Re: [PATCH 16/29] selftests/mm: UFFDIO_API test
From: David Hildenbrand
Date: Tue Apr 04 2023 - 08:50:49 EST
On 03.04.23 22:24, Peter Xu wrote:
On Mon, Apr 03, 2023 at 09:06:26PM +0200, David Hildenbrand wrote:
On 03.04.23 18:43, Peter Xu wrote:
On Mon, Apr 03, 2023 at 09:59:50AM +0200, David Hildenbrand wrote:
There is ksft_print_msg, ksft_test_result, ksft_test_result_fail, ... do we
maybe want to convert properly to ksft while already at it?
Yes, I started with trying to use that but found that there're not a lot of
things that I can leverage.
Starting with ksft_set_plan() - I think this is something we call first. I
want the current unit test to skip everything if UFFD API test failed here,
then I need to feed in a dynamic number of "plan" into ksft_set_plan().
But I never know after I ran the 1st test..
In cow.c I did that. Getting the number of tests right can be challenging
indeed.
IMHO the major thing is not about not easy to set, it's about there's
merely no benefit I can see of having that calculated at the start of a
test.
Thinking about it, I believe I figured out why it makes sense. By
specifying upfront how many tests you intend to run, the framework can
check if you have the right number of pass/fail/skip during that test
case execution.
This requires a different way of writing tests: each test case is
supposed to trigger the exact same number of pass/fail/skip on each
possible path.
If the numbers don't add up, it could indicate a possible bug in your
tests. For example, not triggering a fail on some exit path. While your
test execution might indicate "success", there is actually a hidden
issue in your test.
I started using the framework for all new tests, because I think it's
quite nice and at least things will be a bit consistent and possibly
tests easier to maintain.
Having that said, I can understand why one might not want to use it. And
that there are some things in there that might be improved.
There's one thing it can do, that is when calling ksft_finished() it can be
used to know whether all tests are run, but sadly here we're calculating
everything just to make it match.. so it loses its last purpose.. IMHO.
Basic "feature availability" checks would go first (is uffd even around?),
and depending on that you can set the plan.
For everything else, you can skip instead of test, so it will still be
accounted towards the plan.
I can call ksft_set_plan() later than this, but it misses a few tests which
also looks weird.
Yeah, it would be nice to simply make ksft_set_plan() optional. For example,
make ksft_print_cnts() skip the comparison if ksft_plan == 0. At least
ksft_exit_skip() handles that already in a descend way (below).
It also seems to not really help anything at all and not obvious to use.
E.g. ksft_finished() will reference ksft_plan then it'll trigger
ksft_exit_fail() but here I want to make it SKIP if the 1st test failed
simply because the kernel probably doesn't have CONFIG_USERFAULTFD.
You'd simply do that availability check first and then use ksft_exit_skip()
in case not available I guess.
Another example: I never figured what does x{fail|pass|skip} meant in the
header.. e.g. ksft_inc_xfail_cnt() is used nowhere so I cannot reference
either. Then I don't know when I should increase them.
In cow.c I have the following flow:
ksft_print_header();
ksft_set_plan();
... tests ...
err = ksft_get_fail_cnt();
if (err)
ksft_exit_fail_msg();
return ksft_exit_pass();
That gives me:
# [INFO] detected THP size: 2048 KiB
# [INFO] detected hugetlb size: 2048 KiB
# [INFO] detected hugetlb size: 1048576 KiB
# [INFO] huge zeropage is enabled
TAP version 13
1..190
...
# Totals: pass:87 fail:0 xfail:0 xpass:0 skip:103 error:0
I didn't use xfail or xpass so far, but what I understood is that these are
"expected failures" and "expected passes". fail/pass/skip are straight
Yes, xfail can be expressed that way, but maybe not xpass? Otherwise it's
hard to identify what's the difference between xpass and pass, because IIUC
pass also means "expected to pass".
I'm a simple man, I use pass/fail/skip in my tests. But let's try
figuring that out; a quick internet search (no idea how trustworthy)
tells me that I was wrong about xpass:
xfail: expected failure
xpass: unexpected pass
it essentially is:
xfail -> pass
xpass -> fail
but with a slight semantic difference when thinking about a test case:
ret = mmap(0, 0 ...);
if (ret == MAP_FAILED) {
XFAIL();
} else {
XPASS();
}
vs.
ret = mmap(0, 0 ...);
if (ret == MAP_FAILED) {
PASS();
} else {
FAIL();
}
It's all inherited from other testing frameworks I think. And xpass
seems to be completely unused and xfail mostly unused.
So I wouldn't worry about that and simply use pass/fail/skip.
forward.
ksft_test_result_fail()/ksft_test_result_pass()/ksft_test_result_skip() are
used to set them.
You'd do availability checks before ksft_set_plan() and fail with a
ksft_exit_skip() if the kernel doesn't support it. Then, you'd just use
ksft_test_result_fail()/ksft_test_result_pass()/ksft_test_result_skip().
In short, to make the unit test behave as expected, I figured I'll just
write these few helpers and that's good enough for this unit test. That
takes perhaps 5 min anyway and isn't hugely bad for an unit test.
Then I keep the exit code matching kselftests (KSFT_SKIP, etc.).
What I can do here, though, is at least reuse the counters, e.g:
ksft_inc_pass_cnt() / ksft_inc_fail_cnt()
There's no ksft_inc_skip_cnt() so, maybe, I can just reuse
ksft_inc_xskip_cnt() assuming that counts "skip"s?
Let me know if you have better ideas, I'll be happy to switch in that case.
I guess once you start manually increasing/decreasing the cnt, you might be
abusing the ksft framework indeed and are better off handling it differently
:D
I'm serious considering that to address your comment here, to show that I'm
trying my best to use whatever can help in this test case. :) Here reusing
:) appreciated, but don't let my comments distract you. If you don't
think ksft is a good fit (or any good), then don't use it.
--
Thanks,
David / dhildenb