[systemd-devel] systemd-networkd doesn't delete netdev when parent interface is deleted

[hello at andreborie.name]

Hello,

I'm trying to use systemd-networkd to manage a "sit" tunnel and I've hit 
problem. My internet connection is provided by "ppp0" which isn't 
directly managed by networkd and can come and go at anytime. I have a 
.network file with "[Match] Name=ppp0" that works as expected and 
correctly configures DNS and forwarding on that interface. I then added 
a .netdev file for the tunnel and referenced it using the "[Network] 
Tunnel=..." directive in ppp0's .network file. That works as expected 
and the tunnel is configured with ppp0 as its device :

     heipv6: ipv6/ip  remote 216.66.84.42  local any  dev ppp0  ttl 255  
6rd-prefix 2002::/16

The problem happens when the ppp0 interface goes down. The tunnel netdev 
remains but references a non-existing interface "ifXX" and is obviously 
not operational anymore :

     heipv6: ipv6/ip  remote 216.66.84.42  local any  dev if34  ttl 255  
6rd-prefix 2002::/16

Worse, once the ppp0 interface comes back up, that netdev remains 
untouched and still points to the non-existing interface. Restarting 
systemd-networkd doesn't have any effect either. Only deleting the 
tunnel with "ip tunnel del" and then either restarting systemd-networkd 
or pppd (to recreate an ppp0 interface) causes systemd-networkd to 
create a new tunnel correctly referencing the new ppp0.

According to the manual for systemd.netdev, this is expected behavior :

	If a netdev with the specified name already exists, networkd will use 
that as-is rather than create its own. Note that the settings of the 
pre-existing netdev will not be changed by networkd.

However, in my case it's clearly undesirable behavior and I'd like to 
know what should I do to get this working. Here are the relevant 
configuration files :

# ppp.network

	[Match]
	Name=ppp0

	[Network]
	DHCP=no
	Tunnel=heipv6

# he.netdev

	[NetDev]
	Name=heipv6
	Kind=sit

	[Tunnel]
	Remote=216.66.84.42

Thanks.

TLDR: I need to make systemd-networkd override some settings of an 
existing netdev, or delete a netdev after its parent device has 
disappeared.