Phew... looks like we have plenty of layered problems here:

1) calling "netplan set network.bridges.br54.dhcp4=true" will create an
empty bridge that will never get its DHCP4 configuration, thus will stay
stuck in the "configuring" state of "networkctl". Having empty bridges
is not really a production setup, and for test suites a simple
workaround would be to define "dhcp4=false" instead, thus it will not
trigger this problem.

2) networkctl reload/reconfigure is not super mature in Focal/systemd
v245 yet and there are some races that happen when netplan calls
"networkctl reload && networkctl reconfigure" right after each other
during its "netplan apply" call. I started going down this rabbit hole,
patching systemd-networkd, but this just leads to more problems. IMO we
should not heavily patch systemd-networkd, as long as it works "good
enough". (It works correctly on newer versions of systemd)

3) netplan-dbus does not apply the user's timeout parameter while
waiting for 'netplan try' to execute. this should be fixed by this
upstream PR: https://github.com/canonical/netplan/pull/271

4) The distro patch applied to the Focal package
(https://git.launchpad.net/ubuntu/+source/netplan.io/tree/debian/patches/0006-cli-
apply-give-some-extra-time-for-networkctl-
reload.patch?h=applied/ubuntu/focal-updates) implements a 5 second
timeout (due to the networkctl reload/reconfigure race-condition,
mentioned in (2)) that is in conflict with the 5 seconds timeout in
netplan-dbus (from (3)). This only applies to Focal.


So my proposal to fix this is:
- change the test-suite to call 'netplan set bridges.br54.dhcp4=false'
- The upstream patch from PR#271 was already applied to the netplan packaging 
for Core20, and should be included with the next Focal SRU (and potentially the 
other series, too – but with less urgency, as the conflicting distro patch is 
not in place there).


TL;DR: The root cause is a distro patch that was included in Focal, but we need 
this patch to work around systemd-networkd race conditions in systemd v245, so 
should implement other means to avoid this issue in Focal. This issue does not 
affect newer series of Ubuntu, due to improved systemd-networkd.

** Changed in: netplan
       Status: New => Fix Committed

** Also affects: netplan.io (Ubuntu Focal)
   Importance: Undecided
       Status: New

** Changed in: netplan.io (Ubuntu)
       Status: New => Fix Released

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https://bugs.launchpad.net/bugs/1967084

Title:
  netplan dbus returns "false" in io.netplan.Netplan.Config.Set with
  networkd

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