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

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Message-ID: <20250714-fernhalten-holzkisten-d085d5802884@brauner>
Date: Mon, 14 Jul 2025 10:12:56 +0200
From: Christian Brauner <brauner@...nel.org>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Al Viro <viro@...iv.linux.org.uk>, 
	Luis Chamberlain <mcgrof@...nel.org>, Kees Cook <kees@...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 Mon, Jul 14, 2025 at 07:52:27AM +0200, Thomas Weißschuh wrote:
> (+Luis for the usermode helper discussion)
> 
> On Fri, Jul 11, 2025 at 04:44:23PM +0100, Al Viro wrote:
> > On Fri, Jul 11, 2025 at 12:35:59PM +0200, Thomas Weißschuh wrote:
> > > Hi Kees, Al, Christian and Honza,
> > > 
> > > On Thu, Jun 26, 2025 at 08:10:14AM +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.
> > 
> > What's wrong with kernel/umh.c?
> 
> It gets neutered by CONFIG_STATIC_USERMODEHELPER_PATH. That could be worked
> around be overriding sub_info->path, but it would be a hack.
> It does not allow to implement a custom wait routine to forward the process
> output to KUnit as implemented in kunit_uapi_forward_to_printk() [0].
> That may be solved by adding another thread, but that would also be hacky.
> 
> It would probably be possible to extend kernel/umh.c for my usecase but I
> didn't want bloat the core kernel code for my test-only functionality.
> 
> > > could you take a look at these new symbol exports?
> > 
> > > > +EXPORT_SYMBOL_GPL_FOR_MODULES(put_filesystem, "kunit-uapi");
> > 
> > What's that one for???
> 
> What are you referring to?
> 
> The macro EXPORT_SYMBOL_GPL_FOR_MODULES() will only export the symbol for one
> specific module. Personally I'm also fine with EXPORT_SYMBOL_GPL().

No, we're going to use the new restricted macros going forward that
limit exports to very specific modules. This is a good example. Though
it will be renamed to EXPORT_SYMBOL_FOR_MODULES() anyway.