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

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Date:   Fri, 14 Jul 2023 16:30:02 +0200
From:   Michal Suchánek <msuchanek@...e.de>
To:     Nicolas Schier <nicolas@...sle.eu>
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>,
        Masahiro Yamada <masahiroy@...nel.org>,
        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

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.

> 
> Kind regards,
> Nicolas
> 
> 
> [1]: https://lore.kernel.org/linux-kbuild/1307631448-29848-5-git-send-email-mmarek@suse.cz/

Was busybox ever fixed to not require the hack?

Thanks

Michal