轉載自：http://blog.chinaunix.net/uid-22028566-id-3533856.html
一、Recovery服務的核心install_package（更新update.zip特有）
和Recovery服務中的wipe_data、wipe_cache不同，install_package()是更新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于：/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 © 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);
}
下面順着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挂載。如果沒有則先挂載。
②load_keys()：加載公鑰源檔案，路徑位于/res/keys。這個檔案在Recovery鏡像的根檔案系統中。
③verify_file()：對更新包update.zip包進行簽名驗證。
④mzOpenZipArchive()：打開更新包，并将相關的資訊拷貝到一個臨時的ZipArchinve變量中。這一步并未對我們的update.zip包解壓。
⑤try_update_binary()：在這個函數中才是對我們的update.zip更新的地方。這個函數一開始先根據我們上一步獲得的zip包資訊，以及更新包的絕對路徑将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，用于下面的子程序和父程序之間的通信。
⑦fork()：建立子程序。其中的子程序主要負責執行binary（execv(binary,args)，即執行我們的安裝指令腳本），父程序負責接受子程序發送的指令去更新ui顯示（顯示目前的進度）。子父程序間通信依靠管道。
⑧其中，在建立子程序後，父程序有兩個作用。一是通過管道接受子程序發送的指令來更新UI顯示。二是等待子程序退出并傳回INSTALL SUCCESS。其中子程序在解析執行安裝腳本的同時所發送的指令有以下幾種：
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>：更新firmware時使用，在API V3中不再使用。
ui_print <string>：在螢幕上顯示字元串，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腳本中的指令并執行。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解析并執行updater-script的過程。
上一篇：Android OTA更新原理和流程分析（六）---Recovery服務流程細節
下一篇：Android OTA更新原理和流程分析（八）---更新程式update_binary的執行過程
轉載自：http://blog.chinaunix.net/uid-22028566-id-3533856.html