章节之外：makefile中的函数定义

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build-userimage-ext2-target的调用：
include external/genext2fs/Config.mkifeq ($(TARGET_SYSTEMIMAGES_USE_EXT3),true)## generate an ext3 image# $(1): output filedefine build-radioimage-target    @echo "Target radio fs image: $(1)"    $(call build-userimage-ext2-target,$(1),$(2),radio,journal)endefelse # TARGET_SYSTEMIMAGES_USE_EXT3 != true$(error Radio does not support yaffs!)endif
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