automatic sysfs attribute creation

Hello,

I've read Greg's blog post about sysfs attributes at http://www.kroah.com/log/blog/2013/06/26/how-to-create-a-sysfs-file-correctly/. We've used attribute groups for the whole time, but the post made me wondering whether our drivers might be affected by that too. Unfortunately the blog mentions only struct class, struct bus, struct device and so on. I couldn't find anything about USB interfaces or struct net_device. At least the latter has const struct attribute_group *sysfs_groups[4]; itself. So I tried setting sysfs_groups[0] in the probe function of my usb_driver before calling register_candev (which in return set the attribute groups in struct device later). So IMHO the sysfs files should be created before the new CAN interface is announced to userspace.
But I get the exact problem Greg describes: A udev rules shall set an attribute during ACTION=="add". This USB device create 2 CAN interfaces and only on one device the attribute is set correctly. _Unless_: the rule file is named 75-usbcan.rules in /etc/udev/rules.d or has a higher number at the beginning. This indicates a race condition to me.
Am I doing anything wrong here? The described way should have prevented this.
BTW: Is there something similar for the USB device driver?

Regards and thanks in advance
Alexander

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