g_cdc module causes usb0: link is not ready errors

[Richard Andrews]

I've found that the g_cdc module which Angstrom (2.6.32) loads by
default does not work with /etc/network/interfaces (usb0: link is not
ready), but the g_ether module does work.

If anyone else hits this problem you can try changing
/etc/defaults/usb-gadget and set USB_MODE='networking' (instead of
'composite').
This influences the /usr/bin/usb-gadget program which gets run at boot
time and loads the module.

With this done I found that defining usb0 in
/etc/networking/interfaces actually sets the IP configuration. For
g_cdc it didn't work because the interface was reported ready early by
udev. udevadm showed subsequent events associated with usbmon and only
after these was the CDC ethernet interface actually capable of being
configured.

Hope this helps someone someday.
--
Rich