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

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Message-ID: <20250721075849-b3cf33b6-2516-4707-bab6-53fe95afbffa@linutronix.de>
Date: Mon, 21 Jul 2025 08:42:40 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: 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 Fri, Jul 18, 2025 at 05:44:12PM +0100, Al Viro wrote:
> On Thu, Jul 17, 2025 at 10:48:08AM +0200, Thomas Weißschuh wrote:
> > The KUnit UAPI infrastructure starts userspace processes.
> > As it should be able to be built as a module, export the necessary symbols.
> > 
> > Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> 
> No.  This is just plain wrong.  This is way too low-level; teach kernel/umh.c
> to provide what you need, but do *not* add more kernel_execve() callers.

Sounds good.

> And the situation with ramfs needs cleaning up, but "export put_filesystem()"
> is not a solution.

Cleaning up would mean to stop calling put_filesystem(), as it is a no-op
here anyways, right?


This would still leave the exports for replace_fd(), create_pipe_files()
and set_fs_pwd(). Instead of using kernel/umh.c, 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.


Thomas