Android Binder
2019-03-01 本文已影响0人
一只胖Wa牛
Binder
Binder是什么？
- Binder是一种进程间通信机制
为什么是Binder？
Binder架构
-
Binder通信机制采用C/S架构，这很重要！！！
@Binder架构|center
- Binder框架中主要涉及到4个角色Client、Server、Service Manager及Binder驱动，其中Client、Server、Service Manager运行在用户空间，Binder驱动运行在内核空间
- Client代表客户端进程，Server代表客户端进程提供各种服务，如音视频等
- Service Manager用来管理各种系统服务
- Binder驱动提供进程间通信的能力
- 用户空间的Client、Server、ServiceManager通过open、mmap和ioctl等标准文件操作(详见Unix环境编程)来访问/dev/binder，进而实现进程间通信
基础数据结构
Binder基础数据
关于Binder基础数据，见上图
Binder驱动
Binder驱动工作图
/kernel/drivers/staging/android/binder.c
device_initcall(binder_init);
设备初始化时候会调用binder_init进行binder驱动初始化
/kernel/drivers/staging/android/binder.c
//绑定binder驱动操作函数
static const struct file_operations binder_fops = {
.owner = THIS_MODULE,
.poll = binder_poll,
.unlocked_ioctl = binder_ioctl,
.compat_ioctl = binder_ioctl,
.mmap = binder_mmap,
.open = binder_open,
.flush = binder_flush,
.release = binder_release,
};
//创建misc类型的驱动
static struct miscdevice binder_miscdev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "binder",
.fops = &binder_fops//绑定binder驱动操作函数
};
//binder驱动初始化
static int __init binder_init(void)
{
int ret;
binder_deferred_workqueue = create_singlethread_workqueue("binder");
if (!binder_deferred_workqueue)
return -ENOMEM;
//创建目录/binder
binder_debugfs_dir_entry_root = debugfs_create_dir("binder", NULL);
if (binder_debugfs_dir_entry_root)
//创建目录/binder/proc
binder_debugfs_dir_entry_proc = debugfs_create_dir("proc",
binder_debugfs_dir_entry_root);
//注册binder驱动
ret = misc_register(&binder_miscdev);
//创建其他文件
if (binder_debugfs_dir_entry_root) {
//创建文件/binder/proc/state
debugfs_create_file("state",
S_IRUGO,
binder_debugfs_dir_entry_root,
NULL,
&binder_state_fops);
//创建文件/binder/proc/stats
debugfs_create_file("stats",
S_IRUGO,
binder_debugfs_dir_entry_root,
NULL,
&binder_stats_fops);
//创建文件/binder/proc/transactions
debugfs_create_file("transactions",
S_IRUGO,
binder_debugfs_dir_entry_root,
NULL,
&binder_transactions_fops);
//创建文件/binder/proc/transaction_log
debugfs_create_file("transaction_log",
S_IRUGO,
binder_debugfs_dir_entry_root,
&binder_transaction_log,
&binder_transaction_log_fops);
//创建文件/binder/proc/failed_transaction_log
debugfs_create_file("failed_transaction_log",
S_IRUGO,
binder_debugfs_dir_entry_root,
&binder_transaction_log_failed,
&binder_transaction_log_fops);
}
return ret;
}
初始化主要做了两件事情
- 初始化存储binder存储信息的目录
- 创建binder设备，并绑定操作函数如binder_open、binder_mmap、binder_ioctl等
- 设备启动时候，会调用binder_init，主要做两件事情
- 1.创建/binder/proc目录，之后在这个目录下创建state、stats、transactions、transaction_log、failed_transaction_log文件夹，分别存储进程通信的各种数据
- 2.注册驱动，并绑定文件操作函数binder_open、binder_mmap、binder_ioctl等，之后就可以通过RPC机制去访问binder驱动
Native层级的Binder结构
@Server组件类图|center
@Client组件类图|center
Binder通信机制
@Binder分层|center
Binder进程与线程
@Binder驱动中的线程与用户空间的线程
ServiceManager启动
@ServiceManager启动
预备知识补充
ServiceManager启动流程主要分为三个流程
1.以系统服务形式启动service_manager,之后通过在binder_open函数打开驱动设备，驱动层相应的就会创建service_manager对应的binder_proc，并且这是个特殊的service
2.调用binder_become_context_manager通过ioctl调用内核中的binder_ioctl,经过一系列处理后，binder驱动会将这个特殊的binder_node存到静态指针binder_context_mgr_node
static struct binder_node *binder_context_mgr_node;
...
static int binder_ioctl_set_ctx_mgr(struct file *filp)
{
...
//注意这里后续两个参数都是0
binder_context_mgr_node = binder_new_node(proc, 0, 0);
...
}
...
3.调用binder_loop进入循环解析的过程
int main(int argc, char** argv){
...
//进入循环，等待或处理Client进程的通信请求
binder_loop(bs, svcmgr_handler);
...
}
这里指定循环处理函数为svcmgr_handler,后续再仔细分析这个函数，先看binder_loop实现
void binder_loop(struct binder_state *bs, binder_handler func)
{
...
//通信数据
struct binder_write_read bwr;
bwr.write_size = 0;
bwr.write_consumed = 0;
bwr.write_buffer = 0;
readbuf[0] = BC_ENTER_LOOPER;
binder_write(bs, readbuf, sizeof(uint32_t));
for (;;) {
bwr.read_size = sizeof(readbuf);
bwr.read_consumed = 0;
bwr.read_buffer = (uintptr_t) readbuf;
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);
...
//解析
res = binder_parse(bs, 0, (uintptr_t) readbuf, bwr.read_consumed, func);
...
}
}
int binder_write(struct binder_state *bs, void *data, size_t len)
{
struct binder_write_read bwr;
int res;
bwr.write_size = len;
bwr.write_consumed = 0;
bwr.write_buffer = (uintptr_t) data;
bwr.read_size = 0;
bwr.read_consumed = 0;
bwr.read_buffer = 0;
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);
...
return res;
}
- 首先创建一个binder_write_read结构体，然后通过binder_write向Binder驱动写入命令协议BC_ENTER_LOOPER，注意这个理输出缓冲区是没有数据的,binder驱动经过一系列处理进入循环状态，之后通过一个死循环来不断的从Binder驱动读取数据，之后交由binder_parse去解析各种协议数据，后续再分析细节
- Binder驱动是如何处理交互细节的，我们来看下binder_ioctl_write_read的实现
static int binder_ioctl_write_read(struct file *filp,
unsigned int cmd, unsigned long arg,
struct binder_thread *thread)
{
...
//从文件句柄取出进程信息
struct binder_proc *proc = filp->private_data;
//命令协议
unsigned int size = _IOC_SIZE(cmd);
...
struct binder_write_read bwr;
//取出bwr进程通信协议载体
if (copy_from_user(&bwr, ubuf, sizeof(bwr))) {
...
}
//如果有写入数据，就交由binder_thread_write去处理，之后
//通过copy_to_user将数据返还给用户空间
if (bwr.write_size > 0) {
ret = binder_thread_write(proc, thread,
bwr.write_buffer,
bwr.write_size,
&bwr.write_consumed);
...
if (ret < 0) {
bwr.read_consumed = 0;
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
...
goto out;
}
}
//如果有输出数据，则调用binder_thread_read解析，
//之后判断进程的事务队里是否为空，如果不为空就等待执行
if (bwr.read_size > 0) {
ret = binder_thread_read(proc, thread, bwr.read_buffer,
bwr.read_size,
&bwr.read_consumed,
filp->f_flags & O_NONBLOCK);
...
if (!list_empty(&proc->todo))
wake_up_interruptible(&proc->wait);
if (ret < 0) {
//将写出数据返还给用户空间
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
...
goto out;
}
}
...
out:
return ret;
}
- 至于binder_thread_write与binder_thread_read则是处理命令协(binder_driver_command_protocol)与返回协议(binder_driver_return_protocol )详见/drivers/staging/android/binder.h
ServiceManager注册服务
@Service的注册流程|center
- service的注册流程如上图，这里以media_server的注册为例子去看代码
/frameworks/av/services/mediadrm/mediadrmserver.rc
service mediadrm /system/bin/mediadrmserver
class main
user media
group mediadrm drmrpc
ioprio rt 4
writepid /dev/cpuset/foreground/tasks
- 可以看到以用户权限启动mediadrm服务，文件位于/system/bin/mediadrmserver
- 接下来看main_mediadrmserver.cpp
/frameworks/av/services/mediadrm/mediadrmserver.cpp
int main()
{
...
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm = defaultServiceManager();
...
MediaDrmService::instantiate();
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
- main()中主要做了两件事情：
1.初始化MediaDrmService
2.线程池初始化
先看第一个
/frameworks/av/services/mediadrm/MediaDrmService.cpp
...
void MediaDrmService::instantiate() {
defaultServiceManager()->addService(
String16("media.drm"), new MediaDrmService());
}
...
- 这里面主要通过defaultServiceManager()获取一个BpServiceManager指针然后调用addService，注意这里传入的两个参数“media.drm”和一个MediaDrmService对象
ServiceManager代理对象的获取
- 先来看defaultServiceManager()调用
/frameworks/native/libs/binder/Static.cpp
...
sp<IServiceManager> gDefaultServiceManager;
...
/frameworks/native/libs/binder/ISerivceManager.cpp
...
sp<IServiceManager> defaultServiceManager()
{
if (gDefaultServiceManager != NULL)
return gDefaultServiceManager;
{
...
while (gDefaultServiceManager == NULL) {
gDefaultServiceManager = interface_cast<IServiceManager>(
ProcessState::self()->getContextObject(NULL));
...
}
}
return gDefaultServiceManager;
}
...
- gDefaultServiceManager就是一个IServiceManger的指针
- 首次获取时候一定是通过interface_cast<IServiceManager>(ProcessState::self()->getContextObject(NULL))这一系列method调用获取的，一步步分析
- 先看ProcessState::self()
/frameworks/native/libs/binder/ProcessState
...
sp<ProcessState> ProcessState::self()
{
Mutex::Autolock _l(gProcessMutex);
if (gProcess != NULL) {
return gProcess;
}
//注意这里的文件name
gProcess = new ProcessState("/dev/binder");
return gProcess;
}
...
- 我赌半包辣条，这个类构造一定持有打开/dev/binder的句柄，不信你看构造声明
//这里是cpp构造函数形式，就是成员变量赋值
ProcessState::ProcessState(const char *driver)
: mDriverName(String8(driver))
, mDriverFD(open_driver(driver))
, mVMStart(MAP_FAILED)
, mThreadCountLock(PTHREAD_MUTEX_INITIALIZER)
, mThreadCountDecrement(PTHREAD_COND_INITIALIZER)
, mExecutingThreadsCount(0)
, mMaxThreads(DEFAULT_MAX_BINDER_THREADS)
, mStarvationStartTimeMs(0)
, mManagesContexts(false)
, mBinderContextCheckFunc(NULL)
, mBinderContextUserData(NULL)
, mThreadPoolStarted(false)
, mThreadPoolSeq(1)
{
if (mDriverFD >= 0) {
// mmap the binder, providing a chunk of virtual address space to receive transactions.
//注意这里分配的BINDER_VM_SIZE为1016kb，具体见宏定义处
mVMStart = mmap(0, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE | MAP_NORESERVE, mDriverFD, 0);
if (mVMStart == MAP_FAILED) {
...
close(mDriverFD);
mDriverFD = -1;
mDriverName.clear();
}
}
...
}
- 再来看getContextObject
sp<IBinder> ProcessState::getContextObject(const sp<IBinder>& /*caller*/)
{
//注意这里传入的值为0
return getStrongProxyForHandle(0);
}
...
sp<IBinder> ProcessState::getStrongProxyForHandle(int32_t handle)
{
sp<IBinder> result;
...
handle_entry* e = lookupHandleLocked(handle);
if (e != NULL) {
...
b = BpBinder::create(handle);
e->binder = b;
if (b) e->refs = b->getWeakRefs();
result = b;
}else{
...
}
return result;
}
- getContextObject()内部是调用getStrongProxyForHandle(0)来获取一个IBinder指针(这里0其实就是为了后续查找之前ServiceManager启动注册那个特殊的Service组件)，可以看到其实这里创建的是一个BpBinder对象，并且他的句柄值是0
- 我们来看BpBinder的相关调用
frameworks/native/libs/binder/BpBinder.cpp
//handle句柄值 与binder驱动中的binder引用对象进行关联
BpBinder::BpBinder(int32_t handle, int32_t trackedUid)
//注意这里传入的是0
: mHandle(handle)
//注意这个值为1
, mAlive(1)
, mObitsSent(0)
, mObituaries(NULL)
, mTrackedUid(trackedUid)
{
...
IPCThreadState::self()->incWeakHandle(handle, this);
}
BpBinder* BpBinder::create(int32_t handle) {
...
return new BpBinder(handle, trackedUid);
}
- 回到defaultServiceManager()，最后interface_cast<IServiceManager>(BpBinder(0))实际上转换成了这个，这个在哪里定义呢？
/frameworks/native/include/binder/IInterface.h
template<typename INTERFACE>
inline sp<INTERFACE> interface_cast(const sp<IBinder>& obj)
{
return INTERFACE::asInterface(obj);
}
- 发现他是个内联模板函数，实际上调用的是IServiceManager::asInterface(BpBinder(0))，那么IServiceManager::asInterface在哪里定义呢？
/frameworks/native/libs/binder/IServiceManager.cpp
IMPLEMENT_META_INTERFACE(ServiceManager, "android.os.IServiceManager");
看上面这个宏定义，实际定义在
/frameworks/native/include/binder/IInterface.h
#define IMPLEMENT_META_INTERFACE(INTERFACE, NAME)
const ::android::String16 I##INTERFACE::descriptor(NAME);
const ::android::String16&
I##INTERFACE::getInterfaceDescriptor() const {
return I##INTERFACE::descriptor;
}
::android::sp<I##INTERFACE> I##INTERFACE::asInterface(
const ::android::sp<::android::IBinder>& obj)
{
::android::sp<I##INTERFACE> intr;
if (obj != NULL) {
intr = static_cast<I##INTERFACE*>(
obj->queryLocalInterface(
I##INTERFACE::descriptor).get());
if (intr == NULL) {
intr = new Bp##INTERFACE(obj);
}
}
return intr;
}
I##INTERFACE::I##INTERFACE() { }
I##INTERFACE::~I##INTERFACE() { }
- 带入转换下，发现我们拿到的其实就是一个BpServiceManager
- 接下来我们来看后续的调用
BpServiceManager#addService
virtual status_t addService(const String16& name, const sp<IBinder>& service,bool allowIsolated, int dumpsysPriority) {
//这里data表示要写入的数据，reply表示返回的数据
Parcel data, reply;
//存储描述符"android.os.IServiceManager"
data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
//存储服务名字"media.drm"
data.writeString16(name);
//存储服务MediaDrmService
data.writeStrongBinder(service);
data.writeInt32(allowIsolated ? 1 : 0);
data.writeInt32(dumpsysPriority);
status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);
return err == NO_ERROR ? reply.readExceptionCode() : err;
}
- 这里实际上把上一步传入的数据通过Parcel存起来，然后调用remote()获取一个BpBinder然后调用其transact，传入的code为ADD_SERVICE_TRANSACTION，经过包装后data中的数据长这样子
-
@Parcel数据封装|center
- 记下来我们去看BpBinder#transact
status_t BpBinder::transact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
// Once a binder has died, it will never come back to life.
//构造中mAlive=1，所以这里会走进if
if (mAlive) {
//这里调用的是IPCThreadState#transact
status_t status = IPCThreadState::self()->transact(
mHandle, code, data, reply, flags);
if (status == DEAD_OBJECT) mAlive = 0;
return status;
}
return DEAD_OBJECT;
}
- 前面ServiceManager代理对象获取BpBinder时候，mHandle为0，code为ADD_SERVICE_TRANSACTION，data存储binder信息，reply存储要返回的信息，flags查看method定义默认参数为0
- 接下来分析IPCThreadState#transact
/frameworks/native/libs/binder/IPCThreadState.cpp
status_t IPCThreadState::transact(int32_t handle,
uint32_t code, const Parcel& data,
Parcel* reply, uint32_t flags)
{
status_t err;
//允许返回中携带文件描述符
flags |= TF_ACCEPT_FDS;
...
//封装BC_TRANSACTION通信请求
err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);
...
//同步or异步，这里是同步调用
if ((flags & TF_ONE_WAY) == 0) {
...
if (reply) {
//向Binder驱动发起BC_TRANSACTION
err = waitForResponse(reply);
} else {
Parcel fakeReply;
err = waitForResponse(&fakeReply);
...
}
...
}else{
err = waitForResponse(NULL, NULL);
}
return err;
}
- 上面首先将flags与TF_ACCEPT_FDS做或操作，表示接收文件描述符
- 之后调用writeTransactionData将数据封装成一个BC_TRANSACTION命令协议,这里是同步调用切需要返回，所以执行到的是waitForResponse(reply)，接下来分别来看writeTransactionData、waitForResponse的实现
status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags,
int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer)
{
//对应内核中要求io携带binder_transaction_data结构体
binder_transaction_data tr;
tr.target.ptr = 0; /* Don't pass uninitialized stack data to a remote process */
tr.target.handle = handle;
tr.code = code;
tr.flags = binderFlags;
tr.cookie = 0;
tr.sender_pid = 0;
tr.sender_euid = 0;
const status_t err = data.errorCheck();
if (err == NO_ERROR) {
tr.data_size = data.ipcDataSize();
tr.data.ptr.buffer = data.ipcData();
tr.offsets_size = data.ipcObjectsCount()*sizeof(binder_size_t);
tr.data.ptr.offsets = data.ipcObjects();
} else if (statusBuffer) {
tr.flags |= TF_STATUS_CODE;
*statusBuffer = err;
tr.data_size = sizeof(status_t);
tr.data.ptr.buffer = reinterpret_cast<uintptr_t>(statusBuffer);
tr.offsets_size = 0;
tr.data.ptr.offsets = 0;
} else {
return (mLastError = err);
}
mOut.writeInt32(cmd);
mOut.write(&tr, sizeof(tr));
return NO_ERROR;
}
- 这里主要是创建一个binder_transaction_data，初其始化后将要传输的数据写入到mOut缓冲区中，最终整个数据长这样子
-
@writeTransactionData|center
- 数据封装完成以后，我们来看waitForResponse的实现
status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{
uint32_t cmd;
int32_t err;
while (1) {
if ((err=talkWithDriver()) < NO_ERROR) break;
...
//从输出缓冲区取出返回协议命令
cmd = (uint32_t)mIn.readInt32();
...
}
...
return err;
}
- 这里可以是一个死循环，不断的通过talkWithDriver去跟binder驱动通信，然后从输出缓冲区中取出返回协议然后处理返回协议，这里先不看具体的协议处理，先来看talkWithDriver的实现
//默认doReceive = true
status_t IPCThreadState::talkWithDriver(bool doReceive)
{
...
binder_write_read bwr;
// Is the read buffer empty?
const bool needRead = mIn.dataPosition() >= mIn.dataSize();
// We don't want to write anything if we are still reading
// from data left in the input buffer and the caller
// has requested to read the next data.
const size_t outAvail = (!doReceive || needRead) ? mOut.dataSize() : 0;
bwr.write_size = outAvail;
bwr.write_buffer = (uintptr_t)mOut.data();
// This is what we'll read.
if (doReceive && needRead) {
bwr.read_size = mIn.dataCapacity();
bwr.read_buffer = (uintptr_t)mIn.data();
} else {
bwr.read_size = 0;
bwr.read_buffer = 0;
}
...
// Return immediately if there is nothing to do.
if ((bwr.write_size == 0) && (bwr.read_size == 0)) return NO_ERROR;
bwr.write_consumed = 0;
bwr.read_consumed = 0;
status_t err;
do{
...
//这里通过io想驱动写入一个binder_write_read结构体
if (ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) >= 0)
err = NO_ERROR;
else
err = -errno;
} while (err == -EINTR);
if (err >= NO_ERROR) {
if (bwr.write_consumed > 0) {
if (bwr.write_consumed < mOut.dataSize())
mOut.remove(0, bwr.write_consumed);
else {
mOut.setDataSize(0);
processPostWriteDerefs();
}
}
if (bwr.read_consumed > 0) {
mIn.setDataSize(bwr.read_consumed);
mIn.setDataPosition(0);
}
...
return NO_ERROR;
}
return err;
}
- 这里主要通过io控制命令向Binder驱动写入一个type为BINDER_WRITE_READ，data为binder_write_read，其输出缓冲区为前面mOut中写入的数据
- 接下来的操作就转到Binder驱动中进行了，需要记住，Clinet进程此时执行到的位置
/platform/drivers/staging/android/binder.c
static long binder_ioctl(struct file *filp, unsigned int cmd,
unsigned long arg)
{
int ret;
struct binder_proc *proc = filp->private_data;
struct binder_thread *thread;
unsigned int size = _IOC_SIZE(cmd);
...
//这里根据进程找到对应的thread，如果没找到就创建一个
thread = binder_get_thread(proc);
...
switch (cmd) {
case BINDER_WRITE_READ:
ret = binder_ioctl_write_read(filp, cmd, arg, thread);
if (ret)
goto err;
break;
...
}
- Binder驱动中对应的binder_ioctl()会调用，之后会处理cmd为BINDER_WRITE_READ的分支，之后会调用到binder_ioctl_write_read()
static int binder_ioctl_write_read(struct file *filp,
unsigned int cmd, unsigned long arg,
struct binder_thread *thread)
{
int ret = 0;
//从文件描述符中取出进程地址
struct binder_proc *proc = filp->private_data;
//cmd信息
unsigned int size = _IOC_SIZE(cmd);
void __user *ubuf = (void __user *)arg;
struct binder_write_read bwr;
//cmd校验
if (size != sizeof(struct binder_write_read)) {
ret = -EINVAL;
goto out;
}
//从用户空间中取出binder_write_read结构体
if (copy_from_user(&bwr, ubuf, sizeof(bwr))) {
ret = -EFAULT;
goto out;
}
...
//输出缓冲区有数据就处理输出缓冲区
if (bwr.write_size > 0) {
//这里是真正处理输出缓冲数据的func
ret = binder_thread_write(proc, thread,
bwr.write_buffer,
bwr.write_size,
&bwr.write_consumed);
trace_binder_write_done(ret);
if (ret < 0) {
bwr.read_consumed = 0;
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
ret = -EFAULT;
goto out;
}
}
//输入缓冲区有数据就处理输入缓冲区
if (bwr.read_size > 0) {
//这里是真正处理输出缓冲数据的func
ret = binder_thread_read(proc, thread, bwr.read_buffer,
bwr.read_size,
&bwr.read_consumed,
filp->f_flags & O_NONBLOCK);
trace_binder_read_done(ret);
//如果进程todo队里不为空，说明有事务正在处理，需要等待处理
if (!list_empty(&proc->todo))
wake_up_interruptible(&proc->wait);
if (ret < 0) {
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
ret = -EFAULT;
goto out;
}
}
...
//将数据copy回用户空间
if (copy_to_user(ubuf, &bwr, sizeof(bwr))) {
ret = -EFAULT;
goto out;
}
out:
return ret;
}
- 前面调用可知，输出缓冲区是有数据，输入缓冲区是没有数据的，所以上面方法执行流程应该是，先调用binder_thread_write去处理输出缓冲区
static int binder_thread_write(struct binder_proc *proc,
struct binder_thread *thread,
binder_uintptr_t binder_buffer, size_t size,
binder_size_t *consumed)
{
uint32_t cmd;
void __user *buffer = (void __user *)(uintptr_t)binder_buffer;
void __user *ptr = buffer + *consumed;
void __user *end = buffer + size;
while (ptr < end && thread->return_error == BR_OK) {
//根据cmd取出消费的数据偏移地址
if (get_user(cmd, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
...
switch (cmd) {
...
case BC_TRANSACTION:
case BC_REPLY: {
struct binder_transaction_data tr;
if (copy_from_user(&tr, ptr, sizeof(tr)))
return -EFAULT;
ptr += sizeof(tr);
binder_transaction(proc, thread, &tr, cmd == BC_REPLY);
break;
...
}
*consumed = ptr - buffer;
}
return 0;
}
- 这里是取出cmd，然后处理BC_TRANSACTION时候，再讲binder_transaction_data取出，之后交由binder_transaction去处理
- binder_transaction比较长，其实主要分为三个部分
- 1.初始化目标线程进程
- 2.封装返回数据binder_transaction_data
- 3.为binder_transaction_data分配合适的线程or进程
static void binder_transaction(struct binder_proc *proc,
struct binder_thread *thread,
struct binder_transaction_data *tr, int reply)
{
struct binder_transaction *t;
struct binder_work *tcomplete;
binder_size_t *offp, *off_end;
binder_size_t off_min;
struct binder_proc *target_proc;
struct binder_thread *target_thread = NULL;
struct binder_node *target_node = NULL;
struct list_head *target_list;
wait_queue_head_t *target_wait;
struct binder_transaction *in_reply_to = NULL;
...
uint32_t return_error;
...
//如果是reply走if分支，否则走else分支，这里走else
if (reply) {
...
}else{
//根据句柄找对应的binder_ref、binder_node
if (tr->target.handle) {
struct binder_ref *ref;
ref = binder_get_ref(proc, tr->target.handle);
...
else{
//handle=0，则需要找指向service_manager的binder_node
target_node = binder_context_mgr_node;
...
}
...
//根据binder_node找到对应的进程binder_proc，这里也就是service_manager
target_proc = target_node->proc;
...
//如果是同步请求，尝试寻找一个在等待其他事物执行的线程，tips优化调度
if (!(tr->flags & TF_ONE_WAY) && thread->transaction_stack) {
struct binder_transaction *tmp;
tmp = thread->transaction_stack;
...
//找到一个等待别的事务完成的依赖线程
while (tmp) {
if (tmp->from && tmp->from->proc == target_proc)
target_thread = tmp->from;
tmp = tmp->from_parent;
}
}
}
//有空闲线程就是用空闲线程的等待队列，否则使用进程的事物队列
if (target_thread) {
e->to_thread = target_thread->pid;
target_list = &target_thread->todo;
target_wait = &target_thread->wait;
} else {
target_list = &target_proc->todo;
target_wait = &target_proc->wait;
}
...
//创建binder_transaction结构体，BINDER_WORK_TRANSACTION
//用于向目标进程发送数据
t = kzalloc(sizeof(*t), GFP_KERNEL);
...
binder_stats_created(BINDER_STAT_TRANSACTION);
...
//创建binder_work结构体,BINDER_STAT_TRANSACTION_COMPLETE
//便于向源进程返回数据处理结果
tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL);
...
binder_stats_created(BINDER_STAT_TRANSACTION_COMPLETE);
...
//初始化t
if (!reply && !(tr->flags & TF_ONE_WAY))
t->from = thread;
else
t->from = NULL;
t->sender_euid = task_euid(proc->tsk);
//目标进程
t->to_proc = target_proc;
//目标线程
t->to_thread = target_thread;
//code ADD_SERVICE_TRANSACTION
t->code = tr->code;
//flag = TF_ACCEPT_FLAGS
t->flags = tr->flags;
//优先级
t->priority = task_nice(current);
...
//缓冲区
t->buffer = binder_alloc_buf(target_proc, tr->data_size,
tr->offsets_size, !reply && (t->flags & TF_ONE_WAY));
...
t->buffer->allow_user_free = 0;
t->buffer->debug_id = t->debug_id;
t->buffer->transaction = t;
t->buffer->target_node = target_node;
...
//为t分配内核缓冲区
if (target_node)
binder_inc_node(target_node, 1, 0, NULL);
offp = (binder_size_t *)(t->buffer->data +
ALIGN(tr->data_size, sizeof(void *)));
//数据copy
if (copy_from_user(t->buffer->data, (const void __user *)(uintptr_t)
tr->data.ptr.buffer, tr->data_size)) {
...
goto err_copy_data_failed;
}
if (copy_from_user(offp, (const void __user *)(uintptr_t)
tr->data.ptr.offsets, tr->offsets_size)) {
...
goto err_copy_data_failed;
}
...
//处理Binder请求，内核中很多都是地址起止位置操作
off_end = (void *)offp + tr->offsets_size;
off_min = 0;
for (; offp < off_end; offp++) {
struct flat_binder_object *fp;
...
//前面存储的MediaDrmService信息
fp = (struct flat_binder_object *)(t->buffer->data + *offp);
off_min = *offp + sizeof(struct flat_binder_object);
switch(fp->type){
case BINDER_TYPE_BINDER:
case BINDER_TYPE_WEAK_BINDER: {
struct binder_ref *ref;
struct binder_node *node =
binder_get_node(proc, fp->binder);
//如果是首次就创建新的binder_node
if (node == NULL) {
node = binder_new_node(proc, fp->binder, fp->cookie);
...
//设定线程优先级
node->min_priority = fp->flags & FLAT_BINDER_FLAG_PRIORITY_MASK;
//设置是否接收文件描述符
node->accept_fds = !!(fp->flags & FLAT_BINDER_FLAG_ACCEPTS_FDS);
}
...
//如果是首次就创建对应的binder_ref对象
ref = binder_get_ref_for_node(target_proc, node);
if (ref == NULL) {
return_error = BR_FAILED_REPLY;
goto err_binder_get_ref_for_node_failed;
}
//修改flat_binder_objec.type
if (fp->type == BINDER_TYPE_BINDER)
fp->type = BINDER_TYPE_HANDLE;
else
fp->type = BINDER_TYPE_WEAK_HANDLE;
//设置句柄
fp->handle = ref->desc;
//增加binder_ref的引用计数
binder_inc_ref(ref, fp->type == BINDER_TYPE_HANDLE,
&thread->todo);
...
}break;
...
}
}
//分配事务t的要进入那个栈
if (reply) {
...
binder_pop_transaction(target_thread, in_reply_to);
} else if (!(t->flags & TF_ONE_WAY)) {
...
t->need_reply = 1;
t->from_parent = thread->transaction_stack;
thread->transaction_stack = t;
} else {
...
if (target_node->has_async_transaction) {
target_list = &target_node->async_todo;
target_wait = NULL;
} else
target_node->has_async_transaction = 1;
}
//将binder_transaction_data指针t的类型修改为BINDER_WORK_TRANSACTION
t->work.type = BINDER_WORK_TRANSACTION;
//添加到target_list队列尾部
list_add_tail(&t->work.entry, target_list);
//将binder_work指针tcomplete.type置为BINDER_WORK_TRANSACTION_COMPLETE
tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
list_add_tail(&tcomplete->entry, &thread->todo);
//这里有两个执行分支
//1.处理类型为BINDER_WORK_TRANSACTION的binder_transaction_data
//2.处理类型为BINDER_WORK_TRANSACTION_COMPLETE的binder_work
if (target_wait)
wake_up_interruptible(target_wait);
return;
...
}
- 经过上面func以后，binder驱动中就会为MediaDrmService创建对应的binder_node并加入到整个Binder实体对象的红黑树中，接着会分别向Client进程、ServiceManager发送一个BINDER_WORK_TRANSACTION_COMPLETE的binder_work及BINDER_WORK_TRANSACTION的binder_transaction
- 至此，源线程thread、target_proc或者target_thread会并发的去执行各自todo队列中的任务
- 先来看源线程,回到binder_ioctl_write_read中，接下来要处理输入缓冲区，对应的调用binder_thread_read
static int binder_thread_read(struct binder_proc *proc,
struct binder_thread *thread,
binder_uintptr_t binder_buffer, size_t size,
binder_size_t *consumed, int non_block)
{
void __user *buffer = (void __user *)(uintptr_t)binder_buffer;
void __user *ptr = buffer + *consumed;
void __user *end = buffer + size;
int ret = 0;
int wait_for_proc_work;
...
//线程唤醒
while (1) {
uint32_t cmd;
struct binder_transaction_data tr;
struct binder_work *w;
struct binder_transaction *t = NULL;
//检查工作队列，并将待处理项赋值给w
if (!list_empty(&thread->todo)) {
w = list_first_entry(&thread->todo, struct binder_work,
entry);
} else if (!list_empty(&proc->todo) && wait_for_proc_work) {
w = list_first_entry(&proc->todo, struct binder_work,
entry);
} else {
/* no data added */
if (ptr - buffer == 4 &&
!(thread->looper & BINDER_LOOPER_STATE_NEED_RETURN))
goto retry;
break;
}
switch (w->type) {
...
case BINDER_WORK_TRANSACTION_COMPLETE: {
cmd = BR_TRANSACTION_COMPLETE;
if (put_user(cmd, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
binder_stat_br(proc, thread, cmd);
...
//删除binder_work，并释放资源
list_del(&w->entry);
kfree(w);
binder_stats_deleted(BINDER_STAT_TRANSACTION_COMPLETE);
} break;
}
done:
*consumed = ptr - buffer;
...
return 0;
}
- 这里返回一个BR_TRANSACTION_COMPLETE协议，之后会经过一些列调用会回到IPCThreadState#waitForResponse中
status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{
...
uint32_t cmd;
int32_t err;
while (1) {
...
cmd = (uint32_t)mIn.readInt32();
...
switch (cmd) {
case BR_TRANSACTION_COMPLETE:
if (!reply && !acquireResult) goto finish;
break;
}
...
}
finish:
...
return error;
}
- IPCThreadState::waitForResponse对于BR_TRANSACTION_COMPLETE处理比较简单，就直接返回了
- 我们来看下target_proc即ServiceManager是怎么接收处理BINDER_WORK_TRANSACTION类型的binder_transaction的，假设ServiceManager之前没有通信，那么他就在Binder驱动中一直等待事务的到来，现在有事务了那么对应的就会调用binder_read_thread
static int binder_thread_read(struct binder_proc *proc,
struct binder_thread *thread,
binder_uintptr_t binder_buffer, size_t size,
binder_size_t *consumed, int non_block)
{
void __user *buffer = (void __user *)(uintptr_t)binder_buffer;
void __user *ptr = buffer + *consumed;
void __user *end = buffer + size;
...
//线程唤醒
while (1) {
uint32_t cmd;
struct binder_transaction_data tr;
struct binder_work *w;
struct binder_transaction *t = NULL;
//检查工作队列，并将待处理项赋值给w
if (!list_empty(&thread->todo)) {
w = list_first_entry(&thread->todo, struct binder_work,
entry);
} else if (!list_empty(&proc->todo) && wait_for_proc_work) {
w = list_first_entry(&proc->todo, struct binder_work,
entry);
} else {
/* no data added */
if (ptr - buffer == 4 &&
!(thread->looper & BINDER_LOOPER_STATE_NEED_RETURN))
goto retry;
break;
}
...
switch (w->type) {
case BINDER_WORK_TRANSACTION: {
t = container_of(w, struct binder_transaction, work);
} break;
...
}
//返回协议的处理，现在target_node指向的是binder_context_mgr_node
if (t->buffer->target_node) {
struct binder_node *target_node = t->buffer->target_node;
tr.target.ptr = target_node->ptr;
tr.cookie = target_node->cookie;
//保存原本的线程优先级，便于后续恢复
t->saved_priority = task_nice(current);
//修改binder驱动中对应proc的线程优先级（模拟Client进程的线程优先级）
if (t->priority < target_node->min_priority &&
!(t->flags & TF_ONE_WAY))
binder_set_nice(t->priority);
else if (!(t->flags & TF_ONE_WAY) ||
t->saved_priority > target_node->min_priority)
binder_set_nice(target_node->min_priority);
cmd = BR_TRANSACTION;
} else {
...
}
//拷贝code与flags，
//注册服务过程中这里是ADD_SERVICE_TRANSACTION、TF_ACCEPT_FDS
tr.code = t->code;
tr.flags = t->flags;
if (t->from) {
struct task_struct *sender = t->from->proc->tsk;
tr.sender_pid = task_tgid_nr_ns(sender,
task_active_pid_ns(current));
} else {
...
}
//Binder驱动程序分配给进程的内核缓冲区同时，
//映射了用户的内核地址、用户空间地址
tr.data_size = t->buffer->data_size;
tr.offsets_size = t->buffer->offsets_size;
tr.data.ptr.buffer = (binder_uintptr_t)(
(uintptr_t)t->buffer->data +
proc->user_buffer_offset);
//直接操作offsets
tr.data.ptr.offsets = tr.data.ptr.buffer +
ALIGN(t->buffer->data_size,
sizeof(void *));
//提供一个返回协议数据的缓冲区
if (put_user(cmd, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
if (copy_to_user(ptr, &tr, sizeof(tr)))
return -EFAULT;
ptr += sizeof(tr);
...
list_del(&t->work.entry);
t->buffer->allow_user_free = 1;
//cmd = BR_TRANSACTION && 不是正在处理异步通信请求
//就需要等待该同步进程通信完以后再进行下一步的操作
if (cmd == BR_TRANSACTION && !(t->flags & TF_ONE_WAY)) {
t->to_parent = thread->transaction_stack;
t->to_thread = thread;
thread->transaction_stack = t;
} else {
t->buffer->transaction = NULL;
kfree(t);
binder_stats_deleted(BINDER_STAT_TRANSACTION);
}
break;
}
...
return 0
}
- 这里实际上是返回一个BR_TRANSACTION协议，并且将之前通过binder_transaction传输的数据封装到binder_transaction_data中，由于在service_manager启动中，进入binder_loop时候指定的函数引用为svcmgr_handler,binder_loop中会循环通过ioctl控制命令去与内核交互数据，binder_parse用于解析数据
platform/frameworks/native/cmds/servicemanager/binder.c
int binder_parse(struct binder_state *bs, struct binder_io *bio,
uintptr_t ptr, size_t size, binder_handler func)
{
int r = 1;
uintptr_t end = ptr + (uintptr_t) size;
while (ptr < end) {
uint32_t cmd = *(uint32_t *) ptr;
ptr += sizeof(uint32_t);
...
case BR_TRANSACTION: {
struct binder_transaction_data *txn =
(struct binder_transaction_data *) ptr;
...
if (func) {
unsigned rdata[256/4];
struct binder_io msg;
struct binder_io reply;
int res;
bio_init(&reply, rdata, sizeof(rdata), 4);
bio_init_from_txn(&msg, txn);
//调用svcmgr_handler去处理
res = func(bs, txn, &msg, &reply);
if (txn->flags & TF_ONE_WAY) {
binder_free_buffer(bs, txn->data.ptr.buffer);
} else {
//返回注册的结果给binder驱动
binder_send_reply(bs, &reply,
txn->data.ptr.buffer, res);
}
}
break;
}
}
- 这其中有三个结构体binder_io主要存储数据传输，定义如下:
struct binder_io
{
char *data; /* pointer to read/write from */
binder_size_t *offs; /* array of offsets */
size_t data_avail; /* bytes available in data buffer */
size_t offs_avail; /* entries available in offsets array */
char *data0; /* start of data buffer */
binder_size_t *offs0; /* start of offsets buffer */
uint32_t flags;
uint32_t unused;
};
- binder_parse中先通过bio_init去初始化reply，然后通过bio_init_from_txn去初始化msg，就是数据对齐的过程及flag设置，这里不再细述
-
我们重点关注func,也就是svcmgr_handler，先来回顾前面数据那张图
@writeTransactionData|center
- 接下来再来看svvmgr_handler的实现
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'
};
...
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;
...
strict_policy = bio_get_uint32(msg);
s = bio_get_string16(msg, &len);
...
//svcmgr_id校验,是否为“android.os.IServiceManager”
if ((len != (sizeof(svcmgr_id) / 2)) ||
memcmp(svcmgr_id, s, sizeof(svcmgr_id))) {
fprintf(stderr,"invalid id %s\n", str8(s, len));
return -1;
}
...
switch(txn->code) {
...
//枚举值对应ADD_SERVICE_TRANSACTION
case SVC_MGR_ADD_SERVICE:
s = bio_get_string16(msg, &len);
if (s == NULL) {
return -1;
}
//取出binder_引用对象的句柄值
handle = bio_get_ref(msg);
allow_isolated = bio_get_uint32(msg) ? 1 : 0;
dumpsys_priority = bio_get_uint32(msg);
if (do_add_service(bs, s, len, handle,
txn->sender_euid, allow_isolated, dumpsys_priority,
txn->sender_pid))
return -1;
break;
}
...
bio_put_uint32(reply, 0);
return 0;
}
- 从msg中取出对应的Service的handle、name，然后调用do_add__service去执行后续的操作
- 看do_add_service之前我们先来看一个结构体svcinfo
struct svcinfo
{
//指向下一个引用
struct svcinfo *next;
//句柄值
uint32_t handle;
//死亡代理通知
struct binder_death death;
int allow_isolated;
uint32_t dumpsys_priority;
size_t len;
//服务名称
uint16_t name[0];
};
- 在ServiceManager中每一个服务对应一个svcinfo结构体
- 接下来我们看do_add_service的实现
int do_add_service(struct binder_state *bs, const uint16_t *s,
size_t len, uint32_t handle, uid_t uid, int allow_isolated,
uint32_t dumpsys_priority, pid_t spid) {
//存储要注册的服务信息
struct svcinfo *si;
...
//检查权限
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;
}
/先去找这个服务
si = find_svc(s, len);
if (si) {
if (si->handle) {
...
svcinfo_death(bs, si);
}
si->handle = handle;
} else {
//注册服务
si = malloc(sizeof(*si) + (len + 1) * sizeof(uint16_t));
...
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->dumpsys_priority = dumpsys_priority;
//绑定到svclist中
si->next = svclist;
svclist = si;
}
//增加引用，避免被销毁
binder_acquire(bs, handle);
//绑定死亡通知
binder_link_to_death(bs, handle, &si->death);
return 0;
}
- 这里先检查Service是否有注册权限(不同版本内核加固调用不同，感兴趣可以查看selinux)，然后先去尝试查找这个服务存在不，如果不存在就分配一个新的struct svcinfo，并将其挂到svclist中，由此可见在service_manager中是维护这一个所有Service组件信息的svclist的
- 回到binder_parse中,接下来会调用binder_send_reply向Binder驱动发送一个BC_REPLY
void binder_send_reply(struct binder_state *bs,
struct binder_io *reply,
binder_uintptr_t buffer_to_free,
int status)
{
//匿名结构体
struct {
uint32_t cmd_free;
binder_uintptr_t buffer;
uint32_t cmd_reply;
struct binder_transaction_data txn;
} __attribute__((packed)) data;
data.cmd_free = BC_FREE_BUFFER;
data.buffer = buffer_to_free;
data.cmd_reply = BC_REPLY;
data.txn.target.ptr = 0;
data.txn.cookie = 0;
data.txn.code = 0;
if (status) {
//通信中产生了错误
data.txn.flags = TF_STATUS_CODE;
data.txn.data_size = sizeof(int);
data.txn.offsets_size = 0;
data.txn.data.ptr.buffer = (uintptr_t)&status;
data.txn.data.ptr.offsets = 0;
} else {
//成功处理的一次通信请求
data.txn.flags = 0;
data.txn.data_size = reply->data - reply->data0;
data.txn.offsets_size = ((char*) reply->offs) - ((char*) reply->offs0);
data.txn.data.ptr.buffer = (uintptr_t)reply->data0;
data.txn.data.ptr.offsets = (uintptr_t)reply->offs0;
}
//向Binder驱动写入数据
binder_write(bs, &data, sizeof(data));
}
- 这里会将进程通信结果写入到匿名struct data中，然后调用binder_write去向内核写入BC_FREE_BUFFER\BC_REPLY命令协议
int binder_write(struct binder_state *bs, void *data, size_t len)
{
struct binder_write_read bwr;
int res;
bwr.write_size = len;
bwr.write_consumed = 0;
bwr.write_buffer = (uintptr_t) data;
bwr.read_size = 0;
bwr.read_consumed = 0;
bwr.read_buffer = 0;
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);
if (res < 0) {
fprintf(stderr,"binder_write: ioctl failed (%s)\n",
strerror(errno));
}
return res;
}
- binder_write实际上还是通过IO控制命令写入一个binder_write_read结构体，注意这个结构体输入缓冲区是没有数据的，也就是说不需要处理返回协议
- 略过各种调用我们来看内核中binder_thread_write对于BC_FREE_BUFFER\BC_REPLY的处理
platform/drivers/staging/android/binder.c
static int binder_thread_write(struct binder_proc *proc,
struct binder_thread *thread,
binder_uintptr_t binder_buffer, size_t size,
binder_size_t *consumed)
{
uint32_t cmd;
void __user *buffer = (void __user *)(uintptr_t)binder_buffer;
void __user *ptr = buffer + *consumed;
void __user *end = buffer + size;
while (ptr < end && thread->return_error == BR_OK) {
if (get_user(cmd, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
...
switch (cmd) {
...
case BC_TRANSACTION:
case BC_REPLY: {
struct binder_transaction_data tr;
if (copy_from_user(&tr, ptr, sizeof(tr)))
return -EFAULT;
ptr += sizeof(tr);
binder_transaction(proc, thread, &tr, cmd == BC_REPLY);
break;
}
...
}
- BC_FREE_BUFFER主要是做一些资源释放的操作，感兴趣可以自己看这里不再细看
- 重点看BC_REPLY,查看binder_transaction的处理
static void binder_transaction(struct binder_proc *proc,
struct binder_thread *thread,
struct binder_transaction_data *tr, int reply)
{
...
struct binder_transaction *t;
struct binder_work *tcomplete;
binder_size_t *offp, *off_end;
binder_size_t off_min;
struct binder_proc *target_proc;
struct binder_thread *target_thread = NULL;
struct binder_node *target_node = NULL;
struct list_head *target_list;
wait_queue_head_t *target_wait;
struct binder_transaction *in_reply_to = NULL;
struct binder_transaction_log_entry *e;
uint32_t return_error;
...
if (reply) {
//寻找请求通信的thread
//从之前的thread中取出通信的binder_transaction_data
in_reply_to = thread->transaction_stack;
if (in_reply_to == NULL) {
...
return_error = BR_FAILED_REPLY;
goto err_empty_call_stack;
}
//恢复线程优先级
binder_set_nice(in_reply_to->saved_priority);
if (in_reply_to->to_thread != thread) {
...
return_error = BR_FAILED_REPLY;
in_reply_to = NULL;
goto err_bad_call_stack;
}
thread->transaction_stack = in_reply_to->to_parent;
target_thread = in_reply_to->from;
if (target_thread == NULL) {
return_error = BR_DEAD_REPLY;
goto err_dead_binder;
}
if (target_thread->transaction_stack != in_reply_to) {
...
return_error = BR_FAILED_REPLY;
in_reply_to = NULL;
target_thread = NULL;
goto err_dead_binder;
}
//目标进程
target_proc = target_thread->proc;
}else{
...
}
//有空闲线程就是用空间线程的等待队列，否则使用进程的
if (target_thread) {
...
target_list = &target_thread->todo;
target_wait = &target_thread->wait;
} else {
...
}
...
//创建binder_transaction结构体，BINDER_WORK_TRANSACTION
t = kzalloc(sizeof(*t), GFP_KERNEL);
...
//创建binder_work结构体,BINDER_STAT_TRANSACTION_COMPLETE
tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL);
...
//分配事务t的要进入那个栈
if (reply) {
BUG_ON(t->buffer->async_transaction != 0);
//将事务弹出todo栈
binder_pop_transaction(target_thread, in_reply_to);
} else if (!(t->flags & TF_ONE_WAY)) {
...
}else{
...
}
//将binder_transaction_data指针t的类型修改为BINDER_WORK_TRANSACTION
t->work.type = BINDER_WORK_TRANSACTION;
//添加到target_list队列尾部
list_add_tail(&t->work.entry, target_list);
//将binder_work指针tcomplete.type置为BINDER_WORK_TRANSACTION_COMPLETE
tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
list_add_tail(&tcomplete->entry, &thread->todo);
//这里有两个执行分支
//1.处理类型为BINDER_WORK_TRANSACTION的binder_transaction_data
//2.处理类型为BINDER_WORK_TRANSACTION_COMPLETE的binder_work
if (target_wait)
wake_up_interruptible(target_wait);
return;
...
}
- 这里跟只爱去哪调用不同的地方在于走的是if分支，需要查找到之前通信的目标线程及进程，然后将上次通信的binder_transaction弹栈，然后回想之前通信的进程发送一个type为BINDER_WORK_TRANSACTION的binder_work，之前那个进程对应的binder_thread_read处理如下:
static int binder_thread_read(struct binder_proc *proc,
struct binder_thread *thread,
binder_uintptr_t binder_buffer, size_t size,
binder_size_t *consumed, int non_block)
{
void __user *buffer = (void __user *)(uintptr_t)binder_buffer;
void __user *ptr = buffer + *consumed;
void __user *end = buffer + size;
int ret = 0;
...
//线程唤醒
while (1) {
uint32_t cmd;
struct binder_transaction_data tr;
struct binder_work *w;
struct binder_transaction *t = NULL;
//检查工作队列，并将待处理项赋值给w
if (!list_empty(&thread->todo)) {
w = list_first_entry(&thread->todo, struct binder_work,
entry);
} else if (!list_empty(&proc->todo) && wait_for_proc_work) {
w = list_first_entry(&proc->todo, struct binder_work,
entry);
} else {
...
}
...
switch (w->type) {
case BINDER_WORK_TRANSACTION: {
t = container_of(w, struct binder_transaction, work);
} break;
...
}
//返回协议的处理，现在target_node指向的是binder_context_mgr_node
if (t->buffer->target_node) {
...
}else{
tr.target.ptr = 0;
tr.cookie = 0;
cmd = BR_REPLY;
}
//Binder驱动程序分配给进程的内核缓冲区同时，映射了用户的内核地址、用户空间地址
tr.data_size = t->buffer->data_size;
tr.offsets_size = t->buffer->offsets_size;
tr.data.ptr.buffer = (binder_uintptr_t)(
(uintptr_t)t->buffer->data +
proc->user_buffer_offset);
//直接操作offsets
tr.data.ptr.offsets = tr.data.ptr.buffer +
ALIGN(t->buffer->data_size,
sizeof(void *));
//提供一个返回协议数据的缓冲区
if (put_user(cmd, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
if (copy_to_user(ptr, &tr, sizeof(tr)))
return -EFAULT;
ptr += sizeof(tr);
...
//cmd = BR_TRANSACTION && 不是正在处理异步通信请求
//就需要等待该同步进程通信完以后再进行下一步的操作
if (cmd == BR_TRANSACTION && !(t->flags & TF_ONE_WAY)) {
...
} else {
t->buffer->transaction = NULL;
kfree(t);
binder_stats_deleted(BINDER_STAT_TRANSACTION);
}
break;
}
...
}
- 这里就会封装一个BR_REPLY返回协议，然后返回到IPCThreadState::waitForResponse中
- 接下来看IPCThreadState::waitForResponse对于BR_REPLY的处理
status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{
uint32_t cmd;
...
while (1) {
...
cmd = (uint32_t)mIn.readInt32();
...
switch (cmd) {
case BR_REPLY:
{
binder_transaction_data tr;
err = mIn.read(&tr, sizeof(tr));
...
if (reply) {
if ((tr.flags & TF_STATUS_CODE) == 0) {
//重置Parcel对象内部数据缓冲区，并指定释放函数为freeBuffer
reply->ipcSetDataReference(
reinterpret_cast
<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast
<const binder_size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(binder_size_t),
freeBuffer, this);
} else {
...
} else {
...
}
}
goto finish;
...
}
}
...
}
- 实际上会调用reply->ipcSetDataReference去重置数据缓冲区，这里不再细述，整个Service注册就大致完成了，后续还有Binder线程的启动感兴趣可以自行查看
ServiceManager查找服务
@Service的查找流程|center
完整的通信流程
@完整的通信流程
