[LTP] [PATCH v2 2/3] Add fanotify_get_supported_init_flags() helper function

[Amir Goldstein]

On Mon, Oct 24, 2022 at 4:16 PM Martin Doucha <mdoucha@suse.cz> wrote:
>
> On 24. 10. 22 15:08, Amir Goldstein wrote:
> > Why is skipping the test better than passing the test?
> >
> > The test wants to know that a specific flag combination is not allowed.
> >
> > It is particarly not allowed also on old kernels that do not support
> > either individual flag.
> >
> > What's the difference?
> >
> > Who is going to gain anything from this change?
> >
> > Sorry for being strict on this point
> > I may be missing something.
> >
> > Please clarify what it is the problem use case is and I will suggest a
> > solution, because I disagree with this solution.
>
> We're running fanotify14 on kernel 5.3 and one of the subtests (test
> case #8) is using a flag that was added in kernel 5.9. But in this case,
> fanotify_init() is supposed to pass and then fanotify_mark() is supposed
> to fail because of mismatch between mark() and init() flags. I'm trying
> to fix this particular subtest failure caused by wrong feature check.
>

Got it. If you wrote this information somewhere else
I must have missed it - if you did not, please write explicitly
which test case is being fixed on which kernel version/config.

This is how I would fix the problem:

        if (!tc->mask) {
                /* tc->expected_errno refers to the expected result of
fanotify_init() */
                TST_EXP_FD_OR_FAIL(fanotify_fd =
fanotify_init(tc->init_flags, O_RDONLY),
                                   tc->expected_errno);
        } else {
                /* tc->expected_errno refers to the expected result of
fanotify_mark() */
                fanotify_fd = fanotify_init(tc->init_flags, O_RDONLY);
                if (fanotify_fd < 0) {
                        if (errno == EINVAL)
                                tst_res(TCONF, "fanotify_init flags
XXX not supported");
                        else
                                tst_res(TFAIL, "fanotify_init failed");
                }
        }

Give or take using more macros and your nicer flag prints.
There is no need for auto-detection of the unsupported kernel flags.

If the test case is expected to get to fanotify_mark() (i.e. non-zero tc->mask)
EINVAL from fanotify_init() always means "unsupported".

Thanks,
Amir.