Adding a network interface

[Konrad Hinsen]

Dear Guixers,

I have started to play with GuixSD in a virtual machine, but I quickly 
got stuck. My starting point is the supplied "bare bones" setup, which 
works fine with only trivial modifications such as the disk device name 
and the user accounts to be created.

My virtual machine has two network interfaces, one for connections to 
the outside world and one for connections to/from the host (that's how 
VirtualBox works). The first one gets configured automatically via DHCP, 
presumably via (dhcp-client-service). The second one must be configured 
statically. After some exploration, I added

  (static-networking-service "enp0s8" ...)

to the list of services. No chance:

  service "networking" provided more than once

That must be because "lo" is already configured in %base-services. But 
the documentation explicitly says that I can call 
static-networking-service multiple times for multiple interfaces!

After a look at the source code for service management, I tried

  (modify-services %base-services
     (static-networking-service-type
        interfaces => (cons (static-networking-service "enp0s8" ...)
                            interfaces)))

This yields an error message from static-networking-shepherd-service 
about concerning "no matching pattern", which suggests that I haven't 
read enough of the source code to get this right. Back to the source 
code, and another try:

  (modify-services %base-services
     (static-networking-service-type
        interfaces => (cons (static-networking (interface "enp0s8") ...)
                            interfaces)))

Now I am back to: service "networking" provided more than once. So I am 
giving up... What's the solution to this puzzle?

Konrad.