Add support for networkd ConfigureWithoutCarrier option on interfaces

[n-cc]

Description

The ConfigureWithoutCarrier networkd option allows networkd to configure a specific link even if it has no carrier. This is useful for services such as isc-dhcp-server, which requires that all managed interfaces are up and assigned IP addresses regardless of their physical status.

I chose to put this key under COMMON_LINK_HANDLERS rather than PHYSICAL_LINK_HANDLERS as networkd does not differentiate between physical and virtual links WRT the ConfigureWithoutCarrier option, as far as I can tell. Better names are welcome.

Checklist

• Runs make check successfully.
• Retains 100% code coverage (make check-coverage) *(make check-coverage reports the same coverage on master)
• New/changed keys in YAML format are documented.
• (Optional) Adds example YAML for new feature.
• (Optional) Closes an open bug in Launchpad.

[codecov-commenter]

Codecov Report

Merging #215 (4d5df9b) into main (e533ddf) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #215   +/-   ##
=======================================
  Coverage   99.02%   99.02%           
=======================================
  Files          56       56           
  Lines        9343     9347    +4     
=======================================
+ Hits         9252     9256    +4     
  Misses         91       91           

Impacted Files	Coverage Δ
src/parse.c	100.00% <ø> (ø)
src/netplan.c	100.00% <100.00%> (ø)
src/networkd.c	100.00% <100.00%> (ø)
tests/generator/test_common.py	100.00% <100.00%> (ø)

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[slyon]

Thank you very much for this PR! I didn't do a full review yet, but overall it is looking good from a code POV.

Though, as this contains a change of the YAML schema ("passthrough" of networkd's ConfigureWithoutCarrier= setting), I'd like to get an opinion from @vorlonofportland about if and how we want to support this use case before proceeding.

@n-cc Do you know if a similar feature is available and/or needed to support this with netplan's NetworkManager backend as well?

[n-cc]

@n-cc Do you know if a similar feature is available and/or needed to support this with netplan's NetworkManager backend as well?

I don't have much experience with NetworkManager, but ignore-carrier seems to be the equivalent option (manpage here). Adding the following section to /etc/NetworkManager/NetworkManager.conf allowed my physical interface to gain a static IP (configured separately under the system-connections directory) despite the physical link being down:

[device]
match-device=interface-name:enp0s31f6
managed=1
ignore-carrier=true

However, it doesn't seem that netplan's NetworkManager renderer currently templates the [device] section anywhere.

Looking at some of the common tests, it seems like there are situations where NetworkManager is used as the "main" renderer and networkd used for just specific ethernet interfaces; in these situations, my changes are sufficient to allow an interface to be assigned an IP without a physical link, so this feature can at least coexist with NetworkManager:

# cat /etc/netplan/01-network-manager-all.yaml 
# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager
  ethernets:
    enp0s31f6:
      renderer: networkd
      addresses: [10.0.0.2/24]
      dhcp4: false
      dhcp-identifier: mac
      optional: false
      gateway4: 10.0.0.1
      configure-without-carrier: true
# ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp0s31f6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000
    link/ether 30:5a:3a:83:8c:56 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.2/24 brd 10.0.0.255 scope global enp0s31f6
       valid_lft forever preferred_lft forever
#

[vorlonofportland]

my preference here is for the 'ignore-carrier' syntax, I think 'configure-without-carrier' is unnecessarily verbose.

[slyon]

Thank you Steve for your opinion on the ignore-carrier wording. Let's go with that.

So I think this PR is fine, as soon as the setting is renamed to "ignore-carrier".

Additionally, we should consider adopting it to the NetworkManager backend as well. Thanks for your investigation on this @n-cc ! We should be able to generated drop-in configs for NetworkManager in /run/NetworkManager/conf.d/XX-netplan-NETDEF.conf to contain the [device] section you mentioned. Would you be willing to look into this (as part of an additional PR)?

[slyon]

Suggested change

	``configure-without-carrier`` (bool)
	``ignore-carrier`` (bool) – since **0.104*

[slyon]

Suggested change

	{"configure-without-carrier", YAML_SCALAR_NODE, handle_netdef_bool, NULL, netdef_offset(configure_without_carrier)}, \
	{"ignore-carrier", YAML_SCALAR_NODE, handle_netdef_bool, NULL, netdef_offset(ignore_carrier)}, \

[slyon]

Suggested change

	gboolean configure_without_carrier;
	gboolean ignore_carrier;

[n-cc]

Thanks for the help getting this merged! This will hopefully benefit a lot of use-cases that require IP addresses set on inactive links.

We should be able to generated drop-in configs for NetworkManager in /run/NetworkManager/conf.d/XX-netplan-NETDEF.conf to contain the [device] section you mentioned. Would you be willing to look into this (as part of an additional PR)?

I can give it a shot at some point, but if I recall correctly, the change to get it implemented was a bit more involved, as the [device] section is not currently templated by netplan in any NetworkManager config files, whereas networkd support was essentially a one-line change.