linux-kernel - Re: [PATCH v4 06/15] fs,fork,exit: export symbols necessary for KUnit UAPI support

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Message-ID: <aHeOxh_yaQGFVVwM@infradead.org>
Date: Wed, 16 Jul 2025 04:36:38 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Christoph Hellwig <hch@...radead.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Luis Chamberlain <mcgrof@...nel.org>, Kees Cook <kees@...nel.org>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 06/15] fs,fork,exit: export symbols necessary for
 KUnit UAPI support

On Wed, Jul 16, 2025 at 01:33:05PM +0200, Thomas Weißschuh wrote:
> On Wed, Jul 16, 2025 at 04:11:04AM -0700, Christoph Hellwig wrote:
> > On Wed, Jul 16, 2025 at 10:39:57AM +0200, Thomas Weißschuh wrote:
> > > Let's take kernel_execve() as example, there is no way around using this
> > > function in one way or another. It only has two existing callers.
> > > init/main.c: It is completely unsuitable for this usecase.
> > > kernel/umh.c: It is also what Al suggested and I am all for it.
> > > Unfortunately it is missing features. Citation from my response to Al:
> > 
> > But why does the code that calls it need to be modular?  I get why
> > the actual test cases should be modular, but the core test runner is
> > small and needs a lot of kernel internals.  Just require it to be
> > built-in and all this mess goes away.
> 
> KUnit UAPI calls into KUnit proper which itself is modular.
> As such it needs to be modular, too.

Not if you depend on KUNIT=y.

> > That being said some of this stuff, like get_fs_type / put_filesystem
> > or replace_fd seem like the wrong level of abstractions for something
> > running tests anyway.
> 
> This was modelled after usermode helper and usermode driver.
> To me it makes sense, and I don't see an obvious way to get rid of these.
> 
> Or do you mean to introduce a new in-core helper to abstract this away?
> Then everybody would need to pay the cost for this helper even if it is only
> used from some modular code.

I have no idea what you are doing as you only Cc'ed the exports patch
but not the actual work to the mailing lists, so I have no way of
helping you with the actual code.  I can just tell you my gut feeling
based on the symbols, and they are something that doesn't feel outside
of very core code.