[PATCH v2 1/1] kbuild: install the modules.order for external modules

[Will McVicker <willmcvicker@google.com>]

Add support to install the modules.order file for external modules
during module_install in order to retain the Makefile ordering
of external modules. This helps reduce the extra steps necessary to
properly order loading of external modules when there are multiple
kernel modules compiled within a given KBUILD_EXTMOD directory.

To handle compiling multiple external modules within the same
INSTALL_MOD_DIR, kbuild will append a suffix to the installed
modules.order file defined like so:

  echo "${KBUILD_EXTMOD}" | md5sum | cut -d " " -f 1

Example:
  KBUILD_EXTMOD=/mnt/a.b/c-d/my_driver results in:
  modules.order._mnt_a_b_c_d_my_driver

The installed module.order.$(extmod_suffix) files can then be appended
to the staging modules.order file which defines the order to load all of
the modules during boot.

Example:
  cd $(MODLIB)
  find extra/. -name modules.order.* -exec cat {} >> modules.order \;

Signed-off-by: Will McVicker <willmcvicker@google.com>
---
v2: Use md5sum to fix a "Filename too long" failure when KBUILD_EXTMOD
    exceeds 241 characters.

 scripts/Makefile.modinst | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/scripts/Makefile.modinst b/scripts/Makefile.modinst
index c2c43a0ecfe0..a6ef273d395f 100644
--- a/scripts/Makefile.modinst
+++ b/scripts/Makefile.modinst
@@ -24,6 +24,10 @@ suffix-$(CONFIG_MODULE_COMPRESS_XZ)	:= .xz
 suffix-$(CONFIG_MODULE_COMPRESS_ZSTD)	:= .zst
 
 modules := $(patsubst $(extmod_prefix)%, $(dst)/%$(suffix-y), $(modules))
+ifneq ($(KBUILD_EXTMOD),)
+extmod_suffix := $(shell echo "${KBUILD_EXTMOD}" | md5sum | cut -d " " -f 1)
+modules += $(dst)/modules.order.$(extmod_suffix)
+endif
 
 __modinst: $(modules)
 	@:
@@ -82,6 +86,12 @@ $(dst)/%.ko: $(extmod_prefix)%.ko FORCE
 	$(call cmd,strip)
 	$(call cmd,sign)
 
+ifneq ($(KBUILD_EXTMOD),)
+$(dst)/modules.order.$(extmod_suffix): $(MODORDER) FORCE
+	$(call cmd,install)
+	@sed -i "s:^$(KBUILD_EXTMOD):$(INSTALL_MOD_DIR):g" $@
+endif
+
 else
 
 $(dst)/%.ko: FORCE
-- 
2.35.0.rc0.227.g00780c9af4-goog