linux-kernel - Re: [PATCH v3] depmod: Handle installing modules under a prefix

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Message-ID: <CAK7LNAQMs3QBYfWcLkmOQdbbq7cj=7wWbK=AWhdTC2rAsKHXzQ@mail.gmail.com>
Date:   Tue, 18 Jul 2023 04:13:58 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nicolas Schier <nicolas@...sle.eu>
Cc:     Michal Such�nek <msuchanek@...e.de>,
        linux-modules@...r.kernel.org, Takashi Iwai <tiwai@...e.com>,
        Lucas De Marchi <lucas.de.marchi@...il.com>,
        Michal Koutn� <mkoutny@...e.com>,
        Jiri Slaby <jslaby@...e.com>, Jan Engelhardt <jengelh@...i.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] depmod: Handle installing modules under a prefix

On Fri, Jul 14, 2023 at 11:55 PM Nicolas Schier <nicolas@...sle.eu> 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@...e.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)
>
> Or are I am still missing something?
>
> > Was busybox ever fixed to not require the hack?
>
> I haven't checked that, yet.



I believe we can revert

8fc62e59425389a6d48429b9d146223122743435
bfe5424a8b31624e7a476f959d552999f931e7c7

There is no good reason to keep such old hacky code.


The old module-init-tools project was replaced by kmod.
I do not know whether busybox fixed the issue or not.
Anyway, Linux 3.0 was released 12 years ago.
There was plenty of time to fix the issue if we wanted.
If busybox is still not able to handle the X.Y version form,
it is just that nobody is caring about the busybox's depmod.




--
Best Regards
Masahiro Yamada