FROMLIST: kbuild: install the modules.order for external modules

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} | sed 's:[./_]:_:g'

Ex:
  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 cat'd
together to create a single modules.order file which would define the
order to load all of the modules during boot.

Link: https://lore.kernel.org/all/20211215172349.388497-1-willmcvicker@google.com/
Bug: 210713925
Signed-off-by: Will McVicker <willmcvicker@google.com>
Change-Id: I3c23098d551ef17427436feee78bfddc9f9d36c6

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 := $(subst /,_,$(subst .,_,$(subst -,_,$(KBUILD_EXTMOD))))
+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