Binder
Binder是什么？
- Binder是一種進程間通信機制
為什么是Binder？
Binder架構
-
Binder通信機制采用C/S架構，這很重要！！！
@Binder架構|center - Binder框架中主要涉及到4個角色Client、Server、Service Manager及Binder驅動，其中Client、Server、Service Manager運行在用戶空間，Binder驅動運行在內核空間
- Client代表客戶端進程，Server代表客戶端進程提供各種服務，如音視頻等
- Service Manager用來管理各種系統服務
- Binder驅動提供進程間通信的能力
- 用戶空間的Client、Server、ServiceManager通過open、mmap和ioctl等標準文件操作(詳見Unix環境編程)來訪問/dev/binder，進而實現進程間通信
基礎數據結構
Binder基礎數據
關于Binder基礎數據，見上圖
Binder驅動
Binder驅動工作圖
/kernel/drivers/staging/android/binder.c
device_initcall(binder_init);
設備初始化時候會調用binder_init進行binder驅動初始化
/kernel/drivers/staging/android/binder.c
//綁定binder驅動操作函數
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,
};
//創建misc類型的驅動
static struct miscdevice binder_miscdev = {
.minor = MISC_DYNAMIC_MINOR,
.name = "binder",
.fops = &binder_fops//綁定binder驅動操作函數
};
//binder驅動初始化
static int __init binder_init(void)
{
int ret;
binder_deferred_workqueue = create_singlethread_workqueue("binder");
if (!binder_deferred_workqueue)
return -ENOMEM;
//創建目錄/binder
binder_debugfs_dir_entry_root = debugfs_create_dir("binder", NULL);
if (binder_debugfs_dir_entry_root)
//創建目錄/binder/proc
binder_debugfs_dir_entry_proc = debugfs_create_dir("proc",
binder_debugfs_dir_entry_root);
//注冊binder驅動
ret = misc_register(&binder_miscdev);
//創建其他文件
if (binder_debugfs_dir_entry_root) {
//創建文件/binder/proc/state
debugfs_create_file("state",
S_IRUGO,
binder_debugfs_dir_entry_root,
NULL,
&binder_state_fops);
//創建文件/binder/proc/stats
debugfs_create_file("stats",
S_IRUGO,
binder_debugfs_dir_entry_root,
NULL,
&binder_stats_fops);
//創建文件/binder/proc/transactions
debugfs_create_file("transactions",
S_IRUGO,
binder_debugfs_dir_entry_root,
NULL,
&binder_transactions_fops);
//創建文件/binder/proc/transaction_log
debugfs_create_file("transaction_log",
S_IRUGO,
binder_debugfs_dir_entry_root,
&binder_transaction_log,
&binder_transaction_log_fops);
//創建文件/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;
}
初始化主要做了兩件事情
- 初始化存儲binder存儲信息的目錄
- 創建binder設備，并綁定操作函數如binder_open、binder_mmap、binder_ioctl等
- 設備啟動時候，會調用binder_init，主要做兩件事情
- 1.創建/binder/proc目錄，之后在這個目錄下創建state、stats、transactions、transaction_log、failed_transaction_log文件夾，分別存儲進程通信的各種數據
- 2.注冊驅動，并綁定文件操作函數binder_open、binder_mmap、binder_ioctl等，之后就可以通過RPC機制去訪問binder驅動
Native層級的Binder結構
@Server組件類圖|center
@Client組件類圖|center
Binder通信機制
@Binder分層|center
Binder進程與線程
@Binder驅動中的線程與用戶空間的線程
ServiceManager啟動
@ServiceManager啟動
預備知識補充
ServiceManager啟動流程主要分為三個流程
1.以系統服務形式啟動service_manager,之后通過在binder_open函數打開驅動設備，驅動層相應的就會創建service_manager對應的binder_proc，并且這是個特殊的service
2.調用binder_become_context_manager通過ioctl調用內核中的binder_ioctl,經過一系列處理后，binder驅動會將這個特殊的binder_node存到靜態指針binder_context_mgr_node
static struct binder_node *binder_context_mgr_node;
...
static int binder_ioctl_set_ctx_mgr(struct file *filp)
{
...
//注意這里后續兩個參數都是0
binder_context_mgr_node = binder_new_node(proc, 0, 0);
...
}
...
3.調用binder_loop進入循環解析的過程
int main(int argc, char** argv){
...
//進入循環，等待或處理Client進程的通信請求
binder_loop(bs, svcmgr_handler);
...
}
這里指定循環處理函數為svcmgr_handler,后續再仔細分析這個函數，先看binder_loop實現
void binder_loop(struct binder_state *bs, binder_handler func)
{
...
//通信數據
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;
}
- 首先創建一個binder_write_read結構體，然后通過binder_write向Binder驅動寫入命令協議BC_ENTER_LOOPER，注意這個理輸出緩沖區是沒有數據的,binder驅動經過一系列處理進入循環狀態，之后通過一個死循環來不斷的從Binder驅動讀取數據，之后交由binder_parse去解析各種協議數據，后續再分析細節
- Binder驅動是如何處理交互細節的，我們來看下binder_ioctl_write_read的實現
static int binder_ioctl_write_read(struct file *filp,
unsigned int cmd, unsigned long arg,
struct binder_thread *thread)
{
...
//從文件句柄取出進程信息
struct binder_proc *proc = filp->private_data;
//命令協議
unsigned int size = _IOC_SIZE(cmd);
...
struct binder_write_read bwr;
//取出bwr進程通信協議載體
if (copy_from_user(&bwr, ubuf, sizeof(bwr))) {
...
}
//如果有寫入數據，就交由binder_thread_write去處理，之后
//通過copy_to_user將數據返還給用戶空間
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;
}
}
//如果有輸出數據，則調用binder_thread_read解析，
//之后判斷進程的事務隊里是否為空，如果不為空就等待執行
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) {
//將寫出數據返還給用戶空間
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
...
goto out;
}
}
...
out:
return ret;
}
- 至于binder_thread_write與binder_thread_read則是處理命令協(binder_driver_command_protocol)與返回協議(binder_driver_return_protocol )詳見/drivers/staging/android/binder.h
ServiceManager注冊服務
@Service的注冊流程|center
- service的注冊流程如上圖，這里以media_server的注冊為例子去看代碼
/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
- 可以看到以用戶權限啟動mediadrm服務，文件位于/system/bin/mediadrmserver
- 接下來看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()中主要做了兩件事情：
1.初始化MediaDrmService
2.線程池初始化
先看第一個
/frameworks/av/services/mediadrm/MediaDrmService.cpp
...
void MediaDrmService::instantiate() {
defaultServiceManager()->addService(
String16("media.drm"), new MediaDrmService());
}
...
- 這里面主要通過defaultServiceManager()獲取一個BpServiceManager指針然后調用addService，注意這里傳入的兩個參數“media.drm”和一個MediaDrmService對象
ServiceManager代理對象的獲取
- 先來看defaultServiceManager()調用
/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就是一個IServiceManger的指針
- 首次獲取時候一定是通過interface_cast<IServiceManager>(ProcessState::self()->getContextObject(NULL))這一系列method調用獲取的，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;
}
//注意這里的文件name
gProcess = new ProcessState("/dev/binder");
return gProcess;
}
...
- 我賭半包辣條，這個類構造一定持有打開/dev/binder的句柄，不信你看構造聲明
//這里是cpp構造函數形式，就是成員變量賦值
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.
//注意這里分配的BINDER_VM_SIZE為1016kb，具體見宏定義處
mVMStart = mmap(0, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE | MAP_NORESERVE, mDriverFD, 0);
if (mVMStart == MAP_FAILED) {
...
close(mDriverFD);
mDriverFD = -1;
mDriverName.clear();
}
}
...
}
- 再來看getContextObject
sp<IBinder> ProcessState::getContextObject(const sp<IBinder>& /*caller*/)
{
//注意這里傳入的值為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()內部是調用getStrongProxyForHandle(0)來獲取一個IBinder指針(這里0其實就是為了后續查找之前ServiceManager啟動注冊那個特殊的Service組件)，可以看到其實這里創建的是一個BpBinder對象，并且他的句柄值是0
- 我們來看BpBinder的相關調用
frameworks/native/libs/binder/BpBinder.cpp
//handle句柄值 與binder驅動中的binder引用對象進行關聯
BpBinder::BpBinder(int32_t handle, int32_t trackedUid)
//注意這里傳入的是0
: mHandle(handle)
//注意這個值為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))實際上轉換成了這個，這個在哪里定義呢？
/frameworks/native/include/binder/IInterface.h
template<typename INTERFACE>
inline sp<INTERFACE> interface_cast(const sp<IBinder>& obj)
{
return INTERFACE::asInterface(obj);
}
- 發現他是個內聯模板函數，實際上調用的是IServiceManager::asInterface(BpBinder(0))，那么IServiceManager::asInterface在哪里定義呢？
/frameworks/native/libs/binder/IServiceManager.cpp
IMPLEMENT_META_INTERFACE(ServiceManager, "android.os.IServiceManager");
看上面這個宏定義，實際定義在
/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() { }
- 帶入轉換下，發現我們拿到的其實就是一個BpServiceManager
- 接下來我們來看后續的調用
BpServiceManager#addService
virtual status_t addService(const String16& name, const sp<IBinder>& service,bool allowIsolated, int dumpsysPriority) {
//這里data表示要寫入的數據，reply表示返回的數據
Parcel data, reply;
//存儲描述符"android.os.IServiceManager"
data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
//存儲服務名字"media.drm"
data.writeString16(name);
//存儲服務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;
}
- 這里實際上把上一步傳入的數據通過Parcel存起來，然后調用remote()獲取一個BpBinder然后調用其transact，傳入的code為ADD_SERVICE_TRANSACTION，經過包裝后data中的數據長這樣子
- @Parcel數據封裝|center
- 記下來我們去看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.
//構造中mAlive=1，所以這里會走進if
if (mAlive) {
//這里調用的是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代理對象獲取BpBinder時候，mHandle為0，code為ADD_SERVICE_TRANSACTION，data存儲binder信息，reply存儲要返回的信息，flags查看method定義默認參數為0
- 接下來分析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;
//允許返回中攜帶文件描述符
flags |= TF_ACCEPT_FDS;
...
//封裝BC_TRANSACTION通信請求
err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);
...
//同步or異步，這里是同步調用
if ((flags & TF_ONE_WAY) == 0) {
...
if (reply) {
//向Binder驅動發起BC_TRANSACTION
err = waitForResponse(reply);
} else {
Parcel fakeReply;
err = waitForResponse(&fakeReply);
...
}
...
}else{
err = waitForResponse(NULL, NULL);
}
return err;
}
- 上面首先將flags與TF_ACCEPT_FDS做或操作，表示接收文件描述符
- 之后調用writeTransactionData將數據封裝成一個BC_TRANSACTION命令協議,這里是同步調用切需要返回，所以執行到的是waitForResponse(reply)，接下來分別來看writeTransactionData、waitForResponse的實現
status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags,
int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer)
{
//對應內核中要求io攜帶binder_transaction_data結構體
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;
}
- 這里主要是創建一個binder_transaction_data，初其始化后將要傳輸的數據寫入到mOut緩沖區中，最終整個數據長這樣子
- @writeTransactionData|center
- 數據封裝完成以后，我們來看waitForResponse的實現
status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{
uint32_t cmd;
int32_t err;
while (1) {
if ((err=talkWithDriver()) < NO_ERROR) break;
...
//從輸出緩沖區取出返回協議命令
cmd = (uint32_t)mIn.readInt32();
...
}
...
return err;
}
- 這里可以是一個死循環，不斷的通過talkWithDriver去跟binder驅動通信，然后從輸出緩沖區中取出返回協議然后處理返回協議，這里先不看具體的協議處理，先來看talkWithDriver的實現
//默認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{
...
//這里通過io想驅動寫入一個binder_write_read結構體
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;
}
- 這里主要通過io控制命令向Binder驅動寫入一個type為BINDER_WRITE_READ，data為binder_write_read，其輸出緩沖區為前面mOut中寫入的數據
- 接下來的操作就轉到Binder驅動中進行了，需要記住，Clinet進程此時執行到的位置
/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);
...
//這里根據進程找到對應的thread，如果沒找到就創建一個
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驅動中對應的binder_ioctl()會調用，之后會處理cmd為BINDER_WRITE_READ的分支，之后會調用到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;
//從文件描述符中取出進程地址
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校驗
if (size != sizeof(struct binder_write_read)) {
ret = -EINVAL;
goto out;
}
//從用戶空間中取出binder_write_read結構體
if (copy_from_user(&bwr, ubuf, sizeof(bwr))) {
ret = -EFAULT;
goto out;
}
...
//輸出緩沖區有數據就處理輸出緩沖區
if (bwr.write_size > 0) {
//這里是真正處理輸出緩沖數據的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;
}
}
//輸入緩沖區有數據就處理輸入緩沖區
if (bwr.read_size > 0) {
//這里是真正處理輸出緩沖數據的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);
//如果進程todo隊里不為空，說明有事務正在處理，需要等待處理
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;
}
}
...
//將數據copy回用戶空間
if (copy_to_user(ubuf, &bwr, sizeof(bwr))) {
ret = -EFAULT;
goto out;
}
out:
return ret;
}
- 前面調用可知，輸出緩沖區是有數據，輸入緩沖區是沒有數據的，所以上面方法執行流程應該是，先調用binder_thread_write去處理輸出緩沖區
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) {
//根據cmd取出消費的數據偏移地址
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;
}
- 這里是取出cmd，然后處理BC_TRANSACTION時候，再講binder_transaction_data取出，之后交由binder_transaction去處理
- binder_transaction比較長，其實主要分為三個部分
- 1.初始化目標線程進程
- 2.封裝返回數據binder_transaction_data
- 3.為binder_transaction_data分配合適的線程or進程
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，否則走else分支，這里走else
if (reply) {
...
}else{
//根據句柄找對應的binder_ref、binder_node
if (tr->target.handle) {
struct binder_ref *ref;
ref = binder_get_ref(proc, tr->target.handle);
...
else{
//handle=0，則需要找指向service_manager的binder_node
target_node = binder_context_mgr_node;
...
}
...
//根據binder_node找到對應的進程binder_proc，這里也就是service_manager
target_proc = target_node->proc;
...
//如果是同步請求，嘗試尋找一個在等待其他事物執行的線程，tips優化調度
if (!(tr->flags & TF_ONE_WAY) && thread->transaction_stack) {
struct binder_transaction *tmp;
tmp = thread->transaction_stack;
...
//找到一個等待別的事務完成的依賴線程
while (tmp) {
if (tmp->from && tmp->from->proc == target_proc)
target_thread = tmp->from;
tmp = tmp->from_parent;
}
}
}
//有空閑線程就是用空閑線程的等待隊列，否則使用進程的事物隊列
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;
}
...
//創建binder_transaction結構體，BINDER_WORK_TRANSACTION
//用于向目標進程發送數據
t = kzalloc(sizeof(*t), GFP_KERNEL);
...
binder_stats_created(BINDER_STAT_TRANSACTION);
...
//創建binder_work結構體,BINDER_STAT_TRANSACTION_COMPLETE
//便于向源進程返回數據處理結果
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);
//目標進程
t->to_proc = target_proc;
//目標線程
t->to_thread = target_thread;
//code ADD_SERVICE_TRANSACTION
t->code = tr->code;
//flag = TF_ACCEPT_FLAGS
t->flags = tr->flags;
//優先級
t->priority = task_nice(current);
...
//緩沖區
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;
...
//為t分配內核緩沖區
if (target_node)
binder_inc_node(target_node, 1, 0, NULL);
offp = (binder_size_t *)(t->buffer->data +
ALIGN(tr->data_size, sizeof(void *)));
//數據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;
}
...
//處理Binder請求，內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;
...
//前面存儲的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);
//如果是首次就創建新的binder_node
if (node == NULL) {
node = binder_new_node(proc, fp->binder, fp->cookie);
...
//設定線程優先級
node->min_priority = fp->flags & FLAT_BINDER_FLAG_PRIORITY_MASK;
//設置是否接收文件描述符
node->accept_fds = !!(fp->flags & FLAT_BINDER_FLAG_ACCEPTS_FDS);
}
...
//如果是首次就創建對應的binder_ref對象
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;
//設置句柄
fp->handle = ref->desc;
//增加binder_ref的引用計數
binder_inc_ref(ref, fp->type == BINDER_TYPE_HANDLE,
&thread->todo);
...
}break;
...
}
}
//分配事務t的要進入那個棧
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;
}
//將binder_transaction_data指針t的類型修改為BINDER_WORK_TRANSACTION
t->work.type = BINDER_WORK_TRANSACTION;
//添加到target_list隊列尾部
list_add_tail(&t->work.entry, target_list);
//將binder_work指針tcomplete.type置為BINDER_WORK_TRANSACTION_COMPLETE
tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
list_add_tail(&tcomplete->entry, &thread->todo);
//這里有兩個執行分支
//1.處理類型為BINDER_WORK_TRANSACTION的binder_transaction_data
//2.處理類型為BINDER_WORK_TRANSACTION_COMPLETE的binder_work
if (target_wait)
wake_up_interruptible(target_wait);
return;
...
}
- 經過上面func以后，binder驅動中就會為MediaDrmService創建對應的binder_node并加入到整個Binder實體對象的紅黑樹中，接著會分別向Client進程、ServiceManager發送一個BINDER_WORK_TRANSACTION_COMPLETE的binder_work及BINDER_WORK_TRANSACTION的binder_transaction
- 至此，源線程thread、target_proc或者target_thread會并發的去執行各自todo隊列中的任務
- 先來看源線程,回到binder_ioctl_write_read中，接下來要處理輸入緩沖區，對應的調用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;
...
//線程喚醒
while (1) {
uint32_t cmd;
struct binder_transaction_data tr;
struct binder_work *w;
struct binder_transaction *t = NULL;
//檢查工作隊列，并將待處理項賦值給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);
...
//刪除binder_work，并釋放資源
list_del(&w->entry);
kfree(w);
binder_stats_deleted(BINDER_STAT_TRANSACTION_COMPLETE);
} break;
}
done:
*consumed = ptr - buffer;
...
return 0;
}
- 這里返回一個BR_TRANSACTION_COMPLETE協議，之后會經過一些列調用會回到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對于BR_TRANSACTION_COMPLETE處理比較簡單，就直接返回了
- 我們來看下target_proc即ServiceManager是怎么接收處理BINDER_WORK_TRANSACTION類型的binder_transaction的，假設ServiceManager之前沒有通信，那么他就在Binder驅動中一直等待事務的到來，現在有事務了那么對應的就會調用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;
...
//線程喚醒
while (1) {
uint32_t cmd;
struct binder_transaction_data tr;
struct binder_work *w;
struct binder_transaction *t = NULL;
//檢查工作隊列，并將待處理項賦值給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;
...
}
//返回協議的處理，現在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;
//保存原本的線程優先級，便于后續恢復
t->saved_priority = task_nice(current);
//修改binder驅動中對應proc的線程優先級（模擬Client進程的線程優先級）
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 {
...
}
//拷貝code與flags，
//注冊服務過程中這里是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驅動程序分配給進程的內核緩沖區同時，
//映射了用戶的內核地址、用戶空間地址
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 *));
//提供一個返回協議數據的緩沖區
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 && 不是正在處理異步通信請求
//就需要等待該同步進程通信完以后再進行下一步的操作
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
}
- 這里實際上是返回一個BR_TRANSACTION協議，并且將之前通過binder_transaction傳輸的數據封裝到binder_transaction_data中，由于在service_manager啟動中，進入binder_loop時候指定的函數引用為svcmgr_handler,binder_loop中會循環通過ioctl控制命令去與內核交互數據，binder_parse用于解析數據
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);
//調用svcmgr_handler去處理
res = func(bs, txn, &msg, &reply);
if (txn->flags & TF_ONE_WAY) {
binder_free_buffer(bs, txn->data.ptr.buffer);
} else {
//返回注冊的結果給binder驅動
binder_send_reply(bs, &reply,
txn->data.ptr.buffer, res);
}
}
break;
}
}
- 這其中有三個結構體binder_io主要存儲數據傳輸，定義如下:
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中先通過bio_init去初始化reply，然后通過bio_init_from_txn去初始化msg，就是數據對齊的過程及flag設置，這里不再細述
-
我們重點關注func,也就是svcmgr_handler，先來回顧前面數據那張圖
@writeTransactionData|center - 接下來再來看svvmgr_handler的實現
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校驗,是否為“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) {
...
//枚舉值對應ADD_SERVICE_TRANSACTION
case SVC_MGR_ADD_SERVICE:
s = bio_get_string16(msg, &len);
if (s == NULL) {
return -1;
}
//取出binder_引用對象的句柄值
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;
}
- 從msg中取出對應的Service的handle、name，然后調用do_add__service去執行后續的操作
- 看do_add_service之前我們先來看一個結構體svcinfo
struct svcinfo
{
//指向下一個引用
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;
//服務名稱
uint16_t name[0];
};
- 在ServiceManager中每一個服務對應一個svcinfo結構體
- 接下來我們看do_add_service的實現
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) {
//存儲要注冊的服務信息
struct svcinfo *si;
...
//檢查權限
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;
}
/先去找這個服務
si = find_svc(s, len);
if (si) {
if (si->handle) {
...
svcinfo_death(bs, si);
}
si->handle = handle;
} else {
//注冊服務
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;
//綁定到svclist中
si->next = svclist;
svclist = si;
}
//增加引用，避免被銷毀
binder_acquire(bs, handle);
//綁定死亡通知
binder_link_to_death(bs, handle, &si->death);
return 0;
}
- 這里先檢查Service是否有注冊權限(不同版本內核加固調用不同，感興趣可以查看selinux)，然后先去嘗試查找這個服務存在不，如果不存在就分配一個新的struct svcinfo，并將其掛到svclist中，由此可見在service_manager中是維護這一個所有Service組件信息的svclist的
- 回到binder_parse中,接下來會調用binder_send_reply向Binder驅動發送一個BC_REPLY
void binder_send_reply(struct binder_state *bs,
struct binder_io *reply,
binder_uintptr_t buffer_to_free,
int status)
{
//匿名結構體
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) {
//通信中產生了錯誤
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 {
//成功處理的一次通信請求
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驅動寫入數據
binder_write(bs, &data, sizeof(data));
}
- 這里會將進程通信結果寫入到匿名struct data中，然后調用binder_write去向內核寫入BC_FREE_BUFFER\BC_REPLY命令協議
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實際上還是通過IO控制命令寫入一個binder_write_read結構體，注意這個結構體輸入緩沖區是沒有數據的，也就是說不需要處理返回協議
- 略過各種調用我們來看內核中binder_thread_write對于BC_FREE_BUFFER\BC_REPLY的處理
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主要是做一些資源釋放的操作，感興趣可以自己看這里不再細看
- 重點看BC_REPLY,查看binder_transaction的處理
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) {
//尋找請求通信的thread
//從之前的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;
}
//恢復線程優先級
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;
}
//目標進程
target_proc = target_thread->proc;
}else{
...
}
//有空閑線程就是用空間線程的等待隊列，否則使用進程的
if (target_thread) {
...
target_list = &target_thread->todo;
target_wait = &target_thread->wait;
} else {
...
}
...
//創建binder_transaction結構體，BINDER_WORK_TRANSACTION
t = kzalloc(sizeof(*t), GFP_KERNEL);
...
//創建binder_work結構體,BINDER_STAT_TRANSACTION_COMPLETE
tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL);
...
//分配事務t的要進入那個棧
if (reply) {
BUG_ON(t->buffer->async_transaction != 0);
//將事務彈出todo棧
binder_pop_transaction(target_thread, in_reply_to);
} else if (!(t->flags & TF_ONE_WAY)) {
...
}else{
...
}
//將binder_transaction_data指針t的類型修改為BINDER_WORK_TRANSACTION
t->work.type = BINDER_WORK_TRANSACTION;
//添加到target_list隊列尾部
list_add_tail(&t->work.entry, target_list);
//將binder_work指針tcomplete.type置為BINDER_WORK_TRANSACTION_COMPLETE
tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
list_add_tail(&tcomplete->entry, &thread->todo);
//這里有兩個執行分支
//1.處理類型為BINDER_WORK_TRANSACTION的binder_transaction_data
//2.處理類型為BINDER_WORK_TRANSACTION_COMPLETE的binder_work
if (target_wait)
wake_up_interruptible(target_wait);
return;
...
}
- 這里跟只愛去哪調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標線程及進程，然后將上次通信的binder_transaction彈棧，然后回想之前通信的進程發送一個type為BINDER_WORK_TRANSACTION的binder_work，之前那個進程對應的binder_thread_read處理如下:
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;
...
//線程喚醒
while (1) {
uint32_t cmd;
struct binder_transaction_data tr;
struct binder_work *w;
struct binder_transaction *t = NULL;
//檢查工作隊列，并將待處理項賦值給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;
...
}
//返回協議的處理，現在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驅動程序分配給進程的內核緩沖區同時，映射了用戶的內核地址、用戶空間地址
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 *));
//提供一個返回協議數據的緩沖區
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 && 不是正在處理異步通信請求
//就需要等待該同步進程通信完以后再進行下一步的操作
if (cmd == BR_TRANSACTION && !(t->flags & TF_ONE_WAY)) {
...
} else {
t->buffer->transaction = NULL;
kfree(t);
binder_stats_deleted(BINDER_STAT_TRANSACTION);
}
break;
}
...
}
- 這里就會封裝一個BR_REPLY返回協議，然后返回到IPCThreadState::waitForResponse中
- 接下來看IPCThreadState::waitForResponse對于BR_REPLY的處理
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對象內部數據緩沖區，并指定釋放函數為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;
...
}
}
...
}
- 實際上會調用reply->ipcSetDataReference去重置數據緩沖區，這里不再細述，整個Service注冊就大致完成了，后續還有Binder線程的啟動感興趣可以自行查看
ServiceManager查找服務
@Service的查找流程|center
完整的通信流程
@完整的通信流程
