a service in my system.

Sounds like your system has other issues, but whatever...

To schematize, let's say my device is loaded on port 2 of usb1, I have
the following USB topology:
- 1-2:1.0: tty
- 1-2:1.1: tty
- 1-2:1.2: tty
- 1-2:1.3: tty
- 1-2:1.4: tty
- 1-2:1.5: eth (not desired)

Is there a way to prevent this specific ethXX to mount?

I've already tried to create a udev rules, but I don't manage to stop
the loading process.
Here is a summary of my tries:
1/ I couldn't use the /sys/bus/usb1/.../1-2/activated file in my udev
rule because it's an USB composite device and I want to use the tty
interfaces but not the eth interface

2/ I have tried to stop the udev loading process, but setting MODALIAS
environment variable to a NULL-string doesn(t do the trick and
last-rule udev option has been removed in my udev version (1.8.2).

3/ I have tried to create a custom environment variable IGNORE_ETH and
modify my last rule which run modprobe with the modalias variable. In
the logs I see that modprobe isn't called by udev rules, but the
cdc_ether device is loaded all the same.

4/ I have think of creating a stub cdc_ether driver and use the
/etc/modprobe.d/my_file.conf to preempt the loading for my specific
usb composite device but this solution is ugly and I'm not sure it
will work.

The cdc_ether driver treats any ID entry with .driver_info = 0 as a
blacklist entry.  So you can dynamically blacklist devices by writing
the "VID PID" to /sys/bus/usb/drivers/cdc_ether/new_id before the device
is probed.


Bj?rn