System.img是如何打包的

★★★ 友情链接 : 个人博客导读首页—点击此处 ★★★

当敲击make命令时，会找到第一个目标droid（在build/core/main.mk中），droid依赖droid_targets，droid_targets依赖droidcore和dist_files，droidcore的依赖关系如下：

.PHONY: droidcore
droidcore: files \systemimage \$(INSTALLED_BOOTIMAGE_TARGET) \$(INSTALLED_RECOVERYIMAGE_TARGET) \$(INSTALLED_VBMETAIMAGE_TARGET) \$(INSTALLED_USERDATAIMAGE_TARGET) \$(INSTALLED_CACHEIMAGE_TARGET) \$(INSTALLED_BPTIMAGE_TARGET) \$(INSTALLED_VENDORIMAGE_TARGET) \$(INSTALLED_PRODUCTIMAGE_TARGET) \$(INSTALLED_SYSTEMOTHERIMAGE_TARGET) \$(INSTALLED_FILES_FILE) \$(INSTALLED_FILES_FILE_VENDOR) \$(INSTALLED_FILES_FILE_PRODUCT) \$(INSTALLED_FILES_FILE_SYSTEMOTHER) \soong_docs

切到build/core/Makefile中，我们看到systemimage又依赖INSTALLED_SYSTEMIMAGE，而INSTALLED_SYSTEMIMAGE又依赖BUILT_SYSTEMIMAGE，BUILT_SYSTEMIMAGE其实就是system.img

systemimage: $(INSTALLED_SYSTEMIMAGE)
$(INSTALLED_SYSTEMIMAGE): $(BUILT_SYSTEMIMAGE) $(RECOVERY_FROM_BOOT_PATCH)BUILT_SYSTEMIMAGE := $(systemimage_intermediates)/system.img

我们再来看看BUILT_SYSTEMIMAGE的依赖关系：

$(BUILT_SYSTEMIMAGE): $(FULL_SYSTEMIMAGE_DEPS) $(INSTALLED_FILES_FILE) $(BUILD_IMAGE_SRCS)$(call build-systemimage-target,$@)

BUILT_SYSTEMIMAGE依赖的一些文件生成后，会调用makefile中的build-systemimage-target函数，我们接着去看build-systemimage-target的函数原型:

define build-systemimage-target@echo "Target system fs image: $(1)"$(call create-system-vendor-symlink)@mkdir -p $(dir $(1)) $(systemimage_intermediates) && rm -rf $(systemimage_intermediates)/system_image_info.txt$(call generate-userimage-prop-dictionary, $(systemimage_intermediates)/system_image_info.txt, \skip_fsck=true)$(hide) PATH=$(foreach p,$(INTERNAL_USERIMAGES_BINARY_PATHS),$(p):)$$PATH \./build/tools/releasetools/build_image.py \$(TARGET_OUT) $(systemimage_intermediates)/system_image_info.txt $(1) $(TARGET_OUT) \|| ( echo "Out of space? the tree size of $(TARGET_OUT) is (MB): " 1>&2 ;\du -sm $(TARGET_OUT) 1>&2;\if [ "$(INTERNAL_USERIMAGES_EXT_VARIANT)" == "ext4" ]; then \maxsize=$(BOARD_SYSTEMIMAGE_PARTITION_SIZE); \if [ "$(BOARD_HAS_EXT4_RESERVED_BLOCKS)" == "true" ]; then \maxsize=$$((maxsize - 4096 * 4096)); \fi; \echo "The max is $$(( maxsize / 1048576 )) MB." 1>&2 ;\else \echo "The max is $$(( $(BOARD_SYSTEMIMAGE_PARTITION_SIZE) / 1048576 )) MB." 1>&2 ;\fi; \mkdir -p $(DIST_DIR); cp $(INSTALLED_FILES_FILE) $(DIST_DIR)/installed-files-rescued.txt; \exit 1 )
endef

看起来挺复杂吧，其实都是些shell语句，仔细看还是能看懂的。看不懂也没关系，我们只关心其中的关键语句 ./build/tools/releasetools/build_image.py，其后跟随了一堆的参数，我们不必关心这些参数，只要明白，这里调用了build_image.py
打开build_image.py，main函数如下，其实并不复杂，这里随后调用了BuildImage()

def main(argv):if len(argv) != 4:print __doc__sys.exit(1)in_dir = argv[0]glob_dict_file = argv[1]out_file = argv[2]target_out = argv[3]glob_dict = LoadGlobalDict(glob_dict_file)if "mount_point" in glob_dict:# The caller knows the mount point and provides a dictionay needed by# BuildImage().image_properties = glob_dictelse:image_filename = os.path.basename(out_file)mount_point = ""if image_filename == "system.img":mount_point = "system"elif image_filename == "system_other.img":mount_point = "system_other"elif image_filename == "userdata.img":mount_point = "data"elif image_filename == "cache.img":mount_point = "cache"elif image_filename == "vendor.img":mount_point = "vendor"elif image_filename == "oem.img":mount_point = "oem"else:print >> sys.stderr, "error: unknown image file name ", image_filenameexit(1)image_properties = ImagePropFromGlobalDict(glob_dict, mount_point)if not BuildImage(in_dir, image_properties, out_file, target_out):print >> sys.stderr, "error: failed to build %s from %s" % (out_file,in_dir)exit(1)

继续查看BuildImage()，原型如下：

def BuildImage(in_dir, prop_dict, out_file, target_out=None):"""Build an image to out_file from in_dir with property prop_dict.Args:in_dir: path of input directory.prop_dict: property dictionary.out_file: path of the output image file.target_out: path of the product out directory to read device specific FS config files.Returns:True iff the image is built successfully."""# system_root_image=true: build a system.img that combines the contents of# /system and the ramdisk, and can be mounted at the root of the file system.origin_in = in_dirfs_config = prop_dict.get("fs_config")base_fs_file = Noneif (prop_dict.get("system_root_image") == "true"and prop_dict["mount_point"] == "system"):in_dir = tempfile.mkdtemp()# Change the mount point to "/"prop_dict["mount_point"] = "/"if fs_config:# We need to merge the fs_config files of system and ramdisk.fd, merged_fs_config = tempfile.mkstemp(prefix="root_fs_config",suffix=".txt")os.close(fd)with open(merged_fs_config, "w") as fw:if "ramdisk_fs_config" in prop_dict:with open(prop_dict["ramdisk_fs_config"]) as fr:fw.writelines(fr.readlines())with open(fs_config) as fr:fw.writelines(fr.readlines())fs_config = merged_fs_configbuild_command = []fs_type = prop_dict.get("fs_type", "")run_fsck = Falsefs_spans_partition = Trueif fs_type.startswith("squash"):fs_spans_partition = Falseis_verity_partition = "verity_block_device" in prop_dictverity_supported = prop_dict.get("verity") == "true"verity_fec_supported = prop_dict.get("verity_fec") == "true"# Adjust the partition size to make room for the hashes if this is to be# verified.if verity_supported and is_verity_partition:partition_size = int(prop_dict.get("partition_size"))(adjusted_size, verity_size) = AdjustPartitionSizeForVerity(partition_size,verity_fec_supported)if not adjusted_size:return Falseprop_dict["partition_size"] = str(adjusted_size)prop_dict["original_partition_size"] = str(partition_size)prop_dict["verity_size"] = str(verity_size)# Adjust partition size for AVB hash footer or AVB hashtree footer.avb_footer_type = ''if prop_dict.get("avb_hash_enable") == "true":avb_footer_type = 'hash'elif prop_dict.get("avb_hashtree_enable") == "true":avb_footer_type = 'hashtree'if avb_footer_type:avbtool = prop_dict["avb_avbtool"]partition_size = prop_dict["partition_size"]# avb_add_hash_footer_args or avb_add_hashtree_footer_args.additional_args = prop_dict["avb_add_" + avb_footer_type + "_footer_args"]max_image_size = AVBCalcMaxImageSize(avbtool, avb_footer_type, partition_size,additional_args)if max_image_size == 0:return Falseprop_dict["partition_size"] = str(max_image_size)prop_dict["original_partition_size"] = partition_sizeif fs_type.startswith("ext"):build_command = [prop_dict["ext_mkuserimg"]]if "extfs_sparse_flag" in prop_dict:build_command.append(prop_dict["extfs_sparse_flag"])run_fsck = Truebuild_command.extend([in_dir, out_file, fs_type,prop_dict["mount_point"]])build_command.append(prop_dict["partition_size"])if "journal_size" in prop_dict:build_command.extend(["-j", prop_dict["journal_size"]])if "timestamp" in prop_dict:build_command.extend(["-T", str(prop_dict["timestamp"])])if fs_config:build_command.extend(["-C", fs_config])if target_out:build_command.extend(["-D", target_out])if "block_list" in prop_dict:build_command.extend(["-B", prop_dict["block_list"]])if "base_fs_file" in prop_dict:base_fs_file = ConvertBlockMapToBaseFs(prop_dict["base_fs_file"])if base_fs_file is None:return Falsebuild_command.extend(["-d", base_fs_file])build_command.extend(["-L", prop_dict["mount_point"]])if "extfs_inode_count" in prop_dict:build_command.extend(["-i", prop_dict["extfs_inode_count"]])if "flash_erase_block_size" in prop_dict:build_command.extend(["-e", prop_dict["flash_erase_block_size"]])if "flash_logical_block_size" in prop_dict:build_command.extend(["-o", prop_dict["flash_logical_block_size"]])# Specify UUID and hash_seed if using mke2fs.if prop_dict["ext_mkuserimg"] == "mkuserimg_mke2fs.sh":if "uuid" in prop_dict:build_command.extend(["-U", prop_dict["uuid"]])if "hash_seed" in prop_dict:build_command.extend(["-S", prop_dict["hash_seed"]])if "selinux_fc" in prop_dict:build_command.append(prop_dict["selinux_fc"])elif fs_type.startswith("squash"):build_command = ["mksquashfsimage.sh"]build_command.extend([in_dir, out_file])if "squashfs_sparse_flag" in prop_dict:build_command.extend([prop_dict["squashfs_sparse_flag"]])build_command.extend(["-m", prop_dict["mount_point"]])if target_out:build_command.extend(["-d", target_out])if fs_config:build_command.extend(["-C", fs_config])if "selinux_fc" in prop_dict:build_command.extend(["-c", prop_dict["selinux_fc"]])if "block_list" in prop_dict:build_command.extend(["-B", prop_dict["block_list"]])if "squashfs_compressor" in prop_dict:build_command.extend(["-z", prop_dict["squashfs_compressor"]])if "squashfs_compressor_opt" in prop_dict:build_command.extend(["-zo", prop_dict["squashfs_compressor_opt"]])if "squashfs_block_size" in prop_dict:build_command.extend(["-b", prop_dict["squashfs_block_size"]])if "squashfs_disable_4k_align" in prop_dict and prop_dict.get("squashfs_disable_4k_align") == "true":build_command.extend(["-a"])elif fs_type.startswith("f2fs"):build_command = ["mkf2fsuserimg.sh"]build_command.extend([out_file, prop_dict["partition_size"]])else:print("Error: unknown filesystem type '%s'" % (fs_type))return Falseif in_dir != origin_in:# Construct a staging directory of the root file system.ramdisk_dir = prop_dict.get("ramdisk_dir")if ramdisk_dir:shutil.rmtree(in_dir)shutil.copytree(ramdisk_dir, in_dir, symlinks=True)staging_system = os.path.join(in_dir, "system")shutil.rmtree(staging_system, ignore_errors=True)shutil.copytree(origin_in, staging_system, symlinks=True)has_reserved_blocks = prop_dict.get("has_ext4_reserved_blocks") == "true"ext4fs_output = Nonetry:if fs_type.startswith("ext4"):(ext4fs_output, exit_code) = RunCommand(build_command)else:(_, exit_code) = RunCommand(build_command)finally:if in_dir != origin_in:# Clean up temporary directories and files.shutil.rmtree(in_dir, ignore_errors=True)if fs_config:os.remove(fs_config)if base_fs_file is not None:os.remove(base_fs_file)if exit_code != 0:return False# Bug: 21522719, 22023465# There are some reserved blocks on ext4 FS (lesser of 4096 blocks and 2%).# We need to deduct those blocks from the available space, since they are# not writable even with root privilege. It only affects devices using# file-based OTA and a kernel version of 3.10 or greater (currently just# sprout).# Separately, check if there's enough headroom space available. This is useful for# devices with low disk space that have system image variation between builds.if (has_reserved_blocks or "partition_headroom" in prop_dict) and fs_type.startswith("ext4"):assert ext4fs_output is not Noneext4fs_stats = re.compile(r'Created filesystem with .* (?P<used_blocks>[0-9]+)/'r'(?P<total_blocks>[0-9]+) blocks')m = ext4fs_stats.match(ext4fs_output.strip().split('\n')[-1])used_blocks = int(m.groupdict().get('used_blocks'))total_blocks = int(m.groupdict().get('total_blocks'))reserved_blocks = 0headroom_blocks = 0adjusted_blocks = total_blocksif has_reserved_blocks:reserved_blocks = min(4096, int(total_blocks * 0.02))adjusted_blocks -= reserved_blocksif "partition_headroom" in prop_dict:headroom_blocks = int(prop_dict.get('partition_headroom')) / BLOCK_SIZEadjusted_blocks -= headroom_blocksif used_blocks > adjusted_blocks:mount_point = prop_dict.get("mount_point")print("Error: Not enough room on %s (total: %d blocks, used: %d blocks, ""reserved: %d blocks, headroom: %d blocks, available: %d blocks)" % (mount_point, total_blocks, used_blocks, reserved_blocks,headroom_blocks, adjusted_blocks))return Falseif not fs_spans_partition:mount_point = prop_dict.get("mount_point")partition_size = int(prop_dict.get("partition_size"))image_size = GetSimgSize(out_file)if image_size > partition_size:print("Error: %s image size of %d is larger than partition size of ""%d" % (mount_point, image_size, partition_size))return Falseif verity_supported and is_verity_partition:ZeroPadSimg(out_file, partition_size - image_size)# create the verified image if this is to be verifiedif verity_supported and is_verity_partition:if not MakeVerityEnabledImage(out_file, verity_fec_supported, prop_dict):return False# Add AVB HASH or HASHTREE footer (metadata).if avb_footer_type:avbtool = prop_dict["avb_avbtool"]original_partition_size = prop_dict["original_partition_size"]partition_name = prop_dict["partition_name"]# key_path and algorithm are only available when chain partition is used.key_path = prop_dict.get("avb_key_path")algorithm = prop_dict.get("avb_algorithm")salt = prop_dict.get("avb_salt")# avb_add_hash_footer_args or avb_add_hashtree_footer_argsadditional_args = prop_dict["avb_add_" + avb_footer_type + "_footer_args"]if not AVBAddFooter(out_file, avbtool, avb_footer_type, original_partition_size,partition_name, key_path, algorithm, salt, additional_args):return Falseif run_fsck and prop_dict.get("skip_fsck") != "true":success, unsparse_image = UnsparseImage(out_file, replace=False)if not success:return False# Run e2fsck on the inflated image filee2fsck_command = ["e2fsck", "-f", "-n", unsparse_image](_, exit_code) = RunCommand(e2fsck_command)os.remove(unsparse_image)return exit_code == 0

这里面有一堆的参数，其实都非常有深意后，我们在学习阶段可以不必考虑，当我们遇到相关问题时，那时可能就会对照这些参数，了解其功能和作用。而我们这里重点查看的，如下：

 if prop_dict["ext_mkuserimg"] == "mkuserimg_mke2fs.sh":if "uuid" in prop_dict:build_command.extend(["-U", prop_dict["uuid"]])if "hash_seed" in prop_dict:build_command.extend(["-S", prop_dict["hash_seed"]])

这里是执行了mkuserimg_mke2fs.sh脚本，我们再去看看这个脚本吧
路径：system/extras/ext4_utils/mkuserimg_mke2fs.sh
同样，打开该文件后发现又是一堆的参数命令，看也看不懂，我们依然只是关心其核心的部分，截取如下：

MAKE_EXT4FS_CMD="mke2fs $MKE2FS_OPTS -t $EXT_VARIANT -b $BLOCKSIZE $OUTPUT_FILE $SIZE"
echo $MAKE_EXT4FS_ENV $MAKE_EXT4FS_CMD
env $MAKE_EXT4FS_ENV $MAKE_EXT4FS_CMD
if [ $? -ne 0 ]; thenexit 4
fiif [[ $E2FSPROGS_FAKE_TIME ]]; thenE2FSDROID_ENV="E2FSPROGS_FAKE_TIME=$E2FSPROGS_FAKE_TIME"
fiE2FSDROID_CMD="e2fsdroid $E2FSDROID_OPTS -f $SRC_DIR -a $MOUNT_POINT $OUTPUT_FILE"
echo $E2FSDROID_ENV $E2FSDROID_CMD
env $E2FSDROID_ENV $E2FSDROID_CMD
if [ $? -ne 0 ]; thenrm -f $OUTPUT_FILEexit 4
fi

这里做了两件事：
（1）mke2fs打包生成了system.img
（2）e2fsdroid制作了system.map
mke2fs对应的源码：external/e2fsprogs/misc/mke2fs.c
e2fsdroid对应的源码： external/e2fsprogs/contrib/android/e2fsdroid.c

深思：
其实呢，在正常的android编译，并不会生成system.map，因为最后一个参数$OUTPUT_FILE为空. 在android的设计中system.map是在制作OTA的target-files文件时生成的，然后在制作block差分别时候，会用到system.map，一个block一个block的去求diff。
在制作OTA的target-files时，会重新打包system.img，其流程：
add_img_to_target_files直接调用了build_image.py中的CreateImage（）函数，与正常的打包system.img参数稍微不同，这里增加了一个block_list="system.map"参数，所以其打包结束后，生成了system.map

Q & A:
1、system.img是怎样制作的？
答：使用mke2fs工具制作的
2、system.map是做什么用的？先有的system.img，还是先用的system.map？
答：system.map是制作OTA的target-files文件时，重新打包system.img后，根据system.img做出的system.map，制作差分别时候，会用到system.map文件

不足之处，欢迎指正！

System.img是如何打包的相关推荐

android系统system镜像解包打包制作过程
** android系统system镜像解包打包制作过程首先确认你的system是哪种类型镜像:yaffs2 ? 还是sparse? 这两种镜像使用的解包工具也不一样,下面以sparse类型镜像描述 ...
system.img解包打包工具
最近需要对system.img进行解包,修改系统属性和添加自己的APK,再打包烧录,整理俩个方法. system.img解包打包工具方法一 1.把system.img转换成ext4格式 ./simg2 ...
linux环境systwm.img解包,[教程] system.img解包打包的方法，方便菜鸟们制作直刷ROM...
操作系统:ubuntu10.10可虚拟机可其他linux可其他版本 & Windows 7 Ubuntu下操作: 下载unyaffs和yaffs2.tar.gz,并编译yaffs2再复制到/b ...
system.img解包打包工具_好程序员云计算学习路线分享文件打包及压缩
好程序员云计算学习路线分享文件打包及压缩好程序员建议针对目录 Demo: 复制未打包的文件到远程主机 [root@yangs ~]# du -sh /etc 39M /etc [root@yang ...
Android 系统（137）---android打包解包boot.img,system.img
android打包解包boot.img,system.img 2017年04月28日 15:00:36 阅读数:1822 原帖地址:http://www.52pojie.cn/thread-48802 ...
Image打包流程-Android10.0编译系统（四）
摘要:本节主要来进行Android10.0 Image打包流程,理解system.img是如何打包的阅读本文大约需要花费28分钟. 文章首发微信公众号:IngresGe 专注于Android系统级源 ...
压缩base 64字符串_ftp下载多个文件，ftp下载多个文件打包成一个压缩包
在一些日常的网络批量维护工作中,经常需要使用ftp计划任务,定时上传或下载多个文件.对不太了解ftp命令和windows计划任务的新手来说,确实是一个很棘手的问题.今天我们来看看如何简单的实现这功能. ...
linux rom打包工具,Android rom解包打包工具
eMMC主要是针对手机和平板电脑等产品的内嵌式存储器,由于其在封装中集成了一个控制器,且提供标准接口并管理闪存等优势,越来越受到Android手机厂商的青睐,以eMMC为存储设备的android手机, ...
FTP下载多个文件打包成一个压缩包
@RequestMapping("downloadsByplFromFTP") @ResponseBody public void downloadsByplFr ...

System.img是如何打包的

System.img是如何打包的相关推荐

最新文章

热门文章