On Mon, Jun 22, 2020 at 7:47 PM David Gow davidgow@google.com wrote:
On Mon, Jun 22, 2020 at 6:45 AM Frank Rowand frowand.list@gmail.com wrote:
Tim Bird started a thread [1] proposing that he document the selftest result format used by Linux kernel tests.
[1] https://lore.kernel.org/r/CY4PR13MB1175B804E31E502221BC8163FD830@CY4PR13MB11...
The issue of messages generated by the kernel being tested (that are not messages directly created by the tests, but are instead triggered as a side effect of the test) came up. In this thread, I will call these messages "expected messages". Instead of sidetracking that thread with a proposal to handle expected messages, I am starting this new thread.
Thanks for doing this: I think there are quite a few tests which could benefit from something like this.
I think there were actually two separate questions: what do we do with unexpected messages (most of which I expect are useless, but some of which may end up being related to an unexpected test failure), and how to have tests "expect" a particular message to appear. I'll stick to talking about the latter for this thread, but even there there's two possible interpretations of "expected messages" we probably want to explicitly distinguish between: a message which must be present for the test to pass (which I think best fits the "expected message" name), and a message which the test is likely to produce, but which shouldn't alter the result (an "ignored message"). I don't see much use for the latter at present, but if we wanted to do more things with messages and had some otherwise very verbose tests, it could potentially be useful.
+Dmitry Vyukov, I think you were interested in this for KASAN before we went with the signalling approach. Any thoughts?
The other thing I'd note here is that this proposal seems to be doing all of the actual message filtering in userspace, which makes a lot of sense for kselftest tests, but does mean that the kernel can't know if the test has passed or failed. There's definitely a tradeoff between trying to put too much needless string parsing in the kernel and having to have a userland tool determine the test results. The proposed KCSAN test suite[1] is using tracepoints to do this in the kernel. It's not the cleanest thing, but there's no reason KUnit or similar couldn't implement a nicer API around it.
I implemented an API for expected messages that are triggered by tests in the Devicetree unittest code, with the expectation that the specific details may change when the Devicetree unittest code adapts the KUnit API. It seems appropriate to incorporate the concept of expected messages in Tim's documentation instead of waiting to address the subject when the Devicetree unittest code adapts the KUnit API, since Tim's document may become the kernel selftest standard.
Is having a nice way to handle expected messages the only thing holding up porting this to KUnit?
Instead of creating a very long email containing multiple objects, I will reply to this email with a separate reply for each of:
The "expected messages" API implemention and use can be from drivers/of/unittest.c in the mainline kernel.
of_unittest_expect - A proof of concept perl program to filter console output containing expected messages output
of_unittest_expect is also available by cloning https://github.com/frowand/dt_tools.gitAn example raw console output with timestamps and expect messages.
An example of console output processed by filter program of_unittest_expect to be more human readable. The expected messages are not removed, but are flagged.
An example of console output processed by filter program of_unittest_expect to be more human readable. The expected messages are removed instead of being flagged.
Cheers, -- David