Android OTA 升级(五)：updater

转自 http://blog.csdn.net/myarrow/article/details/8114627
、简介

前面分析的OTA升级的各部分代码都是在搭一个舞台，而主角现在终于登场，它就是updater。Google的代码架构设计非常好，各部分尽量松耦合。前面介绍升级脚本时，可知有两种类型的脚本，amend & edify(Amend脚本<update-script>在Android 1.5中已经被废除，只保留了Edify脚本<updater-script>). 他们各自对应一个updater. 这里，我们主要关注新的edify的updater.

Updater可以作为学习解释器/编译器的同学一个很好的实例，但是我们只关心产品化相关的内容，所以并不去深究lex/yacc相关的东西。

二、入口函数main

bootable/recovery/updater/updater.c

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// 这里定义脚本的位置，注释说明本updater支持edify格式的脚本。

// Where in the package we expect to find the edify script to execute.

// (Note it's "updateR-script", not the older "update-script".)

#define SCRIPT_NAME "META-INF/com/google/android/updater-script"



int main(int argc, char** argv) {

// Various things log information to stdout or stderr more or less

// at random. The log file makes more sense if buffering is

// turned off so things appear in the right order.

setbuf(stdout, NULL);

setbuf(stderr, NULL);



if (argc != 4) {

fprintf(stderr, "unexpected number of arguments (%d)\n", argc);

return 1;

}

// 获取 version 参数。

char* version = argv[1];

if ((version[0] != '1' && version[0] != '2' && version[0] != '3') ||

version[1] != '\0') {

// We support version 1, 2, or 3.

fprintf(stderr, "wrong updater binary API; expected 1, 2, or 3; "

"got %s\n",

argv[1]);

return 2;

}



// 获取命令管道（用于图形显示等，见前篇）

// Set up the pipe for sending commands back to the parent process.

int fd = atoi(argv[2]);

FILE* cmd_pipe = fdopen(fd, "wb");

setlinebuf(cmd_pipe);



// Extract the script from the package.



char* package_data = argv[3];

ZipArchive za;

int err;

err = mzOpenZipArchive(package_data, &za);

if (err != 0) {

fprintf(stderr, "failed to open package %s: %s\n",

package_data, strerror(err));

return 3;

}



// 读入脚本 META-INF/com/google/android/updater-script

const ZipEntry* script_entry = mzFindZipEntry(&za, SCRIPT_NAME);

if (script_entry == NULL) {

fprintf(stderr, "failed to find %s in %s\n", SCRIPT_NAME, package_data);

return 4;

}



char* script = malloc(script_entry->uncompLen+1);

if (!mzReadZipEntry(&za, script_entry, script, script_entry->uncompLen)) {

fprintf(stderr, "failed to read script from package\n");

return 5;

}

script[script_entry->uncompLen] = '\0';



// Configure edify's functions.

// 注册语句处理函数

RegisterBuiltins();

RegisterInstallFunctions();

RegisterDeviceExtensions();

FinishRegistration();



// Parse the script.

// 调用yy* 库函数解析脚本。

Expr* root;

int error_count = 0;

yy_scan_string(script);

int error = yyparse(&root, &error_count);

if (error != 0 || error_count > 0) {

fprintf(stderr, "%d parse errors\n", error_count);

return 6;

}



// Evaluate the parsed script.

UpdaterInfo updater_info;

updater_info.cmd_pipe = cmd_pipe;

updater_info.package_zip = &za;

updater_info.version = atoi(version);



State state;

state.cookie = &updater_info;

state.script = script;

state.errmsg = NULL;



// 解释执行脚本。 核心函数是 Evaluate。它会调用其他callback函数，而这些callback函数

// 又会调用Evaluate去解析不同的脚本片段。从而实现一个简单的解释器

char* result = Evaluate(&state, root);

if (result == NULL) {

if (state.errmsg == NULL) {

fprintf(stderr, "script aborted (no error message)\n");

fprintf(cmd_pipe, "ui_print script aborted (no error message)\n");

} else {

fprintf(stderr, "script aborted: %s\n", state.errmsg);

char* line = strtok(state.errmsg, "\n");

while (line) {

fprintf(cmd_pipe, "ui_print %s\n", line);

line = strtok(NULL, "\n");

}

fprintf(cmd_pipe, "ui_print\n");

}

free(state.errmsg);

return 7;

} else {

fprintf(stderr, "script result was [%s]\n", result);

free(result);

}



if (updater_info.package_zip) {

mzCloseZipArchive(updater_info.package_zip);

}

free(script);



return 0;

}

还没开始，就结束了。代码非常简单，因为细节隐藏在那些callback函数里。我们看一下。

三、callback函数

1) RegisterBuiltins

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void RegisterBuiltins() {

RegisterFunction("ifelse", IfElseFn);

RegisterFunction("abort", AbortFn);

RegisterFunction("assert", AssertFn);

RegisterFunction("concat", ConcatFn);

RegisterFunction("is_substring", SubstringFn);

RegisterFunction("stdout", StdoutFn);

RegisterFunction("sleep", SleepFn);



RegisterFunction("less_than_int", LessThanIntFn);

RegisterFunction("greater_than_int", GreaterThanIntFn);

}

这些语句控制执行流程。

2) RegisterInstallFunctions

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void RegisterInstallFunctions() {

RegisterFunction("mount", MountFn);

RegisterFunction("is_mounted", IsMountedFn);

RegisterFunction("unmount", UnmountFn);

RegisterFunction("format", FormatFn);

RegisterFunction("show_progress", ShowProgressFn);

RegisterFunction("set_progress", SetProgressFn);

RegisterFunction("delete", DeleteFn);

RegisterFunction("delete_recursive", DeleteFn);

RegisterFunction("package_extract_dir", PackageExtractDirFn);

RegisterFunction("package_extract_file", PackageExtractFileFn);

RegisterFunction("retouch_binaries", RetouchBinariesFn);

RegisterFunction("undo_retouch_binaries", UndoRetouchBinariesFn);

RegisterFunction("symlink", SymlinkFn);

RegisterFunction("set_perm", SetPermFn);

RegisterFunction("set_perm_recursive", SetPermFn);



RegisterFunction("getprop", GetPropFn);

RegisterFunction("file_getprop", FileGetPropFn);

RegisterFunction("write_raw_image", WriteRawImageFn);

RegisterFunction("write_raw_parameter_image", WriteRawParameterImageFn);

RegisterFunction("clear_misc_command", ClearMiscCommandFn);



RegisterFunction("apply_patch", ApplyPatchFn);

RegisterFunction("apply_patch_check", ApplyPatchCheckFn);

RegisterFunction("apply_patch_space", ApplyPatchSpaceFn);



RegisterFunction("read_file", ReadFileFn);

RegisterFunction("sha1_check", Sha1CheckFn);



RegisterFunction("wipe_cache", WipeCacheFn);



RegisterFunction("ui_print", UIPrintFn);



RegisterFunction("run_program", RunProgramFn);

}

这些语句执行各种功能。基本上，我们只需要知道用法就可以了。值得注意的是，run_program原语允许我们去执行自定义程序，这应该足够满足我们的个性化需求了。