Android系統Recovery工作原理之使用update.zip升級過程分析（七）—Recovery服務的核心install_package函數

             Android系統Recovery工作原理之使用update.zip升級過程分析（七）---Recovery服務的核心install_package函數

一、       Recovery服務的核心install_package（升級update.zip特有）

              和Recovery服務中的wipe_data、wipe_cache不同，install_package()是升級update.zip特有的一部分，也是最核心的部分。在這一步才真正開始對我們的update.zip包進行處理。下面就開始分析這一部分。還是先看圖例：

                          

            這一部分的源碼檔案位於：/gingerbread0919/bootable/recovery/install.c。這是一個沒有main函數的源碼檔案，還是把源碼先貼出來如下：

/* * 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 inttry_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\n", binary);        return 1;    }    bool ok = mzExtractZipEntryToFile(zip, binary_entry, fd);    close(fd);    mzCloseZipArchive(zip);    if (!ok) {        LOGE("Can't copy %s\n", 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)\n", 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, " \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_show_progress(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_set_progress(fraction);        } else if (strcmp(command, "ui_print") == 0) {            char* str = strtok(NULL, "\n");            if (str) {                ui_print("%s", str);            } else {                ui_print("\n");            }        } 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;}// 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\n", 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\n", 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\n");                goto exit;        }    }    fclose(f);    return out;exit:    if (f) fclose(f);    free(out);    *numKeys = 0;    return NULL;}intinstall_package(const char *path){    ui_set_background(BACKGROUND_ICON_INSTALLING);    ui_print("Finding update package...\n");    ui_show_indeterminate_progress();    LOGI("Update location: %s\n", path);    if (ensure_path_mounted(path) != 0) {        LOGE("Can't mount %s\n", path);        return INSTALL_CORRUPT;    }    ui_print("Opening update package...\n");    int numKeys;    RSAPublicKey* loadedKeys = load_keys(PUBLIC_KEYS_FILE, &numKeys);    if (loadedKeys == NULL) {        LOGE("Failed to load keys\n");        return INSTALL_CORRUPT;    }    LOGI("%d key(s) loaded from %s\n", numKeys, PUBLIC_KEYS_FILE);    // Give verification half the progress bar...    ui_print("Verifying update package...\n");    ui_show_progress(            VERIFICATION_PROGRESS_FRACTION,            VERIFICATION_PROGRESS_TIME);    int err;    err = verify_file(path, loadedKeys, numKeys);    free(loadedKeys);    LOGI("verify_file returned %d\n", err);    if (err != VERIFY_SUCCESS) {        LOGE("signature verification failed\n");        return INSTALL_CORRUPT;    }    /* Try to open the package.     */    ZipArchive zip;    err = mzOpenZipArchive(path, &zip);    if (err != 0) {        LOGE("Can't open %s\n(%s)\n", path, err != -1 ? strerror(err) : "bad");        return INSTALL_CORRUPT;    }    /* Verify and install the contents of the package.     */    ui_print("Installing update...\n");    return try_update_binary(path, &zip);}

             下面順著上面的流程圖和源碼來分析這一流程：

            ①ensure_path_mount()：先判斷所傳的update.zip包路徑所在的分區是否已經掛載。如果沒有則先掛載。

            ②load_keys()：載入公開金鑰源檔案，路徑位於/res/keys。這個檔案在Recovery鏡像的根檔案系統中。

            ③verify_file()：對升級包update.zip包進行簽名驗證。

            ④mzOpenZipArchive()：開啟升級包，並將相關的資訊拷貝到一個臨時的ZipArchinve變數中。這一步並未對我們的update.zip包解壓。

            ⑤try_update_binary()：在這個函數中才是對我們的update.zip升級的地方。這個函數一開始先根據我們上一步獲得的zip包資訊，以及升級包的絕對路徑將update_binary檔案拷貝到記憶體檔案系統的/tmp/update_binary中。以便後面使用。

            ⑥pipe()：建立管道，用於下面的子進程和父進程之間的通訊。

            ⑦fork()：建立子進程。其中的子進程主要負責執行binary（execv(binary,args)，即執行我們的安裝命令指令碼），父進程負責接受子進程發送的命令去更新ui顯示（顯示當前的進度）。子父處理序間通訊依靠管道。

            ⑧其中，在建立子進程後，父進程有兩個作用。一是通過管道接受子進程發送的命令來更新UI顯示。二是等待子進程退出並返回INSTALL SUCCESS。其中子進程在解析執行安裝指令碼的同時所發送的命令有以下幾種：

                       progress  <frac> <secs>：根據第二個參數secs（秒）來設定進度條。

                       set_progress  <frac>：直接設定進度條，frac取值在0.0到0.1之間。

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

                       ui_print <string>：在螢幕上顯示字串，即列印更新過程。

                 execv(binary,args)的作用就是去執行binary程式，這個程式的實質就是去解析update.zip包中的updater-script指令碼中的命令並執行。由此，Recovery服務就進入了實際安裝update.zip包的過程。

                 下一篇繼續分析使用update-binary解析並執行updater-script的過程。