一，serviceManger时序图
本文涉及到的源码文件：
/frameworks/native/cmds/servicemanager/main.cpp
/frameworks/native/libs/binder/ProcessState.cpp
/frameworks/native/cmds/servicemanager/ServiceManager.cpp
/frameworks/native/libs/binder/IPCThreadState.cpp
/system/core/libutils/Looper.cpp
ServiceManager是一个由C/C++编写的系统服务，源码位于/framework/native/cmds/servicemanager中，存在如下文件结构
java层SM
public final class ServiceManager {
private static final String TAG = "ServiceManager";
private static IServiceManager sServiceManager;
private static HashMap<String, IBinder> sCache = new HashMap<String, IBinder>();
private static IServiceManager getIServiceManager() {
if (sServiceManager != null) {
return sServiceManager;
}
// Find the service manager
sServiceManager = ServiceManagerNative
.asInterface(Binder.allowBlocking(BinderInternal.getContextObject()));
return sServiceManager;
}
/**
* Returns a reference to a service with the given name.
*
* @param name the name of the service to get
* @return a reference to the service, or <code>null</code> if the service doesn't exist
*/
public static IBinder getService(String name) {
try {
IBinder service = sCache.get(name);
if (service != null) {
return service;
} else {
return Binder.allowBlocking(getIServiceManager().getService(name));
}
} catch (RemoteException e) {
Log.e(TAG, "error in getService", e);
}
return null;
}
/**
* Returns a reference to a service with the given name, or throws
* {@link NullPointerException} if none is found.
*
* @hide
*/
public static IBinder getServiceOrThrow(String name) throws ServiceNotFoundException {
final IBinder binder = getService(name);
if (binder != null) {
return binder;
} else {
throw new ServiceNotFoundException(name);
}
}
/**
* Place a new @a service called @a name into the service
* manager.
*
* @param name the name of the new service
* @param service the service object
*/
public static void addService(String name, IBinder service) {
try {
getIServiceManager().addService(name, service, false);
} catch (RemoteException e) {
Log.e(TAG, "error in addService", e);
}
}
/**
* Place a new @a service called @a name into the service
* manager.
*
* @param name the name of the new service
* @param service the service object
* @param allowIsolated set to true to allow isolated sandboxed processes
* to access this service
*/
public static void addService(String name, IBinder service, boolean allowIsolated) {
try {
getIServiceManager().addService(name, service, allowIsolated);
} catch (RemoteException e) {
Log.e(TAG, "error in addService", e);
}
}
/**
* Retrieve an existing service called @a name from the
* service manager. Non-blocking.
*/
public static IBinder checkService(String name) {
try {
IBinder service = sCache.get(name);
if (service != null) {
return service;
} else {
return Binder.allowBlocking(getIServiceManager().checkService(name));
}
} catch (RemoteException e) {
Log.e(TAG, "error in checkService", e);
return null;
}
}
/**
* Return a list of all currently running services.
* @return an array of all currently running services, or <code>null</code> in
* case of an exception
*/
public static String[] listServices() {
try {
return getIServiceManager().listServices();
} catch (RemoteException e) {
Log.e(TAG, "error in listServices", e);
return null;
}
}
/**
* This is only intended to be called when the process is first being brought
* up and bound by the activity manager. There is only one thread in the process
* at that time, so no locking is done.
*
* @param cache the cache of service references
* @hide
*/
public static void initServiceCache(Map<String, IBinder> cache) {
if (sCache.size() != 0) {
throw new IllegalStateException("setServiceCache may only be called once");
}
sCache.putAll(cache);
}
/**
* Exception thrown when no service published for given name. This might be
* thrown early during boot before certain services have published
* themselves.
*
* @hide
*/
public static class ServiceNotFoundException extends Exception {
public ServiceNotFoundException(String name) {
super("No service published for: " + name);
}
}
}native层的SM
/*
* Copyright (C) 2005 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.
*/
#define LOG_TAG "ServiceManager"
#include <binder/IServiceManager.h>
#include <utils/Log.h>
#include <binder/IPCThreadState.h>
#include <binder/Parcel.h>
#include <utils/String8.h>
#include <utils/SystemClock.h>
#include <utils/CallStack.h>
#include <private/binder/Static.h>
#include <unistd.h>
namespace android {
sp<IServiceManager> defaultServiceManager()
{
if (gDefaultServiceManager != NULL) return gDefaultServiceManager;
{
AutoMutex _l(gDefaultServiceManagerLock);
while (gDefaultServiceManager == NULL) {
gDefaultServiceManager = interface_cast<IServiceManager>(
ProcessState::self()->getContextObject(NULL));
if (gDefaultServiceManager == NULL)
sleep(1);
}
}
return gDefaultServiceManager;
}
bool checkCallingPermission(const String16& permission)
{
return checkCallingPermission(permission, NULL, NULL);
}
static String16 _permission("permission");
bool checkCallingPermission(const String16& permission, int32_t* outPid, int32_t* outUid)
{
IPCThreadState* ipcState = IPCThreadState::self();
pid_t pid = ipcState->getCallingPid();
uid_t uid = ipcState->getCallingUid();
if (outPid) *outPid = pid;
if (outUid) *outUid = uid;
return checkPermission(permission, pid, uid);
}
bool checkPermission(const String16& permission, pid_t pid, uid_t uid)
{
sp<IPermissionController> pc;
gDefaultServiceManagerLock.lock();
pc = gPermissionController;
gDefaultServiceManagerLock.unlock();
int64_t startTime = 0;
while (true) {
if (pc != NULL) {
bool res = pc->checkPermission(permission, pid, uid);
if (res) {
if (startTime != 0) {
ALOGI("Check passed after %d seconds for %s from uid=%d pid=%d",
(int)((uptimeMillis()-startTime)/1000),
String8(permission).string(), uid, pid);
}
return res;
}
// Is this a permission failure, or did the controller go away?
if (IInterface::asBinder(pc)->isBinderAlive()) {
ALOGW("Permission failure: %s from uid=%d pid=%d",
String8(permission).string(), uid, pid);
return false;
}
// Object is dead!
gDefaultServiceManagerLock.lock();
if (gPermissionController == pc) {
gPermissionController = NULL;
}
gDefaultServiceManagerLock.unlock();
}
// Need to retrieve the permission controller.
sp<IBinder> binder = defaultServiceManager()->checkService(_permission);
if (binder == NULL) {
// Wait for the permission controller to come back...
if (startTime == 0) {
startTime = uptimeMillis();
ALOGI("Waiting to check permission %s from uid=%d pid=%d",
String8(permission).string(), uid, pid);
}
sleep(1);
} else {
pc = interface_cast<IPermissionController>(binder);
// Install the new permission controller, and try again.
gDefaultServiceManagerLock.lock();
gPermissionController = pc;
gDefaultServiceManagerLock.unlock();
}
}
}
// ----------------------------------------------------------------------
class BpServiceManager : public BpInterface<IServiceManager>
{
public:
explicit BpServiceManager(const sp<IBinder>& impl)
: BpInterface<IServiceManager>(impl)
{
}
virtual sp<IBinder> getService(const String16& name) const
{
unsigned n;
for (n = 0; n < 5; n++){
if (n > 0) {
if (!strcmp(ProcessState::self()->getDriverName().c_str(), "/dev/vndbinder")) {
ALOGI("Waiting for vendor service %s...", String8(name).string());
CallStack stack(LOG_TAG);
} else {
ALOGI("Waiting for service %s...", String8(name).string());
}
sleep(1);
}
sp<IBinder> svc = checkService(name);
if (svc != NULL) return svc;
}
return NULL;
}
virtual sp<IBinder> checkService( const String16& name) const
{
Parcel data, reply;
data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
data.writeString16(name);
remote()->transact(CHECK_SERVICE_TRANSACTION, data, &reply);
return reply.readStrongBinder();
}
virtual status_t addService(const String16& name, const sp<IBinder>& service,
bool allowIsolated)
{
Parcel data, reply;
data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
data.writeString16(name);
data.writeStrongBinder(service);
data.writeInt32(allowIsolated ? 1 : 0);
status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);
return err == NO_ERROR ? reply.readExceptionCode() : err;
}
virtual Vector<String16> listServices()
{
Vector<String16> res;
int n = 0;
for (;;) {
Parcel data, reply;
data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
data.writeInt32(n++);
status_t err = remote()->transact(LIST_SERVICES_TRANSACTION, data, &reply);
if (err != NO_ERROR)
break;
res.add(reply.readString16());
}
return res;
}
};
IMPLEMENT_META_INTERFACE(ServiceManager, "android.os.IServiceManager");
}; // namespace android
真正的SM服务
/* Copyright 2008 The Android Open Source Project
*/
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <cutils/android_filesystem_config.h>
#include <cutils/multiuser.h>
#include <selinux/android.h>
#include <selinux/avc.h>
#include "binder.h"
#ifdef VENDORSERVICEMANAGER
#define LOG_TAG "VendorServiceManager"
#else
#define LOG_TAG "ServiceManager"
#endif
#include <log/log.h>
struct audit_data {
pid_t pid;
uid_t uid;
const char *name;
};
const char *str8(const uint16_t *x, size_t x_len)
{
static char buf[128];
size_t max = 127;
char *p = buf;
if (x_len < max) {
max = x_len;
}
if (x) {
while ((max > 0) && (*x != '\0')) {
*p++ = *x++;
max--;
}
}
*p++ = 0;
return buf;
}
int str16eq(const uint16_t *a, const char *b)
{
while (*a && *b)
if (*a++ != *b++) return 0;
if (*a || *b)
return 0;
return 1;
}
static char *service_manager_context;
static struct selabel_handle* sehandle;
static bool check_mac_perms(pid_t spid, uid_t uid, const char *tctx, const char *perm, const char *name)
{
char *sctx = NULL;
const char *class = "service_manager";
bool allowed;
struct audit_data ad;
if (getpidcon(spid, &sctx) < 0) {
ALOGE("SELinux: getpidcon(pid=%d) failed to retrieve pid context.\n", spid);
return false;
}
ad.pid = spid;
ad.uid = uid;
ad.name = name;
int result = selinux_check_access(sctx, tctx, class, perm, (void *) &ad);
allowed = (result == 0);
freecon(sctx);
return allowed;
}
static bool check_mac_perms_from_getcon(pid_t spid, uid_t uid, const char *perm)
{
return check_mac_perms(spid, uid, service_manager_context, perm, NULL);
}
static bool check_mac_perms_from_lookup(pid_t spid, uid_t uid, const char *perm, const char *name)
{
bool allowed;
char *tctx = NULL;
if (!sehandle) {
ALOGE("SELinux: Failed to find sehandle. Aborting service_manager.\n");
abort();
}
if (selabel_lookup(sehandle, &tctx, name, 0) != 0) {
ALOGE("SELinux: No match for %s in service_contexts.\n", name);
return false;
}
allowed = check_mac_perms(spid, uid, tctx, perm, name);
freecon(tctx);
return allowed;
}
static int svc_can_register(const uint16_t *name, size_t name_len, pid_t spid, uid_t uid)
{
const char *perm = "add";
if (multiuser_get_app_id(uid) >= AID_APP) {
return 0; /* Don't allow apps to register services */
}
return check_mac_perms_from_lookup(spid, uid, perm, str8(name, name_len)) ? 1 : 0;
}
static int svc_can_list(pid_t spid, uid_t uid)
{
const char *perm = "list";
return check_mac_perms_from_getcon(spid, uid, perm) ? 1 : 0;
}
static int svc_can_find(const uint16_t *name, size_t name_len, pid_t spid, uid_t uid)
{
const char *perm = "find";
return check_mac_perms_from_lookup(spid, uid, perm, str8(name, name_len)) ? 1 : 0;
}
struct svcinfo
{
struct svcinfo *next;
uint32_t handle;
struct binder_death death;
int allow_isolated;
size_t len;
uint16_t name[0];
};
struct svcinfo *svclist = NULL;
struct svcinfo *find_svc(const uint16_t *s16, size_t len)
{
struct svcinfo *si;
for (si = svclist; si; si = si->next) {
if ((len == si->len) &&
!memcmp(s16, si->name, len * sizeof(uint16_t))) {
return si;
}
}
return NULL;
}
void svcinfo_death(struct binder_state *bs, void *ptr)
{
struct svcinfo *si = (struct svcinfo* ) ptr;
ALOGI("service '%s' died\n", str8(si->name, si->len));
if (si->handle) {
binder_release(bs, si->handle);
si->handle = 0;
}
}
uint16_t svcmgr_id[] = {
'a','n','d','r','o','i','d','.','o','s','.',
'I','S','e','r','v','i','c','e','M','a','n','a','g','e','r'
};
uint32_t do_find_service(const uint16_t *s, size_t len, uid_t uid, pid_t spid)
{
struct svcinfo *si = find_svc(s, len);
if (!si || !si->handle) {
return 0;
}
if (!si->allow_isolated) {
// If this service doesn't allow access from isolated processes,
// then check the uid to see if it is isolated.
uid_t appid = uid % AID_USER;
if (appid >= AID_ISOLATED_START && appid <= AID_ISOLATED_END) {
return 0;
}
}
if (!svc_can_find(s, len, spid, uid)) {
return 0;
}
return si->handle;
}
int do_add_service(struct binder_state *bs,
const uint16_t *s, size_t len,
uint32_t handle, uid_t uid, int allow_isolated,
pid_t spid)
{
struct svcinfo *si;
//ALOGI("add_service('%s',%x,%s) uid=%d\n", str8(s, len), handle,
// allow_isolated ? "allow_isolated" : "!allow_isolated", uid);
if (!handle || (len == 0) || (len > 127))
return -1;
if (!svc_can_register(s, len, spid, uid)) {
ALOGE("add_service('%s',%x) uid=%d - PERMISSION DENIED\n",
str8(s, len), handle, uid);
return -1;
}
si = find_svc(s, len);
if (si) {
if (si->handle) {
ALOGE("add_service('%s',%x) uid=%d - ALREADY REGISTERED, OVERRIDE\n",
str8(s, len), handle, uid);
svcinfo_death(bs, si);
}
si->handle = handle;
} else {
si = malloc(sizeof(*si) + (len + 1) * sizeof(uint16_t));
if (!si) {
ALOGE("add_service('%s',%x) uid=%d - OUT OF MEMORY\n",
str8(s, len), handle, uid);
return -1;
}
si->handle = handle;
si->len = len;
memcpy(si->name, s, (len + 1) * sizeof(uint16_t));
si->name[len] = '\0';
si->death.func = (void*) svcinfo_death;
si->death.ptr = si;
si->allow_isolated = allow_isolated;
si->next = svclist;
svclist = si;
}
binder_acquire(bs, handle);
binder_link_to_death(bs, handle, &si->death);
return 0;
}
int svcmgr_handler(struct binder_state *bs,
struct binder_transaction_data *txn,
struct binder_io *msg,
struct binder_io *reply)
{
struct svcinfo *si;
uint16_t *s;
size_t len;
uint32_t handle;
uint32_t strict_policy;
int allow_isolated;
//ALOGI("target=%p code=%d pid=%d uid=%d\n",
// (void*) txn->target.ptr, txn->code, txn->sender_pid, txn->sender_euid);
if (txn->target.ptr != BINDER_SERVICE_MANAGER)
return -1;
if (txn->code == PING_TRANSACTION)
return 0;
// Equivalent to Parcel::enforceInterface(), reading the RPC
// header with the strict mode policy mask and the interface name.
// Note that we ignore the strict_policy and don't propagate it
// further (since we do no outbound RPCs anyway).
strict_policy = bio_get_uint32(msg);
s = bio_get_string16(msg, &len);
if (s == NULL) {
return -1;
}
if ((len != (sizeof(svcmgr_id) / 2)) ||
memcmp(svcmgr_id, s, sizeof(svcmgr_id))) {
fprintf(stderr,"invalid id %s\n", str8(s, len));
return -1;
}
if (sehandle && selinux_status_updated() > 0) {
#ifdef VENDORSERVICEMANAGER
struct selabel_handle *tmp_sehandle = selinux_android_vendor_service_context_handle();
#else
struct selabel_handle *tmp_sehandle = selinux_android_service_context_handle();
#endif
if (tmp_sehandle) {
selabel_close(sehandle);
sehandle = tmp_sehandle;
}
}
switch(txn->code) {
case SVC_MGR_GET_SERVICE:
case SVC_MGR_CHECK_SERVICE:
s = bio_get_string16(msg, &len);
if (s == NULL) {
return -1;
}
handle = do_find_service(s, len, txn->sender_euid, txn->sender_pid);
if (!handle)
break;
bio_put_ref(reply, handle);
return 0;
case SVC_MGR_ADD_SERVICE:
s = bio_get_string16(msg, &len);
if (s == NULL) {
return -1;
}
handle = bio_get_ref(msg);
allow_isolated = bio_get_uint32(msg) ? 1 : 0;
if (do_add_service(bs, s, len, handle, txn->sender_euid,
allow_isolated, txn->sender_pid))
return -1;
break;
case SVC_MGR_LIST_SERVICES: {
uint32_t n = bio_get_uint32(msg);
if (!svc_can_list(txn->sender_pid, txn->sender_euid)) {
ALOGE("list_service() uid=%d - PERMISSION DENIED\n",
txn->sender_euid);
return -1;
}
si = svclist;
while ((n-- > 0) && si)
si = si->next;
if (si) {
bio_put_string16(reply, si->name);
return 0;
}
return -1;
}
default:
ALOGE("unknown code %d\n", txn->code);
return -1;
}
bio_put_uint32(reply, 0);
return 0;
}
static int audit_callback(void *data, __unused security_class_t cls, char *buf, size_t len)
{
struct audit_data *ad = (struct audit_data *)data;
if (!ad || !ad->name) {
ALOGE("No service manager audit data");
return 0;
}
snprintf(buf, len, "service=%s pid=%d uid=%d", ad->name, ad->pid, ad->uid);
return 0;
}
int main(int argc, char** argv)
{
struct binder_state *bs;
union selinux_callback cb;
char *driver;
if (argc > 1) {
driver = argv[1];
} else {
driver = "/dev/binder";
}
bs = binder_open(driver, 128*1024);
if (!bs) {
#ifdef VENDORSERVICEMANAGER
ALOGW("failed to open binder driver %s\n", driver);
while (true) {
sleep(UINT_MAX);
}
#else
ALOGE("failed to open binder driver %s\n", driver);
#endif
return -1;
}
if (binder_become_context_manager(bs)) {
ALOGE("cannot become context manager (%s)\n", strerror(errno));
return -1;
}
cb.func_audit = audit_callback;
selinux_set_callback(SELINUX_CB_AUDIT, cb);
cb.func_log = selinux_log_callback;
selinux_set_callback(SELINUX_CB_LOG, cb);
#ifdef VENDORSERVICEMANAGER
sehandle = selinux_android_vendor_service_context_handle();
#else
sehandle = selinux_android_service_context_handle();
#endif
selinux_status_open(true);
if (sehandle == NULL) {
ALOGE("SELinux: Failed to acquire sehandle. Aborting.\n");
abort();
}
if (getcon(&service_manager_context) != 0) {
ALOGE("SELinux: Failed to acquire service_manager context. Aborting.\n");
abort();
}
binder_loop(bs, svcmgr_handler);
return 0;
}
二，serviceManger运行时时序图
从上述代码可以明确知道：ServiceManager程序一旦启动运行，则不会停止（系统不宕机的情况下），将会一直looper->pollAll(-1)。除此之外，还知道ServiceManager默认情况依托于/dev/binder这个设备节点，当然可以通过向ServiceManager传递参数指定设备节点。ServiceManager作为binder机制的核心组件之一，在实现进程间通信中占据着不可获取的地位。
从Android.bp可以知道，ServiceManager对应的程序名称是servicemanager。从Android.bp文件中，还存在一个名为vndservicemanager的程序，它们的源码都是一样的，只是rc文件存在出入，将传入/dev/vndbinder作为binder驱动。在Android启动启动过程中，vndservicemanager和vndservicemanager都会被init拉起，他俩的区别总结如下：
1、对于servicemanager:
servicemanager是 Android 系统中的核心服务管理器，用于管理系统级的服务。
servicemanager管理的服务包括系统级服务（如ActivityManager、PackageManager、WindowManager等）和由应用程序注册的系统服务。
servicemanager的访问权限较高，一般只有系统级应用或者具有系统权限的应用程序才能够使用servicemanager进行服务的注册和查询。
2、对于vndservicemanager：
vndservicemanager是 servicemanager的一个扩展，用于管理供应商特定的服务。
vndservicemanager管理的服务通常是供应商（vendor）特定的、定制化的服务，例如硬件厂商提供的驱动程序或服务。
vndservicemanager的访问权限一般较低，通常只有供应商特定的应用程序或系统组件才能够使用vndservicemanager进行服务的注册和查询。
二、ServiceManager的启动
第一小节简要介绍了ServiceManager，我们知道ServiceManager是一个具体程序，如果是个程序，那么该程序是如何启动的呢？又在什么时候触发运行的呢？
我们知道Android系统的第一个进程是init，这是由内核决定的。那么在init中将通过解析init.rc来启动系统的一些关键服务进程。其中ServiceManager就在这个时候启动运行
