Kernel selftests and backward compatibility?

[Vitaly Chikunov <vt@altlinux.org>]

Shuah,

Do kselftests require to be backward-compatible?

I see Documentation/dev-tools/kselftest.rst does not require this, but
maybe it's assumed like in other test suites (or in perf).

| In general, the rules for selftests are
| 
|  * Do as much as you can if you're not root;
| 
|  * Don't take too long;
| 
|  * Don't break the build on any architecture, and
| 
|  * Don't cause the top-level "make run_tests" to fail if your feature is
|    unconfigured.

For example LTP says:

| LTP test should be as backward compatible as possible. [...]
| 
| Therefore LTP test for more current features should be able to cope with older
| systems.

Also, (it's said[1]) perf, even though in kernel tree, is supposed to work
properly on any (older/newer) version of Linux.

Can you clarify this point in kselftest.rst?

I think, this would be useful for future kselftests developers, users,
and packagers. (Currently, I package for ALT Linux kselftests (and perf)
from the latest mainline branch, so people could test even older kernels
with the latest kselftests.

If there is policy to be backward-compatible kselftests in the future
could reach a state where users would run them in all pass mode (without
selecting only working tests). This, in turn, would increase [ease of]
usability of tests and thus frequency of their run and consequentially
quality kernel testing overall.

Thanks,

 [1] https://lkml.org/lkml/2020/7/29/677