install.cpp文件try_update_binary()函数安装过程分析

static int
try_update_binary(const char* path, ZipArchive* zip, bool* wipe_cache) {
    const ZipEntry* binary_entry =
            mzFindZipEntry(zip, ASSUMED_UPDATE_BINARY_NAME);//lefty_lan：在zip格式的更新包文件中得到文件META-INF/com/google/android/update-binary的entry
    if (binary_entry == NULL) {
        mzCloseZipArchive(zip);
        return INSTALL_CORRUPT;//lefty_lan注：安装包中找不到update_binary文件
    }

    const char* binary = "/tmp/update_binary";
    unlink(binary);//lefty_lan注：清除软连接
    int fd = creat(binary, 0755);//lefty_lan注：创建空文件update_binary
    if (fd < 0) {
        mzCloseZipArchive(zip);
        LOGE("Can't make %s\n", binary);
        return INSTALL_ERROR; //lefty_lan注：创建失败，返回
    }
    bool ok = mzExtractZipEntryToFile(zip, binary_entry, fd);//lefty_lan注：把zip更新包中的update_binary文件保存到/tmp/update_binary文件中
    close(fd);
    mzCloseZipArchive(zip);

    if (!ok) {
        LOGE("Can't copy %s\n", ASSUMED_UPDATE_BINARY_NAME);
        return INSTALL_ERROR;//lefty_lan注：拷贝失败，返回
    }

    int pipefd[2];
    pipe(pipefd);//lefty_lan注：创建管道

    // When executing the update binary contained in the package, the
    // arguments passed are:
    //
    //   - the version number for this interface
    //
    //   - an fd to which the program can write in order to update the
    //     progress bar.  The program can write single-line commands:
    //
    //        progress <frac> <secs>
    //            fill up the next <frac> part of of the progress bar
    //            over <secs> seconds.  If <secs> is zero, use
    //            set_progress commands to manually control the
    //            progress of this segment of the bar.
    //
    //        set_progress <frac>
    //            <frac> should be between 0.0 and 1.0; sets the
    //            progress bar within the segment defined by the most
    //            recent progress command.
    //
    //        firmware <"hboot"|"radio"> <filename>
    //            arrange to install the contents of <filename> in the
    //            given partition on reboot.
    //
    //            (API v2: <filename> may start with "PACKAGE:" to
    //            indicate taking a file from the OTA package.)
    //
    //            (API v3: this command no longer exists.)
    //
    //        ui_print <string>
    //            display <string> on the screen.
    //
    //        wipe_cache
    //            a wipe of cache will be performed following a successful
    //            installation.
    //
    //        clear_display
    //            turn off the text display.
    //
    //        enable_reboot
    //            packages can explicitly request that they want the user
    //            to be able to reboot during installation (useful for
    //            debugging packages that don't exit).
    //
    //   - the name of the package zip file.
    //

    const char** args = (const char**)malloc(sizeof(char*) * 5);
    args[0] = binary;
    args[1] = EXPAND(RECOVERY_API_VERSION);   // defined in Android.mk
    char* temp = (char*)malloc(10);
    sprintf(temp, "%d", pipefd[1]);
    args[2] = temp;
    args[3] = (char*)path;
    args[4] = NULL;

	//lefty_lan注：父进程关闭fd[1],子进程关闭fd[0]，
	//lefty_lan注：管道只支持单向通信，
	//lefty_lan注：⽗进程可以从管道⾥读,⼦进程可以往管道⾥写,
	//lefty_lan注：管道是采⽤环形队列实现的,数据从写端流⼊，从读端流出,这样就实现了进程间通信
    pid_t pid = fork();//lefty_lan注：创建子进程
    if (pid == 0) {
        umask(022);
        close(pipefd[0]);//lefty_lan注：⼦进程关闭管道读端，只负责写入
        execv(binary, (char* const*)args);//lefty_lan注：在子进程中执行/tmp/update_binary文件
        fprintf(stdout, "E:Can't run %s (%s)\n", binary, strerror(errno));
        _exit(-1);
    }
    close(pipefd[1]);//lefty_lan注：父进程关闭管道写端，只管读取

    *wipe_cache = false;

    char buffer[1024];
    FILE* from_child = fdopen(pipefd[0], "r");
    while (fgets(buffer, sizeof(buffer), from_child) != NULL) {
        char* command = strtok(buffer, " \n");
        if (command == NULL) {
            continue;
        } else if (strcmp(command, "progress") == 0) {
            char* fraction_s = strtok(NULL, " \n");
            char* seconds_s = strtok(NULL, " \n");

            float fraction = strtof(fraction_s, NULL);
            int seconds = strtol(seconds_s, NULL, 10);

            ui->ShowProgress(fraction * (1-VERIFICATION_PROGRESS_FRACTION), seconds);
        } else if (strcmp(command, "set_progress") == 0) {
            char* fraction_s = strtok(NULL, " \n");
            float fraction = strtof(fraction_s, NULL);
            ui->SetProgress(fraction);
        } else if (strcmp(command, "ui_print") == 0) {
            char* str = strtok(NULL, "\n");
            if (str) {
                ui->Print("%s", str);
            } else {
                ui->Print("\n");
            }
            fflush(stdout);
        } else if (strcmp(command, "wipe_cache") == 0) {
            *wipe_cache = true;
        } else if (strcmp(command, "clear_display") == 0) {
            ui->SetBackground(RecoveryUI::NONE);
        } else if (strcmp(command, "enable_reboot") == 0) {
            // packages can explicitly request that they want the user
            // to be able to reboot during installation (useful for
            // debugging packages that don't exit).
            ui->SetEnableReboot(true);
        } else {
            LOGE("unknown command [%s]\n", command);
        }
    }
    fclose(from_child);

    int status;
    waitpid(pid, &status, 0);
    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
        LOGE("Error in %s\n(Status %d)\n", path, WEXITSTATUS(status));
        return INSTALL_ERROR;
    }

    return INSTALL_SUCCESS;
}