Public bug reported:
[SRU Justification]
== Impact ==
The ubuntu-fan extension is configured using user-space commands
provided by iproute2. Data is passed between user-space and the kernel
at a certain offset in a shared data structure. Since ubuntu-fan is not
upstream that offset can and did change with certain kernel versions.
The last time this happened was when we moved to kernels based on 6.14.
To avoid problems it was decided that user-space should be able to query
what offset to use (/proc/sys/net/fan/IFLA_VXLAN_FAN_MAP contains the
offset once the vxlan kernel module is loaded). The iproute2 package in
24.04/Noble already contains this change.
A common use case for containers is to run applications which have not
or even can not be ported inside older user-space environments but on
more up-to-date host environments. This creates the requirement to
enable old LTS user-space to work with newer kernels. And this causes
issues with fan as the old iproute2 implementations have no way of
predicting which offset to use for newer kernels.
== Fix ==
The proposal is to backport the code change which checks whether the
kernel has the new proc interface and use the provided offset if it is
found. Otherwise we fall back to the default for the series the iproute2
package was compiled for.
== Testcase ==
The test would be to bring up a container of the old series on a host
running the old series and a second time on a series which runs the 6.14
or newer kernel. Run some ubuntu-fan test in either environment and
check that ubuntu-fan can be configured in both cases.
== Regression Potential ==
Regressions would be limited to bringing up ubuntu-fan networks as the
modification only changes that phase. So verifying the bring up and tear
down should be sufficient.
** Affects: iproute2 (Ubuntu)
Importance: Medium
Status: Fix Released
** Affects: iproute2 (Ubuntu Focal)
Importance: Medium
Assignee: Stefan Bader (smb)
Status: Triaged
** Affects: iproute2 (Ubuntu Jammy)
Importance: Medium
Assignee: Stefan Bader (smb)
Status: Triaged
** Also affects: iproute2 (Ubuntu Focal)
Importance: Undecided
Status: New
** Also affects: iproute2 (Ubuntu Jammy)
Importance: Undecided
Status: New
** Changed in: iproute2 (Ubuntu Focal)
Importance: Undecided => Medium
** Changed in: iproute2 (Ubuntu Focal)
Status: New => Triaged
** Changed in: iproute2 (Ubuntu Focal)
Assignee: (unassigned) => Stefan Bader (smb)
** Changed in: iproute2 (Ubuntu Jammy)
Importance: Undecided => Medium
** Changed in: iproute2 (Ubuntu Jammy)
Status: New => Triaged
** Changed in: iproute2 (Ubuntu Jammy)
Assignee: (unassigned) => Stefan Bader (smb)
** Changed in: iproute2 (Ubuntu)
Status: Triaged => Fix Released
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https://bugs.launchpad.net/bugs/2122037
Title:
Backport dynamic ubuntu-fan map handling
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