本文參考《Android系统源代码情景分析》，作者罗升阳
一、service manager代码：
～/Android/frameworks/base/cmd/servicemanager
----binder.c
----service_manager.c
----binder.h
驱动层代码：
～/Android//kernel/goldfish/drivers/staging/android
----binder.c
----binder.h
二、源代码分析
从Android Binder进程间通信---Service Manager进程。处理BC_TRANSACTION，返回BR_TRANSACTIONhttp://blog.csdn.net/jltxgcy/article/details/26151113，我们已经知道Service Manager成功地将一个Service组件注冊到内部的Service组件列表所svclist中之后，接着就会调用函数binder_send_reply将Service组件注冊结果返回给Binder驱动程序，Binder驱动程序再将该结果返回给请求注冊Service组件的进程。
～/Android/frameworks/base/cmd/servicemanager
----binder.c
void binder_send_reply(struct binder_state *bs,
struct binder_io *reply,
void *buffer_to_free,
int status) //status为0。注冊成功代码0写入binder_io结构体reply中
{
struct {
uint32_t cmd_free;
void *buffer;
uint32_t cmd_reply;
struct binder_txn txn;
} __attribute__((packed)) data;
data.cmd_free = BC_FREE_BUFFER;//BC_FREE_BUFFER后面跟的通信数据是一个内核缓冲区的用户空间地址
data.buffer = buffer_to_free;//一个用户空间地址，指向一块用来传输进程间通信数据的内核缓冲区
data.cmd_reply = BC_REPLY;//BC_REPLY后面跟的通信数据是一个binder_transaction_data结构体。即一个binder_txn结构体
data.txn.target = 0;
data.txn.cookie = 0;
data.txn.code = 0;
if (status) {//status为0
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;//0的大小，由于做为do_add_service成功，reply结构体放入0
data.txn.offs_size = ((char*) reply->offs) - ((char*) reply->offs0);//0
data.txn.data = reply->data0;//指向了0
data.txn.offs = reply->offs0;//无
}
binder_write(bs, &data, sizeof(data));
} 首先定义了一个匿名结构体data，用来描写叙述一个BC_FREE_BUFFER和一个BC_REPLY命令协议。分别用成员变量cmd_free和cmd_reply来表示。命令协议BC_FREE_BUFFER后面跟的通信数据是一个内核缓冲区的用户空间地址，它就保存在成员变量buffer中；而命令协议BC_REPLY后面跟的通信数据是一个binder_transaction_data结构体，即一个binder_txn结构体。它就保存在成员变量txn中。然后调用binder_write将匿名结构体data中BC_FREE_BUFFER和BC_REPLY命令协议发送给Binder驱动程序。
实现例如以下：
～/Android/frameworks/base/cmd/servicemanager
----binder.c
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;//匿名结构体data指针
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)
",
strerror(errno));
}
return res;
} 函数binder_write是通过IO控制命令BINDER_WRITE_READ来将BC_FREE_BUFFER和BC_REPLY命令协议发送给Binder驱动程序的，映射到驱动程序binder_thread_write。～/Android//kernel/goldfish/drivers/staging/android
----binder.c
int
binder_thread_write(struct binder_proc *proc, struct binder_thread *thread,
void __user *buffer, int size, signed long *consumed)
{
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);
......
case BC_TRANSACTION:
case BC_REPLY: {
struct binder_transaction_data tr;
if (copy_from_user(&tr, ptr, sizeof(tr)))//上面刚提到的binder_txn结构体data.txn
return -EFAULT;
ptr += sizeof(tr);
binder_transaction(proc, thread, &tr, cmd == BC_REPLY);//tr为上面已经赋值的data.txn
break;
}
........
default:
printk(KERN_ERR "binder: %d:%d unknown command %d
", proc->pid, thread->pid, cmd);
return -EINVAL;
}
*consumed = ptr - buffer;
}
return 0;
} 我们临时不分析BC_FREE_BUFFER命令，仅仅分析BC_REPLY，while第二次循环会运行到这里。tr就是上面已经赋值的data.txn。然后调用binder_transaction函数。实现例如以下：
～/Android//kernel/goldfish/drivers/staging/android
----binder.c
static void
binder_transaction(struct binder_proc *proc, struct binder_thread *thread,
struct binder_transaction_data *tr, int reply)
{
struct binder_transaction *t;
struct binder_work *tcomplete;
......
struct binder_proc *target_proc;
struct binder_thread *target_thread = NULL;
struct binder_node *target_node = NULL;
struct list_head *target_list;
wait_queue_head_t *target_wait;
struct binder_transaction *in_reply_to = NULL;
........
uint32_t return_error;
........
if (reply) {
in_reply_to = thread->transaction_stack;//首先从线程thread的事务堆栈中将该binder_transaction结构体取出来，而且保存在变量in_reply_to中
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) {//在上节中刚设置的
........
return_error = BR_FAILED_REPLY;
in_reply_to = NULL;
goto err_bad_call_stack;
}
thread->transaction_stack = in_reply_to->to_parent;//Server Manager进程的主线程transaction_stack为NULL
target_thread = in_reply_to->from;//找到目标线程
if (target_thread == NULL) {
return_error = BR_DEAD_REPLY;
goto err_dead_binder;
}
if (target_thread->transaction_stack != in_reply_to) {//FregServer进程的主线程的transation_stack就是这个in_reply_to
.........
return_error = BR_FAILED_REPLY;
in_reply_to = NULL;
target_thread = NULL;
goto err_dead_binder;
}
target_proc = target_thread->proc;//找到了目标进程
} else {
........
}
if (target_thread) {
.........
target_list = &target_thread->todo;//分别将它的todo队列和wait等待队列作为目标todo队列target_list和目标wait等待队列target_wait
target_wait = &target_thread->wait;//分别将它的todo队列和wait等待队列作为目标todo队列target_list和目标wait等待队列target_wait
} else {
.........
}
.........
/* TODO: reuse incoming transaction for reply */
t = kzalloc(sizeof(*t), GFP_KERNEL);//分配了binder_transaction结构体
........
tcomplete = kzalloc(sizeof(*tcomplete), GFP_KERNEL);//分配了binder_work结构体
if (tcomplete == NULL) {
return_error = BR_FAILED_REPLY;
goto err_alloc_tcomplete_failed;
}
.......
if (!reply && !(tr->flags & TF_ONE_WAY))
t->from = thread;//service_manager的主线程
else
t->from = NULL;
t->sender_euid = proc->tsk->cred->euid;//service_manager进程号
t->to_proc = target_proc;//目标进程
t->to_thread = target_thread;//目标线程
t->code = tr->code;//0
t->flags = tr->flags;//0
t->priority = task_nice(current);
t->buffer = binder_alloc_buf(target_proc, tr->data_size,
tr->offsets_size, !reply && (t->flags & TF_ONE_WAY));//分配了binder_buffer结构体
if (t->buffer == NULL) {
return_error = BR_FAILED_REPLY;
goto err_binder_alloc_buf_failed;
}
t->buffer->allow_user_free = 0;//不同意释放
.......
t->buffer->transaction = t;
t->buffer->target_node = target_node;//NULL
if (target_node)
binder_inc_node(target_node, 1, 0, NULL);//增加目标Binder实体对象的强引用计数
offp = (size_t *)(t->buffer->data + ALIGN(tr->data_size, sizeof(void *)));//偏移数组在data中起始位置，位于数据缓冲区之后
if (copy_from_user(t->buffer->data, tr->data.ptr.buffer, tr->data_size)) {//数据缓冲区复制到data中
binder_user_error("binder: %d:%d got transaction with invalid "
"data ptr
", 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)) {//偏移数组复制到data中，偏移数组位于数据缓冲区之后
binder_user_error("binder: %d:%d got transaction with invalid "
"offsets ptr
", proc->pid, thread->pid);
return_error = BR_FAILED_REPLY;
goto err_copy_data_failed;
}
if (!IS_ALIGNED(tr->offsets_size, sizeof(size_t))) {
binder_user_error("binder: %d:%d got transaction with "
"invalid offsets size, %zd
",
proc->pid, thread->pid, tr->offsets_size);
return_error = BR_FAILED_REPLY;
goto err_bad_offset;
}
off_end = (void *)offp + tr->offsets_size;
for (; offp < off_end; offp++) {//偏移数组里面没有内容
.....
}
if (reply) {
BUG_ON(t->buffer->async_transaction != 0);
binder_pop_transaction(target_thread, in_reply_to);//FregServer进程的主线程thread->transaction_stack为NULL
} else if (!(t->flags & TF_ONE_WAY)) {
.........
} else {
.........
}
t->work.type = BINDER_WORK_TRANSACTION;
list_add_tail(&t->work.entry, target_list);//增加到目标线程的todo
tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
list_add_tail(&tcomplete->entry, &thread->todo);//增加到本线程的todo
if (target_wait)
wake_up_interruptible(target_wait);//唤醒目标线程
return;
} 当Binder驱动程序分发一个进程间通信请求给一个线程处理时，就会将一个binder_transaction结构体压入到它的事务堆栈中。因此首先从线程thread的事务堆栈中将该binder_transaction结构体取出来。而且保存在变量in_reply_to中。binder_transaction结构体in_reply_to成员变量from指向了之前请求与thread进行进程间通信的线程。因此紧接着获取了目标线程target_thread。
找到目标线程target_thread之后，分别将它的todo队列和wait等待队列作为目标todo队列target_list和目标wait等待队列target_wait。
然后使用初始化binder_transaction结构体t，增加到目标线程的todo。
又初始化了binder_work结构体，增加到本线程(service_manager主线程)的todo队列。最后唤醒目标线程。
我们如果本线程继续运行。运行完成后再运行被唤醒的目标线程。
service_manager主线程继续运行，运行完binder_transaction，一层一层的返回，终于返回到binder_loop中。继续运行for循环。ioctl映射到binder_ioctl，由于仅仅有read_size大于0，所以运行binder_thread_read，实现例如以下：
～/Android//kernel/goldfish/drivers/staging/android
----binder.c
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;//起始位置
void __user *end = buffer + size;//结束位置
int ret = 0;
int wait_for_proc_work;
if (*consumed == 0) {
if (put_user(BR_NOOP, (uint32_t __user *)ptr))//BR_NOOP存入刚才的局部变量中
return -EFAULT;
ptr += sizeof(uint32_t);
}
retry:
wait_for_proc_work = thread->transaction_stack == NULL && list_empty(&thread->todo);//wait_for_proc_work眼下为0，表示线程有要处理的任务
if (thread->return_error != BR_OK && ptr < end) {
..........
}
thread->looper |= BINDER_LOOPER_STATE_WAITING;//looper为BINDER_LOOPER_STATE_ENTERED。BINDER_LOOPER_STATE_WAITING
if (wait_for_proc_work)//为0
proc->ready_threads++;
mutex_unlock(&binder_lock);
if (wait_for_proc_work) {//为0
........
} else {
if (non_block) {//非堵塞要立马返回处理结果
if (!binder_has_thread_work(thread))有任务就接下往下运行。没有任务就返回
ret = -EAGAIN;
} else
ret = wait_event_interruptible(thread->wait, binder_has_thread_work(thread));//有任务不睡眠，继续往下运行
}
mutex_lock(&binder_lock);
if (wait_for_proc_work)//为0
proc->ready_threads--;
thread->looper &= ~BINDER_LOOPER_STATE_WAITING;//looper为BINDER_LOOPER_STATE_ENTERED
if (ret)
return ret;
while (1) {
case BINDER_WORK_TRANSACTION_COMPLETE: {
cmd = BR_TRANSACTION_COMPLETE;
if (put_user(cmd, (uint32_t __user *)ptr))//将一个BR_TRANSACTION_COMPLETE返回协议写入到用户提供的缓冲区。
return -EFAULT;
ptr += sizeof(uint32_t);
binder_stat_br(proc, thread, cmd);
if (binder_debug_mask & BINDER_DEBUG_TRANSACTION_COMPLETE)
printk(KERN_INFO "binder: %d:%d BR_TRANSACTION_COMPLETE
",
proc->pid, thread->pid);
list_del(&w->entry);//删除todo上的工作项
kfree(w);//释放结构体
binder_stats.obj_deleted[BINDER_STAT_TRANSACTION_COMPLETE]++;
} break;
}
done:
*consumed = ptr - buffer;//消耗的大小
..........
return 0;
}
运行完binder_thread_read，返回binder_ioctl。最后返回binder_loop函数。開始运行binder_parse，实现例如以下：
～/Android/frameworks/base/cmd/servicemanager
----binder.c
int binder_parse(struct binder_state *bs, struct binder_io *bio,
uint32_t *ptr, uint32_t size, binder_handler func)//ptr为BR_TRANSACTION_COMPLETE的指针。size为它的大小
{
int r = 1;
uint32_t *end = ptr + (size / 4);
while (ptr < end) {
uint32_t cmd = *ptr++;
.......
switch(cmd) {//cmd为BR_TRANSACTION_COMPLETE
......
case BR_TRANSACTION_COMPLETE:
break;
......}
}
return r;
}
运行完binder_parse后。继续运行binder_loop的for循环，重新睡眠等待直到其所属的进程有新的未处理项为止，停留在以下的代码：wait_event_interruptible_exclusive(proc->wait, binder_has_proc_work(proc, thread));//睡眠等待，直到有一个新的进程属于未经加工的项目到目前为止
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