Android OTA 升级之五：updater

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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 }

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