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

[Nicolas Schier <nsc@kernel.org>]

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/
    
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.



>  
>  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\")

Kind regards,
Nicolas