Allow key configuration for [ip6]gre[tap] tunnels (LP: #1966476)

[slyon]

Description

The following example should configure a GRE tunnel between 172.16.4.2 and 172.16.1.2, with key 33490175. The effect should be like manually configured with: sudo ip tunnel add test1 mode gre local 172.16.4.2 remote 172.16.1.2 key 33490175.

However, the following Netplan configuration fails under Ubuntu 22.04 (latest development version, March 25, 2022):

network:
  version: 2
  renderer: networkd
  tunnels:
    gre1-255-255:
      mode: gre
      ttl: 255
      local: 172.16.4.2
      remote: 172.16.1.2
      key: 33490175
      addresses:
        - 172.20.82.94/30

Result of "sudo netplan generate": Error in network definition: gre1-255-255: 'input-key' is not required for this tunnel type

Some investigation into the sources of Netplan (src/validation.c -> https://github.com/canonical/netplan/blob/main/src/validation.c):
It seems that the cases NETPLAN_TUNNEL_MODE_GRE and NETPLAN_TUNNEL_MODE_IP6GRE are missing for systemd-networkd. According to systemd/systemd#12144, systemd-networkd should support configuration with keys since ca. 2 years.

Checklist

• Runs make check successfully.
• Retains 100% code coverage (make check-coverage).
• New/changed keys in YAML format are documented.
• (Optional) Adds example YAML for new feature.
• (Optional) Closes an open bug in Launchpad. LP#1966476

[codecov-commenter]

Codecov Report

Merging #274 (30f9572) into main (6a47c70) will decrease coverage by 0.11%.
The diff coverage is 100.00%.

❗ Current head 30f9572 differs from pull request most recent head 9e091de. Consider uploading reports for the commit 9e091de to get more accurate results

@@            Coverage Diff             @@
##             main     #274      +/-   ##
==========================================
- Coverage   99.19%   99.07%   -0.12%     
==========================================
  Files          61       61              
  Lines       11206    10862     -344     
==========================================
- Hits        11116    10762     -354     
- Misses         90      100      +10     

Impacted Files	Coverage Δ
src/validation.c	99.61% <ø> (ø)
tests/generator/test_tunnels.py	100.00% <100.00%> (ø)
src/abi_compat.c	83.33% <0.00%> (-16.67%)	⬇️
src/parse.c	99.82% <0.00%> (-0.02%)	⬇️
src/nm.c	100.00% <0.00%> (ø)
src/dbus.c	100.00% <0.00%> (ø)
src/util.c	100.00% <0.00%> (ø)
src/error.c	100.00% <0.00%> (ø)
src/types.c	100.00% <0.00%> (ø)
src/netplan.c	100.00% <0.00%> (ø)
... and 20 more

---

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[dreibh]

The solution is working successfully for configuring a GRE tunnel with key.

[slyon]

Thank you very much for the feedback/confirmation. I still need to find some time to polish up this PR (maybe add an integration tests) and get it landed.

[slyon]

I cleaned this PR up, added some integration tests (autopkgtest) and rebased on top of the current origin/main branch.
Thans again for testing @dreibh! Would you mind doing a code review as well?

[schopin-pro]

LGTM :)

Small nitpick: adding the tests in a commit before adding the implementation means that you'll have a broken test suite in your history. This triggers my inner Git neat freak ;-)

[slyon]

Thanks for the review! I rebased on top of origin/master (and re-ordered the git history while on it, to satisfy Simon's inner Git neat freak). Merging.