OpenWRT rootfs 的生成过程[通俗易懂]

opkg = 省略
TARGET_DIR_ORIG := $(TARGET_ROOTFS_DIR)/root.orig-$(BOARD)
define prepare_rootfs
  ...省略...

root@localhost:/home2/lql/openwrt# grep "rootfs\.mk" include/  package/ scripts/ feeds/  -rn
include/image.mk:22:include $(INCLUDE_DIR)/rootfs.mk
package/Makefile:11:include $(INCLUDE_DIR)/rootfs.mk

$(curdir)/install: $(TMP_DIR)/.build $(curdir)/merge $(if $(CONFIG_TARGET_PER_DEVICE_ROOTFS),$(curdir)/merge-index)
	- find $(STAGING_DIR_ROOT) -type d | $(XARGS) chmod 0755
	rm -rf $(TARGET_DIR) $(TARGET_DIR_ORIG)
	mkdir -p $(TARGET_DIR)/tmp
	$(call opkg,$(TARGET_DIR)) install \
		$(call opkg_package_files,$(shell cat $(PACKAGE_INSTALL_FILES) 2>/dev/null))
	@for file in $(PACKAGE_INSTALL_FILES); do \
		[ -s $$file.flags ] || continue; \
		for flag in `cat $$file.flags`; do \
			$(call opkg,$(TARGET_DIR)) flag $$flag `cat $$file`; \
		done; \
	done || true

	$(CP) $(TARGET_DIR) $(TARGET_DIR_ORIG)

	$(call prepare_rootfs,$(TARGET_DIR),$(TOPDIR)/files)

$(call opkg,$(TARGET_DIR)) install \
		$(call opkg_package_files,$(shell cat $(PACKAGE_INSTALL_FILES) 2>/dev/null))

opkg = \
  IPKG_NO_SCRIPT=1 \
  IPKG_INSTROOT=$(1) \
  TMPDIR=$(1)/tmp \
  $(STAGING_DIR_HOST)/bin/opkg \
	--offline-root $(1) \
	--force-postinstall \
	--add-dest root:/ \
	--add-arch all:100 \
	--add-arch $(if $(ARCH_PACKAGES),$(ARCH_PACKAGES),$(BOARD)):200

//类似于
staging_dir/host/bin/opkg  --offline-root root-sunxi    install  *.ipk