Merge branch 'selftests-xfail'

Jakub Kicinski says:

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selftests: kselftest_harness: support using xfail

When running selftests for our subsystem in our CI we'd like all
tests to pass. Currently some tests use SKIP for cases they
expect to fail, because the kselftest_harness limits the return
codes to pass/fail/skip. XFAIL which would be a great match
here cannot be used.

Remove the no_print handling and use vfork() to run the test in
a different process than the setup. This way we don't need to
pass "failing step" via the exit code. Further clean up the exit
codes so that we can use all KSFT_* values. Rewrite the result
printing to make handling XFAIL/XPASS easier. Support tests
declaring combinations of fixture + variant they expect to fail.

Merge plan is to put it on top of -rc6 and merge into net-next.
That way others should be able to pull the patches without
any networking changes.

v4:
 - rebase on top of Mickael's vfork() changes
v3: https://lore.kernel.org/all/20240220192235.2953484-1-kuba@kernel.org/
 - combine multiple series
 - change to "list of expected failures" rather than SKIP()-like handling
v2: https://lore.kernel.org/all/20240216002619.1999225-1-kuba@kernel.org/
 - fix alignment
follow up RFC: https://lore.kernel.org/all/20240216004122.2004689-1-kuba@kernel.org/
v1: https://lore.kernel.org/all/20240213154416.422739-1-kuba@kernel.org/


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Signed-off-by: David S. Miller <davem@davemloft.net>