linux-kernel - Re: [RFC PATCH 2/5] unwind: Export unwind

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Message-ID: <9ca3a6596596e87e7ee06be3414387859aaadafc.camel@HansenPartnership.com>
Date: Fri, 11 Jul 2025 10:22:50 -0700
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Greg KH <gregkh@...uxfoundation.org>, Steven Rostedt
 <rostedt@...dmis.org>
Cc: Christoph Hellwig <hch@...radead.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, linux-kernel@...r.kernel.org, Josh
 Poimboeuf <jpoimboe@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Jiri
 Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Thomas
 Gleixner <tglx@...utronix.de>, Andrii Nakryiko <andrii@...nel.org>, Indu
 Bhagat <indu.bhagat@...cle.com>, "Jose E. Marchesi" <jemarch@....org>, Beau
 Belgrave <beaub@...ux.microsoft.com>, Jens Remus <jremus@...ux.ibm.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton
 <akpm@...ux-foundation.org>,  tech-board-discuss@...ts.linuxfoundation.org
Subject: Re: [RFC PATCH 2/5] unwind: Export unwind_user symbol to GPL modules

On Fri, 2025-07-11 at 13:38 +0200, Greg KH wrote:
> On Fri, Jul 11, 2025 at 06:57:42AM -0400, Steven Rostedt wrote:
> > 
> > [ Adding the TAB to this as well ]
> > 
> > On Fri, 11 Jul 2025 00:36:28 -0700
> > Christoph Hellwig <hch@...radead.org> wrote:
> > 
> > > On Wed, Jul 09, 2025 at 05:25:49PM -0400, Mathieu Desnoyers
> > > wrote:
> > > > Allow the unwind_user symbol to be used by GPL modules, for
> > > > instance LTTng.  
> > > 
> > > I don't see a LTTng submission or any other user in this series.
> > > So the usual prohibition against adding unused exports applies
> > > here as usual.
> > 
> > I want to bring up this discussion. I understand there's a policy
> > not to add EXPORT_SYMBOL_GPL() unless there's a current user of it
> > in the kernel proper. My question is, does this policy have to be
> > draconian?
> 
> It's not "draconian", it is "we do not add exports for stuff that is
> not in our kernel tree."  Simple, direct, and obvious.  We have no
> idea how, or if, external modules do anything with apis that we
> export and do not use internally, so we can't change them without
> breaking anything, so it's simpler and more obvious to not even
> attempt to care about
> them.

Since the argument is still going on, I've got to say I agree with
Greg: it's not draconian it's a simple technical rule which is easily
enforceable and gets us out of making political decisions like what's a
"good" use of a symbol and what isn't.  Once we start making political
decisions about kernel symbol exports we open ourselves up to
accusations of partisanship and favouritism ... since we have a clear
technical criterion, it's just way easier not to descend that slippery
slope.

Regards,

James