linux-kernel - Re: [PATCH v5 06/15] fs,fork,exit: export symbols necessary for KUnit UAPI support

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Message-ID: <20250721072033.GA30175@lst.de>
Date: Mon, 21 Jul 2025 09:20:33 +0200
From: Christoph Hellwig <hch@....de>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Al Viro <viro@...iv.linux.org.uk>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, Willy Tarreau <w@....eu>,
	Thomas Weißschuh <linux@...ssschuh.net>,
	Brendan Higgins <brendan.higgins@...ux.dev>,
	David Gow <davidgow@...gle.com>, Rae Moar <rmoar@...gle.com>,
	Shuah Khan <shuah@...nel.org>, Jonathan Corbet <corbet@....net>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
	Kees Cook <kees@...nel.org>, Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
	linux-doc@...r.kernel.org, workflows@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v5 06/15] fs,fork,exit: export symbols necessary for
 KUnit UAPI support

On Mon, Jul 21, 2025 at 08:42:40AM +0200, Thomas Weißschuh wrote:
> This would still leave the exports for replace_fd(), create_pipe_files()
> and set_fs_pwd(). Instead of using kernel/umh.c,

Please look into a way to just run your userspace tests from userspace.

It's not that hard, people have done this novel concept for at least
a few decades if you look into it.

> I can also extend
> kernel/usermode_driver.c to provide these in a way that works for me.
> But kernel/usermode_driver.c is dead code, unused since commit
> 98e20e5e13d2 ("bpfilter: remove bpfilter")
> Would it be fine to export those symbols? And delete usermode_driver.c,
> as carrying around an unused generic framework seems pointless.

Unused code should always go away.  Weirdly enough USERMODE_DRIVER is
selected by BPF_PRELOAD despite that not really using any code from
it, though.