Re: [LTP] [PATCH] ioctl_pidfd02-06: Add CONFIG_USER_NS and CONFIG_PID_NS to needs_kconfigs

Terry Tritton
2026-01-05T13:51:32Z

Hi,

> On Mon Dec 15, 2025 at 5:52 PM CET, Petr Vorel wrote:
> > > > And https://www.man7.org/linux/man-pages/man7/user_namespaces.7.html.
> >
> > > > Yeah, I understand that. The dependency of CLONE_NEWUSER/CLONE_NEWPID is also
> > > > visible in kernel sources (e.g. fs/nsfs.c). But my question was different:
> > > > Do we now prefer everything kind of document with .needs_kconfigs, even it's
> > > > possible to detect it otherwise? (speed of parsing kconfig, kind of hard request
> > > > for kconfig being available even we can figure the support otherwise).
> >
> > > I believe we shouldn't see this as black/white but use this feature when
> > > it's really needed. This is the case.
> >
> > Sure, .needs_kconfigs is used when test request some functionality based on
> > kconfig. But many tests use /proc or /sys based detection (e.g. ioctl_ns06.c)
> > or based on certain errno, see include/lapi/syscalls.h or
> > testcases/kernel/syscalls/fanotify/fanotify.h) because these were
> > added before LTP supported kconfig. Later, when kconfig was added it was
> > considering as a last resort (when there was no way to detect dependency
> > otherwise).
> >
> > Have we decide to move everything into kconfig?
> >
> > I'm not sure myself. needs_kconfigs is simpler and obvious, but it requires
> > kernel config. I suppose the speed of parsing config is not an issue.
> >
> > It'd be nice to mention the resolution (preferred vs. only if no other way to
> > detect the support) into
> > https://linux-test-project.readthedocs.io/en/latest/developers/writing_tests.html
>
> Feel free to add this comment, but for me it's obvious that if a
> feature can't be present in the kernel due to kconfigs we should check
> kconfig :-)

I've just taken another look at this and it appears the test would still
fail if the config is not present or if KCONFIG_SKIP_CHECK is set, in
which case perhaps the run time detection may be preferred as it will
still work in these cases?

I'm not sure how common either of those cases are though?

Would it be better to have the run time detection in tst_kconfig_check
as a fall back in case the config is not present?
Then the tests can just define the needs_kconfigs and not have to worry
about other checks.

> > or into upcommig doc/developers/ground_rules.rst
> > https://patchwork.ozlabs.org/project/ltp/patch/20251215124404.16395-2-chrubis@suse.cz/
> >
> > Kind regards,
> > Petr
> >
> > > > And if we decide for forcing kconfig, we should update ioctl_ns06.c, which does
> > > > /proc based detection (i.e. to use the same approach).
> >
> > > I didn't check this, but I'm pretty sure we should go all around and
> > > verify many other tests with the same issue. We should do it in this
> > > patch-set or on a searate one.
> >
> >
> > > > Kind regards,
> > > > Petr
>
> So what we do with the patch? Should we merge it?

I'm happy to go through and update other tests in this patch or another.

Thanks
Terry