linux-kernel - Re: [PATCH rebased] kbuild: rpm-pkg: Fix build with non-default MODLIB

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Date:   Mon, 9 Oct 2023 16:07:33 +0200
From:   Michal Suchánek <msuchanek@...e.de>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nicolas Schier <nicolas@...sle.eu>,
        linux-modules@...r.kernel.org, Takashi Iwai <tiwai@...e.com>,
        Lucas De Marchi <lucas.de.marchi@...il.com>,
        Michal Koutný <mkoutny@...e.com>,
        Jiri Slaby <jslaby@...e.com>, Jan Engelhardt <jengelh@...i.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH rebased] kbuild: rpm-pkg: Fix build with non-default
 MODLIB

On Mon, Oct 09, 2023 at 09:34:10PM +0900, Masahiro Yamada wrote:
> On Mon, Oct 9, 2023 at 5:52 PM Michal Suchánek <msuchanek@...e.de> wrote:
> >
> > Hello,
> >
> > On Mon, Oct 09, 2023 at 05:31:02PM +0900, Masahiro Yamada wrote:
> > > On Fri, Oct 6, 2023 at 12:49 AM Michal Suchanek <msuchanek@...e.de> wrote:
> > > >
> > > > The default MODLIB value is composed of two variables and the hardcoded
> > > > string '/lib/modules/'.
> > > >
> > > > MODLIB = $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
> > > >
> > > > Defining this middle part as a variable was rejected on the basis that
> > > > users can pass the whole MODLIB to make, such as
> > >
> > >
> > > In other words, do you want to say
> > >
> > > "If defining this middle part as a variable had been accepted,
> > > this patch would have been unneeded." ?
> >
> > If it were accepted I would not have to guess what the middle part is,
> > and could use the variable that unambiguosly defines it instead.
> 
> 
> How?
> 
> scripts/package/kernel.spec hardcodes 'lib/modules'
> in a couple of places.
> 
> I am asking how to derive the module path.

Not sure what you are asking here. The path is hardcoded, everywhere.

The current Makefile has

MODLIB	= $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)

and there is no reliable way to learn what the middle part was after the
fact - $(INSTALL_MOD_PATH) can be non-empty.

The rejected patch was changing this to a variable, and also default to
adjusting the content to what kmod exports in pkgconfig after applying a
proposed patch to make this hardcoded part configurable:

export KERNEL_MODULE_DIRECTORY := $(shell pkg-config --print-variables kmod 2>/dev/null | grep '^module_directory$$' >/dev/null && pkg-config --variable=module_directory kmod || echo /lib/modules)

MODLIB	= $(INSTALL_MOD_PATH)$(KERNEL_MODULE_DIRECTORY)/$(KERNELRELEASE)

It would be completely posible to only define the middle part as a
variable that could then be used in rpm-pkg:

export KERNEL_MODULE_DIRECTORY := /lib/modules

MODLIB	= $(INSTALL_MOD_PATH)$(KERNEL_MODULE_DIRECTORY)/$(KERNELRELEASE)

Thanks

Michal