使用ext4格式生成system.img有時候會報錯，原因可能是因為文件分配的大小不夠，默認情況下系統使用128M大小，對於4.0以上系統不做裁剪其實是不夠用的。

build/core/Makefile:

823 $(INSTALLED_SYSTEMIMAGE): $(BUILT_SYSTEMIMAGE) $(RECOVERY_FROM_BOOT_PATCH) | $(ACP)

824 @echo "Install system fs image: $@"

825 $(copy-file-to-target)

826 $(hide) $(call assert-max-image-size,$@ $(RECOVERY_FROM_BOOT_PATCH),$(B OARD_SYSTEMIMAGE_PARTITION_SIZE),yaffs)

827

828 systemimage: $(INSTALLED_SYSTEMIMAGE)

799 $(BUILT_SYSTEMIMAGE): $(FULL_SYSTEMIMAGE_DEPS) $(INSTALLED_FILES_FILE)

800 $(call build-systemimage-target,$@)

build-systemimage-target定義：

790 define build-systemimage-target

791 @echo "Target system fs image: $(1)"

792 @mkdir -p $(dir $(1)) $(systemimage_intermediates) && rm -rf $(systemimag e_intermediates)/system_image_info.txt

793 $(call generate-userimage-prop-dictionary, $(systemimage_intermediates)/s ystem_image_info.txt, skip_fsck=true)

794 $(hide) PATH=$(foreach p,$(INTERNAL_USERIMAGES_BINARY_PATHS),$(p):)$$PATH \

795 ./build/tools/releasetools/build_image.py \

796 $(TARGET_OUT) $(systemimage_intermediates)/system_image_info.txt $(1)

797 endef

核心是調用了build_image.py腳本文件，但system_image_info.txt文件很重要，該文件中描述了生成image的一些屬性，不如類型、分區大小、標記等等，python腳本會根據該文件生成相應的Image。

info.txt文件生成過程：

590 define generate-userimage-prop-dictionary

591 $(if $(INTERNAL_USERIMAGES_EXT_VARIANT),$(hide) echo "fs_type=$(INTERNAL_US ERIMAGES_EXT_VARIANT)" >> $(1))

592 $(if $(BOARD_SYSTEMIMAGE_PARTITION_SIZE),$(hide) echo "system_size=$(BOARD_ SYSTEMIMAGE_PARTITION_SIZE)" >> $(1))

593 $(if $(BOARD_USERDATAIMAGE_PARTITION_SIZE),$(hide) echo "userdata_size=$(BO ARD_USERDATAIMAGE_PARTITION_SIZE)" >> $(1))

594 $(if $(BOARD_CACHEIMAGE_FILE_SYSTEM_TYPE),$(hide) echo "cache_fs_type=$(BOA RD_CACHEIMAGE_FILE_SYSTEM_TYPE)" >> $(1))

595 $(if $(BOARD_CACHEIMAGE_PARTITION_SIZE),$(hide) echo "cache_size=$(BOARD_CA CHEIMAGE_PARTITION_SIZE)" >> $(1))

596 $(if $(BOARD_VENDORIMAGE_FILE_SYSTEM_TYPE),$(hide) echo "vendor_fs_type=$(B OARD_VENDORIMAGE_FILE_SYSTEM_TYPE)" >> $(1))

597 $(if $(BOARD_VENDORIMAGE_PARTITION_SIZE),$(hide) echo "vendor_size=$(BOARD_ VENDORIMAGE_PARTITION_SIZE)" >> $(1))

598 $(if $(INTERNAL_USERIMAGES_SPARSE_EXT_FLAG),$(hide) echo "extfs_sparse_flag =$(INTERNAL_USERIMAGES_SPARSE_EXT_FLAG)" >> $(1))

599 $(if $(mkyaffs2_extra_flags),$(hide) echo "mkyaffs2_extra_flags=$(mkyaffs2_ extra_flags)" >> $(1))

600 $(hide) echo "selinux_fc=$(SELINUX_FC)" >> $(1)

601 $(if $(2),$(hide) $(foreach kv,$(2),echo "$(kv)" >> $(1);))

602 endef

這里可以得到幾個有用的變量來控制幾個鏡像文件的大小等信息。

BOARD_SYSTEMIMAGE_PARTITION_SIZE ，可以修改system.img的文件大小。

看看如果不定義文件大小會是多少

system/extras/ext4_utils/mkuserimg.sh:

47 if [ -z $SIZE ]; then

48 echo "Need size of filesystem"

49 exit 2

50 fi這是最新版的處理辦法，沒有定義會提示。

老版是這樣的：

0046 if [ -z $SIZE ]; then

0047 SIZE=128M

0048 fi默認為128M。