linux-kernel - Re: [PATCH v6 1/2] depmod: Handle installing modules under a different directory

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Message-ID: <CAK7LNAQQe-fdeKe2RHd5TyYpXa95WJO_-f38o12oewGC3rFTHA@mail.gmail.com>
Date:   Mon, 11 Dec 2023 13:29:15 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Michal Suchánek <msuchanek@...e.de>
Cc:     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>,
        Nicolas Schier <nicolas@...sle.eu>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/2] depmod: Handle installing modules under a
 different directory

On Mon, Dec 11, 2023 at 6:07 AM Michal Suchánek <msuchanek@...e.de> wrote:
>
> Hello!
>
> On Mon, Dec 11, 2023 at 03:43:44AM +0900, Masahiro Yamada wrote:
> > On Thu, Dec 7, 2023 at 4:48 AM Michal Suchanek <msuchanek@...e.de> wrote:
> > >
> > > Some distributions aim at shipping all files in /usr.
> > >
> > > The path under which kernel modules are installed is hardcoded to /lib
> > > which conflicts with this goal.
> > >
> > > When kmod provides kmod.pc, use it to determine the correct module
> > > installation path.
> > >
> > > With kmod that does not provide the config /lib/modules is used as
> > > before.
> > >
> > > While pkg-config does not return an error when a variable does not exist
> > > the kmod configure script puts some effort into ensuring that
> > > module_directory is non-empty. With that empty module_directory from
> > > pkg-config can be used to detect absence of the variable.
> > >
> > > Signed-off-by: Michal Suchanek <msuchanek@...e.de>
> > > ---
> > > v6:
> > >  - use ?= instead of := to make it easier to override the value
> >
> >
> > "KERNEL_MODULE_DIRECTORY=/local/usr/lib/modules make modules_install"
> > will override the install destination, but
> > depmod will not be not aware of it.
>
> At the same time if you know what you are doing you can build a src rpm
> for another system that uses a different location.
>
> > How to avoid the depmod error?
>
> Not override the variable?




You are not answering my question.


You intentionally changed := to ?=.

This implies that KERNEL_MODULE_DIRECTORY is an interface to users,
and should be documented in Documentation/kbuild/kbuild.rst


However, it never works if it is overridden from the env variable
or make command line because there is no way to let depmod know
the fact that KERNEL_MODULE_DIRECTORY has been overridden.



In my understanding, depmod does not provide an option to
specify the module directory from a command line option, does it?
If not, is it reasonable to add a new option to depmod?


depmod provides the "-b basedir" option, but it only allows
adding a prefix to the default "/lib/modules/<version>".

(My original idea to provide the prefix_part, it would have worked
like  -b "${INSTALL_MOD_PATH}${MOD_PREFIX}", which you refused)




















> Thanks
>
> Michal
>
> > >  - use shorter expression for determining the module directory assuming
> > >    it's non-empty
> > > ---
> > >  Makefile | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/Makefile b/Makefile
> > > index 511b5616aa41..84f32bd563d4 100644
> > > --- a/Makefile
> > > +++ b/Makefile
> > > @@ -1081,7 +1081,9 @@ export INSTALL_DTBS_PATH ?= $(INSTALL_PATH)/dtbs/$(KERNELRELEASE)
> > >  # makefile but the argument can be passed to make if needed.
> > >  #
> > >
> > > -MODLIB = $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
> > > +export KERNEL_MODULE_DIRECTORY ?= $(or $(shell pkg-config --variable=module_directory kmod 2>/dev/null),/lib/modules)
> > > +
> > > +MODLIB = $(INSTALL_MOD_PATH)$(KERNEL_MODULE_DIRECTORY)/$(KERNELRELEASE)
> > >  export MODLIB
> > >
> > >  PHONY += prepare0
> > > --
> > > 2.42.0
> > >
> > >
> >
> >
> > --
> > Best Regards
> > Masahiro Yamada
>


-- 
Best Regards
Masahiro Yamada