3.0之后在buildbuild_scriptsbuild_common.sh 增加了 build_cmd =" build_target=images"，这句的意思约等于在执行默认编译命令 ./build.sh --product-name Hi3516DV300 会有个默认的参数 --build-target images，具体流程是这样的：

buildbuild_scriptsbuild_common.sh => buildcoregnBUILD.gn => buildohosimagesBUILD.gn

action_with_pydeps("${_platform}_${_image_name}_image") { script = "//build/ohos/images/build_image.py" depfile = "$target_gen_dir/$target_name.d" deps = [ "//build/ohos/packages:${_platform}_install_modules" ] image_config_file = "//build/ohos/images/mkimage/${_image_name}_image_conf.txt" output_image_file = "$current_platform_dir/images/${_image_name}.img" image_input_path = "$current_platform_dir/${_image_name}" if (_image_name == "userdata") { image_input_path = "$current_platform_dir/data" } sources = [ image_config_file, system_module_info_list, system_modules_list, ] outputs = [ output_image_file ] args = [ "--depfile", rebase_path(depfile, root_build_dir), "--image-name", _image_name, "--input-path", rebase_path(image_input_path, root_build_dir), "--image-config-file", rebase_path(image_config_file, root_build_dir), "--output-image", rebase_path(output_image_file, root_build_dir), "--build-image-tools-path", rebase_path(build_image_tools_path, root_build_dir), ] if (sparse_image) { args = [ "--sparse-image" ] }}

通常情况下，gn会使用 action 运行一个脚本来生成一个文件，但是这里使用的是 action_with_pydeps，应该也是内置的目标类型。查看官方手册是这么说明的

Inputs and Depfiles

List all files read (or executed) by an action as inputs.

It is not enough to have inputs listed by dependent targets. They must be listed directly by targets that use them, or added by a depfile.

Non-system Python imports are inputs! For scripts that import such modules, use action_with_pydeps to ensure all dependent Python files are captured as inputs.

前面还定义了一个image_list，然后使用 foreach 执行 action_with_pydeps，要生成几个img文件，就执行几次action_with_pydeps。

image_list = [ "system", "vendor", "userdata", "updater", ] foreach(_image_name, image_list) {... ...}二、调用python脚本

既然知道了img镜像是由 buildohosimagesbuild_image.py 来创建的，那就来分析下这个python脚本。

if os.path.exists(args.output_image_path): os.remove(args.output_image_path) # 删除之前生成的镜像文件夹 if args.image_name == 'userdata': _prepare_userdata(args.input_path) # 准备好 userdata.img 需要的文件 if os.path.isdir(args.input_path): _make_image(args) _dep_files = [] for _root, _, _files in os.walk(args.input_path): for _file in _files: _dep_files.append(os.path.join(_root, _file)) build_utils.write_depfile(args.depfile, args.output_image_path, _dep_files, add_pydeps=False)===================================================================def _make_image(args): if args.image_name == 'system': _prepare_root(args.input_path) # 准备好 system.img 需要的文件 elif args.image_name == 'updater': _prepare_updater(args.input_path) # 准备好 updater.img 需要的文件 image_type = "raw" if args.sparse_image: image_type = "sparse" mk_image_args = [ args.input_path, args.image_config_file, args.output_image_path, image_type ] env_path = "../../build/ohos/images/mkimage" if args.build_image_tools_path: env_path = '{}:{}'.format(env_path, args.build_image_tools_path) os.environ['PATH'] = '{}:{}'.format(env_path, os.environ.get('PATH')) mkimages.mk_images(mk_image_args) # 而真正制作镜像使用的下面的函数===================================================================# buildohosimagesmkimagemkimages.pydef mk_images(args): ... ... if "system.img" in device: src_dir = build_rootdir(src_dir) mkfs_tools, mk_configs = load_config(config_file) mk_configs = src_dir " " device " " mk_configs res = run_cmd(mkfs_tools " " mk_configs) # 制作镜像命令使用的是mkfs_tools=================================================================== if "ext4" in mk_configs: fs_type = "ext4" mkfs_tools = "mkextimage.py" # 而mkfs_tools根据文件系统类型，分别调用对应的python脚本 elif "f2fs" in mk_configs: mkfs_tools = "mkf2fsimage.py" fs_type = "f2fs"===================================================================# buildohosimagesmkimagemkextimage.py # 制作ext4文件系统def build_run_mke2fs(args): .. ... blocks = int(int(args.fs_size) / BLOCKSIZE) mke2fs_cmd = ("mke2fs " str(mke2fs_opts) " -t " FS_TYPE " -b " str(BLOCKSIZE) " " args.device " " str(blocks)) res = run_cmd(mke2fs_cmd) # mke2fs：制作文件系统===================================================================def build_run_e2fsdroid(args): ... ... e2fsdroid_cmd = ("e2fsdroid" e2fsdroid_opts " -f " args.src_dir " -a " args.mount_point " " args.device) res = run_cmd(e2fsdroid_cmd) # e2fsdroid：制作镜像文件

无论前面执行了什么操作，最终都是为了执行mke2fs、e2fsdroid。

关于这两个命令：

mke2fs：Linux下的命令，用于建立ext文件系统。