Bug#812575: udev: predictable network device names fails for USB devices without a permanent hw address

[Bjørn Mork]

Michael Biebl <biebl at debian.org> writes:

>> But even with this in place, the new logic should be prepared for
>> duplicate mac addresses.  There are plenty of USB devices with non-
>> unique mac addresses out there.  It's more of a rule than an exception
>> for GSM/LTE modem devices...
>
> Please consider raising this issue upstream and filing a bug at
> https://github.com/systemd/systemd/issues/new

Just FYI, I stumbled across the upstream systemd sources on my disk
(have a lof cruft laying around :) and noticed that this problem is not
present there.  The "net_setup_link" builtin helper is very careful to
avoid basing its names on local mac addresses or random addresses. Both
which are true in the case I reported.  usbnet based drivers will set
addr_assign_type to NET_ADDR_RANDOM when appropriate:

 bjorn at nemi:~$  grep . /sys/class/net/wwan*/addr_assign_type
 /sys/class/net/wwan0/addr_assign_type:1
 /sys/class/net/wwan1/addr_assign_type:1


The bug was introduced by this commit, trying to work around the
upstream bogus assumption that USB bus numbers are stable:

commit 51009270be5da77a0e11b313190ef12ab401c007
Author: Martin Pitt <martin.pitt at ubuntu.com>
Date:   Wed Jun 3 12:48:42 2015 +0200

    Add debian/extra/01-mac-for-usb.link: Use MAC based names for network interfaces which are (directly or indirectly) on USB
    
    Path based names are inadequate for dynamic buses like USB.
    
    See discussion on
    
      https://lists.debian.org/debian-devel/2015/05/msg00170.html
    
    and revised proposal on
    
      https://lists.debian.org/debian-devel/2015/06/msg00018.html



And I recall even being part of that discussion.  Obviously without
getting the message trough.  So let me try again:

   You CANNOT create a stable name for USB devices.

The reason is pretty simple and should be bloody obvious: You have no
stable and unique input parameteres.  Every single attribute you have
access to is either shared with multiple devices or subject to change.

So if you insist on renaming these devices, then you will fail.



Bjørn