Android系统Recovery工作原理之使用update.zip升级过程分析（七）---Recovery服务的核心install_package函数

http://blog.csdn.net/mu0206mu/article/details/7465514

     Android系统Recovery工作原理之使用update.zip升级过程分析（七）---Recovery服务的核心install_package函数

一、       Recovery服务的核心install_package（升级update.zip特有）

              和Recovery服务中的wipe_data、wipe_cache不同，install_package()是升级update.zip特有的一部分，也是最核心的部分。在这一步才真正开始对我们的update.zip包进行处理。下面就开始分析这一部分。还是先看图例：

                          

            这一部分的源码文件位于：/gingerbread0919/bootable/recovery/install.c。这是一个没有main函数的源码文件，还是把源码先贴出来如下：

/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>

#include "common.h"
#include "install.h"
#include "mincrypt/rsa.h"
#include "minui/minui.h"
#include "minzip/SysUtil.h"
#include "minzip/Zip.h"
#include "mtdutils/mounts.h"
#include "mtdutils/mtdutils.h"
#include "roots.h"
#include "verifier.h"

#define ASSUMED_UPDATE_BINARY_NAME  "META-INF/com/google/android/update-binary"
#define PUBLIC_KEYS_FILE "/res/keys"

// If the package contains an update binary, extract it and run it.
static int
try_update_binary(const char *path, ZipArchive *zip) {
    const ZipEntry* binary_entry =
            mzFindZipEntry(zip, ASSUMED_UPDATE_BINARY_NAME);
    if (binary_entry == NULL) {
        mzCloseZipArchive(zip);
        return INSTALL_CORRUPT;
    }

    char* binary = "/tmp/update_binary";
    unlink(binary);
    int fd = creat(binary, 0755);
    if (fd < 0) {
        mzCloseZipArchive(zip);
        LOGE("Can't make %s
", binary);
        return 1;
    }
    bool ok = mzExtractZipEntryToFile(zip, binary_entry, fd);
    close(fd);
    mzCloseZipArchive(zip);

    if (!ok) {
        LOGE("Can't copy %s
", ASSUMED_UPDATE_BINARY_NAME);
        return 1;
    }

    int pipefd[2];
    pipe(pipefd);

    // 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.
    //
    //   - the name of the package zip file.
    //

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

    pid_t pid = fork();
    if (pid == 0) {
        close(pipefd[0]);
        execv(binary, args);
        fprintf(stdout, "E:Can't run %s (%s)
", binary, strerror(errno));
        _exit(-1);
    }
    close(pipefd[1]);

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

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

            ui_show_progress(fraction * (1-VERIFICATION_PROGRESS_FRACTION),
                             seconds);
        } else if (strcmp(command, "set_progress") == 0) {
            char* fraction_s = strtok(NULL, " 
");
            float fraction = strtof(fraction_s, NULL);
            ui_set_progress(fraction);
        } else if (strcmp(command, "ui_print") == 0) {
            char* str = strtok(NULL, "
");
            if (str) {
                ui_print("%s", str);
            } else {
                ui_print("
");
            }
        } else {
            LOGE("unknown command [%s]
", command);
        }
    }
    fclose(from_child);

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

    return INSTALL_SUCCESS;
}

// Reads a file containing one or more public keys as produced by
// DumpPublicKey:  this is an RSAPublicKey struct as it would appear
// as a C source literal, eg:
//
//  "{64,0xc926ad21,{1795090719,...,-695002876},{-857949815,...,1175080310}}"
//
// (Note that the braces and commas in this example are actual
// characters the parser expects to find in the file; the ellipses
// indicate more numbers omitted from this example.)
//
// The file may contain multiple keys in this format, separated by
// commas.  The last key must not be followed by a comma.
//
// Returns NULL if the file failed to parse, or if it contain zero keys.
static RSAPublicKey*
load_keys(const char* filename, int* numKeys) {
    RSAPublicKey* out = NULL;
    *numKeys = 0;

    FILE* f = fopen(filename, "r");
    if (f == NULL) {
        LOGE("opening %s: %s
", filename, strerror(errno));
        goto exit;
    }

    int i;
    bool done = false;
    while (!done) {
        ++*numKeys;
        out = realloc(out, *numKeys * sizeof(RSAPublicKey));
        RSAPublicKey* key = out + (*numKeys - 1);
        if (fscanf(f, " { %i , 0x%x , { %u",
                   &(key->len), &(key->n0inv), &(key->n[0])) != 3) {
            goto exit;
        }
        if (key->len != RSANUMWORDS) {
            LOGE("key length (%d) does not match expected size
", key->len);
            goto exit;
        }
        for (i = 1; i < key->len; ++i) {
            if (fscanf(f, " , %u", &(key->n[i])) != 1) goto exit;
        }
        if (fscanf(f, " } , { %u", &(key->rr[0])) != 1) goto exit;
        for (i = 1; i < key->len; ++i) {
            if (fscanf(f, " , %u", &(key->rr[i])) != 1) goto exit;
        }
        fscanf(f, " } } ");

        // if the line ends in a comma, this file has more keys.
        switch (fgetc(f)) {
            case ',':
                // more keys to come.
                break;

            case EOF:
                done = true;
                break;

            default:
                LOGE("unexpected character between keys
");
                goto exit;
        }
    }

    fclose(f);
    return out;

exit:
    if (f) fclose(f);
    free(out);
    *numKeys = 0;
    return NULL;
}

int
install_package(const char *path)
{
    ui_set_background(BACKGROUND_ICON_INSTALLING);
    ui_print("Finding update package...
");
    ui_show_indeterminate_progress();
    LOGI("Update location: %s
", path);

    if (ensure_path_mounted(path) != 0) {
        LOGE("Can't mount %s
", path);
        return INSTALL_CORRUPT;
    }

    ui_print("Opening update package...
");

    int numKeys;
    RSAPublicKey* loadedKeys = load_keys(PUBLIC_KEYS_FILE, &numKeys);
    if (loadedKeys == NULL) {
        LOGE("Failed to load keys
");
        return INSTALL_CORRUPT;
    }
    LOGI("%d key(s) loaded from %s
", numKeys, PUBLIC_KEYS_FILE);

    // Give verification half the progress bar...
    ui_print("Verifying update package...
");
    ui_show_progress(
            VERIFICATION_PROGRESS_FRACTION,
            VERIFICATION_PROGRESS_TIME);

    int err;
    err = verify_file(path, loadedKeys, numKeys);
    free(loadedKeys);
    LOGI("verify_file returned %d
", err);
    if (err != VERIFY_SUCCESS) {
        LOGE("signature verification failed
");
        return INSTALL_CORRUPT;
    }

    /* Try to open the package.
     */
    ZipArchive zip;
    err = mzOpenZipArchive(path, &zip);
    if (err != 0) {
        LOGE("Can't open %s
(%s)
", path, err != -1 ? strerror(err) : "bad");
        return INSTALL_CORRUPT;
    }

    /* Verify and install the contents of the package.
     */
    ui_print("Installing update...
");
    return try_update_binary(path, &zip);
}

             下面顺着上面的流程图和源码来分析这一流程：

            ①ensure_path_mount()：先判断所传的update.zip包路径所在的分区是否已经挂载。如果没有则先挂载。

            ②load_keys()：加载公钥源文件，路径位于/res/keys。这个文件在Recovery镜像的根文件系统中。

            ③verify_file()：对升级包update.zip包进行签名验证。

            ④mzOpenZipArchive()：打开升级包，并将相关的信息拷贝到一个临时的ZipArchinve变量中。这一步并未对我们的update.zip包解压。

            ⑤try_update_binary()：在这个函数中才是对我们的update.zip升级的地方。这个函数一开始先根据我们上一步获得的zip包信息，以及升级包的绝对路径将update_binary文件拷贝到内存文件系统的/tmp/update_binary中。以便后面使用。

            ⑥pipe()：创建管道，用于下面的子进程和父进程之间的通信。

            ⑦fork()：创建子进程。其中的子进程主要负责执行binary（execv(binary,args)，即执行我们的安装命令脚本），父进程负责接受子进程发送的命令去更新ui显示（显示当前的进度）。子父进程间通信依靠管道。

            ⑧其中，在创建子进程后，父进程有两个作用。一是通过管道接受子进程发送的命令来更新UI显示。二是等待子进程退出并返回INSTALL SUCCESS。其中子进程在解析执行安装脚本的同时所发送的命令有以下几种：

                       progress  <frac> <secs>：根据第二个参数secs（秒）来设置进度条。

                       set_progress  <frac>：直接设置进度条，frac取值在0.0到0.1之间。

                       firmware <”hboot”|”radio”><filename>：升级firmware时使用，在API  V3中不再使用。

                       ui_print <string>：在屏幕上显示字符串，即打印更新过程。

                 execv(binary,args)的作用就是去执行binary程序，这个程序的实质就是去解析update.zip包中的updater-script脚本中的命令并执行。由此，Recovery服务就进入了实际安装update.zip包的过程。

                 下一篇继续分析使用update-binary解析并执行updater-script的过程。