Re: [PATCH 14/16] tests: add QEMU_TEST_IO_SKIP for skipping I/O tests

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, May 12, 2026 at 09:19:45AM -0700, Pierrick Bouvier wrote:
> On 5/12/2026 9:06 AM, Daniel P. Berrangé wrote:
> > On Tue, May 12, 2026 at 08:56:54AM -0700, Pierrick Bouvier wrote:
> >> On 4/24/2026 8:42 AM, Daniel P. Berrangé wrote:
> >>> The nature of block I/O tests is such that there can be unexpected false
> >>> positive failures in certain scenarios that have not been encountered
> >>> before, and sometimes non-deterministic failures that are hard to
> >>> reproduce.
> >>>
> >>> Before enabling the I/O tests as gating jobs in CI, there needs to be a
> >>> mechanism to dynamically mark tests as skipped, without having to commit
> >>> code changes.
> >>>
> >>> This introduces the QEMU_TEST_IO_SKIP environment variable that is set
> >>> to a list of FORMAT-OR-PROTOCOL:NAME pairs. The intent is that this
> >>> variable can be set as a GitLab CI pipeline variable to temporarily
> >>> disable a test while problems are being debugged.
> >>>
> >>> Reviewed-by: Thomas Huth <thuth@redhat.com>
> >>> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> >>> ---
> >>>  docs/devel/testing/main.rst      |  7 +++++++
> >>>  tests/qemu-iotests/testrunner.py | 16 ++++++++++++++++
> >>>  2 files changed, 23 insertions(+)
> >>>
> >>> diff --git a/docs/devel/testing/main.rst b/docs/devel/testing/main.rst
> >>> index 797111009a..f779a64415 100644
> >>> --- a/docs/devel/testing/main.rst
> >>> +++ b/docs/devel/testing/main.rst
> >>> @@ -284,6 +284,13 @@ that are specific to certain cache mode.
> >>>  More options are supported by the ``./check`` script, run ``./check -h`` for
> >>>  help.
> >>>  
> >>> +If a test program is known to be broken, it can be disabled by setting
> >>> +the ``QEMU_TEST_IO_SKIP`` environment variable with a list of tests to
> >>> +be skipped. The values are of the form FORMAT-OR-PROTOCOL:NAME, the
> >>> +leading component can be omitted to skip the test for all formats and
> >>> +protocols. For example ``export QEMU_TEST_IO_SKIP="luks:149 185 iov-padding``
> >>> +will skip ``149`` for LUKS only, and ``185`` and ``iov-padding`` for all.
> >>> +
> >>>  Writing a new test case
> >>>  ~~~~~~~~~~~~~~~~~~~~~~~
> >>>  
> >>> diff --git a/tests/qemu-iotests/testrunner.py b/tests/qemu-iotests/testrunner.py
> >>> index dbe2dddc32..ecb5d4529f 100644
> >>> --- a/tests/qemu-iotests/testrunner.py
> >>> +++ b/tests/qemu-iotests/testrunner.py
> >>> @@ -145,6 +145,18 @@ def __init__(self, env: TestEnv, tap: bool = False,
> >>>  
> >>>          self._stack: contextlib.ExitStack
> >>>  
> >>> +        self.skip = {}
> >>> +        for rule in os.environ.get("QEMU_TEST_IO_SKIP", "").split(" "):
> >>> +            rule = rule.strip()
> >>> +            if rule == "":
> >>> +                continue
> >>> +            if ":" in rule:
> >>> +                fmt, name = rule.split(":")
> >>> +                if fmt in ("", env.imgfmt, env.imgproto):
> >>> +                    self.skip[name] = True
> >>> +            else:
> >>> +                self.skip[rule] = True
> >>> +
> >>>      def __enter__(self) -> 'TestRunner':
> >>>          self._stack = contextlib.ExitStack()
> >>>          self._stack.enter_context(self.env)
> >>> @@ -251,6 +263,10 @@ def do_run_test(self, test: str) -> TestResult:
> >>>                                description='No qualified output '
> >>>                                            f'(expected {f_reference})')
> >>>  
> >>> +        if f_test.name in self.skip:
> >>> +            return TestResult(status='not run',
> >>> +                              description='Listed in QEMU_TEST_IO_SKIP')
> >>> +
> >>>          args = [str(f_test.resolve())]
> >>>          env = self.env.prepare_subprocess(args)
> >>>  
> >>
> >> Why not simply remove the broken tests, and create issues to add them
> >> again in the future?
> > 
> > In theory that's what our policy today is, but in practice it is
> > too much of a burden on the release co-ordinator, to expect them
> > to create such a patch themselves, or wait on a subsys maintainer
> > todo it for them.
> > 
> > They end up just ignoring brokenness in CI which is a bad practice,
> > and will prevent us ever making CI truely gating or switching to
> > using MRs for pull requests. This gives us a super-fast way to skip
> > flaky tests, while the subsystem maintainers figure out the right
> > permanent answer.
> >
> 
> I disagree on this one, merging a single patch doing a git rm, and a git
> revert later is not more expensive than merging a variable modifying a
> variable in a yaml file.

Any code changes like that need to be sent back to the subsystem
maintainer to be acked. IMHO the release manager should not be
unilaterally deleting tests without peer review.  So that's
got a non-negligible turn around time, during which CI is broken.

Setting an env variable to skip a problematic test is something
reasonable to do with zero oversight.

> The issue with this approach is that people running tests locally will
> not see which tests are skipped, and will see false positives. So you
> just keep CI green, but not the test base itself.

I would still expect the release manager to file a bug about any
flaky test they disable via the env var, and the subsystem maintainer
should still be fixing it or disabling it such that tests won't fail
more broadly, or deciding to remove it if terminally broken.

We're just decoupling the process so that there is an immediate
workaround possible. It can also be used by people working in
their forks - often I've been testing stuff in my fork, but
see spurious failures because git master has a non-deterministic
test failure merged. I would like to easily skip those in my fork
too, without adding extra commits to me working branches, as that
would require the same commit to be duped into several in-progress
branches, vs setting the env var once.

> The risk I see is that some tests will stay forever in this skip
> variable, so it will be dead code for CI, but still alive and failing
> for people running tests manually who hit the regression.

Again, there should be a bug filed for any flaky test. Anyone can
do this, if they see it locally or in their fork CI, or in staging
CI. If no one can see an obvious fix, then anyone can also propose
to disable the test.

> If you still want an alternative to removing test, implementing a
> skip_list in tests/qemu-iotests/meson.build is better than an env var
> IMHO, and achieves the exact same effect, for CI and for users.
> 
> What do you think?

IMHO there needs to be a way to skip flaky tests which does not
require code changes as the only available option. Code changes
are the permanent fix, env var is the immediate workaround.

> >> Once it's green, in theory, code breaking existing tests should not be
> >> merged, right? So what would be the usage of this variable?
> > 
> > We have had a pretty decent chunk of non-deterministic test failures,
> > so there is high likelihood we can merge stuff that passes once and
> > then subsequently fails some subset of the time. This non-determinism
> > is one of the key reasons that we currently only have a hand picked
> > selection of block I/O tests run by meson.
> > 
> > While I've tested this series and haven't see any non-determinstic
> > failures in what I'm proposing to enable thus far, I think there is
> > still a pretty high chance we'll uncover some more.
> >
> 
> Fair point.

With regards,
Daniel
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