Re: [PATCH] r8152: Add support for setting MAC to system's Auxiliary MAC address

On Thursday 02 June 2016 20:04:02 Bjørn Mork wrote:

[off-list ref] writes:

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2) Track whether this is the first or second USB NIC plugged in.
 Only offer it

on the first NIC detected by r8152.  When the second NIC is
plugged in don't match from ACPI.

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There would be a question of what to do if the first NIC is
removed and

added back if it should get the persistent system MAC or not.

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I'd say yes, just make sure that only one NIC can have it at a
time.

You are going to get things very complex very quickly if you try
to do this.

It's really not that hard, track a module wide static variable
whether the feature is in use.  Track in each device whether the
feature was in use.  If it in use, don't assign the next device
plugged in via the ACPI string.  If a device is removed that has
the feature activated, change the module wide static variable.

Having the mac address jump around in an arbitrary way like this is
going to confuse the hell out of your users.  Consider what happens
if the user docks a laptop with an r8152 usb dongle already plugged
in... How are you going to explain that the dock gets some other mac
address in this case? How are you going to explain the difference
between using an r8152 based dongle and some other ethernet usb
dongle with your systems?

Make it behave consistently if you're going to add this.  Which can
be done by specifically matching the Dell dock (doesn't it have an
unique Dell device ID?) and ignoring any other r8152 device.  You
could also choose to set the same mac for all r8152 devices.  Which
is fine, but will probably confuse many users.

What you definitely should not do is to change the mac for some
arbitrary "first" device.  Then you are better off with the userspace
proposal where you and your users have some chance to implement a
sensible policy based on e.g. usb port numbers.

This is exactly what I wanted to write, but you were faster :-)

You can connect more Dell docks (with r8152 devices) and more non-Dell 
r8152 devices in random order into Dell laptop. In any case dependent on 
connect and disconnect order, devices always must have exactly same MAC 
addresses. Otherwise there will be problems! It confuse users and also 
admins of networks...

So if kernel approach is chosen then I think there are only two solution 
those satisfy above conditions:

First one is:
* all non-Dell devices have own MAC address
* all Dell devices have (one, same) AUX MAC address

Second one is:
* all devices (Dell and also non-Dell) have own address
* AUX MAC address is never used

So what do you (netdev maintainers) think about it?

-- 
Pali Rohár
pali.rohar@gmail.com