[systemd-devel] systemd-networkd: setting the MAC address for a .netdev unit?

[Matthias Schiffer]

On 04/22/2014 04:07 PM, Tom Gundersen wrote:
> Hi Matthias,
> 
> On Fri, Apr 18, 2014 at 1:08 AM, Matthias Schiffer
> <mschiffer at universe-factory.net> wrote:
>> On 04/18/2014 12:14 AM, Matthias Schiffer wrote:
>>> On 04/17/2014 11:28 PM, Dave Reisner wrote:
>>>> On Thu, Apr 17, 2014 at 11:02:11PM +0200, Matthias Schiffer wrote:
>>>>> Hi,
>>>>> I'd like to configure the MAC address of a bridge device statically (as
>>>>> bridges tend to change their MAC address depending on the order the
>>>>> ports are added on Linux otherwise), but there doesn't seem to be a way
>>>>> to match for a bridge in a .link unit. This would be very useful for
>>>>> macvlans as well.
>>>>
>>>> Link files can match bridges generally with Type=bridge or Driver=bridge
>>>> in the [Match] section, or more specifically by just matching on name.
>>>> In the [Link] section, MACAddressPolicy=persistent should give you
>>>> persistent hw addresses in the general case, or you can use
>>>> MACAddress=fe:ed:fa:ce:be:ef to set whatever you like for more specific
>>>> matches.
>>>>
>>>> Does this not work for you?
>>> Hmm, I thought I tried that before, but using
>>> MACAddress=fe:ed:fa:ce:be:ef seems to work now. Please note that the
>>> Name= match is not documented in the systemd.link manpage.
>>
>> I have to correct myself: The Name= match does not exist for .link
>> units. My testcase just seemed to work as a [Match] section only
>> consisting of a Name= match was considered an empty [Match] section and
>> matched on all devices...
>>
>> This should really be added as AFAICT there is currently no way to match
>> on virtual devices like briges, TAP devices, batman-adv devices, etc...
>> which have neither a persistent MAC address nor an ID_PATH to match on.
> 
> So I think what we should do here is to allow MAC address (and other
> things) to be set when creating the netdevs. I made an attempt at this
> by generating a "predictable" one based on the interface name and the
> machine-id. Would that do it for you, or are you after a _specific_
> mac address, rather than just one that is always the same? I had to
> revert the code doing this for now as there was a kernel bug, however
> we'll hopefully get that sorted soon and then get back to this.
> 
> Cheers,
> 
> Tom
> 

For my usecase, a predictable, but otherwise random MAC address would
do. But I also see that setting an arbitrary MAC address (or any other
link parameter) for a specific virtual device is useful as well
(especially as it is possible to do so with real devices). As virtual
devices are almost always created with specific names, a Name= match for
.link units would make the most sense in my opinion.

As a workaround, I've added the following udev rule to
80-net-setup-link.rules for now to allow matching for virtual devices
with Path= matches:

ENV{DEVPATH}=="/devices/virtual/net/*", ENV{ID_PATH}=="",
ENV{ID_PATH}="virtual-$kernel"

Thanks,
Matthias

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