Bug#946196: udev: documented way to prevent interface renaming stopped working

[Benjamin Poirier]

On 2019/12/05 11:34, Michael Biebl wrote:
[...]
> 
> The old 73-usb-net-by-mac.rules file contained:
> 
>     TEST!="/etc/systemd/network/99-default.link", \
> 
> This check can't be expressed via .link files.
> The new 73-usb-net-by-mac.link link file does respect the net.ifnames=0
> kernel command line parameter, though.
> 
> I don't see a good way of fixing this with .link files, aside from
> documenting this change. We could say that users have to symlink
> 73-usb-net-by-mac.link as well (or symlink 80-net-setup-link.rules,
> which does the actual renaming).

I think documenting that 73-usb-net-by-mac.link needs to be symlinked as
well is the best approach. It diverges from the upstream instructions in
eg.
https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/#idontlikethishowdoidisablethis
but then, Debian diverges from upstream by adding
73-usb-net-by-mac.rules or .link.

> 
> The other alternative would be to revert the changes from #941636, but I
> kinda like the new .link based approach and would prefer to keep it.
> 
> Thoughts?

Like I pointed out in 941636, that simple TEST for the existence of
/etc/systemd/network/99-default.link is too basic and can lead to
counterintuitive behavior as well:

> This is an incomplete way of reimplementing udev functionality. In
> particular, the user will get a different behavior if they do
> 	$ cp /lib/systemd/network/99-default.link /etc/systemd/network/
> even though the naming rules are effectively the same.

So I don't think it was good.
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