[SRU][L, K, J, F][M, U][PATCH v2 0/1] UBUNTU: [Packaging] Expose base (parent) abinum for derivatives

[Roxana Nicolescu]

BugLink: https://bugs.launchpad.net/bugs/2017006

SRU Justification

[ Impact ]

Upstream stable added a change in the format of jbd2 in 5.15.87 that
was cherry-picked to kinetic:linux.
This is incompatible with the current changes in the lttng-module
kinetic.

We previously encountered this issue for focal #lp2004644
and we proactively released a new version for kinetic, but the fix did
not work as expected.

As shown in the buglink, the build error is triggered because some
function declaration does not match the kernel's.
In `include/instrumentation/events/jbd2.h` in lttng-modules, there is
a conditional declaration based on the kernel version.
But for 5.19 kernels, the upstream kernel version has remained the
same.

[ Fix ]
Versioning based on linux upstream version does not work in this case.
We expose the abi version of the kernel, but it alone will not solve
this issue because we deliver many derivatives, each with its own
version. Hence a base main abi version needs to be exposed in the
headers.

The actual fix for lttng-modules requires 2 steps:
1. Expose UTS_UBUNTU_BASE_RELEASE_ABI variable equal with the parent
abi in <generated/utsrelease.h>. For backports with multiple
inheritance (like jammy:linux-aws-5.19) the version from debian.master
(kinetic:linux) will be used. In case there is no inheritance, the
actual kernel abi will be used. This is needed for jammy, kinetic and
lunar but it may be needed in the future for similar use cases,
so it makes sense to push this to all releases.
This patch will cover the first part.
2. Use this variable in the lttng-module to construct
LTTNG_UBUNTU_BASE_VERSION_CODE and then use it for versioning:
LTTNG_UBUNTU_BASE_VERSION_CODE >= LTTNG_UBUNTU_KERNEL_VERSION(5,19,0,42)
The lttng-module fix will be done only for lunar, kinetic, and jammy.

[ Where problems would occur ]
This patch alone should not have a big impact on our kernels.
It will only expose a variable in the headers.
In terms of the lttng-modules solution:
We may notice new failures in ubuntu_lttng_smoke_test once this
compiles and run. But it was tested locally and the results were good,
so the probability is very very low.

[ Test Plan ]
Since we hit backward issues in the past, multiple kernel versions
were tested out to make sure this is the proper fix.
General test instructions:
1. Install kinetic (desired version)
2. sudo apt install lttng-modules-dkms(or dpkg -i)
3. Depending on the version it may work or not
4. Additionally lttng-modules regression test should be triggered to
confirm everything works fine.

My testing:
I build fixed lttng-modules with the fixes described in launchpad.
A. Kinetic kernel where I expose UTS_UBUNTU_BASE_RELEASE_ABI.
The module built and rts passed:
09:32:05 INFO | PASSED (simple system call tracing with babeltrace)
09:32:05 INFO | Summary: 7 passed, 0 failed
B. The break commit was introduced in 5.19.0.42. Versions between 42
and 44 (depending on where this fix will land) will break.
C. Tested with a kernel version that does not have the break commit:
5.19.0-41 to see if it's backwards compatible. Results were good.
D. Tested with jammy-aws-5.19 that has this patch. It works fine.
E. Tested with jammy-aws-5.19.0-1024 that does not have the break
commit to see backwards compatibility. It succeeded.

Changes since v1:
- used a cleaner version of parsing the abinum from
  debian.master/changelog that lead to removing the useless variables
  created in v1
- added abinum in the title

Roxana Nicolescu (1):
  UBUNTU: [Packaging] Expose base (parent) abinum for derivatives

 debian/rules.d/0-common-vars.mk | 6 ++++++
 debian/rules.d/2-binary-arch.mk | 4 ++++
 2 files changed, 10 insertions(+)

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2.34.1