Android OTA 升级之五：updater

Android OTA 升级之五：updater
作者： 宋立新
Email：zjujoe@yahoo.com

前言

       可以说，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. 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。
 

入口函数 main

(from: bootable/recovery/updater/updater.c)
62 // Where in the package we expect to find the edify script to execute.
 63 // (Note it's "updateR-script", not the older "update-script".)
 64 #define SCRIPT_NAME "META-INF/com/google/android/updater-script"
 65
 
这里定义脚本的位置，注释说明本updater支持edify格式的脚本。
 
 66 int main(int argc, char** argv) {
 67     // Various things log information to stdout or stderr more or less
 68     // at random.  The log file makes more sense if buffering is
 69     // turned off so things appear in the right order.
 70     setbuf(stdout, NULL);
 71     setbuf(stderr, NULL);
 72
 73     if (argc != 4) {
 74         fprintf(stderr, "unexpected number of arguments (%d)/n", argc);
 75         return 1;
 76     }
 77
 78     char* version = argv[1];
 79     if ((version[0] != '1' && version[0] != '2' && version[0] != '3') ||
 80         version[1] != '/0') {
 81         // We support version 1, 2, or 3.
 82         fprintf(stderr, "wrong updater binary API; expected 1, 2, or 3; "
 83                         "got %s/n",
 84                 argv[1]);
 85         return 2;
 86     }
 87
获取 version 参数。
 88     // Set up the pipe for sending commands back to the parent process.
 89
 90     int fd = atoi(argv[2]);
 91     FILE* cmd_pipe = fdopen(fd, "wb");
 92     setlinebuf(cmd_pipe);
 93
 
获取命令管道（用于图形显示等，见前篇）
 
 94     // Extract the script from the package.
 95
 96     char* package_data = argv[3];
 97     ZipArchive za;
 98     int err;
 99     err = mzOpenZipArchive(package_data, &za);
100     if (err != 0) {
101         fprintf(stderr, "failed to open package %s: %s/n",
102                 package_data, strerror(err));
103         return 3;
104     }
105
106     const ZipEntry* script_entry = mzFindZipEntry(&za, SCRIPT_NAME);
107     if (script_entry == NULL) {
108         fprintf(stderr, "failed to find %s in %s/n", SCRIPT_NAME, package_data);
109         return 4;
110     }
111
112     char* script = malloc(script_entry->uncompLen+1);
113     if (!mzReadZipEntry(&za, script_entry, script, script_entry->uncompLen)) {
114         fprintf(stderr, "failed to read script from package/n");
115         return 5;
116     }
117     script[script_entry->uncompLen] = '/0';
118
 
读入脚本 META-INF/com/google/android/updater-script
 
119     // Configure edify's functions.
120
121     RegisterBuiltins();
122     RegisterInstallFunctions();
123     RegisterDeviceExtensions();
124     FinishRegistration();
125
注册语句处理函数
126     // Parse the script.
127
128     Expr* root;
129     int error_count = 0;
130     yy_scan_string(script);
131     int error = yyparse(&root, &error_count);
132     if (error != 0 || error_count > 0) {
133         fprintf(stderr, "%d parse errors/n", error_count);
134         return 6;
135     }
136
调用yy* 库函数解析脚本。
137     // Evaluate the parsed script.
138
139     UpdaterInfo updater_info;
140     updater_info.cmd_pipe = cmd_pipe;
141     updater_info.package_zip = &za;
142     updater_info.version = atoi(version);
143
144     State state;
145     state.cookie = &updater_info;
146     state.script = script;
147     state.errmsg = NULL;
148
149     char* result = Evaluate(&state, root);
150     if (result == NULL) {
151         if (state.errmsg == NULL) {
152             fprintf(stderr, "script aborted (no error message)/n");
153             fprintf(cmd_pipe, "ui_print script aborted (no error message)/n");
154         } else {
155             fprintf(stderr, "script aborted: %s/n", state.errmsg);
156             char* line = strtok(state.errmsg, "/n");
157             while (line) {
158                 fprintf(cmd_pipe, "ui_print %s/n", line);
159                 line = strtok(NULL, "/n");
160             }
161             fprintf(cmd_pipe, "ui_print/n");
162         }
163         free(state.errmsg);
164         return 7;
165     } else {
166         fprintf(stderr, "script result was [%s]/n", result);
167         free(result);
168     }
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。
169
170     mzCloseZipArchive(&za);
171     free(script);
172
173     return 0;
174 }
 
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。

RegisterBuiltins

415 void RegisterBuiltins() {

416     RegisterFunction("ifelse", IfElseFn);

417     RegisterFunction("abort", AbortFn);

418     RegisterFunction("assert", AssertFn);

419     RegisterFunction("concat", ConcatFn);

420     RegisterFunction("is_substring", SubstringFn);

421     RegisterFunction("stdout", StdoutFn);

422     RegisterFunction("sleep", SleepFn);

423

424     RegisterFunction("less_than_int", LessThanIntFn);

425     RegisterFunction("greater_than_int", GreaterThanIntFn);

426 }

这些语句控制执行流程。

RegisterInstallFunctions

1036

1037 void RegisterInstallFunctions() {

1038     RegisterFunction("mount", MountFn);

1039     RegisterFunction("is_mounted", IsMountedFn);

1040     RegisterFunction("unmount", UnmountFn);

1041     RegisterFunction("format", FormatFn);

1042     RegisterFunction("show_progress", ShowProgressFn);

1043     RegisterFunction("set_progress", SetProgressFn);

1044     RegisterFunction("delete", DeleteFn);

1045     RegisterFunction("delete_recursive", DeleteFn);

1046     RegisterFunction("package_extract_dir", PackageExtractDirFn);

1047     RegisterFunction("package_extract_file", PackageExtractFileFn);

1048     RegisterFunction("symlink", SymlinkFn);

1049     RegisterFunction("set_perm", SetPermFn);

1050     RegisterFunction("set_perm_recursive", SetPermFn);

1051

1052     RegisterFunction("getprop", GetPropFn);

1053     RegisterFunction("file_getprop", FileGetPropFn);

1054     RegisterFunction("write_raw_image", WriteRawImageFn);

1055

1056     RegisterFunction("apply_patch", ApplyPatchFn);

1057     RegisterFunction("apply_patch_check", ApplyPatchCheckFn);

1058     RegisterFunction("apply_patch_space", ApplyPatchSpaceFn);

1059

1060     RegisterFunction("read_file", ReadFileFn);

1061     RegisterFunction("sha1_check", Sha1CheckFn);

1062

1063     RegisterFunction("ui_print", UIPrintFn);

1064

1065     RegisterFunction("run_program", RunProgramFn);

1066 }

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。