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Date:   Tue, 18 Jul 2023 10:52:45 +0200
From:   Michal =?iso-8859-1?Q?Such=E1nek?= <msuchanek@suse.de>
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     Nicolas Schier <nicolas@fjasle.eu>, linux-modules@vger.kernel.org,
        Takashi Iwai <tiwai@suse.com>,
        Lucas De Marchi <lucas.de.marchi@gmail.com>,
        Michal =?utf-8?B?S291dG7vv70=?= <mkoutny@suse.com>,
        Jiri Slaby <jslaby@suse.com>, Jan Engelhardt <jengelh@inai.de>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] depmod: Handle installing modules under a prefix
Message-ID: <20230718085245.GV9196@kitsune.suse.cz>
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On Tue, Jul 18, 2023 at 04:14:11AM +0900, Masahiro Yamada wrote:
> On Sat, Jul 15, 2023 at 12:10 AM Michal Suchánek <msuchanek@suse.de> wrote:
> >
> > On Fri, Jul 14, 2023 at 04:54:49PM +0200, Nicolas Schier wrote:
> > > On Fri, Jul 14, 2023 at 04:30:02PM +0200, Michal Such�nek wrote:
> > > > Hello,
> > > >
> > > > On Fri, Jul 14, 2023 at 04:05:10PM +0200, Nicolas Schier wrote:
> > > > > On Fri, Jul 14, 2023 at 02:21:08PM +0200 Michal Suchanek wrote:
> > > > > > Some distributions aim at not shipping any files in / outside of usr.
> > > > >
> > > > > For me, preventing negation often makes things easier, e.g.: "... aim at
> > > > > shipping files only below /usr".
> > > > >
> > > > > >
> > > > > > The path under which kernel modules are installed is hardcoded to /lib
> > > > > > which conflicts with this goal.
> > > > > >
> > > > > > When kmod provides the config command, use it to determine the correct
> > > > > > module installation prefix.
> > > > > >
> > > > > > This is a prefix under which the modules are searched by kmod on the
> > > > > > system, and is separate from the temporary staging location already
> > > > > > supported by INSTALL_MOD_PATH.
> > > > > >
> > > > > > With kmod that does not provide the config command empty prefix is used
> > > > > > as before.
> > > > > >
> > > > > > Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> > > > > > ---
> > > > > > v2: Avoid error on systems with kmod that does not support config
> > > > > > command
> > > > > > v3: More verbose commit message
> > > > > > ---
> > > > > >  Makefile          | 4 +++-
> > > > > >  scripts/depmod.sh | 8 ++++----
> > > > > >  2 files changed, 7 insertions(+), 5 deletions(-)
> > > > > >
> > > > > > diff --git a/Makefile b/Makefile
> > > > > > index 47690c28456a..b1fea135bdec 100644
> > > > > > --- a/Makefile
> > > > > > +++ b/Makefile
> > > > > > @@ -1165,7 +1165,9 @@ 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_PREFIX := $(shell kmod config &> /dev/null && kmod config | jq -r .module_prefix)
> > > > >
> > > > > All other calls of `jq` that I could find are located at tools/; as this here
> > > > > is evaluated on each invocation, this should probably be documented in
> > > > > Documentation/process/changes.rst?
> > > > >
> > > > > (Absence of `jq` will cause error messages, even with CONFIG_MODULES=n.)
> > > >
> > > > That's a good point.
> > > >
> > > > >
> > > > > > +
> > > > > > +MODLIB = $(INSTALL_MOD_PATH)$(KERNEL_MODULE_PREFIX)/lib/modules/$(KERNELRELEASE)
> > > > > >  export MODLIB
> > > > > >
> > > > > >  PHONY += prepare0
> > > > > > diff --git a/scripts/depmod.sh b/scripts/depmod.sh
> > > > > > index 3643b4f896ed..88ac79056153 100755
> > > > > > --- a/scripts/depmod.sh
> > > > > > +++ b/scripts/depmod.sh
> > > > > > @@ -27,16 +27,16 @@ fi
> > > > > >  # numbers, so we cheat with a symlink here
> > > > > >  depmod_hack_needed=true
> > > > > >  tmp_dir=$(mktemp -d ${TMPDIR:-/tmp}/depmod.XXXXXX)
> > > > > > -mkdir -p "$tmp_dir/lib/modules/$KERNELRELEASE"
> > > > > > +mkdir -p "$tmp_dir$KERNEL_MODULE_PREFIX/lib/modules/$KERNELRELEASE"
> > > > > >  if "$DEPMOD" -b "$tmp_dir" $KERNELRELEASE 2>/dev/null; then
> > > > > > -       if test -e "$tmp_dir/lib/modules/$KERNELRELEASE/modules.dep" -o \
> > > > > > -               -e "$tmp_dir/lib/modules/$KERNELRELEASE/modules.dep.bin"; then
> > > > > > +       if test -e "$tmp_dir$KERNEL_MODULE_PREFIX/lib/modules/$KERNELRELEASE/modules.dep" -o \
> > > > > > +               -e "$tmp_dir$KERNEL_MODULE_PREFIX/lib/modules/$KERNELRELEASE/modules.dep.bin"; then
> > > > > >                 depmod_hack_needed=false
> > > > > >         fi
> > > > > >  fi
> > > > >
> > > > > I'd like to come back to the statement from Masahiro: Is the check above,
> > > > > against some very old versions of depmod [1], the only reason for this patch?
> > > > >
> > > > > If we could remove that, would
> > > > >
> > > > >     make INSTALL_MOD_PATH="$(kmod config | jq -r .module_prefix)" modules_install
> > > > >
> > > > > be sufficient?
> > > >
> > > > No, the INSTALL_MOD_PATH is passed as the -b argument to depmod while
> > > > the newly added part is not because it's integral part of where the
> > > > modules are installed on the system, and not the staging area path.
> > >
> > > Ah, thanks.  So just for my understanding, could this be a (non-gentle)
> > > alternative version of your patch, w/o modifying top-level Makefile?
> > >
> > > diff --git a/scripts/depmod.sh b/scripts/depmod.sh
> > > index 3643b4f896ed..72c819de0669 100755
> > > --- a/scripts/depmod.sh
> > > +++ b/scripts/depmod.sh
> > > @@ -1,4 +1,4 @@
> > > -#!/bin/sh
> > > +#!/bin/bash
> > >  # SPDX-License-Identifier: GPL-2.0
> > >  #
> > >  # A depmod wrapper used by the toplevel Makefile
> > > @@ -23,6 +23,8 @@ if [ -z $(command -v $DEPMOD) ]; then
> > >         exit 0
> > >  fi
> > >
> > > +kmod_version=$(( $(kmod --version | sed -rne 's/^kmod version ([0-9]+).*$/\1/p') ))
> > > +
> > >  # older versions of depmod require the version string to start with three
> > >  # numbers, so we cheat with a symlink here
> > >  depmod_hack_needed=true
> > > @@ -35,6 +37,13 @@ if "$DEPMOD" -b "$tmp_dir" $KERNELRELEASE 2>/dev/null; then
> > >         fi
> > >  fi
> > >  rm -rf "$tmp_dir"
> > > +
> > > +if [ "${kmod_version}" -gt 32 ]; then
> > > +       kmod_prefix="$(kmod config | jq -r .module_prefix)"
> > > +       INSTALL_MOD_PATH="${INSTALL_MOD_PATH#${kmod_prefix}"
> > > +       depmod_hack_needed=false
> > > +fi
> > > +
> > >  if $depmod_hack_needed; then
> > >         symlink="$INSTALL_MOD_PATH/lib/modules/99.98.$KERNELRELEASE"
> > >         ln -s "$KERNELRELEASE" "$symlink"
> > >
> > > (untested, and assuming that kmod module prefix is in kmod >= 32)
> >
> > It can be detected by running the 'kmod config' command first and
> > ignoring the output when it fails which the above patch already did.
> > The version check does not sound very reliable.
> >
> > > Or are I am still missing something?
> >
> > MODLIB still needs to include the extra prefix so that files are
> > installed in the correct location. And that's defined in the toplevel
> > Makefile.
> >
> > Thanks
> >
> > Michal
> 
> 
> 
> As Documentation/kbuild/kbuild.rst mentions,
> you can override MODLIB.
> 
> Kbuild already provides the maximum flexibility.
> 
> 
> $ make modules_install \
>   INSTALL_MOD_PATH=/path/to/whatever/staging/dir \
>   MODLIB=/path/to/whatever/real/install/destination

That's great that we have another workaround for the case when the
kernel build system and kmod do not agree on the location of the kernel
modules.

However, they should by default agree, and if this feature is merged
into kmod the kernel should also adapt to make sure the modules are
installed where kmod expects them.

Thanks

Michal