linux-kernel - Re: [PATCH v4] fs: hide names_cachep behind runtime access machinery

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Message-ID: <CAGudoHG_WYnoqAYgN2P5LcjyT6r-vORgeAG2EHbHoH+A-PvDUA@mail.gmail.com>
Date: Thu, 30 Oct 2025 17:35:02 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: brauner@...nel.org, viro@...iv.linux.org.uk, jack@...e.cz, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, pfalcato@...e.de
Subject: Re: [PATCH v4] fs: hide names_cachep behind runtime access machinery

On Thu, Oct 30, 2025 at 5:16 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Thu, 30 Oct 2025 at 03:52, Mateusz Guzik <mjguzik@...il.com> wrote:
> >
> > Should someone(tm) make this work for modules I'm not going to protest.
>
> Btw, that's a good point. When I did this all originally, I explicitly
> did *not* want to make it work for modules, but I do note that it can
> be used for modules very easily by mistake.
>
> > Vast majority of actual usage is coming from core kernel, which *is*
> > getting the new treatment and I don't think the ifdef is particularly
> > nasty.
>
> I suspect we should make that #ifdef be an integral part of the
> runtime const headers. Because right now it's really much too easy to
> get it wrong, and I wonder if we already do.
>

I don't know if you are suggesting to make the entire thing fail to
compile if included for a module, or to transparently convert
runtime-optimized access into plain access.

I presume the former.

Even then, there is the cosmetic issue of deciding whether to ifdef
within headers or create include/linux/runtime-constants.h which pulls
in the per-arch stuff and ifdef in there.

Personally I'm leaning towards just forcing compilation failure and
duplicating the code to do it within per-arch headers, for example:
diff --git a/arch/x86/include/asm/runtime-const.h
b/arch/x86/include/asm/runtime-const.h
index 8d983cfd06ea..42e6303b52f7 100644
--- a/arch/x86/include/asm/runtime-const.h
+++ b/arch/x86/include/asm/runtime-const.h
@@ -2,6 +2,10 @@
 #ifndef _ASM_RUNTIME_CONST_H
 #define _ASM_RUNTIME_CONST_H

+#ifdef MODULE
+#error "this functionality is not available for modules"
+#endif
+
 #ifdef __ASSEMBLY__

 .macro RUNTIME_CONST_PTR sym reg

Just tell me which way you want this sorted out and if it is less than
few minutes of screwing around I'll take care of it.