Android OTA 升级之五：updater

作者：宋立新

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"

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);

73 if (argc != 4) {

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

75 return 1;

76 }

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 }

获取 version 参数。

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

90 intfd = atoi(argv[2]);

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

92 setlinebuf(cmd_pipe);

获取命令管道（用于图形显示等，见前篇）

94 // Extract the script from the package.

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);

424     RegisterFunction("less_than_int", LessThanIntFn);

425     RegisterFunction("greater_than_int", GreaterThanIntFn);

426 }

这些语句控制执行流程。

RegisterInstallFunctions

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);

1052     RegisterFunction("getprop", GetPropFn);

1053     RegisterFunction("file_getprop", FileGetPropFn);

1054     RegisterFunction("write_raw_image", WriteRawImageFn);

1056     RegisterFunction("apply_patch", ApplyPatchFn);

1057     RegisterFunction("apply_patch_check", ApplyPatchCheckFn);

1058     RegisterFunction("apply_patch_space", ApplyPatchSpaceFn);

1060     RegisterFunction("read_file", ReadFileFn);

1061     RegisterFunction("sha1_check", Sha1CheckFn);

1063     RegisterFunction("ui_print", UIPrintFn);

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。

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Android OTA 升级之五：updater

前言

入口函数 main

RegisterBuiltins

RegisterInstallFunctions

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