三，系统服务初始化和package 扫描
在启动系统服务的init2()时会启动应用层（Java层）的所有服务。
public static void main(String[] args) {
System.loadLibrary("Android_servers");
init1(args); //init1 初始化，完成之后会回调init2()
}
在init2()中会启动一个线程来启动所有服务
public static final void init2() {
Log.i(TAG, "Entered the Android system server!");
Thread thr = new ServerThread();
thr.setName("Android.server.ServerThread");
thr.start();
}
class ServerThread extends Thread {
。。。
public void run() {
。。。
关键服务：
ServiceManager.addService("entropy", new EntropyService());
ServiceManager.addService(Context.POWER_SERVICE, power);
context = ActivityManagerService.main(factoryTest);
ServiceManager.addService("telephony.registry", new TelephonyRegistry(context));
PackageManagerService.main(context,
factoryTest != SystemServer.FACTORY_TEST_OFF);//apk扫描的服务
ServiceManager.addService(Context.ACCOUNT_SERVICE,
new AccountManagerService(context));
ContentService.main(context,
factoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL);
battery = new BatteryService(context);
ServiceManager.addService("battery", battery);
hardware = new HardwareService(context);
ServiceManager.addService("hardware", hardware);
AlarmManagerService alarm = new AlarmManagerService(context);
ServiceManager.addService(Context.ALARM_SERVICE, alarm);
ServiceManager.addService(Context.SENSOR_SERVICE, new SensorService(context));
WindowManagerService.main(context, power,
factoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL);
ServiceManager.addService(Context.WINDOW_SERVICE, wm);
上面这些都是关键服务，不建议进行裁剪。
下面的这些不是很关键，可以进行裁剪，当是必须相应的修改framework部分的代码，工作量比较大和复杂。我去掉了20个服务，大概需要相应修改大概20多个文件。
statusBar = new StatusBarService(context);
ServiceManager.addService("statusbar", statusBar);
ServiceManager.addService("clipboard", new ClipboardService(context));
imm = new InputMethodManagerService(context, statusBar);
ServiceManager.addService(Context.INPUT_METHOD_SERVICE, imm);
ServiceManager.addService("netstat", new NetStatService(context));
connectivity = ConnectivityService.getInstance(context);
ServiceManager.addService(Context.CONNECTIVITY_SERVICE, connectivity);
ServiceManager.addService(Context.ACCESSIBILITY_SERVICE,
new AccessibilityManagerService(context));
notification = new NotificationManagerService(context, statusBar, hardware);
ServiceManager.addService(Context.NOTIFICATION_SERVICE, notification);
ServiceManager.addService("mount", new MountService(context));
ServiceManager.addService(DeviceStorageMonitorService.SERVICE,
new DeviceStorageMonitorService(context));
ServiceManager.addService(Context.LOCATION_SERVICE, new LocationManagerService(context));
ServiceManager.addService( Context.SEARCH_SERVICE, new SearchManagerService(context) );
if (INCLUDE_DEMO) {
Log.i(TAG, "Installing demo data...");
(new DemoThread(context)).start();
}
Intent intent = new Intent().setComponent(new ComponentName(
"com.google.Android.server.checkin",
"com.google.Android.server.checkin.CheckinService"));
ServiceManager.addService("checkin", new FallbackCheckinService(context));
wallpaper = new WallpaperManagerService(context);
ServiceManager.addService(Context.WALLPAPER_SERVICE, wallpaper);
ServiceManager.addService(Context.AUDIO_SERVICE, new AudioService(context));
headset = new HeadsetObserver(context);
dock = new DockObserver(context, power);
ServiceManager.addService(Context.BACKUP_SERVICE, new BackupManagerService(context));
ServiceManager.addService(Context.APPWIDGET_SERVICE, appWidget);
callstatic("com/Android/server/SystemServer","init2")
init2()
main(context, factoryTest)
PackageManagerService(context, factoryTest)
scanDirLI(dir, flags, mode)
scanPackageLI(file, file resfile, flags, mode)
parsePackage(file, dest filename, metrics, flags)
parsePackage(file, dest, metrics, flags)
openXmlResourceParser(cookie, filename) (“AndroidManifest.xml“)
openXmlBlockAsset(cookie, filename)
openXmlAssetNative(cookie, filename)
Android_content_AssetManager_openXmlAssetNative
openNonAsset(cookie, filename, flag)
openNonAssetInPathLocked(filename, mode, asset_path)
getZipFileLocked(asset_path)
getZip(ap.path)
get(path)
getZip()
SharedZip(path, modWhen)
ZipFileRO::open(path)
parseZipArchive(void)
get4LE(ptr)
(memory access)
最终的zip文件（apk）读取是在下面这两个函数：
/*
* Open the specified file read-only. We memory-map the entire thing and
* close the file before returning.
*/
status_t ZipFileRO::open(const char* zipFileName)
{
int fd = -1;
off_t length;
assert(mFileMap == NULL);
LOGD("opening zip '%s'\n", zipFileName);
/*
* Open and map the specified file.
*/
fd = ::open(zipFileName, O_RDONLY);
if (fd < 0) {
LOGW("Unable to open zip '%s': %s\n", zipFileName, strerror(errno));
return NAME_NOT_FOUND;
}
length = lseek(fd, 0, SEEK_END);
if (length < 0) {
close(fd);
return UNKNOWN_ERROR;
}
mFileMap = new FileMap();
if (mFileMap == NULL) {
close(fd);
return NO_MEMORY;
}
if (!mFileMap->create(zipFileName, fd, 0, length, true)) {
LOGW("Unable to map '%s': %s\n", zipFileName, strerror(errno));
close(fd);
return UNKNOWN_ERROR;
}
mFd = fd;
/*
* Got it mapped, verify it and create data structures for fast access.
*/
if (!parseZipArchive()) {
mFileMap->release();
mFileMap = NULL;
return UNKNOWN_ERROR;
}
LOGD("done opening zip\n");
return OK;
}
/*
* Parse the Zip archive, verifying its contents and initializing internal
* data structures.
*/
bool ZipFileRO::parseZipArchive(void)
{
#define CHECK_OFFSET(_off) { \
if ((unsigned int) (_off) >= maxOffset) { \
LOGE("ERROR: bad offset %u (max %d): %s\n", \
(unsigned int) (_off), maxOffset, #_off); \
goto bail; \
} \
}
const unsigned char* basePtr = (const unsigned char*)mFileMap->getDataPtr();
const unsigned char* ptr;
size_t length = mFileMap->getDataLength();
bool result = false;
unsigned int i, numEntries, cdOffset;
unsigned int val;
/*
* The first 4 bytes of the file will either be the local header
* signature for the first file (kLFHSignature) or, if the archive doesn't
* have any files in it, the end-of-central-directory signature
* (kEOCDSignature).
*/
val = get4LE(basePtr);
if (val == kEOCDSignature) {
LOGI("Found Zip archive, but it looks empty\n");
goto bail;
} else if (val != kLFHSignature) {
LOGV("Not a Zip archive (found 0x%08x)\n", val);
goto bail;
}
/*
* Find the EOCD. We'll find it immediately unless they have a file
* comment.
*/
ptr = basePtr + length - kEOCDLen;
while (ptr >= basePtr) {
if (*ptr == (kEOCDSignature & 0xff) && get4LE(ptr) == kEOCDSignature)
break;
ptr--;
}
if (ptr < basePtr) {
LOGI("Could not find end-of-central-directory in Zip\n");
goto bail;
}
/*
* There are two interesting items in the EOCD block: the number of
* entries in the file, and the file offset of the start of the
* central directory.
*
* (There's actually a count of the #of entries in this file, and for
* all files which comprise a spanned archive, but for our purposes
* we're only interested in the current file. Besides, we expect the
* two to be equivalent for our stuff.)
*/
numEntries = get2LE(ptr + kEOCDNumEntries);
cdOffset = get4LE(ptr + kEOCDFileOffset);
/* valid offsets are [0,EOCD] */
unsigned int maxOffset;
maxOffset = (ptr - basePtr) +1;
LOGV("+++ numEntries=%d cdOffset=%d\n", numEntries, cdOffset);
if (numEntries == 0 || cdOffset >= length) {
LOGW("Invalid entries=%d offset=%d (len=%zd)\n",
numEntries, cdOffset, length);
goto bail;
}
/*
* Create hash table. We have a minimum 75% load factor, possibly as
* low as 50% after we round off to a power of 2.
*/
mNumEntries = numEntries;
mHashTableSize = roundUpPower2(1 + ((numEntries * 4) / 3));
mHashTable = (HashEntry*) calloc(1, sizeof(HashEntry) * mHashTableSize);
/*
* Walk through the central directory, adding entries to the hash
* table.
*/
ptr = basePtr + cdOffset;
for (i = 0; i < numEntries; i++) {
unsigned int fileNameLen, extraLen, commentLen, localHdrOffset;
const unsigned char* localHdr;
unsigned int hash;
if (get4LE(ptr) != kCDESignature) {
LOGW("Missed a central dir sig (at %d)\n", i);
goto bail;
}
if (ptr + kCDELen > basePtr + length) {
LOGW("Ran off the end (at %d)\n", i);
goto bail;
}
localHdrOffset = get4LE(ptr + kCDELocalOffset);
CHECK_OFFSET(localHdrOffset);
fileNameLen = get2LE(ptr + kCDENameLen);
extraLen = get2LE(ptr + kCDEExtraLen);
commentLen = get2LE(ptr + kCDECommentLen);
//LOGV("+++ %d: localHdr=%d fnl=%d el=%d cl=%d\n",
// i, localHdrOffset, fileNameLen, extraLen, commentLen);
//LOGV(" '%.*s'\n", fileNameLen, ptr + kCDELen);
/* add the CDE filename to the hash table */
hash = computeHash((const char*)ptr + kCDELen, fileNameLen);
addToHash((const char*)ptr + kCDELen, fileNameLen, hash);
// localHdr = basePtr + localHdrOffset;
// if (get4LE(localHdr) != kLFHSignature) {
// LOGW("Bad offset to local header: %d (at %d)\n",
// localHdrOffset, i);
// goto bail;
// }
ptr += kCDELen + fileNameLen + extraLen + commentLen;
CHECK_OFFSET(ptr - basePtr);
}
result = true;
bail:
return result;
#undef CHECK_OFFSET
}