Re: LKFT CI: improving Networking selftests results when validating stable kernels

On Fri, Nov 08, 2024 at 07:21:59PM +0100, Matthieu Baerts wrote:

KSelftests from the same version
--------------------------------

According to the doc [2], kselftests should support all previous kernel
versions. The LKFT CI is then using the kselftests from the last stable
release to validate all stable versions. Even if there are good reasons
to do that, we would like to ask for an opt-out for this policy for the
networking tests: this is hard to maintain with the increased
complexity, hard to validate on all stable kernels before applying
patches, and hard to put in place in some situations. As a result, many
tests are failing on older kernels, and it looks like it is a lot of
work to support older kernels, and to maintain this.

Many networking tests are validating the internal behaviour that is not
exposed to the userspace. A typical example: some tests look at the raw
packets being exchanged during a test, and this behaviour can change
without modifying how the userspace is interacting with the kernel. The
kernel could expose capabilities, but that's not something that seems
natural to put in place for internal behaviours that are not exposed to
end users. Maybe workarounds could be used, e.g. looking at kernel
symbols, etc. Nut that doesn't always work, increase the complexity, and
often "false positive" issue will be noticed only after a patch hits
stable, and will cause a bunch of tests to be ignored.

Regarding fixes, ideally they will come with a new or modified test that
can also be backported. So the coverage can continue to grow in stable
versions too.

Do you think that from the kernel v6.12 (or before?), the LKFT CI could
run the networking kselftests from the version that is being validated,
and not from a newer one? So validating the selftests from v6.12.1 on a
v6.12.1, and not the ones from a future v6.16.y on a v6.12.42.

These kinds of decisions are something that Greg and Shuah need to decide on.

You would still need some way to automatically detect that kselftest is running
on an old kernel and disable the networking checks.  Otherwise when random
people on the internet try to run selftests they would run into issues.

regards,
dan carpenter