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

Petr Vorel
2025-12-15T16:53:21Z

> > 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

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