Android系统进程间通信(IPC)机制Binder中的Server启动过程源代码分析
2012-03-29 20:17
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在前面一篇文章浅谈Android系统进程间通信(IPC)机制Binder中的Server和Client获得Service Manager接口之路中,介绍了在Android系统中Binder进程间通信机制中的Server角色是如何获得Service Manager远程接口的,即defaultServiceManager函数的实现。Server获得了Service
Manager远程接口之后,就要把自己的Service添加到Service Manager中去,然后把自己启动起来,等待Client的请求。本文将通过分析源代码了解Server的启动过程是怎么样的。
本文通过一个具体的例子来说明Binder机制中Server的启动过程。我们知道,在Android系统中,提供了多媒体播放的功能,这个功能是以服务的形式来提供的。这里,我们就通过分析MediaPlayerService的实现来了解Media Server的启动过程。
首先,看一下MediaPlayerService的类图,以便我们理解下面要描述的内容。
我们将要介绍的主角MediaPlayerService继承于BnMediaPlayerService类,熟悉Binder机制的同学应该知道BnMediaPlayerService是一个Binder Native类,用来处理Client请求的。BnMediaPlayerService继承于BnInterface<IMediaPlayerService>类,BnInterface是一个模板类,它定义在frameworks/base/include/binder/IInterface.h文件中:
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template<typename INTERFACE>
class BnInterface : public INTERFACE, public BBinder
{
public:
virtual sp<IInterface> queryLocalInterface(const String16& _descriptor);
virtual const String16& getInterfaceDescriptor() const;
protected:
virtual IBinder* onAsBinder();
};
先看下面这句代码:
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sp<ProcessState> proc(ProcessState::self());
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Mutex gProcessMutex;
sp<ProcessState> gProcess;
先看open_driver函数的实现,这个函数同样位于frameworks/base/libs/binder/ProcessState.cpp文件中:
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static int open_driver()
{
if (gSingleProcess) {
return -1;
}
int fd = open("/dev/binder", O_RDWR);
if (fd >= 0) {
fcntl(fd, F_SETFD, FD_CLOEXEC);
int vers;
#if defined(HAVE_ANDROID_OS)
status_t result = ioctl(fd, BINDER_VERSION, &vers);
#else
status_t result = -1;
errno = EPERM;
#endif
if (result == -1) {
LOGE("Binder ioctl to obtain version failed: %s", strerror(errno));
close(fd);
fd = -1;
}
if (result != 0 || vers != BINDER_CURRENT_PROTOCOL_VERSION) {
LOGE("Binder driver protocol does not match user space protocol!");
close(fd);
fd = -1;
}
#if defined(HAVE_ANDROID_OS)
size_t maxThreads = 15;
result = ioctl(fd, BINDER_SET_MAX_THREADS, &maxThreads);
if (result == -1) {
LOGE("Binder ioctl to set max threads failed: %s", strerror(errno));
}
#endif
} else {
LOGW("Opening '/dev/binder' failed: %s\n", strerror(errno));
}
return fd;
}
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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;
/*printk(KERN_INFO "binder_ioctl: %d:%d %x %lx\n", proc->pid, current->pid, cmd, arg);*/
ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret)
return ret;
mutex_lock(&binder_lock);
thread = binder_get_thread(proc);
if (thread == NULL) {
ret = -ENOMEM;
goto err;
}
switch (cmd) {
......
case BINDER_VERSION:
if (size != sizeof(struct binder_version)) {
ret = -EINVAL;
goto err;
}
if (put_user(BINDER_CURRENT_PROTOCOL_VERSION, &((struct binder_version *)ubuf)->protocol_version)) {
ret = -EINVAL;
goto err;
}
break;
......
}
ret = 0;
err:
......
return ret;
}
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/* Use with BINDER_VERSION, driver fills in fields. */
struct binder_version {
/* driver protocol version -- increment with incompatible change */
signed long protocol_version;
};
这个函数调用最终进入到Binder驱动程序的binder_ioctl函数中,我们只关注BINDER_SET_MAX_THREADS相关的部分逻辑:
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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;
/*printk(KERN_INFO "binder_ioctl: %d:%d %x %lx\n", proc->pid, current->pid, cmd, arg);*/
ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret)
return ret;
mutex_lock(&binder_lock);
thread = binder_get_thread(proc);
if (thread == NULL) {
ret = -ENOMEM;
goto err;
}
switch (cmd) {
......
case BINDER_SET_MAX_THREADS:
if (copy_from_user(&proc->max_threads, ubuf, sizeof(proc->max_threads))) {
ret = -EINVAL;
goto err;
}
break;
......
}
ret = 0;
err:
......
return ret;
}
这样,ProcessState全局唯一变量gProcess就创建完毕了,回到frameworks/base/media/mediaserver/main_mediaserver.cpp文件中的main函数,下一步是调用defaultServiceManager函数来获得Service Manager的远程接口,这个已经在上一篇文章浅谈Android系统进程间通信(IPC)机制Binder中的Server和Client获得Service
Manager接口之路有详细描述,读者可以回过头去参考一下。
再接下来,就进入到MediaPlayerService::instantiate函数把MediaPlayerService添加到Service Manger中去了。这个函数定义在frameworks/base/media/libmediaplayerservice/MediaPlayerService.cpp文件中:
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void MediaPlayerService::instantiate() {
defaultServiceManager()->addService(
String16("media.player"), new MediaPlayerService());
}
这里的Parcel类是用来于序列化进程间通信数据用的。
先来看这一句的调用:
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data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
再来看下面的调用:
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data.writeString16(name);
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status_t Parcel::writeStrongBinder(const sp<IBinder>& val)
{
return flatten_binder(ProcessState::self(), val, this);
}
我们进入到flatten_binder函数看看:
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status_t flatten_binder(const sp<ProcessState>& proc,
const sp<IBinder>& binder, Parcel* out)
{
flat_binder_object obj;
obj.flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS;
if (binder != NULL) {
IBinder *local = binder->localBinder();
if (!local) {
BpBinder *proxy = binder->remoteBinder();
if (proxy == NULL) {
LOGE("null proxy");
}
const int32_t handle = proxy ? proxy->handle() : 0;
obj.type = BINDER_TYPE_HANDLE;
obj.handle = handle;
obj.cookie = NULL;
} else {
obj.type = BINDER_TYPE_BINDER;
obj.binder = local->getWeakRefs();
obj.cookie = local;
}
} else {
obj.type = BINDER_TYPE_BINDER;
obj.binder = NULL;
obj.cookie = NULL;
}
return finish_flatten_binder(binder, obj, out);
}
传进来的binder即为MediaPlayerService::instantiate函数中new出来的MediaPlayerService实例,因此,不为空。又由于MediaPlayerService继承自BBinder类,它是一个本地Binder实体,因此binder->localBinder返回一个BBinder指针,而且肯定不为空,于是执行下面语句:
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obj.type = BINDER_TYPE_BINDER;
obj.binder = local->getWeakRefs();
obj.cookie = local;
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status_t Parcel::writeObject(const flat_binder_object& val, bool nullMetaData)
{
const bool enoughData = (mDataPos+sizeof(val)) <= mDataCapacity;
const bool enoughObjects = mObjectsSize < mObjectsCapacity;
if (enoughData && enoughObjects) {
restart_write:
*reinterpret_cast<flat_binder_object*>(mData+mDataPos) = val;
// Need to write meta-data?
if (nullMetaData || val.binder != NULL) {
mObjects[mObjectsSize] = mDataPos;
acquire_object(ProcessState::self(), val, this);
mObjectsSize++;
}
// remember if it's a file descriptor
if (val.type == BINDER_TYPE_FD) {
mHasFds = mFdsKnown = true;
}
return finishWrite(sizeof(flat_binder_object));
}
if (!enoughData) {
const status_t err = growData(sizeof(val));
if (err != NO_ERROR) return err;
}
if (!enoughObjects) {
size_t newSize = ((mObjectsSize+2)*3)/2;
size_t* objects = (size_t*)realloc(mObjects, newSize*sizeof(size_t));
if (objects == NULL) return NO_MEMORY;
mObjects = objects;
mObjectsCapacity = newSize;
}
goto restart_write;
}
再回到BpServiceManager::addService函数中,调用下面语句:
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status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);
Manager接口之路一文。
再进入到IPCThreadState::transact函数,看看做了些什么事情:
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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;
IF_LOG_TRANSACTIONS() {
TextOutput::Bundle _b(alog);
alog << "BC_TRANSACTION thr " << (void*)pthread_self() << " / hand "
<< handle << " / code " << TypeCode(code) << ": "
<< indent << data << dedent << endl;
}
if (err == NO_ERROR) {
LOG_ONEWAY(">>>> SEND from pid %d uid %d %s", getpid(), getuid(),
(flags & TF_ONE_WAY) == 0 ? "READ REPLY" : "ONE WAY");
err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);
}
if (err != NO_ERROR) {
if (reply) reply->setError(err);
return (mLastError = err);
}
if ((flags & TF_ONE_WAY) == 0) {
#if 0
if (code == 4) { // relayout
LOGI(">>>>>> CALLING transaction 4");
} else {
LOGI(">>>>>> CALLING transaction %d", code);
}
#endif
if (reply) {
err = waitForResponse(reply);
} else {
Parcel fakeReply;
err = waitForResponse(&fakeReply);
}
#if 0
if (code == 4) { // relayout
LOGI("<<<<<< RETURNING transaction 4");
} else {
LOGI("<<<<<< RETURNING transaction %d", code);
}
#endif
IF_LOG_TRANSACTIONS() {
TextOutput::Bundle _b(alog);
alog << "BR_REPLY thr " << (void*)pthread_self() << " / hand "
<< handle << ": ";
if (reply) alog << indent << *reply << dedent << endl;
else alog << "(none requested)" << endl;
}
} else {
err = waitForResponse(NULL, NULL);
}
return err;
}
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status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags,
int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer)
{
binder_transaction_data tr;
tr.target.handle = handle;
tr.code = code;
tr.flags = binderFlags;
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(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 = statusBuffer;
tr.offsets_size = 0;
tr.data.ptr.offsets = NULL;
} else {
return (mLastError = err);
}
mOut.writeInt32(cmd);
mOut.write(&tr, sizeof(tr));
return NO_ERROR;
}
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writeInt32(IPCThreadState::self()->getStrictModePolicy() |
STRICT_MODE_PENALTY_GATHER);
writeString16("android.os.IServiceManager");
writeString16("media.player");
writeStrongBinder(new MediaPlayerService());
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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();
// 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 = (long unsigned int)mOut.data();
// This is what we'll read.
if (doReceive && needRead) {
bwr.read_size = mIn.dataCapacity();
bwr.read_buffer = (long unsigned int)mIn.data();
} else {
bwr.read_size = 0;
}
IF_LOG_COMMANDS() {
TextOutput::Bundle _b(alog);
if (outAvail != 0) {
alog << "Sending commands to driver: " << indent;
const void* cmds = (const void*)bwr.write_buffer;
const void* end = ((const uint8_t*)cmds)+bwr.write_size;
alog << HexDump(cmds, bwr.write_size) << endl;
while (cmds < end) cmds = printCommand(alog, cmds);
alog << dedent;
}
alog << "Size of receive buffer: " << bwr.read_size
<< ", needRead: " << needRead << ", doReceive: " << doReceive << endl;
}
// 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 {
IF_LOG_COMMANDS() {
alog << "About to read/write, write size = " << mOut.dataSize() << endl;
}
#if defined(HAVE_ANDROID_OS)
if (ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) >= 0)
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_LOG_COMMANDS() {
alog << "Our err: " << (void*)err << ", write consumed: "
<< bwr.write_consumed << " (of " << mOut.dataSize()
<< "), read consumed: " << bwr.read_consumed << endl;
}
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);
}
IF_LOG_COMMANDS() {
TextOutput::Bundle _b(alog);
alog << "Remaining data size: " << mOut.dataSize() << endl;
alog << "Received commands from driver: " << indent;
const void* cmds = mIn.data();
const void* end = mIn.data() + mIn.dataSize();
alog << HexDump(cmds, mIn.dataSize()) << endl;
while (cmds < end) cmds = printReturnCommand(alog, cmds);
alog << dedent;
}
return NO_ERROR;
}
return err;
}
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binder_thread_write(struct binder_proc *proc, struct binder_thread *thread,
void __user *buffer, int size, signed long *consumed)
{
uint32_t cmd;
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);
if (_IOC_NR(cmd) < ARRAY_SIZE(binder_stats.bc)) {
binder_stats.bc[_IOC_NR(cmd)]++;
proc->stats.bc[_IOC_NR(cmd)]++;
thread->stats.bc[_IOC_NR(cmd)]++;
}
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;
}
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target_node = binder_context_mgr_node;
target_proc = target_node->proc;
target_list = &target_proc->todo;
target_wait = &target_proc->wait;
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t->buffer = binder_alloc_buf(target_proc, tr->data_size,
tr->offsets_size, !reply && (t->flags & TF_ONE_WAY));
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if (target_node)
binder_inc_node(target_node, 1, 0, NULL);
现在,由于要把这个Binder实体MediaPlayerService交给target_proc,也就是Service Manager来管理,也就是说Service Manager要引用这个MediaPlayerService了,于是通过binder_get_ref_for_node为MediaPlayerService创建一个引用,并且通过binder_inc_ref来增加这个引用计数,防止这个引用还在使用过程当中就被销毁。注意,到了这里的时候,t->buffer中的flat_binder_obj的type已经改为BINDER_TYPE_HANDLE,handle已经改为ref->desc,跟原来不一样了,因为这个flat_binder_obj是最终是要传给Service
Manager的,而Service Manager只能够通过句柄值来引用这个Binder实体。
最后,把待处理事务加入到target_list列表中去:
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list_add_tail(&t->work.entry, target_list);
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if (target_wait)
wake_up_interruptible(target_wait);
这里,thread->transaction_stack和thread->todo均不为空,于是wait_for_proc_work为false,由于binder_has_thread_work的时候,返回true,这里因为thread->todo不为空,因此,线程虽然调用了wait_event_interruptible,但是不会睡眠,于是继续往下执行。
由于thread->todo不为空,执行下列语句:
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if (!list_empty(&thread->todo))
w = list_first_entry(&thread->todo, struct binder_work, entry);
binder_ioctl函数返回到用户空间之前,把数据消耗情况拷贝回用户空间中:
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if (copy_to_user(ubuf, &bwr, sizeof(bwr))) {
ret = -EFAULT;
goto err;
}
首先是把mOut的数据清空:
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mOut.setDataSize(0);
这时候,下面语句执行后:
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const bool needRead = mIn.dataPosition() >= mIn.dataSize();
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switch (cmd) {
case BR_TRANSACTION_COMPLETE:
if (!reply && !acquireResult) goto finish;
break;
......
}
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wait_event_interruptible(thread->wait, binder_has_thread_work(thread));
Service Manager被唤醒之后,就进入while循环开始处理事务了。这里wait_for_proc_work等于1,并且proc->todo不为空,所以从proc->todo列表中得到第一个工作项:
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w = list_first_entry(&proc->todo, struct binder_work, entry);
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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;
......
cmd = BR_TRANSACTION;
} else {
......
}
tr.code = t->code;
tr.flags = t->flags;
tr.sender_euid = t->sender_euid;
if (t->from) {
struct task_struct *sender = t->from->proc->tsk;
tr.sender_pid = task_tgid_nr_ns(sender, current->nsproxy->pid_ns);
} else {
tr.sender_pid = 0;
}
tr.data_size = t->buffer->data_size;
tr.offsets_size = t->buffer->offsets_size;
tr.data.ptr.buffer = (void *)t->buffer->data + proc->user_buffer_offset;
tr.data.ptr.offsets = tr.data.ptr.buffer + ALIGN(t->buffer->data_size, sizeof(void *));
Manager成为Android进程间通信(IPC)机制Binder守护进程之路,那里有详细描述。这里只要将t->buffer->data加上一个偏移值proc->user_buffer_offset就可以得到t->buffer->data对应的用户空间虚拟地址了。调整了tr.data.ptr.buffer的值之后,不要忘记也要一起调整tr.data.ptr.offsets的值。
接着就是把tr的内容拷贝到用户传进来的缓冲区去了,指针ptr指向这个用户缓冲区的地址:
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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);
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t->to_parent = thread->transaction_stack;
t->to_thread = thread;
thread->transaction_stack = t;
这里就是返回到frameworks/base/cmds/servicemanager/binder.c文件中的binder_loop函数了:
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void binder_loop(struct binder_state *bs, binder_handler func)
{
int res;
struct binder_write_read bwr;
unsigned readbuf[32];
bwr.write_size = 0;
bwr.write_consumed = 0;
bwr.write_buffer = 0;
readbuf[0] = BC_ENTER_LOOPER;
binder_write(bs, readbuf, sizeof(unsigned));
for (;;) {
bwr.read_size = sizeof(readbuf);
bwr.read_consumed = 0;
bwr.read_buffer = (unsigned) readbuf;
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);
if (res < 0) {
LOGE("binder_loop: ioctl failed (%s)\n", strerror(errno));
break;
}
res = binder_parse(bs, 0, readbuf, bwr.read_consumed, func);
if (res == 0) {
LOGE("binder_loop: unexpected reply?!\n");
break;
}
if (res < 0) {
LOGE("binder_loop: io error %d %s\n", res, strerror(errno));
break;
}
}
}
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struct binder_txn
{
void *target;
void *cookie;
uint32_t code;
uint32_t flags;
uint32_t sender_pid;
uint32_t sender_euid;
uint32_t data_size;
uint32_t offs_size;
void *data;
void *offs;
};
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void bio_init(struct binder_io *bio, void *data,
uint32_t maxdata, uint32_t maxoffs)
{
uint32_t n = maxoffs * sizeof(uint32_t);
if (n > maxdata) {
bio->flags = BIO_F_OVERFLOW;
bio->data_avail = 0;
bio->offs_avail = 0;
return;
}
bio->data = bio->data0 = data + n;
bio->offs = bio->offs0 = data;
bio->data_avail = maxdata - n;
bio->offs_avail = maxoffs;
bio->flags = 0;
}
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int svcmgr_handler(struct binder_state *bs,
struct binder_txn *txn,
struct binder_io *msg,
struct binder_io *reply)
{
struct svcinfo *si;
uint16_t *s;
unsigned len;
void *ptr;
uint32_t strict_policy;
if (txn->target != svcmgr_handle)
return -1;
// Equivalent to Parcel::enforceInterface(), reading the RPC
// header with the strict mode policy mask and the interface name.
// Note that we ignore the strict_policy and don't propagate it
// further (since we do no outbound RPCs anyway).
strict_policy = bio_get_uint32(msg);
s = bio_get_string16(msg, &len);
if ((len != (sizeof(svcmgr_id) / 2)) ||
memcmp(svcmgr_id, s, sizeof(svcmgr_id))) {
fprintf(stderr,"invalid id %s\n", str8(s));
return -1;
}
switch(txn->code) {
......
case SVC_MGR_ADD_SERVICE:
s = bio_get_string16(msg, &len);
ptr = bio_get_ref(msg);
if (do_add_service(bs, s, len, ptr, txn->sender_euid))
return -1;
break;
......
}
bio_put_uint32(reply, 0);
return 0;
}
[cpp]
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strict_policy = bio_get_uint32(msg);
s = bio_get_string16(msg, &len);
s = bio_get_string16(msg, &len);
ptr = bio_get_ref(msg);
接着看bio_get_ref实现:
[cpp]
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void *bio_get_ref(struct binder_io *bio)
{
struct binder_object *obj;
obj = _bio_get_obj(bio);
if (!obj)
return 0;
if (obj->type == BINDER_TYPE_HANDLE)
return obj->pointer;
return 0;
}
这个函数执行完成后,返回到svcmgr_handler函数,函数的最后,将一个错误码0写到reply变量中去,表示一切正常:
[cpp]
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bio_put_uint32(reply, 0);
[cpp]
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void binder_send_reply(struct binder_state *bs,
struct binder_io *reply,
void *buffer_to_free,
int status)
{
struct {
uint32_t cmd_free;
void *buffer;
uint32_t cmd_reply;
struct binder_txn txn;
} __attribute__((packed)) data;
data.cmd_free = BC_FREE_BUFFER;
data.buffer = buffer_to_free;
data.cmd_reply = BC_REPLY;
data.txn.target = 0;
data.txn.cookie = 0;
data.txn.code = 0;
if (status) {
data.txn.flags = TF_STATUS_CODE;
data.txn.data_size = sizeof(int);
data.txn.offs_size = 0;
data.txn.data = &status;
data.txn.offs = 0;
} else {
data.txn.flags = 0;
data.txn.data_size = reply->data - reply->data0;
data.txn.offs_size = ((char*) reply->offs) - ((char*) reply->offs0);
data.txn.data = reply->data0;
data.txn.offs = reply->offs0;
}
binder_write(bs, &data, sizeof(data));
}
这里又是一个ioctl的BINDER_WRITE_READ操作。直入到驱动程序的binder_ioctl函数后,执行BINDER_WRITE_READ命令,这里就不累述了。
最后,从binder_ioctl执行到binder_thread_write函数,我们首先看第一个命令BC_FREE_BUFFER:
[cpp]
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int
binder_thread_write(struct binder_proc *proc, struct binder_thread *thread,
void __user *buffer, int size, signed long *consumed)
{
uint32_t cmd;
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);
if (_IOC_NR(cmd) < ARRAY_SIZE(binder_stats.bc)) {
binder_stats.bc[_IOC_NR(cmd)]++;
proc->stats.bc[_IOC_NR(cmd)]++;
thread->stats.bc[_IOC_NR(cmd)]++;
}
switch (cmd) {
......
case BC_FREE_BUFFER: {
void __user *data_ptr;
struct binder_buffer *buffer;
if (get_user(data_ptr, (void * __user *)ptr))
return -EFAULT;
ptr += sizeof(void *);
buffer = binder_buffer_lookup(proc, data_ptr);
if (buffer == NULL) {
binder_user_error("binder: %d:%d "
"BC_FREE_BUFFER u%p no match\n",
proc->pid, thread->pid, data_ptr);
break;
}
if (!buffer->allow_user_free) {
binder_user_error("binder: %d:%d "
"BC_FREE_BUFFER u%p matched "
"unreturned buffer\n",
proc->pid, thread->pid, data_ptr);
break;
}
if (binder_debug_mask & BINDER_DEBUG_FREE_BUFFER)
printk(KERN_INFO "binder: %d:%d BC_FREE_BUFFER u%p found buffer %d for %s transaction\n",
proc->pid, thread->pid, data_ptr, buffer->debug_id,
buffer->transaction ? "active" : "finished");
if (buffer->transaction) {
buffer->transaction->buffer = NULL;
buffer->transaction = NULL;
}
if (buffer->async_transaction && buffer->target_node) {
BUG_ON(!buffer->target_node->has_async_transaction);
if (list_empty(&buffer->target_node->async_todo))
buffer->target_node->has_async_transaction = 0;
else
list_move_tail(buffer->target_node->async_todo.next, &thread->todo);
}
binder_transaction_buffer_release(proc, buffer, NULL);
binder_free_buf(proc, buffer);
break;
}
......
*consumed = ptr - buffer;
}
return 0;
}
[cpp]
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buffer = binder_buffer_lookup(proc, data_ptr);
[cpp]
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int
binder_thread_write(struct binder_proc *proc, struct binder_thread *thread,
void __user *buffer, int size, signed long *consumed)
{
uint32_t cmd;
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);
if (_IOC_NR(cmd) < ARRAY_SIZE(binder_stats.bc)) {
binder_stats.bc[_IOC_NR(cmd)]++;
proc->stats.bc[_IOC_NR(cmd)]++;
thread->stats.bc[_IOC_NR(cmd)]++;
}
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;
}
前面Service Manager正在binder_thread_read函数中被MediaPlayerService启动后进程唤醒后,在最后会把当前处理完的事务放在thread->transaction_stack中:
[cpp]
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if (cmd == BR_TRANSACTION && !(t->flags & TF_ONE_WAY)) {
t->to_parent = thread->transaction_stack;
t->to_thread = thread;
thread->transaction_stack = t;
}
[cpp]
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target_thread = in_reply_to->from;
target_proc = target_thread->proc;
[cpp]
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/* TODO: reuse incoming transaction for reply */
t = kzalloc(sizeof(*t), GFP_KERNEL);
if (t == NULL) {
return_error = BR_FAILED_REPLY;
goto err_alloc_t_failed;
}
tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL);
if (tcomplete == NULL) {
return_error = BR_FAILED_REPLY;
goto err_alloc_tcomplete_failed;
}
if (!reply && !(tr->flags & TF_ONE_WAY))
t->from = thread;
else
t->from = NULL;
t->sender_euid = proc->tsk->cred->euid;
t->to_proc = target_proc;
t->to_thread = target_thread;
t->code = tr->code;
t->flags = tr->flags;
t->priority = task_nice(current);
t->buffer = binder_alloc_buf(target_proc, tr->data_size,
tr->offsets_size, !reply && (t->flags & TF_ONE_WAY));
if (t->buffer == NULL) {
return_error = BR_FAILED_REPLY;
goto err_binder_alloc_buf_failed;
}
t->buffer->allow_user_free = 0;
t->buffer->debug_id = t->debug_id;
t->buffer->transaction = t;
t->buffer->target_node = target_node;
if (target_node)
binder_inc_node(target_node, 1, 0, NULL);
offp = (size_t *)(t->buffer->data + ALIGN(tr->data_size, sizeof(void *)));
if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) {
binder_user_error("binder: %d:%d got transaction with invalid "
"data ptr\n", proc->pid, thread->pid);
return_error = BR_FAILED_REPLY;
goto err_copy_data_failed;
}
if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) {
binder_user_error("binder: %d:%d got transaction with invalid "
"offsets ptr\n", proc->pid, thread->pid);
return_error = BR_FAILED_REPLY;
goto err_copy_data_failed;
}
[cpp]
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static void
binder_pop_transaction(
struct binder_thread *target_thread, struct binder_transaction *t)
{
if (target_thread) {
BUG_ON(target_thread->transaction_stack != t);
BUG_ON(target_thread->transaction_stack->from != target_thread);
target_thread->transaction_stack =
target_thread->transaction_stack->from_parent;
t->from = NULL;
}
t->need_reply = 0;
if (t->buffer)
t->buffer->transaction = NULL;
kfree(t);
binder_stats.obj_deleted[BINDER_STAT_TRANSACTION]++;
}
最后,唤醒等待在target_wait队列上的线程了,就是最初调用IServiceManager::addService的MediaPlayerService的Server主线程了,它最后在binder_thread_read函数中睡眠在thread->wait上,就是这里的target_wait了:
[cpp]
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if (target_wait)
wake_up_interruptible(target_wait);
[cpp]
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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);
list_del(&w->entry);
kfree(w);
} break;
......
}
执行完这个函数后,就返回到binder_ioctl函数,执行下面语句,把数据返回给用户空间:
[cpp]
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if (copy_to_user(ubuf, &bwr, sizeof(bwr))) {
ret = -EFAULT;
goto err;
}
注意,这里的tr.flags等于0,这个是在上面的binder_send_reply函数里设置的。最终把结果保存在reply了:
[cpp]
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reply->ipcSetDataReference(
reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast<const size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(size_t),
freeBuffer, this);
[cpp]
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void ProcessState::startThreadPool()
{
AutoMutex _l(mLock);
if (!mThreadPoolStarted) {
mThreadPoolStarted = true;
spawnPooledThread(true);
}
}
[cpp]
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virtual bool threadLoop()
{
IPCThreadState::self()->joinThreadPool(mIsMain);
return false;
}
[cpp]
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status_t IPCThreadState::executeCommand(int32_t cmd)
{
BBinder* obj;
RefBase::weakref_type* refs;
status_t result = NO_ERROR;
switch (cmd) {
......
case BR_TRANSACTION:
{
binder_transaction_data tr;
result = mIn.read(&tr, sizeof(tr));
......
Parcel reply;
......
if (tr.target.ptr) {
sp<BBinder> b((BBinder*)tr.cookie);
const status_t error = b->transact(tr.code, buffer, &reply, tr.flags);
if (error < NO_ERROR) reply.setError(error);
} else {
const status_t error = the_context_object->transact(tr.code, buffer, &reply, tr.flags);
if (error < NO_ERROR) reply.setError(error);
}
......
}
break;
.......
}
if (result != NO_ERROR) {
mLastError = result;
}
return result;
}
[cpp]
view plaincopyprint?
status_t BnMediaPlayerService::onTransact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
switch(code) {
case CREATE_URL: {
......
} break;
case CREATE_FD: {
......
} break;
case DECODE_URL: {
......
} break;
case DECODE_FD: {
......
} break;
case CREATE_MEDIA_RECORDER: {
......
} break;
case CREATE_METADATA_RETRIEVER: {
......
} break;
case GET_OMX: {
......
} break;
default:
return BBinder::onTransact(code, data, reply, flags);
}
}
status_t BnMediaPlayerService::onTransact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
switch(code) {
case CREATE_URL: {
......
} break;
case CREATE_FD: {
......
} break;
case DECODE_URL: {
......
} break;
case DECODE_FD: {
......
} break;
case CREATE_MEDIA_RECORDER: {
......
} break;
case CREATE_METADATA_RETRIEVER: {
......
} break;
case GET_OMX: {
......
} break;
default:
return BBinder::onTransact(code, data, reply, flags);
}
}
至此,我们就以MediaPlayerService为例,完整地介绍了Android系统进程间通信Binder机制中的Server启动过程。Server启动起来之后,就会在一个无穷循环中等待Client的请求了。在下一篇文章中,我们将介绍Client如何通过Service Manager远程接口来获得Server远程接口,进而调用Server远程接口来使用Server提供的服务,敬请关注。
Manager远程接口之后,就要把自己的Service添加到Service Manager中去,然后把自己启动起来,等待Client的请求。本文将通过分析源代码了解Server的启动过程是怎么样的。
本文通过一个具体的例子来说明Binder机制中Server的启动过程。我们知道,在Android系统中,提供了多媒体播放的功能,这个功能是以服务的形式来提供的。这里,我们就通过分析MediaPlayerService的实现来了解Media Server的启动过程。
首先,看一下MediaPlayerService的类图,以便我们理解下面要描述的内容。
我们将要介绍的主角MediaPlayerService继承于BnMediaPlayerService类,熟悉Binder机制的同学应该知道BnMediaPlayerService是一个Binder Native类,用来处理Client请求的。BnMediaPlayerService继承于BnInterface<IMediaPlayerService>类,BnInterface是一个模板类,它定义在frameworks/base/include/binder/IInterface.h文件中:
[cpp]
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template<typename INTERFACE>
class BnInterface : public INTERFACE, public BBinder
{
public:
virtual sp<IInterface> queryLocalInterface(const String16& _descriptor);
virtual const String16& getInterfaceDescriptor() const;
protected:
virtual IBinder* onAsBinder();
};
[cpp] view plaincopyprint? int main(int argc, char** argv) { sp<ProcessState> proc(ProcessState::self()); sp<IServiceManager> sm = defaultServiceManager(); LOGI("ServiceManager: %p", sm.get()); AudioFlinger::instantiate(); MediaPlayerService::instantiate(); CameraService::instantiate(); AudioPolicyService::instantiate(); ProcessState::self()->startThreadPool(); IPCThreadState::self()->joinThreadPool(); } int main(int argc, char** argv) { sp<ProcessState> proc(ProcessState::self()); sp<IServiceManager> sm = defaultServiceManager(); LOGI("ServiceManager: %p", sm.get()); AudioFlinger::instantiate(); MediaPlayerService::instantiate(); CameraService::instantiate(); AudioPolicyService::instantiate(); ProcessState::self()->startThreadPool(); IPCThreadState::self()->joinThreadPool(); }这里我们不关注AudioFlinger和CameraService相关的代码。
先看下面这句代码:
[cpp]
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sp<ProcessState> proc(ProcessState::self());
[cpp] view plaincopyprint? sp<ProcessState> ProcessState::self() { if (gProcess != NULL) return gProcess; AutoMutex _l(gProcessMutex); if (gProcess == NULL) gProcess = new ProcessState; return gProcess; } sp<ProcessState> ProcessState::self() { if (gProcess != NULL) return gProcess; AutoMutex _l(gProcessMutex); if (gProcess == NULL) gProcess = new ProcessState; return gProcess; }这里可以看出,这个函数作用是返回一个全局唯一的ProcessState实例gProcess。全局唯一实例变量gProcess定义在frameworks/base/libs/binder/Static.cpp文件中:
[cpp]
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Mutex gProcessMutex;
sp<ProcessState> gProcess;
[cpp] view plaincopyprint? ProcessState::ProcessState() : mDriverFD(open_driver()) , mVMStart(MAP_FAILED) , mManagesContexts(false) , mBinderContextCheckFunc(NULL) , mBinderContextUserData(NULL) , mThreadPoolStarted(false) , mThreadPoolSeq(1) { if (mDriverFD >= 0) { // XXX Ideally, there should be a specific define for whether we // have mmap (or whether we could possibly have the kernel module // availabla). #if !defined(HAVE_WIN32_IPC) // mmap the binder, providing a chunk of virtual address space to receive transactions. mVMStart = mmap(0, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE | MAP_NORESERVE, mDriverFD, 0); if (mVMStart == MAP_FAILED) { // *sigh* LOGE("Using /dev/binder failed: unable to mmap transaction memory.\n"); close(mDriverFD); mDriverFD = -1; } #else mDriverFD = -1; #endif } if (mDriverFD < 0) { // Need to run without the driver, starting our own thread pool. } } ProcessState::ProcessState() : mDriverFD(open_driver()) , mVMStart(MAP_FAILED) , mManagesContexts(false) , mBinderContextCheckFunc(NULL) , mBinderContextUserData(NULL) , mThreadPoolStarted(false) , mThreadPoolSeq(1) { if (mDriverFD >= 0) { // XXX Ideally, there should be a specific define for whether we // have mmap (or whether we could possibly have the kernel module // availabla). #if !defined(HAVE_WIN32_IPC) // mmap the binder, providing a chunk of virtual address space to receive transactions. mVMStart = mmap(0, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE | MAP_NORESERVE, mDriverFD, 0); if (mVMStart == MAP_FAILED) { // *sigh* LOGE("Using /dev/binder failed: unable to mmap transaction memory.\n"); close(mDriverFD); mDriverFD = -1; } #else mDriverFD = -1; #endif } if (mDriverFD < 0) { // Need to run without the driver, starting our own thread pool. } }这个函数有两个关键地方,一是通过open_driver函数打开Binder设备文件/dev/binder,并将打开设备文件描述符保存在成员变量mDriverFD中;二是通过mmap来把设备文件/dev/binder映射到内存中。
先看open_driver函数的实现,这个函数同样位于frameworks/base/libs/binder/ProcessState.cpp文件中:
[cpp]
view plaincopyprint?
static int open_driver()
{
if (gSingleProcess) {
return -1;
}
int fd = open("/dev/binder", O_RDWR);
if (fd >= 0) {
fcntl(fd, F_SETFD, FD_CLOEXEC);
int vers;
#if defined(HAVE_ANDROID_OS)
status_t result = ioctl(fd, BINDER_VERSION, &vers);
#else
status_t result = -1;
errno = EPERM;
#endif
if (result == -1) {
LOGE("Binder ioctl to obtain version failed: %s", strerror(errno));
close(fd);
fd = -1;
}
if (result != 0 || vers != BINDER_CURRENT_PROTOCOL_VERSION) {
LOGE("Binder driver protocol does not match user space protocol!");
close(fd);
fd = -1;
}
#if defined(HAVE_ANDROID_OS)
size_t maxThreads = 15;
result = ioctl(fd, BINDER_SET_MAX_THREADS, &maxThreads);
if (result == -1) {
LOGE("Binder ioctl to set max threads failed: %s", strerror(errno));
}
#endif
} else {
LOGW("Opening '/dev/binder' failed: %s\n", strerror(errno));
}
return fd;
}
[cpp] view plaincopyprint? status_t result = ioctl(fd, BINDER_VERSION, &vers); status_t result = ioctl(fd, BINDER_VERSION, &vers);这个函数调用最终进入到Binder驱动程序的binder_ioctl函数中,我们只关注BINDER_VERSION相关的部分逻辑:
[cpp]
view plaincopyprint?
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;
/*printk(KERN_INFO "binder_ioctl: %d:%d %x %lx\n", proc->pid, current->pid, cmd, arg);*/
ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret)
return ret;
mutex_lock(&binder_lock);
thread = binder_get_thread(proc);
if (thread == NULL) {
ret = -ENOMEM;
goto err;
}
switch (cmd) {
......
case BINDER_VERSION:
if (size != sizeof(struct binder_version)) {
ret = -EINVAL;
goto err;
}
if (put_user(BINDER_CURRENT_PROTOCOL_VERSION, &((struct binder_version *)ubuf)->protocol_version)) {
ret = -EINVAL;
goto err;
}
break;
......
}
ret = 0;
err:
......
return ret;
}
[cpp] view plaincopyprint? /* This is the current protocol version. */ #define BINDER_CURRENT_PROTOCOL_VERSION 7 /* This is the current protocol version. */ #define BINDER_CURRENT_PROTOCOL_VERSION 7这里为什么要把ubuf转换成struct binder_version之后,再通过其protocol_version成员变量再来写入呢,转了一圈,最终内容还是写入到ubuf中。我们看一下struct binder_version的定义就会明白,同样是在kernel/common/drivers/staging/android/binder.h文件中:
[cpp]
view plaincopyprint?
/* Use with BINDER_VERSION, driver fills in fields. */
struct binder_version {
/* driver protocol version -- increment with incompatible change */
signed long protocol_version;
};
[cpp] view plaincopyprint? result = ioctl(fd, BINDER_SET_MAX_THREADS, &maxThreads); result = ioctl(fd, BINDER_SET_MAX_THREADS, &maxThreads);
这个函数调用最终进入到Binder驱动程序的binder_ioctl函数中,我们只关注BINDER_SET_MAX_THREADS相关的部分逻辑:
[cpp]
view plaincopyprint?
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;
/*printk(KERN_INFO "binder_ioctl: %d:%d %x %lx\n", proc->pid, current->pid, cmd, arg);*/
ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret)
return ret;
mutex_lock(&binder_lock);
thread = binder_get_thread(proc);
if (thread == NULL) {
ret = -ENOMEM;
goto err;
}
switch (cmd) {
......
case BINDER_SET_MAX_THREADS:
if (copy_from_user(&proc->max_threads, ubuf, sizeof(proc->max_threads))) {
ret = -EINVAL;
goto err;
}
break;
......
}
ret = 0;
err:
......
return ret;
}
[cpp] view plaincopyprint? #define BINDER_VM_SIZE ((1*1024*1024) - (4096 *2)) #define BINDER_VM_SIZE ((1*1024*1024) - (4096 *2))mmap函数调用完成之后,Binder驱动程序就为当前进程预留了BINDER_VM_SIZE大小的内存空间了。
这样,ProcessState全局唯一变量gProcess就创建完毕了,回到frameworks/base/media/mediaserver/main_mediaserver.cpp文件中的main函数,下一步是调用defaultServiceManager函数来获得Service Manager的远程接口,这个已经在上一篇文章浅谈Android系统进程间通信(IPC)机制Binder中的Server和Client获得Service
Manager接口之路有详细描述,读者可以回过头去参考一下。
再接下来,就进入到MediaPlayerService::instantiate函数把MediaPlayerService添加到Service Manger中去了。这个函数定义在frameworks/base/media/libmediaplayerservice/MediaPlayerService.cpp文件中:
[cpp]
view plaincopyprint?
void MediaPlayerService::instantiate() {
defaultServiceManager()->addService(
String16("media.player"), new MediaPlayerService());
}
[cpp] view plaincopyprint? class BpServiceManager : public BpInterface<IServiceManager> { public: BpServiceManager(const sp<IBinder>& impl) : BpInterface<IServiceManager>(impl) { } ...... virtual status_t addService(const String16& name, const sp<IBinder>& service) { Parcel data, reply; data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor()); data.writeString16(name); data.writeStrongBinder(service); status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply); return err == NO_ERROR ? reply.readExceptionCode() } ...... }; class BpServiceManager : public BpInterface<IServiceManager> { public: BpServiceManager(const sp<IBinder>& impl) : BpInterface<IServiceManager>(impl) { } ...... virtual status_t addService(const String16& name, const sp<IBinder>& service) { Parcel data, reply; data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor()); data.writeString16(name); data.writeStrongBinder(service); status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply); return err == NO_ERROR ? reply.readExceptionCode() } ...... };
这里的Parcel类是用来于序列化进程间通信数据用的。
先来看这一句的调用:
[cpp]
view plaincopyprint?
data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
[cpp] view plaincopyprint? // Write RPC headers. (previously just the interface token) status_t Parcel::writeInterfaceToken(const String16& interface) { writeInt32(IPCThreadState::self()->getStrictModePolicy() | STRICT_MODE_PENALTY_GATHER); // currently the interface identification token is just its name as a string return writeString16(interface); } // Write RPC headers. (previously just the interface token) status_t Parcel::writeInterfaceToken(const String16& interface) { writeInt32(IPCThreadState::self()->getStrictModePolicy() | STRICT_MODE_PENALTY_GATHER); // currently the interface identification token is just its name as a string return writeString16(interface); }它的作用是写入一个整数和一个字符串到Parcel中去。
再来看下面的调用:
[cpp]
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data.writeString16(name);
[cpp] view plaincopyprint? data.writeStrongBinder(service); data.writeStrongBinder(service);这里定入一个Binder对象到Parcel去。我们重点看一下这个函数的实现,因为它涉及到进程间传输Binder实体的问题,比较复杂,需要重点关注,同时,也是理解Binder机制的一个重点所在。注意,这里的service参数是一个MediaPlayerService对象。
[cpp]
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status_t Parcel::writeStrongBinder(const sp<IBinder>& val)
{
return flatten_binder(ProcessState::self(), val, this);
}
[cpp] view plaincopyprint? /* * This is the flattened representation of a Binder object for transfer * between processes. The 'offsets' supplied as part of a binder transaction * contains offsets into the data where these structures occur. The Binder * driver takes care of re-writing the structure type and data as it moves * between processes. */ struct flat_binder_object { /* 8 bytes for large_flat_header. */ unsigned long type; unsigned long flags; /* 8 bytes of data. */ union { void *binder; /* local object */ signed long handle; /* remote object */ }; /* extra data associated with local object */ void *cookie; }; /* * This is the flattened representation of a Binder object for transfer * between processes. The 'offsets' supplied as part of a binder transaction * contains offsets into the data where these structures occur. The Binder * driver takes care of re-writing the structure type and data as it moves * between processes. */ struct flat_binder_object { /* 8 bytes for large_flat_header. */ unsigned long type; unsigned long flags; /* 8 bytes of data. */ union { void *binder; /* local object */ signed long handle; /* remote object */ }; /* extra data associated with local object */ void *cookie; };各个成员变量的含义请参考资料Android Binder设计与实现。
我们进入到flatten_binder函数看看:
[cpp]
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status_t flatten_binder(const sp<ProcessState>& proc,
const sp<IBinder>& binder, Parcel* out)
{
flat_binder_object obj;
obj.flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS;
if (binder != NULL) {
IBinder *local = binder->localBinder();
if (!local) {
BpBinder *proxy = binder->remoteBinder();
if (proxy == NULL) {
LOGE("null proxy");
}
const int32_t handle = proxy ? proxy->handle() : 0;
obj.type = BINDER_TYPE_HANDLE;
obj.handle = handle;
obj.cookie = NULL;
} else {
obj.type = BINDER_TYPE_BINDER;
obj.binder = local->getWeakRefs();
obj.cookie = local;
}
} else {
obj.type = BINDER_TYPE_BINDER;
obj.binder = NULL;
obj.cookie = NULL;
}
return finish_flatten_binder(binder, obj, out);
}
[cpp] view plaincopyprint? obj.flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS; obj.flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS;0x7f表示处理本Binder实体请求数据包的线程的最低优先级,FLAT_BINDER_FLAG_ACCEPTS_FDS表示这个Binder实体可以接受文件描述符,Binder实体在收到文件描述符时,就会在本进程中打开这个文件。
传进来的binder即为MediaPlayerService::instantiate函数中new出来的MediaPlayerService实例,因此,不为空。又由于MediaPlayerService继承自BBinder类,它是一个本地Binder实体,因此binder->localBinder返回一个BBinder指针,而且肯定不为空,于是执行下面语句:
[cpp]
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obj.type = BINDER_TYPE_BINDER;
obj.binder = local->getWeakRefs();
obj.cookie = local;
[cpp] view plaincopyprint? inline static status_t finish_flatten_binder( const sp<IBinder>& binder, const flat_binder_object& flat, Parcel* out) { return out->writeObject(flat, false); } inline static status_t finish_flatten_binder( const sp<IBinder>& binder, const flat_binder_object& flat, Parcel* out) { return out->writeObject(flat, false); }Parcel::writeObject的实现如下:
[cpp]
view plaincopyprint?
status_t Parcel::writeObject(const flat_binder_object& val, bool nullMetaData)
{
const bool enoughData = (mDataPos+sizeof(val)) <= mDataCapacity;
const bool enoughObjects = mObjectsSize < mObjectsCapacity;
if (enoughData && enoughObjects) {
restart_write:
*reinterpret_cast<flat_binder_object*>(mData+mDataPos) = val;
// Need to write meta-data?
if (nullMetaData || val.binder != NULL) {
mObjects[mObjectsSize] = mDataPos;
acquire_object(ProcessState::self(), val, this);
mObjectsSize++;
}
// remember if it's a file descriptor
if (val.type == BINDER_TYPE_FD) {
mHasFds = mFdsKnown = true;
}
return finishWrite(sizeof(flat_binder_object));
}
if (!enoughData) {
const status_t err = growData(sizeof(val));
if (err != NO_ERROR) return err;
}
if (!enoughObjects) {
size_t newSize = ((mObjectsSize+2)*3)/2;
size_t* objects = (size_t*)realloc(mObjects, newSize*sizeof(size_t));
if (objects == NULL) return NO_MEMORY;
mObjects = objects;
mObjectsCapacity = newSize;
}
goto restart_write;
}
[cpp] view plaincopyprint? mObjects[mObjectsSize] = mDataPos; mObjects[mObjectsSize] = mDataPos;这里因为,如果进程间传输的数据间带有Binder对象的时候,Binder驱动程序需要作进一步的处理,以维护各个Binder实体的一致性,下面我们将会看到Binder驱动程序是怎么处理这些Binder对象的。
再回到BpServiceManager::addService函数中,调用下面语句:
[cpp]
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status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);
[cpp] view plaincopyprint? 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. if (mAlive) { status_t status = IPCThreadState::self()->transact( mHandle, code, data, reply, flags); if (status == DEAD_OBJECT) mAlive = 0; return status; } return DEAD_OBJECT; } 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. if (mAlive) { status_t status = IPCThreadState::self()->transact( mHandle, code, data, reply, flags); if (status == DEAD_OBJECT) mAlive = 0; return status; } return DEAD_OBJECT; }这里又调用了IPCThreadState::transact进执行实际的操作。注意,这里的mHandle为0,code为ADD_SERVICE_TRANSACTION。ADD_SERVICE_TRANSACTION是上面以参数形式传进来的,那mHandle为什么是0呢?因为这里表示的是Service Manager远程接口,它的句柄值一定是0,具体请参考浅谈Android系统进程间通信(IPC)机制Binder中的Server和Client获得Service
Manager接口之路一文。
再进入到IPCThreadState::transact函数,看看做了些什么事情:
[cpp]
view plaincopyprint?
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;
IF_LOG_TRANSACTIONS() {
TextOutput::Bundle _b(alog);
alog << "BC_TRANSACTION thr " << (void*)pthread_self() << " / hand "
<< handle << " / code " << TypeCode(code) << ": "
<< indent << data << dedent << endl;
}
if (err == NO_ERROR) {
LOG_ONEWAY(">>>> SEND from pid %d uid %d %s", getpid(), getuid(),
(flags & TF_ONE_WAY) == 0 ? "READ REPLY" : "ONE WAY");
err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);
}
if (err != NO_ERROR) {
if (reply) reply->setError(err);
return (mLastError = err);
}
if ((flags & TF_ONE_WAY) == 0) {
#if 0
if (code == 4) { // relayout
LOGI(">>>>>> CALLING transaction 4");
} else {
LOGI(">>>>>> CALLING transaction %d", code);
}
#endif
if (reply) {
err = waitForResponse(reply);
} else {
Parcel fakeReply;
err = waitForResponse(&fakeReply);
}
#if 0
if (code == 4) { // relayout
LOGI("<<<<<< RETURNING transaction 4");
} else {
LOGI("<<<<<< RETURNING transaction %d", code);
}
#endif
IF_LOG_TRANSACTIONS() {
TextOutput::Bundle _b(alog);
alog << "BR_REPLY thr " << (void*)pthread_self() << " / hand "
<< handle << ": ";
if (reply) alog << indent << *reply << dedent << endl;
else alog << "(none requested)" << endl;
}
} else {
err = waitForResponse(NULL, NULL);
}
return err;
}
[cpp] view plaincopyprint? struct binder_transaction_data { /* The first two are only used for bcTRANSACTION and brTRANSACTION, * identifying the target and contents of the transaction. */ union { size_t handle; /* target descriptor of command transaction */ void *ptr; /* target descriptor of return transaction */ } target; void *cookie; /* target object cookie */ unsigned int code; /* transaction command */ /* General information about the transaction. */ unsigned int flags; pid_t sender_pid; uid_t sender_euid; size_t data_size; /* number of bytes of data */ size_t offsets_size; /* number of bytes of offsets */ /* If this transaction is inline, the data immediately * follows here; otherwise, it ends with a pointer to * the data buffer. */ union { struct { /* transaction data */ const void *buffer; /* offsets from buffer to flat_binder_object structs */ const void *offsets; } ptr; uint8_t buf[8]; } data; }; struct binder_transaction_data { /* The first two are only used for bcTRANSACTION and brTRANSACTION, * identifying the target and contents of the transaction. */ union { size_t handle; /* target descriptor of command transaction */ void *ptr; /* target descriptor of return transaction */ } target; void *cookie; /* target object cookie */ unsigned int code; /* transaction command */ /* General information about the transaction. */ unsigned int flags; pid_t sender_pid; uid_t sender_euid; size_t data_size; /* number of bytes of data */ size_t offsets_size; /* number of bytes of offsets */ /* If this transaction is inline, the data immediately * follows here; otherwise, it ends with a pointer to * the data buffer. */ union { struct { /* transaction data */ const void *buffer; /* offsets from buffer to flat_binder_object structs */ const void *offsets; } ptr; uint8_t buf[8]; } data; };writeTransactionData函数的实现如下:
[cpp]
view plaincopyprint?
status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags,
int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer)
{
binder_transaction_data tr;
tr.target.handle = handle;
tr.code = code;
tr.flags = binderFlags;
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(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 = statusBuffer;
tr.offsets_size = 0;
tr.data.ptr.offsets = NULL;
} else {
return (mLastError = err);
}
mOut.writeInt32(cmd);
mOut.write(&tr, sizeof(tr));
return NO_ERROR;
}
[cpp] view plaincopyprint? tr.data_size = data.ipcDataSize(); tr.data.ptr.buffer = data.ipcData(); tr.offsets_size = data.ipcObjectsCount()*sizeof(size_t); tr.data.ptr.offsets = data.ipcObjects(); tr.data_size = data.ipcDataSize(); tr.data.ptr.buffer = data.ipcData(); tr.offsets_size = data.ipcObjectsCount()*sizeof(size_t); tr.data.ptr.offsets = data.ipcObjects();回忆一下上面的内容,写入到tr.data.ptr.buffer的内容相当于下面的内容:
[cpp]
view plaincopyprint?
writeInt32(IPCThreadState::self()->getStrictModePolicy() |
STRICT_MODE_PENALTY_GATHER);
writeString16("android.os.IServiceManager");
writeString16("media.player");
writeStrongBinder(new MediaPlayerService());
[cpp] view plaincopyprint? 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(); IF_LOG_COMMANDS() { alog << "Processing waitForResponse Command: " << getReturnString(cmd) << endl; } switch (cmd) { case BR_TRANSACTION_COMPLETE: if (!reply && !acquireResult) goto finish; break; case BR_DEAD_REPLY: err = DEAD_OBJECT; goto finish; case BR_FAILED_REPLY: err = FAILED_TRANSACTION; goto finish; case BR_ACQUIRE_RESULT: { LOG_ASSERT(acquireResult != NULL, "Unexpected brACQUIRE_RESULT"); const int32_t result = mIn.readInt32(); if (!acquireResult) continue; *acquireResult = result ? NO_ERROR : INVALID_OPERATION; } goto finish; case BR_REPLY: { binder_transaction_data tr; err = mIn.read(&tr, sizeof(tr)); LOG_ASSERT(err == NO_ERROR, "Not enough command data for brREPLY"); if (err != NO_ERROR) goto finish; if (reply) { if ((tr.flags & TF_STATUS_CODE) == 0) { reply->ipcSetDataReference( reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer), tr.data_size, reinterpret_cast<const size_t*>(tr.data.ptr.offsets), tr.offsets_size/sizeof(size_t), freeBuffer, this); } else { err = *static_cast<const status_t*>(tr.data.ptr.buffer); freeBuffer(NULL, reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer), tr.data_size, reinterpret_cast<const size_t*>(tr.data.ptr.offsets), tr.offsets_size/sizeof(size_t), this); } } else { freeBuffer(NULL, reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer), tr.data_size, reinterpret_cast<const size_t*>(tr.data.ptr.offsets), tr.offsets_size/sizeof(size_t), this); continue; } } goto finish; default: err = executeCommand(cmd); if (err != NO_ERROR) goto finish; break; } } finish: if (err != NO_ERROR) { if (acquireResult) *acquireResult = err; if (reply) reply->setError(err); mLastError = err; } return err; } 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(); IF_LOG_COMMANDS() { alog << "Processing waitForResponse Command: " << getReturnString(cmd) << endl; } switch (cmd) { case BR_TRANSACTION_COMPLETE: if (!reply && !acquireResult) goto finish; break; case BR_DEAD_REPLY: err = DEAD_OBJECT; goto finish; case BR_FAILED_REPLY: err = FAILED_TRANSACTION; goto finish; case BR_ACQUIRE_RESULT: { LOG_ASSERT(acquireResult != NULL, "Unexpected brACQUIRE_RESULT"); const int32_t result = mIn.readInt32(); if (!acquireResult) continue; *acquireResult = result ? NO_ERROR : INVALID_OPERATION; } goto finish; case BR_REPLY: { binder_transaction_data tr; err = mIn.read(&tr, sizeof(tr)); LOG_ASSERT(err == NO_ERROR, "Not enough command data for brREPLY"); if (err != NO_ERROR) goto finish; if (reply) { if ((tr.flags & TF_STATUS_CODE) == 0) { reply->ipcSetDataReference( reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer), tr.data_size, reinterpret_cast<const size_t*>(tr.data.ptr.offsets), tr.offsets_size/sizeof(size_t), freeBuffer, this); } else { err = *static_cast<const status_t*>(tr.data.ptr.buffer); freeBuffer(NULL, reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer), tr.data_size, reinterpret_cast<const size_t*>(tr.data.ptr.offsets), tr.offsets_size/sizeof(size_t), this); } } else { freeBuffer(NULL, reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer), tr.data_size, reinterpret_cast<const size_t*>(tr.data.ptr.offsets), tr.offsets_size/sizeof(size_t), this); continue; } } goto finish; default: err = executeCommand(cmd); if (err != NO_ERROR) goto finish; break; } } finish: if (err != NO_ERROR) { if (acquireResult) *acquireResult = err; if (reply) reply->setError(err); mLastError = err; } return err; }这个函数虽然很长,但是主要调用了talkWithDriver函数来与Binder驱动程序进行交互:
[cpp]
view plaincopyprint?
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();
// 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 = (long unsigned int)mOut.data();
// This is what we'll read.
if (doReceive && needRead) {
bwr.read_size = mIn.dataCapacity();
bwr.read_buffer = (long unsigned int)mIn.data();
} else {
bwr.read_size = 0;
}
IF_LOG_COMMANDS() {
TextOutput::Bundle _b(alog);
if (outAvail != 0) {
alog << "Sending commands to driver: " << indent;
const void* cmds = (const void*)bwr.write_buffer;
const void* end = ((const uint8_t*)cmds)+bwr.write_size;
alog << HexDump(cmds, bwr.write_size) << endl;
while (cmds < end) cmds = printCommand(alog, cmds);
alog << dedent;
}
alog << "Size of receive buffer: " << bwr.read_size
<< ", needRead: " << needRead << ", doReceive: " << doReceive << endl;
}
// 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 {
IF_LOG_COMMANDS() {
alog << "About to read/write, write size = " << mOut.dataSize() << endl;
}
#if defined(HAVE_ANDROID_OS)
if (ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) >= 0)
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_LOG_COMMANDS() {
alog << "Our err: " << (void*)err << ", write consumed: "
<< bwr.write_consumed << " (of " << mOut.dataSize()
<< "), read consumed: " << bwr.read_consumed << endl;
}
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);
}
IF_LOG_COMMANDS() {
TextOutput::Bundle _b(alog);
alog << "Remaining data size: " << mOut.dataSize() << endl;
alog << "Received commands from driver: " << indent;
const void* cmds = mIn.data();
const void* end = mIn.data() + mIn.dataSize();
alog << HexDump(cmds, mIn.dataSize()) << endl;
while (cmds < end) cmds = printReturnCommand(alog, cmds);
alog << dedent;
}
return NO_ERROR;
}
return err;
}
[cpp] view plaincopyprint? 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; /*printk(KERN_INFO "binder_ioctl: %d:%d %x %lx\n", proc->pid, current->pid, cmd, arg);*/ ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2); if (ret) return ret; mutex_lock(&binder_lock); thread = binder_get_thread(proc); if (thread == NULL) { ret = -ENOMEM; goto err; } switch (cmd) { 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))) { ret = -EFAULT; goto err; } if (binder_debug_mask & BINDER_DEBUG_READ_WRITE) printk(KERN_INFO "binder: %d:%d write %ld at %08lx, read %ld at %08lx\n", proc->pid, thread->pid, bwr.write_size, bwr.write_buffer, bwr.read_size, bwr.read_buffer); if (bwr.write_size > 0) { 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) { 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 (binder_debug_mask & BINDER_DEBUG_READ_WRITE) printk(KERN_INFO "binder: %d:%d wrote %ld of %ld, read return %ld of %ld\n", proc->pid, thread->pid, bwr.write_consumed, bwr.write_size, bwr.read_consumed, bwr.read_size); if (copy_to_user(ubuf, &bwr, sizeof(bwr))) { ret = -EFAULT; goto err; } break; } ...... } ret = 0; err: ...... return ret; } 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; /*printk(KERN_INFO "binder_ioctl: %d:%d %x %lx\n", proc->pid, current->pid, cmd, arg);*/ ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2); if (ret) return ret; mutex_lock(&binder_lock); thread = binder_get_thread(proc); if (thread == NULL) { ret = -ENOMEM; goto err; } switch (cmd) { 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))) { ret = -EFAULT; goto err; } if (binder_debug_mask & BINDER_DEBUG_READ_WRITE) printk(KERN_INFO "binder: %d:%d write %ld at %08lx, read %ld at %08lx\n", proc->pid, thread->pid, bwr.write_size, bwr.write_buffer, bwr.read_size, bwr.read_buffer); if (bwr.write_size > 0) { 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) { 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 (binder_debug_mask & BINDER_DEBUG_READ_WRITE) printk(KERN_INFO "binder: %d:%d wrote %ld of %ld, read return %ld of %ld\n", proc->pid, thread->pid, bwr.write_consumed, bwr.write_size, bwr.read_consumed, bwr.read_size); if (copy_to_user(ubuf, &bwr, sizeof(bwr))) { ret = -EFAULT; goto err; } break; } ...... } ret = 0; err: ...... return ret; }函数首先是将用户传进来的参数拷贝到本地变量struct binder_write_read bwr中去。这里bwr.write_size > 0为true,因此,进入到binder_thread_write函数中,我们只关注BC_TRANSACTION部分的逻辑:
[cpp]
view plaincopyprint?
binder_thread_write(struct binder_proc *proc, struct binder_thread *thread,
void __user *buffer, int size, signed long *consumed)
{
uint32_t cmd;
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);
if (_IOC_NR(cmd) < ARRAY_SIZE(binder_stats.bc)) {
binder_stats.bc[_IOC_NR(cmd)]++;
proc->stats.bc[_IOC_NR(cmd)]++;
thread->stats.bc[_IOC_NR(cmd)]++;
}
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;
}
[cpp] view plaincopyprint? 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; struct binder_transaction_log_entry *e; uint32_t return_error; ...... if (reply) { ...... } else { if (tr->target.handle) { ...... } else { target_node = binder_context_mgr_node; if (target_node == NULL) { return_error = BR_DEAD_REPLY; goto err_no_context_mgr_node; } } ...... target_proc = target_node->proc; if (target_proc == NULL) { return_error = BR_DEAD_REPLY; goto err_dead_binder; } ...... } if (target_thread) { ...... } else { target_list = &target_proc->todo; target_wait = &target_proc->wait; } ...... /* TODO: reuse incoming transaction for reply */ t = kzalloc(sizeof(*t), GFP_KERNEL); if (t == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_t_failed; } ...... tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL); if (tcomplete == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_tcomplete_failed; } ...... if (!reply && !(tr->flags & TF_ONE_WAY)) t->from = thread; else t->from = NULL; t->sender_euid = proc->tsk->cred->euid; t->to_proc = target_proc; t->to_thread = target_thread; t->code = tr->code; t->flags = tr->flags; t->priority = task_nice(current); t->buffer = binder_alloc_buf(target_proc, tr->data_size, tr->offsets_size, !reply && (t->flags & TF_ONE_WAY)); if (t->buffer == NULL) { return_error = BR_FAILED_REPLY; goto err_binder_alloc_buf_failed; } t->buffer->allow_user_free = 0; t->buffer->debug_id = t->debug_id; t->buffer->transaction = t; t->buffer->target_node = target_node; if (target_node) binder_inc_node(target_node, 1, 0, NULL); offp = (size_t *)(t->buffer->data + ALIGN(tr->data_size, sizeof(void *))); if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } ...... off_end = (void *)offp + tr->offsets_size; for (; offp < off_end; offp++) { struct flat_binder_object *fp; ...... fp = (struct flat_binder_object *)(t->buffer->data + *offp); 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); if (node == NULL) { 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); } if (fp->cookie != node->cookie) { ...... goto err_binder_get_ref_for_node_failed; } 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; } if (fp->type == BINDER_TYPE_BINDER) fp->type = BINDER_TYPE_HANDLE; else fp->type = BINDER_TYPE_WEAK_HANDLE; fp->handle = ref->desc; binder_inc_ref(ref, fp->type == BINDER_TYPE_HANDLE, &thread->todo); ...... } break; ...... } } if (reply) { ...... } else if (!(t->flags & TF_ONE_WAY)) { BUG_ON(t->buffer->async_transaction != 0); t->need_reply = 1; t->from_parent = thread->transaction_stack; thread->transaction_stack = t; } else { ...... } t->work.type = BINDER_WORK_TRANSACTION; list_add_tail(&t->work.entry, target_list); tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE; list_add_tail(&tcomplete->entry, &thread->todo); if (target_wait) wake_up_interruptible(target_wait); return; ...... } 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; struct binder_transaction_log_entry *e; uint32_t return_error; ...... if (reply) { ...... } else { if (tr->target.handle) { ...... } else { target_node = binder_context_mgr_node; if (target_node == NULL) { return_error = BR_DEAD_REPLY; goto err_no_context_mgr_node; } } ...... target_proc = target_node->proc; if (target_proc == NULL) { return_error = BR_DEAD_REPLY; goto err_dead_binder; } ...... } if (target_thread) { ...... } else { target_list = &target_proc->todo; target_wait = &target_proc->wait; } ...... /* TODO: reuse incoming transaction for reply */ t = kzalloc(sizeof(*t), GFP_KERNEL); if (t == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_t_failed; } ...... tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL); if (tcomplete == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_tcomplete_failed; } ...... if (!reply && !(tr->flags & TF_ONE_WAY)) t->from = thread; else t->from = NULL; t->sender_euid = proc->tsk->cred->euid; t->to_proc = target_proc; t->to_thread = target_thread; t->code = tr->code; t->flags = tr->flags; t->priority = task_nice(current); t->buffer = binder_alloc_buf(target_proc, tr->data_size, tr->offsets_size, !reply && (t->flags & TF_ONE_WAY)); if (t->buffer == NULL) { return_error = BR_FAILED_REPLY; goto err_binder_alloc_buf_failed; } t->buffer->allow_user_free = 0; t->buffer->debug_id = t->debug_id; t->buffer->transaction = t; t->buffer->target_node = target_node; if (target_node) binder_inc_node(target_node, 1, 0, NULL); offp = (size_t *)(t->buffer->data + ALIGN(tr->data_size, sizeof(void *))); if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } ...... off_end = (void *)offp + tr->offsets_size; for (; offp < off_end; offp++) { struct flat_binder_object *fp; ...... fp = (struct flat_binder_object *)(t->buffer->data + *offp); 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); if (node == NULL) { 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); } if (fp->cookie != node->cookie) { ...... goto err_binder_get_ref_for_node_failed; } 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; } if (fp->type == BINDER_TYPE_BINDER) fp->type = BINDER_TYPE_HANDLE; else fp->type = BINDER_TYPE_WEAK_HANDLE; fp->handle = ref->desc; binder_inc_ref(ref, fp->type == BINDER_TYPE_HANDLE, &thread->todo); ...... } break; ...... } } if (reply) { ...... } else if (!(t->flags & TF_ONE_WAY)) { BUG_ON(t->buffer->async_transaction != 0); t->need_reply = 1; t->from_parent = thread->transaction_stack; thread->transaction_stack = t; } else { ...... } t->work.type = BINDER_WORK_TRANSACTION; list_add_tail(&t->work.entry, target_list); tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE; list_add_tail(&tcomplete->entry, &thread->todo); if (target_wait) wake_up_interruptible(target_wait); return; ...... }注意,这里传进来的参数reply为0,tr->target.handle也为0。因此,target_proc、target_thread、target_node、target_list和target_wait的值分别为:
[cpp]
view plaincopyprint?
target_node = binder_context_mgr_node;
target_proc = target_node->proc;
target_list = &target_proc->todo;
target_wait = &target_proc->wait;
[cpp] view plaincopyprint? /* TODO: reuse incoming transaction for reply */ t = kzalloc(sizeof(*t), GFP_KERNEL); if (t == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_t_failed; } ...... tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL); if (tcomplete == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_tcomplete_failed; } ...... if (!reply && !(tr->flags & TF_ONE_WAY)) t->from = thread; else t->from = NULL; t->sender_euid = proc->tsk->cred->euid; t->to_proc = target_proc; t->to_thread = target_thread; t->code = tr->code; t->flags = tr->flags; t->priority = task_nice(current); t->buffer = binder_alloc_buf(target_proc, tr->data_size, tr->offsets_size, !reply && (t->flags & TF_ONE_WAY)); if (t->buffer == NULL) { return_error = BR_FAILED_REPLY; goto err_binder_alloc_buf_failed; } t->buffer->allow_user_free = 0; t->buffer->debug_id = t->debug_id; t->buffer->transaction = t; t->buffer->target_node = target_node; if (target_node) binder_inc_node(target_node, 1, 0, NULL); offp = (size_t *)(t->buffer->data + ALIGN(tr->data_size, sizeof(void *))); if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } /* TODO: reuse incoming transaction for reply */ t = kzalloc(sizeof(*t), GFP_KERNEL); if (t == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_t_failed; } ...... tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL); if (tcomplete == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_tcomplete_failed; } ...... if (!reply && !(tr->flags & TF_ONE_WAY)) t->from = thread; else t->from = NULL; t->sender_euid = proc->tsk->cred->euid; t->to_proc = target_proc; t->to_thread = target_thread; t->code = tr->code; t->flags = tr->flags; t->priority = task_nice(current); t->buffer = binder_alloc_buf(target_proc, tr->data_size, tr->offsets_size, !reply && (t->flags & TF_ONE_WAY)); if (t->buffer == NULL) { return_error = BR_FAILED_REPLY; goto err_binder_alloc_buf_failed; } t->buffer->allow_user_free = 0; t->buffer->debug_id = t->debug_id; t->buffer->transaction = t; t->buffer->target_node = target_node; if (target_node) binder_inc_node(target_node, 1, 0, NULL); offp = (size_t *)(t->buffer->data + ALIGN(tr->data_size, sizeof(void *))); if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; }注意,这里的事务t是要交给target_proc处理的,在这个场景之下,就是Service Manager了。因此,下面的语句:
[cpp]
view plaincopyprint?
t->buffer = binder_alloc_buf(target_proc, tr->data_size,
tr->offsets_size, !reply && (t->flags & TF_ONE_WAY));
[cpp] view plaincopyprint? if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) { ...... return_error = BR_FAILED_REPLY; goto err_copy_data_failed; }由于现在target_node要被使用了,增加它的引用计数:
[cpp]
view plaincopyprint?
if (target_node)
binder_inc_node(target_node, 1, 0, NULL);
[cpp] view plaincopyprint? 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); if (node == NULL) { 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); } if (fp->cookie != node->cookie) { ...... goto err_binder_get_ref_for_node_failed; } 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; } if (fp->type == BINDER_TYPE_BINDER) fp->type = BINDER_TYPE_HANDLE; else fp->type = BINDER_TYPE_WEAK_HANDLE; fp->handle = ref->desc; binder_inc_ref(ref, fp->type == BINDER_TYPE_HANDLE, &thread->todo); ...... } break; 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); if (node == NULL) { 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); } if (fp->cookie != node->cookie) { ...... goto err_binder_get_ref_for_node_failed; } 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; } if (fp->type == BINDER_TYPE_BINDER) fp->type = BINDER_TYPE_HANDLE; else fp->type = BINDER_TYPE_WEAK_HANDLE; fp->handle = ref->desc; binder_inc_ref(ref, fp->type == BINDER_TYPE_HANDLE, &thread->todo); ...... } break;由于是第一次在Binder驱动程序中传输这个MediaPlayerService,调用binder_get_node函数查询这个Binder实体时,会返回空,于是binder_new_node在proc中新建一个,下次就可以直接使用了。
现在,由于要把这个Binder实体MediaPlayerService交给target_proc,也就是Service Manager来管理,也就是说Service Manager要引用这个MediaPlayerService了,于是通过binder_get_ref_for_node为MediaPlayerService创建一个引用,并且通过binder_inc_ref来增加这个引用计数,防止这个引用还在使用过程当中就被销毁。注意,到了这里的时候,t->buffer中的flat_binder_obj的type已经改为BINDER_TYPE_HANDLE,handle已经改为ref->desc,跟原来不一样了,因为这个flat_binder_obj是最终是要传给Service
Manager的,而Service Manager只能够通过句柄值来引用这个Binder实体。
最后,把待处理事务加入到target_list列表中去:
[cpp]
view plaincopyprint?
list_add_tail(&t->work.entry, target_list);
[cpp] view plaincopyprint? list_add_tail(&tcomplete->entry, &thread->todo); list_add_tail(&tcomplete->entry, &thread->todo);现在目标进程有事情可做了,于是唤醒它:
[cpp]
view plaincopyprint?
if (target_wait)
wake_up_interruptible(target_wait);
[cpp] view plaincopyprint? 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); ....... if (wait_for_proc_work) { ....... } else { if (non_block) { if (!binder_has_thread_work(thread)) ret = -EAGAIN; } else ret = wait_event_interruptible(thread->wait, binder_has_thread_work(thread)); } ...... 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); 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; } if (end - ptr < sizeof(tr) + 4) 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); if (binder_debug_mask & BINDER_DEBUG_TRANSACTION_COMPLETE) printk(KERN_INFO "binder: %d:%d BR_TRANSACTION_COMPLETE\n", proc->pid, thread->pid); list_del(&w->entry); kfree(w); binder_stats.obj_deleted[BINDER_STAT_TRANSACTION_COMPLETE]++; } break; ...... } if (!t) continue; ...... } done: ...... return 0; } 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); ....... if (wait_for_proc_work) { ....... } else { if (non_block) { if (!binder_has_thread_work(thread)) ret = -EAGAIN; } else ret = wait_event_interruptible(thread->wait, binder_has_thread_work(thread)); } ...... 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); 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; } if (end - ptr < sizeof(tr) + 4) 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); if (binder_debug_mask & BINDER_DEBUG_TRANSACTION_COMPLETE) printk(KERN_INFO "binder: %d:%d BR_TRANSACTION_COMPLETE\n", proc->pid, thread->pid); list_del(&w->entry); kfree(w); binder_stats.obj_deleted[BINDER_STAT_TRANSACTION_COMPLETE]++; } break; ...... } if (!t) continue; ...... } done: ...... return 0; }
这里,thread->transaction_stack和thread->todo均不为空,于是wait_for_proc_work为false,由于binder_has_thread_work的时候,返回true,这里因为thread->todo不为空,因此,线程虽然调用了wait_event_interruptible,但是不会睡眠,于是继续往下执行。
由于thread->todo不为空,执行下列语句:
[cpp]
view plaincopyprint?
if (!list_empty(&thread->todo))
w = list_first_entry(&thread->todo, struct binder_work, entry);
[cpp] view plaincopyprint? 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); ...... list_del(&w->entry); kfree(w); } 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); ...... list_del(&w->entry); kfree(w); } break; ...... }这里就将w从thread->todo删除了。由于这里t为空,重新执行while循环,这时由于已经没有事情可做了,最后就返回到binder_ioctl函数中。注间,这里一共往用户传进来的缓冲区buffer写入了两个整数,分别是BR_NOOP和BR_TRANSACTION_COMPLETE。
binder_ioctl函数返回到用户空间之前,把数据消耗情况拷贝回用户空间中:
[cpp]
view plaincopyprint?
if (copy_to_user(ubuf, &bwr, sizeof(bwr))) {
ret = -EFAULT;
goto err;
}
[cpp] view plaincopyprint? 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) { <pre name="code" class="cpp"> mIn.setDataSize(bwr.read_consumed); mIn.setDataPosition(0); 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) { <pre name="code" class="cpp"> mIn.setDataSize(bwr.read_consumed); mIn.setDataPosition(0);} ...... return NO_ERROR; }
首先是把mOut的数据清空:
[cpp]
view plaincopyprint?
mOut.setDataSize(0);
[cpp] view plaincopyprint? mIn.setDataSize(bwr.read_consumed); mIn.setDataPosition(0); mIn.setDataSize(bwr.read_consumed); mIn.setDataPosition(0);然后返回到IPCThreadState::waitForResponse函数中。在IPCThreadState::waitForResponse函数,先是从mIn读出一个整数,这个便是BR_NOOP了,这是一个空操作,什么也不做。然后继续进入IPCThreadState::talkWithDriver函数中。
这时候,下面语句执行后:
[cpp]
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const bool needRead = mIn.dataPosition() >= mIn.dataSize();
[cpp] view plaincopyprint? const size_t outAvail = (!doReceive || needRead) ? mOut.dataSize() : 0; const size_t outAvail = (!doReceive || needRead) ? mOut.dataSize() : 0;outAvail等于0。因此,最后bwr.write_size和bwr.read_size均为0,IPCThreadState::talkWithDriver函数什么也不做,直接返回到IPCThreadState::waitForResponse函数中。在IPCThreadState::waitForResponse函数,又继续从mIn读出一个整数,这个便是BR_TRANSACTION_COMPLETE:
[cpp]
view plaincopyprint?
switch (cmd) {
case BR_TRANSACTION_COMPLETE:
if (!reply && !acquireResult) goto finish;
break;
......
}
[cpp] view plaincopyprint? ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr)进入到Binder驱动程序中的binder_ioctl函数中。由于bwr.write_size为0,bwr.read_size不为0,这次直接就进入到binder_thread_read函数中。这时候,thread->transaction_stack不等于0,但是thread->todo为空,于是线程就通过:
[cpp]
view plaincopyprint?
wait_event_interruptible(thread->wait, binder_has_thread_work(thread));
[cpp] view plaincopyprint? 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); ...... if (wait_for_proc_work) { ...... if (non_block) { if (!binder_has_proc_work(proc, thread)) ret = -EAGAIN; } else ret = wait_event_interruptible_exclusive(proc->wait, binder_has_proc_work(proc, thread)); } else { ...... } ...... 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); 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; } if (end - ptr < sizeof(tr) + 4) break; switch (w->type) { case BINDER_WORK_TRANSACTION: { t = container_of(w, struct binder_transaction, work); } break; ...... } if (!t) continue; BUG_ON(t->buffer == NULL); 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; ...... cmd = BR_TRANSACTION; } else { ...... } tr.code = t->code; tr.flags = t->flags; tr.sender_euid = t->sender_euid; if (t->from) { struct task_struct *sender = t->from->proc->tsk; tr.sender_pid = task_tgid_nr_ns(sender, current->nsproxy->pid_ns); } else { tr.sender_pid = 0; } tr.data_size = t->buffer->data_size; tr.offsets_size = t->buffer->offsets_size; tr.data.ptr.buffer = (void *)t->buffer->data + proc->user_buffer_offset; tr.data.ptr.offsets = tr.data.ptr.buffer + ALIGN(t->buffer->data_size, sizeof(void *)); 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; 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.obj_deleted[BINDER_STAT_TRANSACTION]++; } break; } done: ...... return 0; } 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); ...... if (wait_for_proc_work) { ...... if (non_block) { if (!binder_has_proc_work(proc, thread)) ret = -EAGAIN; } else ret = wait_event_interruptible_exclusive(proc->wait, binder_has_proc_work(proc, thread)); } else { ...... } ...... 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); 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; } if (end - ptr < sizeof(tr) + 4) break; switch (w->type) { case BINDER_WORK_TRANSACTION: { t = container_of(w, struct binder_transaction, work); } break; ...... } if (!t) continue; BUG_ON(t->buffer == NULL); 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; ...... cmd = BR_TRANSACTION; } else { ...... } tr.code = t->code; tr.flags = t->flags; tr.sender_euid = t->sender_euid; if (t->from) { struct task_struct *sender = t->from->proc->tsk; tr.sender_pid = task_tgid_nr_ns(sender, current->nsproxy->pid_ns); } else { tr.sender_pid = 0; } tr.data_size = t->buffer->data_size; tr.offsets_size = t->buffer->offsets_size; tr.data.ptr.buffer = (void *)t->buffer->data + proc->user_buffer_offset; tr.data.ptr.offsets = tr.data.ptr.buffer + ALIGN(t->buffer->data_size, sizeof(void *)); 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; 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.obj_deleted[BINDER_STAT_TRANSACTION]++; } break; } done: ...... return 0; }
Service Manager被唤醒之后,就进入while循环开始处理事务了。这里wait_for_proc_work等于1,并且proc->todo不为空,所以从proc->todo列表中得到第一个工作项:
[cpp]
view plaincopyprint?
w = list_first_entry(&proc->todo, struct binder_work, entry);
[cpp] view plaincopyprint? t = container_of(w, struct binder_transaction, work); t = container_of(w, struct binder_transaction, work);接着就是把事务项t中的数据拷贝到本地局部变量struct binder_transaction_data tr中去了:
[cpp]
view plaincopyprint?
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;
......
cmd = BR_TRANSACTION;
} else {
......
}
tr.code = t->code;
tr.flags = t->flags;
tr.sender_euid = t->sender_euid;
if (t->from) {
struct task_struct *sender = t->from->proc->tsk;
tr.sender_pid = task_tgid_nr_ns(sender, current->nsproxy->pid_ns);
} else {
tr.sender_pid = 0;
}
tr.data_size = t->buffer->data_size;
tr.offsets_size = t->buffer->offsets_size;
tr.data.ptr.buffer = (void *)t->buffer->data + proc->user_buffer_offset;
tr.data.ptr.offsets = tr.data.ptr.buffer + ALIGN(t->buffer->data_size, sizeof(void *));
[cpp] view plaincopyprint? tr.data.ptr.buffer = (void *)t->buffer->data + proc->user_buffer_offset; tr.data.ptr.offsets = tr.data.ptr.buffer + ALIGN(t->buffer->data_size, sizeof(void *)); tr.data.ptr.buffer = (void *)t->buffer->data + proc->user_buffer_offset; tr.data.ptr.offsets = tr.data.ptr.buffer + ALIGN(t->buffer->data_size, sizeof(void *));t->buffer->data所指向的地址是内核空间的,现在要把数据返回给Service Manager进程的用户空间,而Service Manager进程的用户空间是不能访问内核空间的数据的,所以这里要作一下处理。怎么处理呢?我们在学面向对象语言的时候,对象的拷贝有深拷贝和浅拷贝之分,深拷贝是把另外分配一块新内存,然后把原始对象的内容搬过去,浅拷贝是并没有为新对象分配一块新空间,而只是分配一个引用,而个引用指向原始对象。Binder机制用的是类似浅拷贝的方法,通过在用户空间分配一个虚拟地址,然后让这个用户空间虚拟地址与 t->buffer->data这个内核空间虚拟地址指向同一个物理地址,这样就可以实现浅拷贝了。怎么样用户空间和内核空间的虚拟地址同时指向同一个物理地址呢?请参考前面一篇文章浅谈Service
Manager成为Android进程间通信(IPC)机制Binder守护进程之路,那里有详细描述。这里只要将t->buffer->data加上一个偏移值proc->user_buffer_offset就可以得到t->buffer->data对应的用户空间虚拟地址了。调整了tr.data.ptr.buffer的值之后,不要忘记也要一起调整tr.data.ptr.offsets的值。
接着就是把tr的内容拷贝到用户传进来的缓冲区去了,指针ptr指向这个用户缓冲区的地址:
[cpp]
view plaincopyprint?
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);
[cpp] view plaincopyprint? list_del(&t->work.entry); t->buffer->allow_user_free = 1; 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.obj_deleted[BINDER_STAT_TRANSACTION]++; } list_del(&t->work.entry); t->buffer->allow_user_free = 1; 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.obj_deleted[BINDER_STAT_TRANSACTION]++; }注意,这里的cmd == BR_TRANSACTION && !(t->flags & TF_ONE_WAY)为true,表明这个事务虽然在驱动程序中已经处理完了,但是它仍然要等待Service Manager完成之后,给驱动程序一个确认,也就是需要等待回复,于是把当前事务t放在thread->transaction_stack队列的头部:
[cpp]
view plaincopyprint?
t->to_parent = thread->transaction_stack;
t->to_thread = thread;
thread->transaction_stack = t;
[cpp] view plaincopyprint? 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; ...... switch (cmd) { 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))) { ret = -EFAULT; goto err; } ...... if (bwr.read_size > 0) { 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))) { ret = -EFAULT; goto err; } break; } ...... default: ret = -EINVAL; goto err; } ret = 0; err: ...... return ret; } 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; ...... switch (cmd) { 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))) { ret = -EFAULT; goto err; } ...... if (bwr.read_size > 0) { 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))) { ret = -EFAULT; goto err; } break; } ...... default: ret = -EINVAL; goto err; } ret = 0; err: ...... return ret; }从binder_thread_read返回来后,再看看proc->todo是否还有事务等待处理,如果是,就把睡眠在proc->wait队列的线程唤醒来处理。最后,把本地变量struct binder_write_read bwr的内容拷贝回到用户传进来的缓冲区中,就返回了。
这里就是返回到frameworks/base/cmds/servicemanager/binder.c文件中的binder_loop函数了:
[cpp]
view plaincopyprint?
void binder_loop(struct binder_state *bs, binder_handler func)
{
int res;
struct binder_write_read bwr;
unsigned readbuf[32];
bwr.write_size = 0;
bwr.write_consumed = 0;
bwr.write_buffer = 0;
readbuf[0] = BC_ENTER_LOOPER;
binder_write(bs, readbuf, sizeof(unsigned));
for (;;) {
bwr.read_size = sizeof(readbuf);
bwr.read_consumed = 0;
bwr.read_buffer = (unsigned) readbuf;
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);
if (res < 0) {
LOGE("binder_loop: ioctl failed (%s)\n", strerror(errno));
break;
}
res = binder_parse(bs, 0, readbuf, bwr.read_consumed, func);
if (res == 0) {
LOGE("binder_loop: unexpected reply?!\n");
break;
}
if (res < 0) {
LOGE("binder_loop: io error %d %s\n", res, strerror(errno));
break;
}
}
}
[cpp] view plaincopyprint? int binder_parse(struct binder_state *bs, struct binder_io *bio, uint32_t *ptr, uint32_t size, binder_handler func) { int r = 1; uint32_t *end = ptr + (size / 4); while (ptr < end) { uint32_t cmd = *ptr++; ...... case BR_TRANSACTION: { struct binder_txn *txn = (void *) ptr; if ((end - ptr) * sizeof(uint32_t) < sizeof(struct binder_txn)) { LOGE("parse: txn too small!\n"); return -1; } binder_dump_txn(txn); 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); res = func(bs, txn, &msg, &reply); binder_send_reply(bs, &reply, txn->data, res); } ptr += sizeof(*txn) / sizeof(uint32_t); break; } ...... default: LOGE("parse: OOPS %d\n", cmd); return -1; } } return r; } int binder_parse(struct binder_state *bs, struct binder_io *bio, uint32_t *ptr, uint32_t size, binder_handler func) { int r = 1; uint32_t *end = ptr + (size / 4); while (ptr < end) { uint32_t cmd = *ptr++; ...... case BR_TRANSACTION: { struct binder_txn *txn = (void *) ptr; if ((end - ptr) * sizeof(uint32_t) < sizeof(struct binder_txn)) { LOGE("parse: txn too small!\n"); return -1; } binder_dump_txn(txn); 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); res = func(bs, txn, &msg, &reply); binder_send_reply(bs, &reply, txn->data, res); } ptr += sizeof(*txn) / sizeof(uint32_t); break; } ...... default: LOGE("parse: OOPS %d\n", cmd); return -1; } } return r; }首先把从Binder驱动程序读出来的数据转换为一个struct binder_txn结构体,保存在txn本地变量中,struct binder_txn定义在frameworks/base/cmds/servicemanager/binder.h文件中:
[cpp]
view plaincopyprint?
struct binder_txn
{
void *target;
void *cookie;
uint32_t code;
uint32_t flags;
uint32_t sender_pid;
uint32_t sender_euid;
uint32_t data_size;
uint32_t offs_size;
void *data;
void *offs;
};
[cpp] view plaincopyprint? struct binder_io { char *data; /* pointer to read/write from */ uint32_t *offs; /* array of offsets */ uint32_t data_avail; /* bytes available in data buffer */ uint32_t offs_avail; /* entries available in offsets array */ char *data0; /* start of data buffer */ uint32_t *offs0; /* start of offsets buffer */ uint32_t flags; uint32_t unused; }; struct binder_io { char *data; /* pointer to read/write from */ uint32_t *offs; /* array of offsets */ uint32_t data_avail; /* bytes available in data buffer */ uint32_t offs_avail; /* entries available in offsets array */ char *data0; /* start of data buffer */ uint32_t *offs0; /* start of offsets buffer */ uint32_t flags; uint32_t unused; };接着往下看,函数调bio_init来初始化reply变量:
[cpp]
view plaincopyprint?
void bio_init(struct binder_io *bio, void *data,
uint32_t maxdata, uint32_t maxoffs)
{
uint32_t n = maxoffs * sizeof(uint32_t);
if (n > maxdata) {
bio->flags = BIO_F_OVERFLOW;
bio->data_avail = 0;
bio->offs_avail = 0;
return;
}
bio->data = bio->data0 = data + n;
bio->offs = bio->offs0 = data;
bio->data_avail = maxdata - n;
bio->offs_avail = maxoffs;
bio->flags = 0;
}
[cpp] view plaincopyprint? void bio_init_from_txn(struct binder_io *bio, struct binder_txn *txn) { bio->data = bio->data0 = txn->data; bio->offs = bio->offs0 = txn->offs; bio->data_avail = txn->data_size; bio->offs_avail = txn->offs_size / 4; bio->flags = BIO_F_SHARED; } void bio_init_from_txn(struct binder_io *bio, struct binder_txn *txn) { bio->data = bio->data0 = txn->data; bio->offs = bio->offs0 = txn->offs; bio->data_avail = txn->data_size; bio->offs_avail = txn->offs_size / 4; bio->flags = BIO_F_SHARED; }最后,真正进行处理的函数是从参数中传进来的函数指针func,这里就是定义在frameworks/base/cmds/servicemanager/service_manager.c文件中的svcmgr_handler函数:
[cpp]
view plaincopyprint?
int svcmgr_handler(struct binder_state *bs,
struct binder_txn *txn,
struct binder_io *msg,
struct binder_io *reply)
{
struct svcinfo *si;
uint16_t *s;
unsigned len;
void *ptr;
uint32_t strict_policy;
if (txn->target != svcmgr_handle)
return -1;
// Equivalent to Parcel::enforceInterface(), reading the RPC
// header with the strict mode policy mask and the interface name.
// Note that we ignore the strict_policy and don't propagate it
// further (since we do no outbound RPCs anyway).
strict_policy = bio_get_uint32(msg);
s = bio_get_string16(msg, &len);
if ((len != (sizeof(svcmgr_id) / 2)) ||
memcmp(svcmgr_id, s, sizeof(svcmgr_id))) {
fprintf(stderr,"invalid id %s\n", str8(s));
return -1;
}
switch(txn->code) {
......
case SVC_MGR_ADD_SERVICE:
s = bio_get_string16(msg, &len);
ptr = bio_get_ref(msg);
if (do_add_service(bs, s, len, ptr, txn->sender_euid))
return -1;
break;
......
}
bio_put_uint32(reply, 0);
return 0;
}
[cpp] view plaincopyprint? writeInt32(IPCThreadState::self()->getStrictModePolicy() | STRICT_MODE_PENALTY_GATHER); writeString16("android.os.IServiceManager"); writeString16("media.player"); writeStrongBinder(new MediaPlayerService()); writeInt32(IPCThreadState::self()->getStrictModePolicy() | STRICT_MODE_PENALTY_GATHER); writeString16("android.os.IServiceManager"); writeString16("media.player"); writeStrongBinder(new MediaPlayerService());这里的语句:
[cpp]
view plaincopyprint?
strict_policy = bio_get_uint32(msg);
s = bio_get_string16(msg, &len);
s = bio_get_string16(msg, &len);
ptr = bio_get_ref(msg);
[cpp] view plaincopyprint? struct binder_object { uint32_t type; uint32_t flags; void *pointer; void *cookie; }; struct binder_object { uint32_t type; uint32_t flags; void *pointer; void *cookie; };这个结构体其实就是对应struct flat_binder_obj的。
接着看bio_get_ref实现:
[cpp]
view plaincopyprint?
void *bio_get_ref(struct binder_io *bio)
{
struct binder_object *obj;
obj = _bio_get_obj(bio);
if (!obj)
return 0;
if (obj->type == BINDER_TYPE_HANDLE)
return obj->pointer;
return 0;
}
[cpp] view plaincopyprint? int do_add_service(struct binder_state *bs, uint16_t *s, unsigned len, void *ptr, unsigned uid) { struct svcinfo *si; // LOGI("add_service('%s',%p) uid=%d\n", str8(s), ptr, uid); if (!ptr || (len == 0) || (len > 127)) return -1; if (!svc_can_register(uid, s)) { LOGE("add_service('%s',%p) uid=%d - PERMISSION DENIED\n", str8(s), ptr, uid); return -1; } si = find_svc(s, len); if (si) { if (si->ptr) { LOGE("add_service('%s',%p) uid=%d - ALREADY REGISTERED\n", str8(s), ptr, uid); return -1; } si->ptr = ptr; } else { si = malloc(sizeof(*si) + (len + 1) * sizeof(uint16_t)); if (!si) { LOGE("add_service('%s',%p) uid=%d - OUT OF MEMORY\n", str8(s), ptr, uid); return -1; } si->ptr = ptr; si->len = len; memcpy(si->name, s, (len + 1) * sizeof(uint16_t)); si->name[len] = '\0'; si->death.func = svcinfo_death; si->death.ptr = si; si->next = svclist; svclist = si; } binder_acquire(bs, ptr); binder_link_to_death(bs, ptr, &si->death); return 0; } int do_add_service(struct binder_state *bs, uint16_t *s, unsigned len, void *ptr, unsigned uid) { struct svcinfo *si; // LOGI("add_service('%s',%p) uid=%d\n", str8(s), ptr, uid); if (!ptr || (len == 0) || (len > 127)) return -1; if (!svc_can_register(uid, s)) { LOGE("add_service('%s',%p) uid=%d - PERMISSION DENIED\n", str8(s), ptr, uid); return -1; } si = find_svc(s, len); if (si) { if (si->ptr) { LOGE("add_service('%s',%p) uid=%d - ALREADY REGISTERED\n", str8(s), ptr, uid); return -1; } si->ptr = ptr; } else { si = malloc(sizeof(*si) + (len + 1) * sizeof(uint16_t)); if (!si) { LOGE("add_service('%s',%p) uid=%d - OUT OF MEMORY\n", str8(s), ptr, uid); return -1; } si->ptr = ptr; si->len = len; memcpy(si->name, s, (len + 1) * sizeof(uint16_t)); si->name[len] = '\0'; si->death.func = svcinfo_death; si->death.ptr = si; si->next = svclist; svclist = si; } binder_acquire(bs, ptr); binder_link_to_death(bs, ptr, &si->death); return 0; }这个函数的实现很简单,就是把MediaPlayerService这个Binder实体的引用写到一个struct svcinfo结构体中,主要是它的名称和句柄值,然后插入到链接svclist的头部去。这样,Client来向Service Manager查询服务接口时,只要给定服务名称,Service Manger就可以返回相应的句柄值了。
这个函数执行完成后,返回到svcmgr_handler函数,函数的最后,将一个错误码0写到reply变量中去,表示一切正常:
[cpp]
view plaincopyprint?
bio_put_uint32(reply, 0);
[cpp] view plaincopyprint? binder_send_reply(bs, &reply, txn->data, res); binder_send_reply(bs, &reply, txn->data, res);我们看一下binder_send_reply的实现,从函数名就可以猜到它要做什么了,告诉Binder驱动程序,它完成了Binder驱动程序交给它的任务了。
[cpp]
view plaincopyprint?
void binder_send_reply(struct binder_state *bs,
struct binder_io *reply,
void *buffer_to_free,
int status)
{
struct {
uint32_t cmd_free;
void *buffer;
uint32_t cmd_reply;
struct binder_txn txn;
} __attribute__((packed)) data;
data.cmd_free = BC_FREE_BUFFER;
data.buffer = buffer_to_free;
data.cmd_reply = BC_REPLY;
data.txn.target = 0;
data.txn.cookie = 0;
data.txn.code = 0;
if (status) {
data.txn.flags = TF_STATUS_CODE;
data.txn.data_size = sizeof(int);
data.txn.offs_size = 0;
data.txn.data = &status;
data.txn.offs = 0;
} else {
data.txn.flags = 0;
data.txn.data_size = reply->data - reply->data0;
data.txn.offs_size = ((char*) reply->offs) - ((char*) reply->offs0);
data.txn.data = reply->data0;
data.txn.offs = reply->offs0;
}
binder_write(bs, &data, sizeof(data));
}
[cpp] view plaincopyprint? int binder_write(struct binder_state *bs, void *data, unsigned len) { struct binder_write_read bwr; int res; bwr.write_size = len; bwr.write_consumed = 0; bwr.write_buffer = (unsigned) 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; } int binder_write(struct binder_state *bs, void *data, unsigned len) { struct binder_write_read bwr; int res; bwr.write_size = len; bwr.write_consumed = 0; bwr.write_buffer = (unsigned) 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; }这里可以看出,只有写操作,没有读操作,即read_size为0。
这里又是一个ioctl的BINDER_WRITE_READ操作。直入到驱动程序的binder_ioctl函数后,执行BINDER_WRITE_READ命令,这里就不累述了。
最后,从binder_ioctl执行到binder_thread_write函数,我们首先看第一个命令BC_FREE_BUFFER:
[cpp]
view plaincopyprint?
int
binder_thread_write(struct binder_proc *proc, struct binder_thread *thread,
void __user *buffer, int size, signed long *consumed)
{
uint32_t cmd;
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);
if (_IOC_NR(cmd) < ARRAY_SIZE(binder_stats.bc)) {
binder_stats.bc[_IOC_NR(cmd)]++;
proc->stats.bc[_IOC_NR(cmd)]++;
thread->stats.bc[_IOC_NR(cmd)]++;
}
switch (cmd) {
......
case BC_FREE_BUFFER: {
void __user *data_ptr;
struct binder_buffer *buffer;
if (get_user(data_ptr, (void * __user *)ptr))
return -EFAULT;
ptr += sizeof(void *);
buffer = binder_buffer_lookup(proc, data_ptr);
if (buffer == NULL) {
binder_user_error("binder: %d:%d "
"BC_FREE_BUFFER u%p no match\n",
proc->pid, thread->pid, data_ptr);
break;
}
if (!buffer->allow_user_free) {
binder_user_error("binder: %d:%d "
"BC_FREE_BUFFER u%p matched "
"unreturned buffer\n",
proc->pid, thread->pid, data_ptr);
break;
}
if (binder_debug_mask & BINDER_DEBUG_FREE_BUFFER)
printk(KERN_INFO "binder: %d:%d BC_FREE_BUFFER u%p found buffer %d for %s transaction\n",
proc->pid, thread->pid, data_ptr, buffer->debug_id,
buffer->transaction ? "active" : "finished");
if (buffer->transaction) {
buffer->transaction->buffer = NULL;
buffer->transaction = NULL;
}
if (buffer->async_transaction && buffer->target_node) {
BUG_ON(!buffer->target_node->has_async_transaction);
if (list_empty(&buffer->target_node->async_todo))
buffer->target_node->has_async_transaction = 0;
else
list_move_tail(buffer->target_node->async_todo.next, &thread->todo);
}
binder_transaction_buffer_release(proc, buffer, NULL);
binder_free_buf(proc, buffer);
break;
}
......
*consumed = ptr - buffer;
}
return 0;
}
[cpp] view plaincopyprint? get_user(data_ptr, (void * __user *)ptr) get_user(data_ptr, (void * __user *)ptr)这个是获得要删除的Buffer的用户空间地址,接着通过下面这个语句来找到这个地址对应的struct binder_buffer信息:
[cpp]
view plaincopyprint?
buffer = binder_buffer_lookup(proc, data_ptr);
[cpp] view plaincopyprint? binder_transaction_buffer_release(proc, buffer, NULL); binder_free_buf(proc, buffer); binder_transaction_buffer_release(proc, buffer, NULL); binder_free_buf(proc, buffer);再来看另外一个命令BC_REPLY:
[cpp]
view plaincopyprint?
int
binder_thread_write(struct binder_proc *proc, struct binder_thread *thread,
void __user *buffer, int size, signed long *consumed)
{
uint32_t cmd;
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);
if (_IOC_NR(cmd) < ARRAY_SIZE(binder_stats.bc)) {
binder_stats.bc[_IOC_NR(cmd)]++;
proc->stats.bc[_IOC_NR(cmd)]++;
thread->stats.bc[_IOC_NR(cmd)]++;
}
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;
}
[cpp] view plaincopyprint? 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; struct binder_transaction_log_entry *e; uint32_t return_error; ...... if (reply) { in_reply_to = thread->transaction_stack; if (in_reply_to == NULL) { ...... return_error = BR_FAILED_REPLY; goto err_empty_call_stack; } binder_set_nice(in_reply_to->saved_priority); if (in_reply_to->to_thread != thread) { ....... 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; } target_proc = target_thread->proc; } else { ...... } if (target_thread) { e->to_thread = target_thread->pid; target_list = &target_thread->todo; target_wait = &target_thread->wait; } else { ...... } /* TODO: reuse incoming transaction for reply */ t = kzalloc(sizeof(*t), GFP_KERNEL); if (t == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_t_failed; } tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL); if (tcomplete == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_tcomplete_failed; } if (!reply && !(tr->flags & TF_ONE_WAY)) t->from = thread; else t->from = NULL; t->sender_euid = proc->tsk->cred->euid; t->to_proc = target_proc; t->to_thread = target_thread; t->code = tr->code; t->flags = tr->flags; t->priority = task_nice(current); t->buffer = binder_alloc_buf(target_proc, tr->data_size, tr->offsets_size, !reply && (t->flags & TF_ONE_WAY)); if (t->buffer == NULL) { return_error = BR_FAILED_REPLY; goto err_binder_alloc_buf_failed; } t->buffer->allow_user_free = 0; t->buffer->debug_id = t->debug_id; t->buffer->transaction = t; t->buffer->target_node = target_node; if (target_node) binder_inc_node(target_node, 1, 0, NULL); offp = (size_t *)(t->buffer->data + ALIGN(tr->data_size, sizeof(void *))); if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) { binder_user_error("binder: %d:%d got transaction with invalid " "data ptr\n", proc->pid, thread->pid); return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) { binder_user_error("binder: %d:%d got transaction with invalid " "offsets ptr\n", proc->pid, thread->pid); return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } ...... if (reply) { BUG_ON(t->buffer->async_transaction != 0); binder_pop_transaction(target_thread, in_reply_to); } else if (!(t->flags & TF_ONE_WAY)) { ...... } else { ...... } t->work.type = BINDER_WORK_TRANSACTION; list_add_tail(&t->work.entry, target_list); tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE; list_add_tail(&tcomplete->entry, &thread->todo); if (target_wait) wake_up_interruptible(target_wait); return; ...... } 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; struct binder_transaction_log_entry *e; uint32_t return_error; ...... if (reply) { in_reply_to = thread->transaction_stack; if (in_reply_to == NULL) { ...... return_error = BR_FAILED_REPLY; goto err_empty_call_stack; } binder_set_nice(in_reply_to->saved_priority); if (in_reply_to->to_thread != thread) { ....... 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; } target_proc = target_thread->proc; } else { ...... } if (target_thread) { e->to_thread = target_thread->pid; target_list = &target_thread->todo; target_wait = &target_thread->wait; } else { ...... } /* TODO: reuse incoming transaction for reply */ t = kzalloc(sizeof(*t), GFP_KERNEL); if (t == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_t_failed; } tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL); if (tcomplete == NULL) { return_error = BR_FAILED_REPLY; goto err_alloc_tcomplete_failed; } if (!reply && !(tr->flags & TF_ONE_WAY)) t->from = thread; else t->from = NULL; t->sender_euid = proc->tsk->cred->euid; t->to_proc = target_proc; t->to_thread = target_thread; t->code = tr->code; t->flags = tr->flags; t->priority = task_nice(current); t->buffer = binder_alloc_buf(target_proc, tr->data_size, tr->offsets_size, !reply && (t->flags & TF_ONE_WAY)); if (t->buffer == NULL) { return_error = BR_FAILED_REPLY; goto err_binder_alloc_buf_failed; } t->buffer->allow_user_free = 0; t->buffer->debug_id = t->debug_id; t->buffer->transaction = t; t->buffer->target_node = target_node; if (target_node) binder_inc_node(target_node, 1, 0, NULL); offp = (size_t *)(t->buffer->data + ALIGN(tr->data_size, sizeof(void *))); if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) { binder_user_error("binder: %d:%d got transaction with invalid " "data ptr\n", proc->pid, thread->pid); return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) { binder_user_error("binder: %d:%d got transaction with invalid " "offsets ptr\n", proc->pid, thread->pid); return_error = BR_FAILED_REPLY; goto err_copy_data_failed; } ...... if (reply) { BUG_ON(t->buffer->async_transaction != 0); binder_pop_transaction(target_thread, in_reply_to); } else if (!(t->flags & TF_ONE_WAY)) { ...... } else { ...... } t->work.type = BINDER_WORK_TRANSACTION; list_add_tail(&t->work.entry, target_list); tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE; list_add_tail(&tcomplete->entry, &thread->todo); if (target_wait) wake_up_interruptible(target_wait); return; ...... }注意,这里的reply为1,我们忽略掉其它无关代码。
前面Service Manager正在binder_thread_read函数中被MediaPlayerService启动后进程唤醒后,在最后会把当前处理完的事务放在thread->transaction_stack中:
[cpp]
view plaincopyprint?
if (cmd == BR_TRANSACTION && !(t->flags & TF_ONE_WAY)) {
t->to_parent = thread->transaction_stack;
t->to_thread = thread;
thread->transaction_stack = t;
}
[cpp] view plaincopyprint? in_reply_to = thread->transaction_stack; in_reply_to = thread->transaction_stack;接着就可以通过in_reply_to得到最终发出这个事务请求的线程和进程:
[cpp]
view plaincopyprint?
target_thread = in_reply_to->from;
target_proc = target_thread->proc;
[cpp] view plaincopyprint? target_list = &target_thread->todo; target_wait = &target_thread->wait; target_list = &target_thread->todo; target_wait = &target_thread->wait;下面这一段代码:
[cpp]
view plaincopyprint?
/* TODO: reuse incoming transaction for reply */
t = kzalloc(sizeof(*t), GFP_KERNEL);
if (t == NULL) {
return_error = BR_FAILED_REPLY;
goto err_alloc_t_failed;
}
tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL);
if (tcomplete == NULL) {
return_error = BR_FAILED_REPLY;
goto err_alloc_tcomplete_failed;
}
if (!reply && !(tr->flags & TF_ONE_WAY))
t->from = thread;
else
t->from = NULL;
t->sender_euid = proc->tsk->cred->euid;
t->to_proc = target_proc;
t->to_thread = target_thread;
t->code = tr->code;
t->flags = tr->flags;
t->priority = task_nice(current);
t->buffer = binder_alloc_buf(target_proc, tr->data_size,
tr->offsets_size, !reply && (t->flags & TF_ONE_WAY));
if (t->buffer == NULL) {
return_error = BR_FAILED_REPLY;
goto err_binder_alloc_buf_failed;
}
t->buffer->allow_user_free = 0;
t->buffer->debug_id = t->debug_id;
t->buffer->transaction = t;
t->buffer->target_node = target_node;
if (target_node)
binder_inc_node(target_node, 1, 0, NULL);
offp = (size_t *)(t->buffer->data + ALIGN(tr->data_size, sizeof(void *)));
if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) {
binder_user_error("binder: %d:%d got transaction with invalid "
"data ptr\n", proc->pid, thread->pid);
return_error = BR_FAILED_REPLY;
goto err_copy_data_failed;
}
if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) {
binder_user_error("binder: %d:%d got transaction with invalid "
"offsets ptr\n", proc->pid, thread->pid);
return_error = BR_FAILED_REPLY;
goto err_copy_data_failed;
}
[cpp] view plaincopyprint? binder_pop_transaction(target_thread, in_reply_to); binder_pop_transaction(target_thread, in_reply_to);我们看看做了什么事情:
[cpp]
view plaincopyprint?
static void
binder_pop_transaction(
struct binder_thread *target_thread, struct binder_transaction *t)
{
if (target_thread) {
BUG_ON(target_thread->transaction_stack != t);
BUG_ON(target_thread->transaction_stack->from != target_thread);
target_thread->transaction_stack =
target_thread->transaction_stack->from_parent;
t->from = NULL;
}
t->need_reply = 0;
if (t->buffer)
t->buffer->transaction = NULL;
kfree(t);
binder_stats.obj_deleted[BINDER_STAT_TRANSACTION]++;
}
[cpp] view plaincopyprint? t->work.type = BINDER_WORK_TRANSACTION; list_add_tail(&t->work.entry, target_list); tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE; list_add_tail(&tcomplete->entry, &thread->todo); t->work.type = BINDER_WORK_TRANSACTION; list_add_tail(&t->work.entry, target_list); tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE; list_add_tail(&tcomplete->entry, &thread->todo);和前面一样,分别把t和tcomplete分别放在target_list和thread->todo队列中,这里的target_list指的就是最初调用IServiceManager::addService的MediaPlayerService的Server主线程的的thread->todo队列了,而thread->todo指的是Service Manager中用来回复IServiceManager::addService请求的线程。
最后,唤醒等待在target_wait队列上的线程了,就是最初调用IServiceManager::addService的MediaPlayerService的Server主线程了,它最后在binder_thread_read函数中睡眠在thread->wait上,就是这里的target_wait了:
[cpp]
view plaincopyprint?
if (target_wait)
wake_up_interruptible(target_wait);
[cpp] view plaincopyprint? list_add_tail(&tcomplete->entry, &thread->todo); list_add_tail(&tcomplete->entry, &thread->todo);把一个工作项tcompelete放在了在thread->todo中,这个tcompelete的type为BINDER_WORK_TRANSACTION_COMPLETE,因此,Binder驱动程序会执行下面操作:
[cpp]
view plaincopyprint?
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);
list_del(&w->entry);
kfree(w);
} break;
......
}
[cpp] view plaincopyprint? 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); ...... if (wait_for_proc_work) { ...... } else { if (non_block) { if (!binder_has_thread_work(thread)) ret = -EAGAIN; } else ret = wait_event_interruptible(thread->wait, binder_has_thread_work(thread)); } ...... 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); 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) { case BINDER_WORK_TRANSACTION: { t = container_of(w, struct binder_transaction, work); } break; ...... } if (!t) continue; BUG_ON(t->buffer == NULL); if (t->buffer->target_node) { ...... } else { tr.target.ptr = NULL; tr.cookie = NULL; cmd = BR_REPLY; } tr.code = t->code; tr.flags = t->flags; tr.sender_euid = t->sender_euid; if (t->from) { ...... } else { tr.sender_pid = 0; } tr.data_size = t->buffer->data_size; tr.offsets_size = t->buffer->offsets_size; tr.data.ptr.buffer = (void *)t->buffer->data + proc->user_buffer_offset; tr.data.ptr.offsets = tr.data.ptr.buffer + ALIGN(t->buffer->data_size, sizeof(void *)); 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; if (cmd == BR_TRANSACTION && !(t->flags & TF_ONE_WAY)) { ...... } else { t->buffer->transaction = NULL; kfree(t); binder_stats.obj_deleted[BINDER_STAT_TRANSACTION]++; } break; } done: ...... return 0; } 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); ...... if (wait_for_proc_work) { ...... } else { if (non_block) { if (!binder_has_thread_work(thread)) ret = -EAGAIN; } else ret = wait_event_interruptible(thread->wait, binder_has_thread_work(thread)); } ...... 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); 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) { case BINDER_WORK_TRANSACTION: { t = container_of(w, struct binder_transaction, work); } break; ...... } if (!t) continue; BUG_ON(t->buffer == NULL); if (t->buffer->target_node) { ...... } else { tr.target.ptr = NULL; tr.cookie = NULL; cmd = BR_REPLY; } tr.code = t->code; tr.flags = t->flags; tr.sender_euid = t->sender_euid; if (t->from) { ...... } else { tr.sender_pid = 0; } tr.data_size = t->buffer->data_size; tr.offsets_size = t->buffer->offsets_size; tr.data.ptr.buffer = (void *)t->buffer->data + proc->user_buffer_offset; tr.data.ptr.offsets = tr.data.ptr.buffer + ALIGN(t->buffer->data_size, sizeof(void *)); 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; if (cmd == BR_TRANSACTION && !(t->flags & TF_ONE_WAY)) { ...... } else { t->buffer->transaction = NULL; kfree(t); binder_stats.obj_deleted[BINDER_STAT_TRANSACTION]++; } break; } done: ...... return 0; }在while循环中,从thread->todo得到w,w->type为BINDER_WORK_TRANSACTION,于是,得到t。从上面可以知道,Service Manager反回了一个0回来,写在t->buffer->data里面,现在把t->buffer->data加上proc->user_buffer_offset,得到用户空间地址,保存在tr.data.ptr.buffer里面,这样用户空间就可以访问这个返回码了。由于cmd不等于BR_TRANSACTION,这时就可以把t删除掉了,因为以后都不需要用了。
执行完这个函数后,就返回到binder_ioctl函数,执行下面语句,把数据返回给用户空间:
[cpp]
view plaincopyprint?
if (copy_to_user(ubuf, &bwr, sizeof(bwr))) {
ret = -EFAULT;
goto err;
}
[cpp] view plaincopyprint? status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult) { int32_t cmd; int32_t err; while (1) { if ((err=talkWithDriver()) < NO_ERROR) break; ...... cmd = mIn.readInt32(); ...... switch (cmd) { ...... case BR_REPLY: { binder_transaction_data tr; err = mIn.read(&tr, sizeof(tr)); LOG_ASSERT(err == NO_ERROR, "Not enough command data for brREPLY"); if (err != NO_ERROR) goto finish; if (reply) { if ((tr.flags & TF_STATUS_CODE) == 0) { reply->ipcSetDataReference( reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer), tr.data_size, reinterpret_cast<const size_t*>(tr.data.ptr.offsets), tr.offsets_size/sizeof(size_t), freeBuffer, this); } else { ...... } } else { ...... } } goto finish; ...... } } finish: ...... return err; } status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult) { int32_t cmd; int32_t err; while (1) { if ((err=talkWithDriver()) < NO_ERROR) break; ...... cmd = mIn.readInt32(); ...... switch (cmd) { ...... case BR_REPLY: { binder_transaction_data tr; err = mIn.read(&tr, sizeof(tr)); LOG_ASSERT(err == NO_ERROR, "Not enough command data for brREPLY"); if (err != NO_ERROR) goto finish; if (reply) { if ((tr.flags & TF_STATUS_CODE) == 0) { reply->ipcSetDataReference( reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer), tr.data_size, reinterpret_cast<const size_t*>(tr.data.ptr.offsets), tr.offsets_size/sizeof(size_t), freeBuffer, this); } else { ...... } } else { ...... } } goto finish; ...... } } finish: ...... return err; }
注意,这里的tr.flags等于0,这个是在上面的binder_send_reply函数里设置的。最终把结果保存在reply了:
[cpp]
view plaincopyprint?
reply->ipcSetDataReference(
reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast<const size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(size_t),
freeBuffer, this);
[cpp] view plaincopyprint? ProcessState::self()->startThreadPool(); IPCThreadState::self()->joinThreadPool(); ProcessState::self()->startThreadPool(); IPCThreadState::self()->joinThreadPool();首先看ProcessState::startThreadPool函数的实现:
[cpp]
view plaincopyprint?
void ProcessState::startThreadPool()
{
AutoMutex _l(mLock);
if (!mThreadPoolStarted) {
mThreadPoolStarted = true;
spawnPooledThread(true);
}
}
[cpp] view plaincopyprint? void ProcessState::spawnPooledThread(bool isMain) { if (mThreadPoolStarted) { int32_t s = android_atomic_add(1, &mThreadPoolSeq); char buf[32]; sprintf(buf, "Binder Thread #%d", s); LOGV("Spawning new pooled thread, name=%s\n", buf); sp<Thread> t = new PoolThread(isMain); t->run(buf); } } void ProcessState::spawnPooledThread(bool isMain) { if (mThreadPoolStarted) { int32_t s = android_atomic_add(1, &mThreadPoolSeq); char buf[32]; sprintf(buf, "Binder Thread #%d", s); LOGV("Spawning new pooled thread, name=%s\n", buf); sp<Thread> t = new PoolThread(isMain); t->run(buf); } }这里主要是创建一个线程,PoolThread继续Thread类,Thread类定义在frameworks/base/libs/utils/Threads.cpp文件中,其run函数最终调用子类的threadLoop函数,这里即为PoolThread::threadLoop函数:
[cpp]
view plaincopyprint?
virtual bool threadLoop()
{
IPCThreadState::self()->joinThreadPool(mIsMain);
return false;
}
[cpp] view plaincopyprint? void IPCThreadState::joinThreadPool(bool isMain) { LOG_THREADPOOL("**** THREAD %p (PID %d) IS JOINING THE THREAD POOL\n", (void*)pthread_self(), getpid()); mOut.writeInt32(isMain ? BC_ENTER_LOOPER : BC_REGISTER_LOOPER); ...... status_t result; do { int32_t cmd; ....... // now get the next command to be processed, waiting if necessary result = talkWithDriver(); if (result >= NO_ERROR) { size_t IN = mIn.dataAvail(); if (IN < sizeof(int32_t)) continue; cmd = mIn.readInt32(); ...... } result = executeCommand(cmd); } ...... } while (result != -ECONNREFUSED && result != -EBADF); ....... mOut.writeInt32(BC_EXIT_LOOPER); talkWithDriver(false); } void IPCThreadState::joinThreadPool(bool isMain) { LOG_THREADPOOL("**** THREAD %p (PID %d) IS JOINING THE THREAD POOL\n", (void*)pthread_self(), getpid()); mOut.writeInt32(isMain ? BC_ENTER_LOOPER : BC_REGISTER_LOOPER); ...... status_t result; do { int32_t cmd; ....... // now get the next command to be processed, waiting if necessary result = talkWithDriver(); if (result >= NO_ERROR) { size_t IN = mIn.dataAvail(); if (IN < sizeof(int32_t)) continue; cmd = mIn.readInt32(); ...... } result = executeCommand(cmd); } ...... } while (result != -ECONNREFUSED && result != -EBADF); ....... mOut.writeInt32(BC_EXIT_LOOPER); talkWithDriver(false); }这个函数最终是在一个无穷循环中,通过调用talkWithDriver函数来和Binder驱动程序进行交互,实际上就是调用talkWithDriver来等待Client的请求,然后再调用executeCommand来处理请求,而在executeCommand函数中,最终会调用BBinder::transact来真正处理Client的请求:
[cpp]
view plaincopyprint?
status_t IPCThreadState::executeCommand(int32_t cmd)
{
BBinder* obj;
RefBase::weakref_type* refs;
status_t result = NO_ERROR;
switch (cmd) {
......
case BR_TRANSACTION:
{
binder_transaction_data tr;
result = mIn.read(&tr, sizeof(tr));
......
Parcel reply;
......
if (tr.target.ptr) {
sp<BBinder> b((BBinder*)tr.cookie);
const status_t error = b->transact(tr.code, buffer, &reply, tr.flags);
if (error < NO_ERROR) reply.setError(error);
} else {
const status_t error = the_context_object->transact(tr.code, buffer, &reply, tr.flags);
if (error < NO_ERROR) reply.setError(error);
}
......
}
break;
.......
}
if (result != NO_ERROR) {
mLastError = result;
}
return result;
}
[cpp] view plaincopyprint? status_t BBinder::transact( uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags) { data.setDataPosition(0); status_t err = NO_ERROR; switch (code) { case PING_TRANSACTION: reply->writeInt32(pingBinder()); break; default: err = onTransact(code, data, reply, flags); break; } if (reply != NULL) { reply->setDataPosition(0); } return err; } status_t BBinder::transact( uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags) { data.setDataPosition(0); status_t err = NO_ERROR; switch (code) { case PING_TRANSACTION: reply->writeInt32(pingBinder()); break; default: err = onTransact(code, data, reply, flags); break; } if (reply != NULL) { reply->setDataPosition(0); } return err; }最终会调用onTransact函数来处理。在这个场景中,BnMediaPlayerService继承了BBinder类,并且重载了onTransact函数,因此,这里实际上是调用了BnMediaPlayerService::onTransact函数,这个函数定义在frameworks/base/libs/media/libmedia/IMediaPlayerService.cpp文件中:
[cpp]
view plaincopyprint?
status_t BnMediaPlayerService::onTransact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
switch(code) {
case CREATE_URL: {
......
} break;
case CREATE_FD: {
......
} break;
case DECODE_URL: {
......
} break;
case DECODE_FD: {
......
} break;
case CREATE_MEDIA_RECORDER: {
......
} break;
case CREATE_METADATA_RETRIEVER: {
......
} break;
case GET_OMX: {
......
} break;
default:
return BBinder::onTransact(code, data, reply, flags);
}
}
status_t BnMediaPlayerService::onTransact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
switch(code) {
case CREATE_URL: {
......
} break;
case CREATE_FD: {
......
} break;
case DECODE_URL: {
......
} break;
case DECODE_FD: {
......
} break;
case CREATE_MEDIA_RECORDER: {
......
} break;
case CREATE_METADATA_RETRIEVER: {
......
} break;
case GET_OMX: {
......
} break;
default:
return BBinder::onTransact(code, data, reply, flags);
}
}
至此,我们就以MediaPlayerService为例,完整地介绍了Android系统进程间通信Binder机制中的Server启动过程。Server启动起来之后,就会在一个无穷循环中等待Client的请求了。在下一篇文章中,我们将介绍Client如何通过Service Manager远程接口来获得Server远程接口,进而调用Server远程接口来使用Server提供的服务,敬请关注。
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