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【转】

本文转载自：http://blog.csdn.net/mu0206mu/article/details/7465514

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：

[cpp] view plain copy

/*

* 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\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;

}

int

install_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。