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

[Janne Grunau]

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@xxxxxxxxxx>
---
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
 
 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: /))'
 	@echo '  perf-tar-src-pkg    - Build the perf source tarball with no compression'
 	@echo '  perf-targz-src-pkg  - Build the perf source tarball with gzip compression'
 	@echo '  perf-tarbz2-src-pkg - Build the perf source tarball with bz2 compression'

---
base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
change-id: 20260320-kbuild-modules-cpio-pkg-usr-merge-4266a460282c

Best regards,
-- 
Janne Grunau <j@xxxxxxxxxx>