[Bug 2064508] Re: re-enable Ubuntu FAN in the Noble kernel

** Tags removed: verification-needed-oracular-linux
** Tags added: verification-done-oracular-linux

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https://bugs.launchpad.net/bugs/2064508

Title:
re-enable Ubuntu FAN in the Noble kernel

Status in iproute2 package in Ubuntu:
Fix Released
Status in linux package in Ubuntu:
In Progress
Status in iproute2 source package in Noble:
Invalid
Status in linux source package in Noble:
Fix Released
Status in iproute2 source package in Oracular:
Fix Released
Status in linux source package in Oracular:
In Progress

Bug description:
[Impact]

In LP: #2063298, we have opted to deprecate Ubuntu FAN support because
of the maintenance overhead and the possibility of regressions /
conflicts with the new networking eBPF APIs in kernels >= 6.8.

However, we cannot disable this feature in HWE/backport kernels, so it
seems safer to adjust the Ubuntu FAN kernel patch set to ensure proper
co-existence with the updated vxlan policy requirements in newer 6.8
kernels.

The re-introduction of Ubuntu FAN should be considered as a temporary
measure, aimed at facilitating a smooth transition during its
deprecation without disrupting existing users (specifically Juju), and
enabling the backporting of 6.8 kernels to older releases.

The main plan is still to deprecate Ubuntu FAN at some point in the
future.

[Test case]

Rely on the specific Ubuntu FAN regression test to validate the proper
kernel support of this feature:

https://git.launchpad.net/~canonical-kernel-team/+git/autotest-client-
tests/tree/ubuntu_fan_smoke_test?h=autotest3

[Fix]

Re-apply the Ubuntu FAN patch set to the latest Noble kernel 6.8 and
integrate the IFLA_VXLAN_FAN_MAP attribute type in vxlan_policy to
satisfy the strict length validation check.

[Regression potential]

We may experience regressions with eBPF vxlan capabilities and
potentially specific use cases of the Ubuntu FAN technology (Juju
installations).

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