Re: [PATCH] kbuild: modules-cpio-pkg: Respect INSTALL_MOD_PATH

[Janne Grunau <j@jannau.net>]

On Sat, Mar 21, 2026 at 04:18:46PM +0100, Nicolas Schier wrote:
> On Fri, Mar 20, 2026 at 03:30:32PM +0100, Janne Grunau wrote:
> > The modules-cpio-pkg target added in commit 2a9c8c0b59d3 ("kbuild: add
> > target to build a cpio containing modules") is incompatible with
> > initramfs with merged /lib and /usr/lib directories [1]. "/lib" cannot
> > be a link and directory at the same time.
> > Respect a non-empty INSTALL_MOD_PATH in the modules-cpio-pkg target so
> > that `make INSTALL_MOD_PATH=/usr modules-cpio-pkg` results in the same
> > module install location as `make INSTALL_MOD_PATH=/usr modules_install`.
> > 
> > Tested with Fedora distribution initramfs produced by dracut.
> > 
> > Link: https://systemd.io/THE_CASE_FOR_THE_USR_MERGE/ [1]
> > Signed-off-by: Janne Grunau <j@jannau.net>
> > ---
> > Hej,
> > 
> > this patch allows to produce modules-cpio initramfs which are compatible
> > with initramfs with merged /lib and /usr/lib (/lib as symlink to
> > /usr/lib). I expect initramfs of distributions with merged /usr to have
> > a merged /usr as well. This is at least true for Fedora initramfs built
> > with dracut.
> > 
> > I'm not sure whether the trickery to avoid repeated '/' is justified. It
> > is necessary to add a slash between "$@" and a non empty
> > $(INSTALL_MOD_PATH) to avoid make failures due to non existing
> > .tmp_modules_cpio when INSTALL_MOD_PATH without leading slash is used.
> > modules-cpio-pkg`.
> > 
> > Better or shorter ways to document this not completely obvious behavior
> > would be appreciated.
> > 
> > Janne
> > ---
> >  scripts/Makefile.package | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/scripts/Makefile.package b/scripts/Makefile.package
> > index 0ec946f9b905f74f8698d8d6967d22f5b76f64e0..ab18cf81622ae319380528c401f9aeb6d32070c6 100644
> > --- a/scripts/Makefile.package
> > +++ b/scripts/Makefile.package
> > @@ -195,7 +195,9 @@ tar%-pkg: linux-$(KERNELRELEASE)-$(ARCH).tar.% FORCE
> >  .tmp_modules_cpio: FORCE
> >  	$(Q)$(MAKE) -f $(srctree)/Makefile
> >  	$(Q)rm -rf $@
> > -	$(Q)$(MAKE) -f $(srctree)/Makefile INSTALL_MOD_PATH=$@ modules_install
> > +	$(Q)$(MAKE) -f $(srctree)/Makefile \
> > +		INSTALL_MOD_PATH=$@$(if $(INSTALL_MOD_PATH),/$(INSTALL_MOD_PATH:/%=%)) \
> > +		modules_install
> 
> Thanks for the patch along with its detailed description!
> 
> For completeness: I'd rather use $(addprefix):
> 
>     INSTALL_MOD_PATH=$@$(addprefix /,$(INSTALL_MOD_PATH:/%=%))
> 
> but as POSIX states:
> 
> | Multiple successive <slash> characters are considered to be the same
> | as one <slash>, except it is implementation-defined whether the case
> | of exactly two leading <slash> characters is treated specially.
> https://pubs.opengroup.org/onlinepubs/9799919799.2024edition/

argh, I did read this but confused myself by the second part to think it
was only for leading slashes.

> there is no need for handling possible repeated slashes here.  So, from
> my point of view we can keep it as simple as:
> 
>     INSTALL_MOD_PATH=$@/$(INSTALL_MOD_PATH)
> 
> as a trailing slash in INSTALL_MOD_PATH should not be a problem here.

ack, I'll just do that and I would have sent it if I did not confuse
myself with the POSIX wording.

> 
> >  
> >  quiet_cmd_cpio = CPIO    $@
> >        cmd_cpio = $(CONFIG_SHELL) $(srctree)/usr/gen_initramfs.sh -o $@ $<
> > @@ -263,7 +265,7 @@ help:
> >  	@echo '  tarbz2-pkg          - Build the kernel as a bzip2 compressed tarball'
> >  	@echo '  tarxz-pkg           - Build the kernel as a xz compressed tarball'
> >  	@echo '  tarzst-pkg          - Build the kernel as a zstd compressed tarball'
> > -	@echo '  modules-cpio-pkg    - Build the kernel modules as cpio archive'
> > +	@echo '  modules-cpio-pkg    - Build the kernel modules as cpio archive (modules installed in INSTALL_MOD_PATH (default: /))'
> 
> Please break that line, e.g.:
> 
> 	@echo '  modules-cpio-pkg    - Build the kernel modules as cpio archive'
> 	@echo '                        (modules installed in INSTALL_MOD_PATH (default: /))'
> 
> 
> Fixes: 2a9c8c0b59d3 (\"kbuild: add target to build a cpio containing modules\")

I saw it more as an additional thing but without the complications of
suppressing repeated slashes the change is easy enough

thanks,
Janne