Android OTA 升级之五:updater

时间:2022-09-07 11:16:41

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 #defineSCRIPT_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 intmain(intargc, 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     intfd = 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     interr;

 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     constZipEntry* 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     interror_count = 0;

130    yy_scan_string(script);

131     interror =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。