target/linux/$(ARCH)/image/Makefile解析---openWRT

# 
# Copyright (C) 2010 OpenWrt.org
#
# This is free software, licensed under the GNU General Public License v2.
# See /LICENSE for more information.
#


include $(TOPDIR)/rules.mk
include $(INCLUDE_DIR)/image.mk


UIMAGE:=$(BIN_DIR)/$(IMG_PREFIX)-uImage

define MkuImage
mkimage -A arm -O linux -T kernel -a 0x30008000 -C none \
-e 0x30008000 -n 'Webee210 OpenWrt Linux-$(LINUX_VERSION)' \
-d $(1) $(2)
endef
 
define Image/Prepare
    cp $(LINUX_DIR)/arch/arm/boot/zImage $(KDIR)/zImage
endef

define Image/BuildKernel
$(call MkuImage,$(KDIR)/zImage,$(UIMAGE))
cp $(KDIR)/zImage $(BIN_DIR)/$(IMG_PREFIX)-zImage
endef--------------------------------->以上这几项定义全部都是为了生成uimage，若只用到zimage可将上面的内容直接去掉。


define Image/Build
$(call Image/Build/$(1),$(1))
endef


define Image/Build/squashfs
$(call prepare_generic_squashfs,$(KDIR)/root.squashfs)
( \
dd if=$(KDIR)/uImage bs=1024k conv=sync; \
dd if=$(KDIR)/root.$(1) bs=64k conv=sync; \
) > $(BIN_DIR)/openwrt-$(BOARD)-$(1).img
$(STAGING_DIR_HOST)/bin/mkyaffs2image-page2k $(STAGING_DIR_ROOT)/ $(BIN_DIR)/openwrt-$(BOARD)-yaffs2-128k.img
endef


#define Image/Build/yaffs2-128k
# $(STAGING_DIR_HOST)/bin/mkyaffs2image-page2k $(STAGING_DIR_ROOT)/ $(BIN_DIR)/openwrt-$(BOARD)-$(1).yaffs2
#endef


$(eval $(call BuildImage))-----BuildImage定义在include/image.mk165行，具体内容如下：
define BuildImage
166 
167   download:
168   prepare:
169 
170   ifeq ($(IB),)
171     compile: compile-targets FORCE
172                 $(call Build/Compile)
173   else
174     compile:
175   endif
176 
177   ifeq ($(IB),)
178     install: compile install-targets FORCE
179                 $(call Image/Prepare)
180                 $(call Image/mkfs/prepare)
181                 $(call Image/BuildKernel)
182                 $(call Image/mkfs/cpiogz)
183                 $(call Image/mkfs/targz)
184                 $(call Image/mkfs/ext4)
185                 $(call Image/mkfs/iso)
186                 $(call Image/mkfs/jffs2)
187                 $(call Image/mkfs/squashfs)------>Image/mkfs/squashfs也定义在image.mk90行，查看知其调$(call Image/Build,squashfs)
                        ------->又Image/Build定义如下：(在/target/linux/$(ARCH)/image/makefile中定义)
define Image/Build
$(call Image/Build/$(1),$(1))
endef
---------->故其最终调用了Image/Build/squashfs。
注：如下所示，只有CONFIG_TARGET_ROOTFS_SQUASHFS在menuconfig的Target Image的菜单中被配置了，最终才能调用Image/Build/squashfs并生成squashfs映像。
 89   ifneq ($(CONFIG_TARGET_ROOTFS_SQUASHFS),)
 90     define Image/mkfs/squashfs

188                 $(call Image/mkfs/ubifs)
189                 $(call Image/Checksum)
190   else
191     install: compile install-targets
192                 $(call Image/BuildKernel)
193                 $(call Image/mkfs/cpiogz)
194                 $(call Image/mkfs/targz)
195                 $(call Image/mkfs/ext4)
196                 $(call Image/mkfs/iso)
197                 $(call Image/mkfs/jffs2)
198                 $(call Image/mkfs/squashfs)
199                 $(call Image/mkfs/ubifs)
200                 $(call Image/Checksum)
201   endif
202 
203   ifeq ($(IB),)
204     clean: clean-targets
205                 $(call Build/Clean)
206   else
207     clean:
208   endif
209 
210   compile-targets:
211   install-targets:
212   clean-targets:
213 
214 endef