Android Binder进程间通信-登记Service组件-Client发送BC_TRANSACTION
Android Binder进程间通信---注册Service组件---Client发送BC_TRANSACTION
remote()获取BpBinder对象，调用它的成员函数transact函数，实现如下：
本文参考《Android系统源代码情景分析》，作者罗升阳
一、测试代码：
～/Android/external/binder/server
----FregServer.cpp
~/Android/external/binder/common
----IFregService.cpp
----IFregService.h
~/Android/external/binder/client
----FregClient.cpp
Binder库(libbinder)代码：
~/Android/frameworks/base/libs/binder
----BpBinder.cpp
----Parcel.cpp
----ProcessState.cpp
----Binder.cpp
----IInterface.cpp
----IPCThreadState.cpp
----IServiceManager.cpp
----Static.cpp
~/Android/frameworks/base/include/binder
----Binder.h
----BpBinder.h
----IInterface.h
----IPCThreadState.h
----IServiceManager.h
----IBinder.h
----Parcel.h
----ProcessState.h
驱动层代码：
～/Android//kernel/goldfish/drivers/staging/android
----binder.c
----binder.h
二、源码分析
上一篇文章Android Binder进程间通信---注册Service组件---封装进程间通信数据http://blog.csdn.net/jltxgcy/article/details/26059215，我们执行完了addService中封装数据部分代码，如下：
～/Android/frameworks/base/libs/binder
----IServiceManager.cpp
class BpServiceManager : public BpInterface<IServiceManager>
{
public:
.........
virtual status_t addService(const String16& name, const sp<IBinder>& service)
{
Parcel data, reply;
data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());//写入一个Binder进程间通信请求头
data.writeString16(name);//写入将要注册的Service组件的名称
data.writeStrongBinder(service);//将要注册的Service组件封装成一个flat_binder_object结构体，写入data
status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);//remote为BpBinder对象
return err == NO_ERROR ? reply.readExceptionCode() : err;
}
..........
}; 接下来调用内部的一个Binder代理对象的成员函数transact发送一个ADD_SERVICE_TRANSACTION命令协议。remote()获取BpBinder对象，调用它的成员函数transact函数，实现如下：
～/Android/frameworks/base/libs/binder
----BpBinder.cpp
status_t BpBinder::transact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)//注意data是一个引用，reply是一个指针
{
// Once a binder has died, it will never come back to life.
if (mAlive) {
status_t status = IPCThreadState::self()->transact(
mHandle, code, data, reply, flags);//每个参数的介绍在下面
if (status == DEAD_OBJECT) mAlive = 0;
return status;
}
return DEAD_OBJECT;
} 目前mHandle为0，code为ADD_SERVICE_TRANSACTION，data包含了要传递给Binder驱动程序的进程间通信数据；第三个参数reply是一个输出参数，用来保存进程间通信结果，第四个参数flags用来描述这是一个同步的进程间通信请求，还是一个异步的进程间通信请求，它是一个默认参数，默认值为0，表示这是一个同步的进程请求。
调用上文http://blog.csdn.net/jltxgcy/article/details/25953361已经创建的IPCThreadState对象的成员函数transact，实现如下：
～/Android/frameworks/base/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 = data.errorCheck();
flags |= TF_ACCEPT_FDS;//flags等于0|TF_ACCEPT_FDS
.......
if (err == NO_ERROR) {
..........
err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);//将data的内容写入到一个binder_transaction_data结构体中
}
........
if ((flags & TF_ONE_WAY) == 0) {//最后一位为0，按位与TF_ONE_WAY等于0，表示同步的进程间通信请求
..........
if (reply) {//reply不为空，是一个指针
err = waitForResponse(reply);
} else {
.........
}
..........
} else {
..........
}
return err;
} 其中， TF_ACCEPT_FDS，TF_ONE_WAY定义在一个枚举中。实现如下：
～/Android/frameworks/base/include/binder
----binder.h
enum transaction_flags {
TF_ONE_WAY = 0x01,
TF_ROOT_OBJECT = 0x04,
TF_STATUS_CODE = 0x08,
TF_ACCEPT_FDS = 0x10,
};
首先检查Parcel对象中的进程间通信数据是否正确，然后将参数flags的TF_ACCEPT_FDS位设置为1，表示允许Server进程在返回结果中携带文件描述符。如果Parcel对象data中的进程间通信数据没有问题，那么就会调用成员函数writeTransactionData将它的内容写入到一个binder_transaction_data结构体中。接着判断flags的TF_ONE_WAY位是否等于0。如果是，那么就说明这是一个同步的进程间通信请求，这时候如果用来保存通信结果的Parcel对象reply不等于NULL，那么就调用成员函数waitForResponse函数。
我们先来分析writeTransactionData函数，实现如下：
～/Android/frameworks/base/include/binder
----IPCThreadState.cpp
status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags,//此时cmd为BC_TRANSACTION,binderFlags为0|TF_ACCEPT_FDS
int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer)//handle为0，code为ADD_SERVICE_TRANSACTION,data包含了包含了要传递给Binder驱动程序的进程间通信数据，statusBuffer为NULL
{
binder_transaction_data tr;
tr.target.handle = handle;//0
tr.code = code;//ADD_SERVICE_TRANSACTION
tr.flags = binderFlags;//0|TF_ACCEPT_FDS
const status_t err = data.errorCheck();
if (err == NO_ERROR) {
tr.data_size = data.ipcDataSize();//数据缓冲区大小
tr.data.ptr.buffer = data.ipcData();//数据缓冲区的起始位置
tr.offsets_size = data.ipcObjectsCount()*sizeof(size_t);//偏移数组大小
tr.data.ptr.offsets = data.ipcObjects();//偏移数组起始位置
} else if (statusBuffer) {
........
} else {
........
}
mOut.writeInt32(cmd);//BC_TRANSACTION
mOut.write(&tr, sizeof(tr));
return NO_ERROR;
} 其中binder_transaction_data结构体，实现如下：
struct binder_transaction_data {
union {
size_t handle;
void *ptr;
} target;
void *cookie;
unsigned int code;
unsigned int flags;
pid_t sender_pid;
uid_t sender_euid;
size_t data_size;
size_t offsets_size;
union {
struct {
const void *buffer;
const void *offsets;
}ptr;
uint8_t buf[8];
} data;
};
执行完writeTransactionData，此时命令协议缓冲区mOut的内存布局如下图：
注意此图有错误，flat_binder_object中cookie为BBinder类指针，即binder本地对象指针。binder为本地对象弱引用计数的地址。
执行完writeTransactionData函数，该执行waitForResponse函数了，实现如下：
～/Android/frameworks/base/include/binder
----IPCThreadState.cpp
status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{
int32_t cmd;
int32_t err;
while (1) {
if ((err=talkWithDriver()) < NO_ERROR) break;
.....
}
.......
}
这个函数通过一个while循环不断地调用成员函数talkWithDriver来与Binder驱动程序进行交互，以便可以将前面准备好的BC_TRANSACTION命令协议发送给Binder驱动程序处理，并等待Binder驱动程序将进程间通信结果返回来。
talkWithDriver函数实现如下：
～/Android/frameworks/base/include/binder
----IPCThreadState.cpp
status_t IPCThreadState::talkWithDriver(bool doReceive)
{
LOG_ASSERT(mProcess->mDriverFD >= 0, "Binder driver is not opened");
binder_write_read bwr;
// Is the read buffer empty?
const bool needRead = mIn.dataPosition() >= mIn.dataSize();//needRead为1，表示有需要读的数据
// 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;//doReceive为true表示，只接受Binder驱动程序发送给该进程的返回协议。默认为true。doReceive为false，即不只接受Binder驱动程序发送给该进程的返回协议，或者有需要读的数据，那么outAvail就不为0
bwr.write_size = outAvail;//要写入的数据大小，为mOut的实际大小
bwr.write_buffer = (long unsigned int)mOut.data();//要写入的数据起始位置
// This is what we'll read.
if (doReceive && needRead) {
bwr.read_size = mIn.dataCapacity();//读入数据的大小，为它的所有容量
bwr.read_buffer = (long unsigned int)mIn.data();//读入数据的起始位置
} else {
bwr.read_size = 0;
}
.........
// Return immediately if there is nothing to do.
if ((bwr.write_size == 0) && (bwr.read_size == 0)) return NO_ERROR;//如果两者都为0，就不用继续执行驱动程序了
bwr.write_consumed = 0;//消费清0
bwr.read_consumed = 0;//消费清0
status_t err;
do {
.........
#if defined(HAVE_ANDROID_OS)
if (ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) >= 0)//IPCThreadState在构造函数初始化时，初始化了mProcess
err = NO_ERROR;
else
err = -errno;
#else
err = INVALID_OPERATION;
#endif
IF_LOG_COMMANDS() {
alog << "Finished read/write, write size = " << mOut.dataSize() << endl;
}
} while (err == -EINTR);
........
if (err >= NO_ERROR) {
if (bwr.write_consumed > 0) {
if (bwr.write_consumed < (ssize_t)mOut.dataSize())
mOut.remove(0, bwr.write_consumed);
else
mOut.setDataSize(0);
}
if (bwr.read_consumed > 0) {
mIn.setDataSize(bwr.read_consumed);
mIn.setDataPosition(0);
}
.........
return NO_ERROR;
}
return err;
}
在IPCThreadState类内部，除了使用缓冲区mOut来保存即将要发送给Binder驱动程序的命令协议外，还使用缓冲区mIn来保存那些从Binder驱动程序接受到的返回协议。
通过IPCThreadState类的mIn，mOut设置一个局部变量binder_write_read结构体，最后调用了ioctl映射到Binder驱动程序去执行。
～/Android/kernel/goldfish/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);
void __user *ubuf = (void __user *)arg;//上面传递的过来的局部变量binder_write_read结构体的地址
.........
mutex_lock(&binder_lock);
thread = binder_get_thread(proc);//由于在初始化Process过程中，调用了open_driver，在open_driver中也调用了ioctl，所以looper为0
if (thread == NULL) {
ret = -ENOMEM;
goto err;
}
switch (cmd) {//cmd为上面传递过来的BINDER_WRITE_READ
case BINDER_WRITE_READ: {
struct binder_write_read bwr;
if (size != sizeof(struct binder_write_read)) {
ret = -EINVAL;
goto err;
}
if (copy_from_user(&bwr, ubuf, sizeof(bwr))) {//从用户空间传进来的一个binder_write_read结构体拷贝出来，并且保存在变量bwr中，里面有数据地址，数据总大小，数据现在消费了多少
ret = -EFAULT;
goto err;
}
.........
if (bwr.write_size > 0) {//bwr.write_size大于0，执行这里
ret = binder_thread_write(proc, thread, (void __user *)bwr.write_buffer, bwr.write_size, &bwr.write_consumed);
if (ret < 0) {
bwr.read_consumed = 0;
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
ret = -EFAULT;
goto err;
}
}
if (bwr.read_size > 0) {//bwr.read_size大于0，执行这里
ret = binder_thread_read(proc, thread, (void __user *)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) {
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
ret = -EFAULT;
goto err;
}
}
...........
if (copy_to_user(ubuf, &bwr, sizeof(bwr))) {//将结果返回用户空间bwr
ret = -EFAULT;
goto err;
}
break;
}
..........
ret = 0;
err:
if (thread)
thread->looper &= ~BINDER_LOOPER_STATE_NEED_RETURN;//looper还是0
mutex_unlock(&binder_lock);
...........
return ret;
}
由于write_size大于0，read_size大于0，所以首先会执行binder_thread_write，然后执行binder_thread_read。
binder_thread_write函数实现如下：
～/Android/kernel/goldfish/drivers/staging/android
----binder.c
int
binder_thread_write(struct binder_proc *proc, struct binder_thread *thread,
void __user *buffer, int size, signed long *consumed)//注意consumed为指针
{
uint32_t cmd;
void __user *ptr = buffer + *consumed;//起始位置
void __user *end = buffer + size;//末尾位置
while (ptr < end && thread->return_error == BR_OK) {
if (get_user(cmd, (uint32_t __user *)ptr))//cmd为BC_TRANSACTION
return -EFAULT;
ptr += sizeof(uint32_t);//取出命令后，ptr自增长
......
switch (cmd) {
......
case BC_TRANSACTION:
case BC_REPLY: {
struct binder_transaction_data tr;
if (copy_from_user(&tr, ptr, sizeof(tr)))//将进程间通信数据读取出来，并且保存在binder_transation_data结构体tr中
return -EFAULT;
ptr += sizeof(tr);
binder_transaction(proc, thread, &tr, cmd == BC_REPLY);//调用函数binder_transaction来处理进程发送给它的BC_TRANSACTION命令协议
break;
}
.......
*consumed = ptr - buffer;//consumed为传入的参数size，因此数据已经全部使用完毕
}
return 0;
} 从前面的调用过程可以知道，这个输出缓冲区包含了一个BC_TRANSACTION命令协议，接着就将BC_TRANSACTION命令协议后面所跟的进程间通信数据读取出来，并且保存在binder_transation_data结构体tr中。最后调用函数binder_transaction来处理进程发送给它的BC_TRANSACTION命令协议。
函数binder_transaction负责处理命令协议BC_TRANSACTION和命令BC_REPLY，它的实现比较长，我们来分段阅读：
～/Android/kernel/goldfish/drivers/staging/android
----binder.c
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;
size_t *offp, *off_end;
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;
.........
if (reply) {//为0
.........
} else {
if (tr->target.handle) {//为0
struct binder_ref *ref;
ref = binder_get_ref(proc, tr->target.handle);
.......
target_node = ref->node;
} else {
target_node = binder_context_mgr_node;//Service Manager的Binder实体对象binder_context_mgr_node
........
}
........
target_proc = target_node->proc;//找到了目标进程
........
if (!(tr->flags & TF_ONE_WAY) && thread->transaction_stack) {//目前thread->transaction_stack为NULL，所以暂时不执行这里
struct binder_transaction *tmp;
tmp = thread->transaction_stack;
........
while (tmp) {
if (tmp->from && tmp->from->proc == target_proc)
target_thread = tmp->from;
tmp = tmp->from_parent;
}
}
}
if (target_thread) {//target_thread为NULL
........
target_list = &target_thread->todo;
target_wait = &target_thread->wait;
} else {
target_list = &target_proc->todo;//target_list和target_wait分别指向该目标进程target_proc的todo队列和wait等待队列
target_wait = &target_proc->wait;
} 找到了target_node，target_proc，初始化了target_list和target_wait。
函数继续执行：
t = kzalloc(sizeof(*t), GFP_KERNEL);//分配了一个binder_transaction结构体t
......
tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL);//分配了一个binder_work结构体tcomplete
......
if (!reply && !(tr->flags & TF_ONE_WAY))//如果正在处理BC_TRANSATION命令协议，而且是一个同步的进程间通信请求
t->from = thread;//from指向源线程thread，以便目标进程target_proc或者目标线程target_thread处理完该进程间通信请求之后，能够找回发送该进程间通信请求的线程，最终将进程间通信结果返回给它。
else
t->from = NULL;
t->sender_euid = proc->tsk->cred->euid;
t->to_proc = target_proc;//目标进程
t->to_thread = target_thread;//目标线程
t->code = tr->code;//ADD_SERVICE_TRANCATION
t->flags = tr->flags;//TF_ACCEPTS_FDS
t->priority = task_nice(current);
t->buffer = binder_alloc_buf(target_proc, tr->data_size,
tr->offsets_size, !reply && (t->flags & TF_ONE_WAY));//分配了binder_buffer结构体
.......
t->buffer->allow_user_free = 0;//不允许释放
.......
t->buffer->transaction = t;
t->buffer->target_node = target_node;//binder_context_mgr_node
if (target_node)
binder_inc_node(target_node, 1, 0, NULL);//增加目标Binder实体对象的强引用计数
offp = (size_t *)(t->buffer->data + ALIGN(tr->data_size, sizeof(void *)));//偏移数组在data中起始位置，位于数据缓冲区之后
if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) {//数据缓冲区拷贝到data中
.......
goto err_copy_data_failed;
}
if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) {//偏移数组拷贝到data中，偏移数组位于数据缓冲区之后
.......
goto err_copy_data_failed;
}
........
off_end = (void *)offp + tr->offsets_size;//偏移数组在data中的结束位置 binder_transaction结构体实现如下：
～/Android/kernel/goldfish/drivers/staging/android
----binder.c
struct binder_transaction {
int debug_id;
struct binder_work work;
struct binder_thread *from;
struct binder_transaction *from_parent;
struct binder_proc *to_proc;
struct binder_thread *to_thread;
struct binder_transaction *to_parent;
unsigned need_reply : 1;
/*unsigned is_dead : 1;*/ /* not used at the moment */
struct binder_buffer *buffer;
unsigned int code;
unsigned int flags;
long priority;
long saved_priority;
uid_t sender_euid;
}; 其中，binder_buffer结构体实现如下：
～/Android/kernel/goldfish/drivers/staging/android
----binder.c
struct binder_buffer {
struct list_head entry; /* free and allocated entries by addesss */
struct rb_node rb_node; /* free entry by size or allocated entry */
/* by address */
unsigned free : 1;
unsigned allow_user_free : 1;
unsigned async_transaction : 1;
unsigned debug_id : 29;
struct binder_transaction *transaction;
struct binder_node *target_node;
size_t data_size;
size_t offsets_size;
uint8_t data[0];
};
首先分配了一个binder_transaction结构体t，然后初始化各参数。
函数binder_transaction接着执行：
for (; offp < off_end; offp++) {
struct flat_binder_object *fp;
.......
fp = (struct flat_binder_object *)(t->buffer->data + *offp);//取得flat_binder_object结构体
switch (fp->type) {//BINDER_TYPE_BINDER
case BINDER_TYPE_BINDER:
case BINDER_TYPE_WEAK_BINDER: {
struct binder_ref *ref;
struct binder_node *node = binder_get_node(proc, fp->binder);//第一次取得为NULL
if (node == NULL) {//执行这里
node = binder_new_node(proc, fp->binder, fp->cookie);
if (node == NULL) {
return_error = BR_FAILED_REPLY;
goto err_binder_new_node_failed;
}
node->min_priority = fp->flags & FLAT_BINDER_FLAG_PRIORITY_MASK;
node->accept_fds = !!(fp->flags & FLAT_BINDER_FLAG_ACCEPTS_FDS);//accept_fds为1
}
........
ref = binder_get_ref_for_node(target_proc, node);
........
if (fp->type == BINDER_TYPE_BINDER)
fp->type = BINDER_TYPE_HANDLE;//type变成了HANDLE
else
fp->type = BINDER_TYPE_WEAK_HANDLE;
fp->handle = ref->desc;//由于上面type变成了HANDLE,所以这里也设置handle
binder_inc_ref(ref, fp->type == BINDER_TYPE_HANDLE, &thread->todo);//增加引用计数
.......
} break;
.......
} 由于调用函数binder_get_node无法获得一个引用了它的Binder实体对象，所以调用函数binder_new_node为它创建一个Binder实体对象node。binder_new_node实现如下：
～/Android/kernel/goldfish/drivers/staging/android
----binder.c
static struct binder_node *
binder_new_node(struct binder_proc *proc, void __user *ptr, void __user *cookie)
{
struct rb_node **p = &proc->nodes.rb_node;
struct rb_node *parent = NULL;
struct binder_node *node;
while (*p) {//根据node的ptr,来查找是否已经分配了binder_node结构体
parent = *p;
node = rb_entry(parent, struct binder_node, rb_node);
if (ptr < node->ptr)
p = &(*p)->rb_left;
else if (ptr > node->ptr)
p = &(*p)->rb_right;
else
return NULL;
}
node = kzalloc(sizeof(*node), GFP_KERNEL);//如果没有找到，分配binder_node结构体
if (node == NULL)
return NULL;
binder_stats.obj_created[BINDER_STAT_NODE]++;
rb_link_node(&node->rb_node, parent, p);//根据ptr将node->rb_node插入proc->nodes中
rb_insert_color(&node->rb_node, &proc->nodes);
node->debug_id = ++binder_last_id;//初始化各个变量
node->proc = proc;
node->ptr = ptr;//弱引用计数地址
node->cookie = cookie;//BBinder(Binder本地对象地址)
node->work.type = BINDER_WORK_NODE;
INIT_LIST_HEAD(&node->work.entry);
INIT_LIST_HEAD(&node->async_todo);
if (binder_debug_mask & BINDER_DEBUG_INTERNAL_REFS)
printk(KERN_INFO "binder: %d:%d node %d u%p c%p created\n",
proc->pid, current->pid, node->debug_id,
node->ptr, node->cookie);
return node;
} 返回for循环，接下来执行，binder_get_ref_for_node，实现如下：～/Android/kernel/goldfish/drivers/staging/android
----binder.c
static struct binder_ref *
binder_get_ref_for_node(struct binder_proc *proc, struct binder_node *node)
{
struct rb_node *n;
struct rb_node **p = &proc->refs_by_node.rb_node;
struct rb_node *parent = NULL;
struct binder_ref *ref, *new_ref;
while (*p) {//根据node,在proc->refs_by_node中来查找是否已经分配了binder_ref结构体
parent = *p;
ref = rb_entry(parent, struct binder_ref, rb_node_node);
if (node < ref->node)
p = &(*p)->rb_left;
else if (node > ref->node)
p = &(*p)->rb_right;
else
return ref;
}
new_ref = kzalloc(sizeof(*ref), GFP_KERNEL);//如果没有找到，分配binder_ref结构体
if (new_ref == NULL)
return NULL;
binder_stats.obj_created[BINDER_STAT_REF]++;
........
new_ref->proc = proc;
new_ref->node = node;//刚刚创建的node
rb_link_node(&new_ref->rb_node_node, parent, p);////将new_ref->rb_node_node插入proc->refs_by_node中
rb_insert_color(&new_ref->rb_node_node, &proc->refs_by_node);
new_ref->desc = (node == binder_context_mgr_node) ? 0 : 1;//为1
for (n = rb_first(&proc->refs_by_desc); n != NULL; n = rb_next(n)) {
ref = rb_entry(n, struct binder_ref, rb_node_desc);
if (ref->desc > new_ref->desc)
break;
new_ref->desc = ref->desc + 1;
}
p = &proc->refs_by_desc.rb_node;
while (*p) {
parent = *p;
ref = rb_entry(parent, struct binder_ref, rb_node_desc);
if (new_ref->desc < ref->desc)
p = &(*p)->rb_left;
else if (new_ref->desc > ref->desc)
p = &(*p)->rb_right;
else
BUG();
}
rb_link_node(&new_ref->rb_node_desc, parent, p);//将new_ref->rb_node_desc插入到proc->refs_by_desc中
rb_insert_color(&new_ref->rb_node_desc, &proc->refs_by_desc);
if (node) {
hlist_add_head(&new_ref->node_entry, &node->refs);
......
} else {
......
}
return new_ref;
} 获取了Binder引用对象后，重新设置了flat_binder_object结构体的type为BINDER_TYPE_HANDLE(原来为BINDER_TYPE_BINDER)，所以设置fp->handle（原来为fp->binder）为refs->decs。
函数接着执行：
if (reply) {
.....
} else if (!(t->flags & TF_ONE_WAY)) {
BUG_ON(t->buffer->async_transaction != 0);
t->need_reply = 1;//need_reply为1
t->from_parent = thread->transaction_stack;
thread->transaction_stack = t;
} else {
BUG_ON(target_node == NULL);
BUG_ON(t->buffer->async_transaction != 1);
if (target_node->has_async_transaction) {
target_list = &target_node->async_todo;
target_wait = NULL;
} else
target_node->has_async_transaction = 1;
}
t->work.type = BINDER_WORK_TRANSACTION;
list_add_tail(&t->work.entry, target_list);//加入到目标进程的todo
tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
list_add_tail(&tcomplete->entry, &thread->todo);//加入到本线程的todo
if (target_wait)
wake_up_interruptible(target_wait);//唤醒目标进程
return; 我们假设本线程继续执行，执行完毕后再执行被唤醒的目标进程。
返回到binder_ioctl，继续执行binder_thread_read，实现如下：
static int
binder_thread_read(struct binder_proc *proc, struct binder_thread *thread,
void __user *buffer, int size, signed long *consumed, int non_block)
{
void __user *ptr = buffer + *consumed;
void __user *end = buffer + size;
int ret = 0;
int wait_for_proc_work;
if (*consumed == 0) {
if (put_user(BR_NOOP, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
}
retry:
wait_for_proc_work = thread->transaction_stack == NULL && list_empty(&thread->todo);//wait_for_proc_work为0
.......
thread->looper |= BINDER_LOOPER_STATE_WAITING;//looper为BINDER_LOOPER_STATE_WAITING
if (wait_for_proc_work)
proc->ready_threads++;
mutex_unlock(&binder_lock);
if (wait_for_proc_work) {
........
} else {
if (non_block) {
if (!binder_has_thread_work(thread))
ret = -EAGAIN;
} else//执行这里
ret = wait_event_interruptible(thread->wait, binder_has_thread_work(thread));//由于thread上有数据，那么继续执行，不会睡眠等待
}
mutex_lock(&binder_lock);
if (wait_for_proc_work)
proc->ready_threads--;
thread->looper &= ~BINDER_LOOPER_STATE_WAITING;//looper为0
if (ret)
return ret;
while (1) {
uint32_t cmd;
struct binder_transaction_data tr;
struct binder_work *w;
struct binder_transaction *t = NULL;
if (!list_empty(&thread->todo))
w = list_first_entry(&thread->todo, struct binder_work, entry);//将线程thread的todo队列中类型为BINDER_WORK_TRANSACTION_COMPLETE的工作项取出来
else if (!list_empty(&proc->todo) && wait_for_proc_work)
w = list_first_entry(&proc->todo, struct binder_work, entry);
else {
if (ptr - buffer == 4 && !(thread->looper & BINDER_LOOPER_STATE_NEED_RETURN)) /* no data added */
goto retry;
break;
}
........
switch (w->type) {//刚取出来，类型为BINDER_WORK_TRANSACTION_COMPLETE
.......
case BINDER_WORK_TRANSACTION_COMPLETE: {
cmd = BR_TRANSACTION_COMPLETE;
if (put_user(cmd, (uint32_t __user *)ptr))//将一个BR_TRANSACTION_COMPLETE返回协议写入到用户提供的缓冲区。
return -EFAULT;
ptr += sizeof(uint32_t);
.......
list_del(&w->entry);//删除todo上的工作项
kfree(w);//释放结构体
.......
} break;
........
*consumed = ptr - buffer;//消耗的大小
...........
return 0;
}
首先，将线程thread的todo队列中类型为BINDER_WORK_TRANSACTION_COMPLETE的工作项取出来，将一个BR_TRANSACTION_COMPLETE返回协议写入到用户提供的缓冲区。
函数binder_thread_read执行完成之后，就返回到函数binder_ioctl中，然后再返回到IPCThreadState类的成员函数talkWithDriver中，在此函数中，还有一段代码要执行：
talkWithDriver函数实现如下：
～/Android/frameworks/base/include/binder
----IPCThreadState.cpp
if (err >= NO_ERROR) {
if (bwr.write_consumed > 0) {
if (bwr.write_consumed < (ssize_t)mOut.dataSize())
mOut.remove(0, bwr.write_consumed);//mOut中移除已经写过的数据
else
mOut.setDataSize(0);
}
if (bwr.read_consumed > 0) {
mIn.setDataSize(bwr.read_consumed);//mIn中设置了读取数据的大小，即BR_TRANSACTION_COMPLETE大小
mIn.setDataPosition(0);//mIn中设置了读取数据的位置，为0，指向了BR_TRANSACTION_COMPLETE开头
}
.........
return NO_ERROR;
}
return err; 最后，又返回到IPCThreadState类的成员函数waitForResponse，实现如下：
～/Android/frameworks/base/include/binder
----IPCThreadState.cpp
status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{
int32_t cmd;
int32_t err;
while (1) {
if ((err=talkWithDriver()) < NO_ERROR) break;
err = mIn.errorCheck();
if (err < NO_ERROR) break;
if (mIn.dataAvail() == 0) continue;
cmd = mIn.readInt32();//读取了BR_TRANSACTION_COMPLETE协议，mIn中就没有数据了
.....
switch (cmd) {
case BR_TRANSACTION_COMPLETE:
if (!reply && !acquireResult) goto finish;//reply不为NULL
break;
.....
}
........
return err;
}
继续往下执行，读取的cmd为BR_TRANSACTION_COMPLETE，执行switch，break跳出switch函数，继续执行while循环，又开始执行talkWithDriver，由于IPCThreadState类内部的命令协议缓冲区mOut中的命令协议，以及返回协议缓冲区mIn中的返回协议都已经处理完成了，因此，当它再次通过IO控制命令BINDER_WRITE_READ进入到Binder驱动程序binder_ioctl中时，就会调用函数binder_thread_read睡眠等待目标进程将上次发出的进程间通信请求的结果返回来。
睡眠在这句代码上。
ret = wait_event_interruptible(thread->wait, binder_has_thread_work(thread));