本文详细解析了Android中的Binder机制，包括ServiceManager的启动流程、服务注册与获取的过程。介绍了Binder驱动中的关键数据结构，并通过实例说明了进程间通信的实现。
写在前面：看过很多大牛写的Binder详解，因为讲得太过晦涩难懂，所以对于新手好像不太友好，为了让新手对于Binder有一个大概的认识，故准备了半个月写了这篇博客，博客的大概流程应该是正确的，希望看过的新手能够有一些收获。本文主要讲解了三个部分：ServiceManager 启动流程、ServiceManager 注册服务过程、ServiceManager 获取服务过程
1. ServiceManager的启动流程
system\core\roodir\init.rc：
service servicemanager /system/bin/servicemanager //可知孵化器的目录为servicemanager
class core
user system
group system
critical
onrestart restart healthd
onrestart restart zygote
onrestart restart media
onrestart restart surfaceflinger
onrestart restart drm分析Android启动流程可知，Android启动时会解析init.rc，servicemanager 服务的孵化器的目录为/system/bin/servicemanager，在此目录下有service_manager.c、binder.c
frameworks\native\cmds\servicemanager\Service_manager.c：
int main(int argc, char **argv)
{
struct binder_state *bs
bs = binder_open(128*1024); //1. 打开Binder驱动，建立128K = 128*1024内存映射
if (binder_become_context_manager(bs)) { //2. 设置自己（ServiceManager）为Binder的大管家
ALOGE("cannot become context manager (%s)\n", strerror(errno));
return -1;
}
...
svcmgr_handle = BINDER_SERVICE_MANAGER;
binder_loop(bs, svcmgr_handler); //3. 开启for循环，充当Server的角色，等待Client连接
return 0;
}分析binder_state：`
struct binder_state
{
int fd; //表示打开的/dev/binder文件句柄
void *mapped; //把设备文件/dev/binder映射到进程空间的起始地址
size_t mapsize; //内存映射空间的大小
};分析BINDER_SERVICE_MANAGER：`
#define BINDER_SERVICE_MANAGER 0U //表示Service Manager的句柄为01.1 分析binder_open(128*1024)
frameworks/native/cmds/servicemanager/Binder.c：
struct binder_state *binder_open(size_t mapsize)
{
struct binder_state *bs;
struct binder_version vers;
bs = malloc(sizeof(*bs));
if (!bs) {
errno = ENOMEM;
return NULL;
}
bs->fd = open("/dev/binder", O_RDWR); //调用Binder驱动注册的file_operation结构体的open、ioctl、mmap函数
if (bs->fd < 0) { //a. binder_state.fd保存打开的/dev/binder文件句柄
goto fail_open;
}
if ((ioctl(bs->fd, BINDER_VERSION, &vers) == -1) ||
(vers.protocol_version != BINDER_CURRENT_PROTOCOL_VERSION)) {
goto fail_open;
}
bs->mapsize = mapsize; //b. binder_state.mapsize保存内存映射空间的大小128K = 128*1024
bs->mapped = mmap(NULL, mapsize, PROT_READ, MAP_PRIVATE, bs->fd, 0); //c. binder_state.mapped保存设备文件/dev/binder映射到进程空间的起始地址
if (bs->mapped == MAP_FAILED) {
fprintf(stderr,"binder: cannot map device (%s)\n",
strerror(errno));
goto fail_map;
}
return bs;
fail_map:
close(bs->fd);
fail_open:
free(bs);
return NULL;
}执行open(“/dev/binder”, O_RDWR);时从用户态进入内核态，因此会执行：
drivers/staging/android/binder.c
static int binder_open(struct inode *nodp, struct file *filp)
{
struct binder_proc *proc;
proc = kzalloc(sizeof(*proc), GFP_KERNEL); //a. 创建Service_manager进程对应的binder_proc，保存Service_manager进程的信息
if (proc == NULL)
return -ENOMEM;
get_task_struct(current);
proc->tsk = current;
INIT_LIST_HEAD(&proc->todo);
init_waitqueue_head(&proc->wait);
proc->default_priority = task_nice(current);
binder_lock(__func__);
binder_stats_created(BINDER_STAT_PROC);
hlist_add_head(&proc->proc_node, &binder_procs); //binder_procs是一个全局变量，hlist_add_head是将proc->proc_node（proc->proc_node是一个hlist_node链表）加入binder_procs的list中
proc->pid = current->group_leader->pid;
INIT_LIST_HEAD(&proc->delivered_death);
filp->private_data = proc; //将binder_proc保存在打开文件file的私有数据成员变量private_data中
binder_unlock(__func__);
return 0;
}在此函数中创建Service_manager进程对应的binder_proc，保存Service_manager进程的信息，并将binder_proc保存在打开文件file的私有数据成员变量private_data中
//分析下面这个函数可以得出：函数功能是将proc->proc_node放入binder_procs链表的头部，注意是从右向左，最开始插入的binder_proc在binder_procs链表的最右边
static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
{
struct hlist_node *first = h->first;
n->next = first;
if (first)
first->pprev = &n->next;
h->first = n;
n->pprev = &h->first;
}分析binder_open(128*1024)可知：
a. 创建binder_state结构体保存/dev/binder文件句柄fd、内存映射的起始地址和大小
b. 创建binder_procs链表，将保存Service_manager进程信息的binder_proc对应的binder_proc->proc_node加入binder_procs的list中（proc->proc_node是一个hlist_node链表）
1.2 分析binder_become_context_manager(bs)
frameworks\native\cmds\servicemanager\Binder.c：
int binder_become_context_manager(struct binder_state *bs)
{
return ioctl(bs->fd, BINDER_SET_CONTEXT_MGR, 0); //传入参数BINDER_SET_CONTEXT_MGR
}
static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) //cmd = BINDER_SET_CONTEXT_MGR
{
int ret;
struct binder_proc *proc = filp->private_data; //获得binder_proc，binder_proc对应Service_manager进程 --- 从打开文件file的私有数据成员变量private_data中获取binder_proc
struct binder_thread *thread;
unsigned int size = _IOC_SIZE(cmd);
void __user *ubuf = (void __user *)arg;
ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret)
return ret;
binder_lock(__func__);
thread = binder_get_thread(proc); //获得Service_manager线程的信息binder_thread
if (thread == NULL) {
ret = -ENOMEM;
goto err;
}
switch (cmd) {
...
case BINDER_SET_CONTEXT_MGR:
if (binder_context_mgr_node != NULL) { //由binder_context_mgr_node = binder_new_node(proc, NULL, NULL);可知：binder_context_mgr_node为ServiceManager对应的binder_node
...
}
ret = security_binder_set_context_mgr(proc->tsk);
if (ret < 0)
goto err;
if (binder_context_mgr_uid != -1) { //binder_context_mgr_uid表示ServiceManager进程的uid
if (binder_context_mgr_uid != current->cred->euid) {
...
}
} else {
binder_context_mgr_uid = current->cred->euid;
binder_context_mgr_node = binder_new_node(proc, NULL, NULL); //binder_context_mgr_node为ServiceManager对应的binder_node，且binder_node.proc对应Service_manager进程
binder_context_mgr_node->local_weak_refs++;
binder_context_mgr_node->local_strong_refs++;
binder_context_mgr_node->has_strong_ref = 1;
binder_context_mgr_node->has_weak_ref = 1;
break;
}
ret = 0;
...
return ret;
}1.2.1 分析thread = binder_get_thread(proc);
static struct binder_thread *binder_get_thread(struct binder_proc *proc) //proc对应Service_manager进程
{
struct binder_thread *thread = NULL;
struct rb_node *parent = NULL;
struct rb_node **p = &proc->threads.rb_node;
/*尽量从threads树中查找和current线程匹配的binder_thread节点*/
while (*p) {
parent = *p;
thread = rb_entry(parent, struct binder_thread, rb_node);
if (current->pid < thread->pid)
p = &(*p)->rb_left;
else if (current->pid > thread->pid)
p = &(*p)->rb_right;
else
break;
}
/*“找不到就创建”一个binder_thread节点*/
if (*p == NULL) { //第一次执行时，p为NULL，下一次执行时会进入while
thread = kzalloc(sizeof(*thread), GFP_KERNEL); //b. 创建Service_manager进程对应的binder_thread
if (thread == NULL)
return NULL;
binder_stats_created(BINDER_STAT_THREAD);
thread->proc = proc; //将Service_manager进程的binder_proc保存到binder_thread.proc
thread->pid = current->pid; //将Service_manager进程的PID保存到binder_thread.pid
init_waitqueue_head(&thread->wait);
INIT_LIST_HEAD(&thread->todo);
rb_link_node(&thread->rb_node, parent, p); //将binder_thread保存到红黑树中
rb_insert_color(&thread->rb_node, &proc->threads);
thread->looper |= BINDER_LOOPER_STATE_NEED_RETURN;
thread->return_error = BR_OK;
thread->return_error2 = BR_OK;
}
return thread;
}此函数为获得proc对应进程下的所有线程中和当前线程pid相等的binder_thread
1.2.2 分析binder_context_mgr_node = binder_new_node(proc, NULL, NULL);
static struct binder_thread *binder_get_thread(struct binder_proc *proc) //proc对应Service_manager进程
{
struct binder_thread *thread = NULL;
struct rb_node *parent = NULL;
struct rb_node **p = &proc->threads.rb_node;
/*尽量从threads树中查找和current线程匹配的binder_thread节点*/
while (*p) {
parent = *p;
thread = rb_entry(parent, struct binder_thread, rb_node);
if (current->pid < thread->pid)
p = &(*p)->rb_left;
else if (current->pid > thread->pid)
p = &(*p)->rb_right;
else
break;
}
/*“找不到就创建”一个binder_thread节点*/
if (*p == NULL) { //第一次执行时，p为NULL，下一次执行时会进入while
thread = kzalloc(sizeof(*thread), GFP_KERNEL); //b. 创建Service_manager进程对应的binder_thread
if (thread == NULL)
return NULL;
binder_stats_created(BINDER_STAT_THREAD);
thread->proc = proc; //将Service_manager进程的binder_proc保存到binder_thread.proc
thread->pid = current->pid; //将Service_manager进程的PID保存到binder_thread.pid
init_waitqueue_head(&thread->wait);
INIT_LIST_HEAD(&thread->todo);
rb_link_node(&thread->rb_node, parent, p); //将binder_thread保存到红黑树中
rb_insert_color(&thread->rb_node, &proc->threads);
thread->looper |= BINDER_LOOPER_STATE_NEED_RETURN;
thread->return_error = BR_OK;
thread->return_error2 = BR_OK;
}
return thread;
}1.2.2 分析binder_context_mgr_node = binder_new_node(proc, NULL, NULL);
static struct binder_node *binder_new_node(struct binder_proc *proc,
void __user *ptr,
void __user *cookie)
{
struct rb_node **p = &proc->nodes.rb_node;
struct rb_node *parent = NULL;
struct binder_node *node;
while (*p) {
parent = *p;
node = rb_entry(parent, struct binder_node, rb_node);
if (ptr < node->ptr)
p = &(*p)->rb_left;
else if (ptr > node->ptr)
p = &(*p)->rb_right;
else
return NULL;
}
node = kzalloc(sizeof(*node), GFP_KERNEL); //c. 创建Service_manager进程对应的binder_node
if (node == NULL)
return NULL;
binder_stats_created(BINDER_STAT_NODE);
rb_link_node(&node->rb_node, parent, p); //将binder_node保存到红黑树中
rb_insert_color(&node->rb_node, &proc->nodes);
node->debug_id = ++binder_last_id;
node->proc = proc; //将binder_proc保存到binder_node.proc
node->ptr = ptr;
node->cookie = cookie;
node->work.type = BINDER_WORK_NODE;
INIT_LIST_HEAD(&node->work.entry);
INIT_LIST_HEAD(&node->async_todo);
return node;
}分析binder_become_context_manager(bs)可知：
a. 创建ServiceManager线程的binder_thread，binder_thread.proc保存ServiceManager进程对应的binder_proc，binder_thread.pid保存当前进程ServiceManager的PID
b. 创建ServiceManager进程的binder_node，binder_node.proc保存binder_proc
c. 把ServiceManager进程对应的binder_proc保存到全局变量filp->private_data中
1.3 分析binder_loop(bs, svcmgr_handler)
frameworks\native\cmds\servicemanager\Binder.c：
void binder_loop(struct binder_state *bs, binder_handler func) //开启for循环，充当Server的角色，等待Client连接
{
int res;
struct binder_write_read bwr;
uint32_t readbuf[32];
bwr.write_size = 0;
bwr.write_consumed = 0;
bwr.write_buffer = 0;
readbuf[0] = BC_ENTER_LOOPER; //readbuf[0] = BC_ENTER_LOOPER
binder_write(bs, readbuf, sizeof(uint32_t));
for (;;) {
bwr.read_size = sizeof(readbuf);
bwr.read_consumed = 0;
bwr.read_buffer = (uintptr_t) readbuf; //bwr.read_buffer = BC_ENTER_LOOPER
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr); //bs->fd记录/dev/binder文件句柄，因此调用binder驱动的ioctl函数，传入参数BINDER_WRITE_READ，bwr.read_buffer = BC_ENTER_LOOPER，bwr.write_buffer = 0
...
res = binder_parse(bs, 0, (uintptr_t) readbuf, bwr.read_consumed, func);
}
}1.3.1 分析binder_write(bs, readbuf, sizeof(uint32_t));
int binder_write(struct binder_state *bs, void *data, size_t len)
{
struct binder_write_read bwr;
int res;
bwr.write_size = len;
bwr.write_consumed = 0;
bwr.write_buffer = (uintptr_t) data; //bwr.write_buffer = data = BC_ENTER_LOOPER
bwr.read_size = 0;
bwr.read_consumed = 0;
bwr.read_buffer = 0;
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);
return res;
}
static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) //cmd = BINDER_WRITE_READ，bwr.read_size = 0，bwr.write_size = len
{
int ret;
struct binder_proc *proc = filp->private_data; //获得Service_manager进程的binder_proc，从打开文件file的私有数据成员变量private_data中获取binder_proc
struct binder_thread *thread;
unsigned int size = _IOC_SIZE(cmd);
void __user *ubuf = (void __user *)arg;
ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret)
return ret;
binder_lock(__func__);
thread = binder_get_thread(proc); //获得proc对应进程(Service_manager进程)下的所有线程中和当前线程pid相等的binder_thread
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))) { //把用户传递进来的参数转换成binder_write_read结构体，并保存在本地变量bwr中，bwr.write_buffer = BC_ENTER_LOOPER
ret = -EFAULT; bwr.read_buffer = 0
goto err;
}
if (bwr.write_size > 0) { //bwr.write_size = len
ret = binder_thread_write(proc, thread, (void __user *)bwr.write_buffer, bwr.write_size, &bwr.write_consumed); //bwr.write_buffer = BC_ENTER_LOOPER，bwr.write_consumed = 0
if (ret < 0) {
bwr.read_consumed = 0;
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
ret = -EFAULT;
goto err;
}
}
if (bwr.read_size > 0) { //bwr.read_size = 0
...
}
if (copy_to_user(ubuf, &bwr, sizeof(bwr))) { //将bwr返回到用户空间
ret = -EFAULT;
goto err;
}
break;
}
ret = 0;
...
return ret;
}
int binder_thread_write(struct binder_proc *proc, struct binder_thread *thread, //参数binder_proc、binder_thread、binder_write_read
void __user *buffer, int size, signed long *consumed) //buffer = bwr.write_buffer = BC_ENTER_LOOPER
{
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)) //cmd = BC_ENTER_LOOPER
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) { //cmd = BC_ENTER_LOOPER
case BC_ENTER_LOOPER:
...
thread->looper |= BINDER_LOOPER_STATE_ENTERED; //binder_thread.looper值变为BINDER_LOOPER_STATE_ENTERED，表明当前线程ServiceManager已经进入循环状态
break;
}
return 0;
}1.3.2 分析res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);
static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) //cmd = BINDER_WRITE_READ
{
int ret;
struct binder_proc *proc = filp->private_data; //获得Service_manager进程的binder_proc，从打开文件file的私有数据成员变量private_data中获取binder_proc
struct binder_thread *thread;
unsigned int size = _IOC_SIZE(cmd);
void __user *ubuf = (void __user *)arg;
ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret)
return ret;
binder_lock(__func__);
thread = binder_get_thread(proc); //获得proc对应进程(Service_manager进程)下的所有线程中和当前线程pid相等的binder_thread
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))) { //把用户传递进来的参数转换成binder_write_read结构体，并保存在本地变量bwr中，bwr.read_buffer = BC_ENTER_LOOPER
ret = -EFAULT; bwr.write_buffer = BC_ENTER_LOOPER
goto err;
}
if (bwr.write_size > 0) { //由binder_loop函数可知bwr.write_buffer = 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) { //由binder_loop函数可知bwr.read_buffer = BC_ENTER_LOOPER
/*读取binder_thread->todo的事物，并处理，执行完后bwr.read_buffer = BR_NOOP*/
ret = binder_thread_read(proc, thread, (void __user *)bwr.read_buffer, bwr.read_size, &bwr.read_consumed, filp->f_flags & O_NONBLOCK); //proc和thread分别发起传输动作的进程和线程
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;
}
ret = 0;
...
return ret;
}1.3.2.1 分析binder_thread_write
int binder_thread_write(struct binder_proc *proc, struct binder_thread *thread,
void __user *buffer, int size, signed long *consumed)
{
...
return 0;
}1.3.2.2 分析binder_thread_read
static int binder_thread_read(struct binder_proc *proc,
struct binder_thread *thread,
void __user *buffer, int size, //buffer = bwr.read_buffer = BC_ENTER_LOOPER，consumed = 0
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)) //把BR_NOOP写回到用户传进来的缓冲区ptr = *buffer + *consumed = bwr.read_buffer + bwr.read_consumed = bwr.read_buffer，即ptr = bwr.read_buffer = BR_NOOP
return -EFAULT;
ptr += sizeof(uint32_t);
}
...
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); //从thread->todo队列中取出待处理的事项
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) { //由待处理事项的type分类处理
...
}
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;
t->saved_priority = task_nice(current);
if (t->priority < target_node->min_priority &&
!(t->flags & TF_ONE_WAY))
binder_set_nice(t->priority);
else if (!(t->flags & TF_ONE_WAY) ||
t->saved_priority > target_node->min_priority)
binder_set_nice(target_node->min_priority);
cmd = BR_TRANSACTION; //cmd = BR_TRANSACTION
} else {
...
}
...
if (put_user(cmd, (uint32_t __user *)ptr)) //把cmd = BR_TRANSACTION写回到用户传进来的缓冲区ptr = bwr.read_buffer，故执行完binder_thread_read后cmd = bwr.read_buffer = BR_TRANSACTION
return -EFAULT;
ptr += sizeof(uint32_t);
if (copy_to_user(ptr, &tr, sizeof(tr)))
return -EFAULT;
ptr += sizeof(tr);
}
return 0;
}分析binder_loop(bs, svcmgr_handler)可知：
a. 进入for (;;)死循环，执行binder_thread_write
b. 执行binder_thread_read，从binder_thread->todo队列中取出待处理的事项并处理，处理完thread->todo队列中待处理的事项后：cmd = bwr.read_buffer = BR_TRANSACTION
总结：
ServiceManager 的启动分为三步
a. 打开Binder驱动，建立128K = 128*1024内存映射
b. 设置自己（ServiceManager）为Binder的大管家
c. 开启for循环，充当Server的角色，等待Client连接
在Binder驱动程序中为ServiceManager建立了三个结构体：binder_proc、binder_thread、binder_node
binder_node.proc保存binder_proc，进程间通信的数据会发送到binder_proc的todo链表
binder_proc进程里有很多线程，每个线程对应一个binder_thread，每个binder_thread用来处理一个Client的跨进程通信的请求
2. ServiceManager 注册服务
以注册WindowManagerService为例
ServiceManager.addService(Context.WINDOW_SERVICE, wm); //向ServiceManager注册WMS，wm为WindowManagerService，WindowManagerService继承
等价：ServiceManager.addService(“window”, new WindowManagerService(…));
frameworks/base/core/java/android/os/ServiceManager.java：
public static void addService(String name, IBinder service) {
try {
getIServiceManager().addService(name, service, false);
} catch (RemoteException e) {
Log.e(TAG, "error in addService", e);
}
}2.1 分析getIServiceManager()
private static IServiceManager getIServiceManager() {
if (sServiceManager != null) {
return sServiceManager;
}
// Find the service manager
sServiceManager = ServiceManagerNative.asInterface(BinderInternal.getContextObject()); //获得ServiceManager的代理
return sServiceManager;
}2.1.1 分析BinderInternal.getContextObject()：
frameworks/base/core/java/com/android/internal/os/BinderInternal.java:
public static final native IBinder getContextObject();
frameworks/base/core/jni/android_util_Binder.cpp：
{ "getContextObject", "()Landroid/os/IBinder;", (void*)android_os_BinderInternal_getContextObject },
static jobject android_os_BinderInternal_getContextObject(JNIEnv* env, jobject clazz)
{
sp<IBinder> b = ProcessState::self()->getContextObject(NULL); //返回new BpBinder(0);
return javaObjectForIBinder(env, b); //把这个BpBinder对象转换成一个BinderProxy对象
}2.1.1.1 分析sp b = ProcessState::self()->getContextObject(NULL);
sp<IBinder> ProcessState::getContextObject(const sp<IBinder>& /*caller*/)
{
return getStrongProxyForHandle(0);
}
sp<IBinder> ProcessState::getStrongProxyForHandle(int32_t handle) //handle = 0
{
sp<IBinder> result;
AutoMutex _l(mLock);
handle_entry* e = lookupHandleLocked(handle);
if (e != NULL) {
IBinder* b = e->binder;
if (b == NULL || !e->refs->attemptIncWeak(this)) {
if (handle == 0) {
Parcel data;
status_t status = IPCThreadState::self()->transact(
0, IBinder::PING_TRANSACTION, data, NULL, 0);
if (status == DEAD_OBJECT)
return NULL;
}
b = new BpBinder(handle); //b = new BpBinder(0);，最终直接返回b
e->binder = b;
if (b) e->refs = b->getWeakRefs();
result = b;
} else {
result.force_set(b);
e->refs->decWeak(this);
}
}
return result;
}2.1.1.2 分析return javaObjectForIBinder(env, b);
frameworks/base/core/jni/android_util_Binder.cpp：
jobject javaObjectForIBinder(JNIEnv* env, const sp<IBinder>& val)
{
jobject object = env->NewObject(gBinderProxyOffsets.mClass, gBinderProxyOffsets.mConstructor); //创建BinderProxy对象
if (object != NULL) {
env->SetLongField(object, gBinderProxyOffsets.mObject, (jlong)val.get()); //把BpBinder对象和BinderProxy对象关联起来；BinderProxy.mObject成员记录了new BpBinder(0)对象的地址
val->incStrong((void*)javaObjectForIBinder);
...
}
return object;
}因此：BinderInternal.getContextObject()相当于new BinderProxy()，且BinderProxy.mObject成员记录了new BpBinder(0)对象的地址
2.1.2 分析ServiceManagerNative.asInterface(…)
ServiceManagerNative.asInterface(new BinderProxy())
frameworks/base/core/java/android/os/ServiceManagerNative.java：
static public IServiceManager asInterface(IBinder obj) //obj = new BinderProxy()，且BinderProxy.mObject成员记录了new BpBinder(0)对象的地址
{
if (obj == null) {
return null;
}
IServiceManager in = (IServiceManager)obj.queryLocalInterface(descriptor);
if (in != null) {
return in;
}
return new ServiceManagerProxy(obj); //返回ServiceManagerProxy，其中ServiceManagerProxy.mRemote = new BinderProxy()
}
class ServiceManagerProxy implements IServiceManager {
public ServiceManagerProxy(IBinder remote) {
mRemote = remote;
}
}总结：分析getIServiceManager()可知，最终返回ServiceManagerProxy，其中ServiceManagerProxy.mRemote = new BinderProxy()，且BinderProxy.mObject成员记录了new BpBinder(0)对象的地址
2.2 分析ServiceManagerProxy.addService(…)
因此：getIServiceManager().addService(name, service, false);
等价：ServiceManagerProxy.addService(“window”, new WindowManagerService(…), false);
frameworks/base/core/java/android/os/ServiceManagerNative.java：
class ServiceManagerProxy implements IServiceManager {
public void addService(String name, IBinder service, boolean allowIsolated) //name = "window"，service = new WindowManagerService(...)
throws RemoteException {
Parcel data = Parcel.obtain(); //创建一个Parcel
Parcel reply = Parcel.obtain();
/*向Parcel中写入需要传输的数据*/
data.writeInterfaceToken(IServiceManager.descriptor);
data.writeString(name); //name = "window"，向Parcel中写入服务名"window"
data.writeStrongBinder(service); //service = new WindowManagerService(...)，向Parcel中写入服务的本地对象new WindowManagerService(...)
data.writeInt(allowIsolated ? 1 : 0);
mRemote.transact(ADD_SERVICE_TRANSACTION, data, reply, 0); //mRemote = new BinderProxy()，且BinderProxy.mObject成员记录了new BpBinder(0)对象的地址
reply.recycle();
data.recycle();
}
}2.2.1 分析Parcel.obtain();
frameworks/base/core/java/android/os/Parcel.java：
public static Parcel obtain() {
...
return new Parcel(0);
}2.2.2 data.writeString(“window”);
frameworks/base/core/java/android/os/Parcel.java：
public final void writeString(String val) {
nativeWriteString(mNativePtr, val);
}
frameworks/base/core/jni/android_os_Parcel.cpp：
{"nativeWriteString", "(JLjava/lang/String;)V", (void*)android_os_Parcel_writeString},
static void android_os_Parcel_writeString(JNIEnv* env, jclass clazz, jlong nativePtr, jstring val)
{
Parcel* parcel = reinterpret_cast<Parcel*>(nativePtr);
if (parcel != NULL) {
...
err = parcel->writeString16(str, env->GetStringLength(val));
}
}
frameworks/native/libs/binder/Parcel.cpp：
status_t Parcel::writeString16(const String16& str)
{
return writeString16(str.string(), str.size());
}
status_t Parcel::writeString16(const char16_t* str, size_t len)
{
status_t err = writeInt32(len); //写入数据长度
if (err == NO_ERROR) {
len *= sizeof(char16_t);
uint8_t* data = (uint8_t*)writeInplace(len+sizeof(char16_t)); //计算复制数据的目标地址 = mData + mDataPos
if (data) {
memcpy(data, str, len); //复制数据到目标地址
*reinterpret_cast<char16_t*>(data+len) = 0;
return NO_ERROR;
}
err = mError;
}
return err;
}
status_t Parcel::writeInt32(int32_t val)
{
return writeAligned(val);
}
void* Parcel::writeInplace(size_t len)
{
...
uint8_t* const data = mData+mDataPos; //复制数据的目标地址 = mData+mDataPos
return data;
}
static void memcpy(void* dst, void* src, size_t size) {
char* dst_c = (char*) dst, *src_c = (char*) src;
for (; size > 0; size--) {
*dst_c++ = *src_c++;
}
}分析data.writeString(“window”);可知：data.mData保存着”window”
2.2.3 分析data.writeStrongBinder(new WindowManagerService(…));
frameworks/base/core/java/android/os/Parcel.java：
public final void writeStrongBinder(IBinder val) {
nativeWriteStrongBinder(mNativePtr, val); //val = new WindowManagerService(...)
}
frameworks/base/core/jni/android_os_Parcel.cpp：
{"nativeWriteStrongBinder", "(JLandroid/os/IBinder;)V", (void*)android_os_Parcel_writeStrongBinder},
static void android_os_Parcel_writeStrongBinder(JNIEnv* env, jclass clazz, jlong nativePtr, jobject object)
{
Parcel* parcel = reinterpret_cast<Parcel*>(nativePtr);
if (parcel != NULL) {
const status_t err = parcel->writeStrongBinder(ibinderForJavaObject(env, object)); //object = new WindowManagerService(...)
if (err != NO_ERROR) {
signalExceptionForError(env, clazz, err);
}
}
}
frameworks/native/libs/binder/Parcel.cpp：
status_t Parcel::writeStrongBinder(const sp<IBinder>& val)
{
return flatten_binder(ProcessState::self(), val, this); //val = new WindowManagerService(...)
}
status_t flatten_binder(const sp<ProcessState>& /*proc*/,
const sp<IBinder>& binder, Parcel* out) //binder = new WindowManagerService(...)，out = data
{
flat_binder_object obj;
obj.flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS;
if (binder != NULL) {
IBinder *local = binder->localBinder(); //返回BBinder //localBinder和remoteBinder是虚函数，服务端BBinder实现了localBinder, 客户端BpBinder实现了remoteBinder
if (!local) {
BpBinder *proxy = binder->remoteBinder(); //返回BpBinder
if (proxy == NULL) {
ALOGE("null proxy");
}
const int32_t handle = proxy ? proxy->handle() : 0;
...
} else {
/*构造flat_binder_object*/
obj.type = BINDER_TYPE_BINDER; //flat_binder_object.type = BINDER_TYPE_BINDER
obj.binder = reinterpret_cast<uintptr_t>(local->getWeakRefs()); //reinterpret_cast<uintptr_t>为类型的强制转换
obj.cookie = reinterpret_cast<uintptr_t>(local); //flat_binder_object.cookie = BBinder，其中BBinder对应着new WindowManagerService(...)的服务端
}
} else {
...
}
return finish_flatten_binder(binder, obj, out);
}
inline static status_t finish_flatten_binder(
const sp<IBinder>& /*binder*/, const flat_binder_object& flat, Parcel* out) //flat = flat_binder_object， out = Parcel
{
return out->writeObject(flat, false); //向Parcel中写入flat_binder_object，其中flat_binder_object.cookie保存着new WindowManagerService(...)的服务端
}
status_t Parcel::writeObject(const flat_binder_object& val, bool nullMetaData) //val = flat_binder_object，其中flat_binder_object.cookie保存着new WindowManagerService(...)的服务端
{
const bool enoughData = (mDataPos+sizeof(val)) <= mDataCapacity;
const bool enoughObjects = mObjectsSize < mObjectsCapacity;
if (enoughData && enoughObjects) {
*reinterpret_cast<flat_binder_object*>(mData+mDataPos) = val;
if (nullMetaData || val.binder != 0) {
mObjects[mObjectsSize] = mDataPos; //Parcel.mObjects保存new WindowManagerService(...)的服务端
acquire_object(ProcessState::self(), val, this);
mObjectsSize++;
}
}
...
}分析data.writeStrongBinder(new WindowManagerService(…));可知：data.mObjects保存new WindowManagerService(…)的服务端
2.2.4 分析mRemote.transact(ADD_SERVICE_TRANSACTION, data, reply, 0);
frameworks/base/core/java/android/os/Binder.java：
final class BinderProxy implements IBinder {
public boolean transact(int code, Parcel data, Parcel reply, int flags) throws RemoteException { //code = ADD_SERVICE_TRANSACTION，data = Parcel，data.mData保存着"window"，data.mObjects保存new WindowManagerService(...)的服务端
Binder.checkParcel(this, code, data, "Unreasonably large binder buffer");
return transactNative(code, data, reply, flags);
}
public native boolean transactNative(int code, Parcel data, Parcel reply, //JNI
int flags) throws RemoteException;
}
frameworks/base/core/jni/android_util_Binder.cpp：
{"transactNative", "(ILandroid/os/Parcel;Landroid/os/Parcel;I)Z", (void*)android_os_BinderProxy_transact},
static jboolean android_os_BinderProxy_transact(JNIEnv* env, jobject obj,
jint code, jobject dataObj, jobject replyObj, jint flags) //code = ADD_SERVICE_TRANSACTION，dataObj = Parcel，dataObj.mData保存着"window"，dataObj.mObjects保存new WindowManagerService(...)的服务端
{
/*在2.1.1.2分析env->SetLongField(object, gBinderProxyOffsets.mObject, (jlong)val.get());可知BinderProxy.mObject成员记录了new BpBinder(0)对象的地址*/
IBinder* target = (IBinder*)env->GetLongField(obj, gBinderProxyOffsets.mObject); //通过此方法获得BpBinder --- ServiceManager客户端的内存地址
status_t err = target->transact(code, *data, reply, flags);
}
frameworks/native/libs/binder/BpBinder.cpp：
status_t BpBinder::transact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
if (mAlive) {
status_t status = IPCThreadState::self()->transact(
mHandle, code, data, reply, flags);
if (status == DEAD_OBJECT) mAlive = 0;
return status;
}
return DEAD_OBJECT;
}
frameworks/native/libs/binder/IPCThreadState.cpp：
status_t IPCThreadState::transact(int32_t handle,
uint32_t code, const Parcel& data,
Parcel* reply, uint32_t flags) //code = ADD_SERVICE_TRANSACTION，data = Parcel，data.mData保存着"window"，data.mObjects保存new WindowManagerService(...)的服务端
{
status_t err = data.errorCheck();
err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL); //打包数据成Binder驱动规定的格式
err = waitForResponse(reply);
return err;
}
status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags,
int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer) //cmd = BC_TRANSACTION，code = ADD_SERVICE_TRANSACTION
{
binder_transaction_data tr; //由输入数据Parcel构造binder_transaction_data结构体
tr.target.ptr = 0;
tr.target.handle = handle; //handle = BpBinder.mHandle对应着ServiceManager进程的handle，在注册服务时ServiceManager相当于Server
tr.code = code; //binder_transaction_data.code = ADD_SERVICE_TRANSACTION
tr.flags = binderFlags;
tr.cookie = 0;
tr.sender_pid = 0;
tr.sender_euid = 0;
tr.data_size = data.ipcDataSize();
tr.data.ptr.buffer = data.ipcData(); //tr.data.ptr.buffer = data.ipcData() = mData = "window"，更开始写入数据时mDataPos = 0，故mData + mDataPos = mData
tr.offsets_size = data.ipcObjectsCount()*sizeof(binder_size_t);
tr.data.ptr.offsets = data.ipcObjects(); //tr.data.ptr.offsets = data.ipcObjects() = mObjects = new WindowManagerService(...)的服务端
mOut.writeInt32(cmd); //向IPCThreadState.mOut中写入cmd = BC_TRANSACTION
mOut.write(&tr, sizeof(tr)); //向IPCThreadState.mOut中写入tr = binder_transaction_data，其中binder_transaction_data.target.handle = BpBinder.mHandle对应着ServiceManager进程的handle，在注册服务时ServiceManager相当于Server
return NO_ERROR; binder_transaction_data.data.ptr.buffer = data.ipcData() = mData = "window"
} binder_transaction_data.data.ptr.offsets = data.ipcObjects() = mObjects = new WindowManagerService(...)的服务端
status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{
int32_t cmd;
int32_t err;
while (1) { //死循环等待，直到talkWithDriver返回NO_ERROR
if ((err=talkWithDriver()) < NO_ERROR) break; //把数据发送给binder驱动
err = mIn.errorCheck();
if (err < NO_ERROR) break;
if (mIn.dataAvail() == 0) continue;
cmd = mIn.readInt32(); //读取cmd = BC_TRANSACTION
switch (cmd) {
...
default:
err = executeCommand(cmd);
}
}
}
status_t IPCThreadState::talkWithDriver(bool doReceive)
{
binder_write_read bwr;
const bool needRead = mIn.dataPosition() >= mIn.dataSize(); //needRead = true，doReceive = false
const size_t outAvail = (!doReceive || needRead) ? mOut.dataSize() : 0;
bwr.write_size = outAvail;
bwr.write_buffer = (uintptr_t)mOut.data(); //binder_write_read.write_buffer = mOut，mOut保存binder_transaction_data，其中binder_transaction_data.target.handle = BpBinder.mHandle对应着ServiceManager进程的handle，在注册服务时ServiceManager相当于Server
if (doReceive && needRead) { binder_transaction_data.data.ptr.buffer = data.ipcData() = mData = "window"
bwr.read_size = mIn.dataCapacity(); binder_transaction_data.data.ptr.offsets = data.ipcObjects() = mObjects = new WindowManagerService(...)的服务端
bwr.read_buffer = (uintptr_t)mIn.data();
} else {
bwr.read_size = 0;
bwr.read_buffer = 0; //binder_write_read.read_buffer = 0
}
if ((bwr.write_size == 0) && (bwr.read_size == 0)) return NO_ERROR;
bwr.write_consumed = 0; //binder_write_read.write_consumed = 0
bwr.read_consumed = 0; //binder_write_read.read_consumed = 0
status_t err;
do {
if (ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) >= 0) //fd = mProcess->mDriverFD为/dev/binder文件句柄（表示调用Binder驱动的ioctl），binder_write_read.write_buffer保存binder_transaction_data
err = NO_ERROR;
else
err = -errno;
...
} while (err == -EINTR);
if (err >= NO_ERROR) {
if (bwr.write_consumed > 0) {
if (bwr.write_consumed < mOut.dataSize())
mOut.remove(0, bwr.write_consumed); //清空之前写入Binder驱动的内容
else
mOut.setDataSize(0);
}
if (bwr.read_consumed > 0) {
mIn.setDataSize(bwr.read_consumed); //设置从Binder驱动读取的内容
mIn.setDataPosition(0);
}
return NO_ERROR;
}
return err;
}
drivers/staging/android/binder.c
static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) //cmd = BINDER_WRITE_READ，arg = binder_write_read，其中binder_write_read.write_buffer = mOut，mOut保存binder_transaction_data，其中binder_transaction_data.target.handle = BpBinder.mHandle对应着ServiceManager进程的handle，在注册服务时ServiceManager相当于Server
{ binder_transaction_data.data.ptr.buffer = data.ipcData() = mData = "window"
int ret; binder_transaction_data.data.ptr.offsets = data.ipcObjects() = mObjects = new WindowManagerService(...)的服务端
struct binder_proc *proc = filp->private_data; //获得ServiceManager进程对应的binder_proc --- 从打开文件file的私有数据成员变量private_data中获取binder_proc
struct binder_thread *thread;
unsigned int size = _IOC_SIZE(cmd);
void __user *ubuf = (void __user *)arg;
ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret)
return ret;
thread = binder_get_thread(proc); //获得ServiceManager进程用于处理当前跨进程传输数据的线程binder_thread --- 此线程专门用于处理此跨进程间通信
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))) { //读取执行ioctl传进的参数ubuf = arg并保存到本地对象binder_write_read中
ret = -EFAULT;
goto err;
}
if (bwr.write_size > 0) { //binder_write_read.write_buffer = mOut，mOut保存binder_transaction_data，其中binder_transaction_data.target.handle = BpBinder.mHandle对应着ServiceManager进程的handle，在注册服务时ServiceManager相当于Server
// binder_transaction_data.data.ptr.buffer = data.ipcData() = mData = "window"
// binder_transaction_data.data.ptr.offsets = data.ipcObjects() = mObjects = new WindowManagerService(...)的服务端
ret = binder_thread_write(proc, thread, (void __user *)bwr.write_buffer, bwr.write_size, &bwr.write_consumed); //参数binder_proc、binder_thread、binder_write_read
if (ret < 0) {
bwr.read_consumed = 0;
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
ret = -EFAULT;
goto err;
}
}
if (bwr.read_size > 0) { //由函数talkWithDriver知：binder_write_read.read_size = 0即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 (copy_to_user(ubuf, &bwr, sizeof(bwr))) { //将操作结果bwr返回到用户空间ubuf
ret = -EFAULT;
goto err;
}
break;
}
...
}
ret = 0;
err:
...
return ret;
}
//创建binder_node结构体，binder_node.cookie = new WindowManagerService(...)的服务端
int binder_thread_write(struct binder_proc *proc, struct binder_thread *thread, //参数binder_proc、binder_thread、binder_write_read
void __user *buffer, int size, signed long *consumed) //buffer = binder_write_read.write_buffer，binder_write_read.write_buffer = mOut，mOut保存binder_transaction_data
{
uint32_t cmd;
void __user *ptr = buffer + *consumed; //*ptr = *buffer + *consumed = bwr.write_buffer + bwr.write_consumed = bwr.write_buffer = mOut，mOut保存binder_transaction_data
//binder_transaction_data.target.handle = BpBinder.mHandle对应着ServiceManager进程的handle，在注册服务时ServiceManager相当于Server
//binder_transaction_data.data.ptr.buffer = data.ipcData() = mData = "window"
//binder_transaction_data.data.ptr.offsets = data.ipcObjects() = mObjects = new WindowManagerService(...)的服务端
void __user *end = buffer + size;
while (ptr < end && thread->return_error == BR_OK) {
if (get_user(cmd, (uint32_t __user *)ptr)) //在IPCThreadState::writeTransactionData执行mOut.writeInt32(cmd);向IPCThreadState.mOut中写入cmd = BC_TRANSACTION，又*ptr = mOut可知获得用户输入命令cmd = BC_TRANSACTION
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) { //cmd = BC_TRANSACTION
case BC_TRANSACTION:
case BC_REPLY: {
struct binder_transaction_data tr;
if (copy_from_user(&tr, ptr, sizeof(tr))) //读取用户空间ptr的数据，保存到tr
return -EFAULT;
ptr += sizeof(tr);
binder_transaction(proc, thread, &tr, cmd); //cmd = BC_TRANSACTION，tr保存bwr.write_buffer = mOut，mOut保存binder_transaction_data
break;
}
}
return 0;
}
static void binder_transaction(struct binder_proc *proc,
struct binder_thread *thread,
struct binder_transaction_data *tr, int reply) //reply = BC_TRANSACTION，tr保存bwr.write_buffer = mOut，mOut保存binder_transaction_data
//binder_transaction_data.target.handle = BpBinder.mHandle对应着ServiceManager进程的handle，在注册服务时ServiceManager相当于Server
//binder_transaction_data.data.ptr.buffer = data.ipcData() = mData = "window"
//binder_transaction_data.data.ptr.offsets = data.ipcObjects() = mObjects = new WindowManagerService(...)的服务端
{
struct binder_transaction *t; //binder_transaction结构体
struct binder_work *tcomplete;
size_t *offp, *off_end;
size_t off_min;
struct binder_proc *target_proc; //3个关键结构体binder_proc、binder_thread、binder_node
struct binder_thread *target_thread = NULL;
struct binder_node *target_node = NULL;
struct list_head *target_list; //list_head
wait_queue_head_t *target_wait;
struct binder_transaction *in_reply_to = NULL;
struct binder_transaction_log_entry *e;
uint32_t return_error = BR_OK;
struct binder_ref *ref;
ref = binder_get_ref(proc, tr->target.handle); //由handle = binder_transaction_data.target.handle = BpBinder.mHandle找到binder_ref，它是对服务ServiceManager的引用
target_node = ref->node; //由binder_ref.node找到服务ServiceManager的binder_node
target_proc = target_node->proc; //服务ServiceManager的binder_node.proc找到目标进程ServiceManager的binder_proc
if (!reply && !(tr->flags & TF_ONE_WAY))
t->from = thread;
else
t->from = NULL;
if (target_thread) {
e->to_thread = target_thread->pid;
target_list = &target_thread->todo;
target_wait = &target_thread->wait;
} else {
target_list = &target_proc->todo;
target_wait = &target_proc->wait;
}
t->sender_euid = proc->tsk->cred->euid;
t->to_proc = target_proc; //目标进程ServiceManager对应的binder_proc
t->to_thread = target_thread; //目标进程ServiceManager用于处理此次进程通信对应的binder_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));
t->buffer->allow_user_free = 0;
t->buffer->debug_id = t->debug_id;
t->buffer->transaction = t;
t->buffer->target_node = target_node; //目标进程ServiceManager对应的binder_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)) { //t->buffer->data = tr->data.ptr.buffer = "window"
...
}
/*tr保存binder_transaction_data，其中binder_transaction_data.data.ptr.offsets = data.ipcObjects() = mObjects = new WindowManagerService(...)的服务端*/
if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) { //offp = binder_transaction_data.data.ptr.offsets = new WindowManagerService(...)的服务端
...
}
off_end = (void *)offp + tr->offsets_size;
for (; offp < off_end; offp++) { //即遍历从保存flat_binder_object的起始地址到结束地址
struct flat_binder_object *fp;
fp = (struct flat_binder_object *)(t->buffer->data + *offp);
off_min = *offp + sizeof(struct flat_binder_object);
switch (fp->type) {
case BINDER_TYPE_BINDER: //由2.2.3中flatten_binder函数的obj.type = BINDER_TYPE_BINDER;知flat_binder_object.type = BINDER_TYPE_BINDER
// obj.binder = reinterpret_cast<uintptr_t>(local->getWeakRefs());
// obj.cookie = reinterpret_cast<uintptr_t>(local); 其中local对应着new WindowManagerService(...)的服务端
case BINDER_TYPE_WEAK_BINDER: {
struct binder_ref *ref;
struct binder_node *node = binder_get_node(proc, fp->binder);
if (node == NULL) {
/*为每一个服务创建一个binder_node结构体，binder_node.cookie = new WindowManagerService(...)的服务端*/
node = binder_new_node(proc, fp->binder, fp->cookie); //proc对应目标进程ServiceManager的binder_proc，fp->cookie对应着new WindowManagerService(...)的服务端
node->min_priority = fp->flags & FLAT_BINDER_FLAG_PRIORITY_MASK;
node->accept_fds = !!(fp->flags & FLAT_BINDER_FLAG_ACCEPTS_FDS);
}
...
} break;
...
}
if (reply) {
binder_pop_transaction(target_thread, in_reply_to);
} else if (!(t->flags & TF_ONE_WAY)) {
t->need_reply = 1;
t->from_parent = thread->transaction_stack;
thread->transaction_stack = t; //把binder_transaction结构体t保存到thread->transaction_stack，表示ServiceManager线程还有任务未完成
}
t->work.type = BINDER_WORK_TRANSACTION;
list_add_tail(&t->work.entry, target_list); //把binder_transaction结构体t保存到ServiceManager线程的thread->todo队列，事项类型为BINDER_WORK_TRANSACTION
tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE;
list_add_tail(&tcomplete->entry, &thread->todo);
if (target_wait)
wake_up_interruptible(target_wait); //唤醒ServiceManager线程，ServiceManager线程执行waitForResponse时休眠，直到talkWithDriver返回NO_ERROR
return;
}
//为每一个服务创建一个binder_node结构体，binder_node.cookie = new WindowManagerService(...)的服务端
static struct binder_node *binder_new_node(struct binder_proc *proc, //proc = binder_proc，cookie = new WindowManagerService(...)的服务端
void __user *ptr,
void __user *cookie)
{
struct rb_node **p = &proc->nodes.rb_node;
struct rb_node *parent = NULL;
struct binder_node *node;
while (*p) {
parent = *p;
node = rb_entry(parent, struct binder_node, rb_node);
if (ptr < node->ptr)
p = &(*p)->rb_left;
else if (ptr > node->ptr)
p = &(*p)->rb_right;
else
return NULL;
}
/*分配binder_node结构体*/
node = kzalloc(sizeof(*node), GFP_KERNEL);
if (node == NULL)
return NULL;
binder_stats_created(BINDER_STAT_NODE);
rb_link_node(&node->rb_node, parent, p); //将new WindowManagerService(...)服务对应的binder_node保存到红黑树中
rb_insert_color(&node->rb_node, &proc->nodes);
node->debug_id = ++binder_last_id;
node->proc = proc; //binder_node.proc = ServiceManager进程的binder_proc
node->ptr = ptr;
node->cookie = cookie; //binder_node.cookie = new WindowManagerService(...)的服务端
node->work.type = BINDER_WORK_NODE;
INIT_LIST_HEAD(&node->work.entry);
INIT_LIST_HEAD(&node->async_todo);
...
return node;
}执行到这里：ServiceManager的todo队列里面已经添加了一条注册服务成功的事项，事项类型为BINDER_WORK_TRANSACTION
2.2.5 分析Binder_Loop
ServiceManager线程的thread->todo队列保存着binder_transaction结构体t，t->buffer->data = tr->data.ptr.buffer = “window”
frameworks/native/cmds/servicemanager/Binder.c：
void Binder_Loop(struct binder_state *bs, binder_handler func) //开启for循环，充当Server的角色，等待Client连接
{
int res;
struct binder_write_read bwr;
uint32_t readbuf[32];
bwr.write_size = 0;
bwr.write_consumed = 0;
bwr.write_buffer = 0;
readbuf[0] = BC_ENTER_LOOPER;
binder_write(bs, readbuf, sizeof(uint32_t));
for (;;) {
bwr.read_size = sizeof(readbuf);
bwr.read_consumed = 0;
bwr.read_buffer = (uintptr_t) readbuf; //由talkWithDriver函数可知bwr.read_buffer保存BR_TRANSACTION
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr); //bs->fd记录/dev/binder文件句柄，因此调用binder驱动的ioctl函数，传入参数BINDER_WRITE_READ
... //执行完ioctl后bwr.read_buffer = BR_TRANSACTION
res = binder_parse(bs, 0, (uintptr_t) readbuf, bwr.read_consumed, func);
}
}
static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) //cmd = BINDER_WRITE_READ
{
int ret;
struct binder_proc *proc = filp->private_data; //获得Service_manager进程的binder_proc，从打开文件file的私有数据成员变量private_data中获取binder_proc
struct binder_thread *thread;
unsigned int size = _IOC_SIZE(cmd);
void __user *ubuf = (void __user *)arg;
ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret)
return ret;
binder_lock(__func__);
thread = binder_get_thread(proc); //获得proc对应进程(Service_manager进程)下的所有线程中和当前线程pid相等的binder_thread
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))) { //把用户传递进来的参数转换成binder_write_read结构体，并保存在本地变量bwr中，bwr.read_buffer = BC_ENTER_LOOPER
ret = -EFAULT; bwr.write_buffer = 0
goto err;
}
if (bwr.write_size > 0) { //开始为0
...
}
if (bwr.read_size > 0) { //由binder_loop函数可知bwr.read_buffer = BC_ENTER_LOOPER
/*读取binder_thread->todo的事物，并处理，执行完后bwr.read_buffer = BR_TRANSACTION*/
ret = binder_thread_read(proc, thread, (void __user *)bwr.read_buffer, bwr.read_size, &bwr.read_consumed, filp->f_flags & O_NONBLOCK); //proc和thread分别发起传输动作的进程和线程
if (!list_empty(&proc->todo))
wake_up_interruptible(&proc->wait);
if (ret < 0) {
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
ret = -EFAULT;
goto err;
}
}
if (copy_to_user(ubuf, &bwr, sizeof(bwr))) { //将bwr返回到用户空间
ret = -EFAULT;
goto err;
}
break;
}
ret = 0;
...
return ret;
}
static int binder_thread_read(struct binder_proc *proc,
struct binder_thread *thread,
void __user *buffer, int size, //buffer = bwr.read_buffer = BC_ENTER_LOOPER，consumed = 0
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)) //把BR_NOOP写回到用户传进来的缓冲区ptr = *buffer + *consumed = bwr.read_buffer + bwr.read_consumed = bwr.read_buffer，即ptr = bwr.read_buffer = BR_NOOP
return -EFAULT; 即bwr.read_buffer = BR_NOOP
ptr += sizeof(uint32_t);
}
...
while (1) {
uint32_t cmd;
struct binder_transaction_data tr;
struct binder_work *w;
struct binder_transaction *t = NULL;
/*在分析2.2.4 mRemote.transact执行binder_transaction时，向ServiceManager进程的todo链表插入类型BINDER_WORK_TRANSACTION的事项*/
if (!list_empty(&thread->todo))
w = list_first_entry(&thread->todo, struct binder_work, entry); //从thread->todo队列中取出待处理的事项，事项类型BINDER_WORK_TRANSACTION
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) { //由待处理事项的type分类处理，w->type = BINDER_WORK_TRANSACTION
...
case BINDER_WORK_TRANSACTION: {
t = container_of(w, struct binder_transaction, work);
} break;
}
if (t->buffer->target_node) {
struct binder_node *target_node = t->buffer->target_node;
tr.target.ptr = target_node->ptr; //tr.target.ptr = "window"
tr.cookie = target_node->cookie; //tr.cookie = new WindowManagerService(...)
t->saved_priority = task_nice(current);
if (t->priority < target_node->min_priority &&
!(t->flags & TF_ONE_WAY))
binder_set_nice(t->priority);
else if (!(t->flags & TF_ONE_WAY) ||
t->saved_priority > target_node->min_priority)
binder_set_nice(target_node->min_priority);
cmd = BR_TRANSACTION; //cmd = BR_TRANSACTION
} else {
tr.target.ptr = NULL;
tr.cookie = NULL;
cmd = BR_REPLY;
}
...
if (put_user(cmd, (uint32_t __user *)ptr)) //把cmd = BR_TRANSACTION写回到用户传进来的缓冲区ptr = bwr.read_buffer，故执行完binder_thread_read后cmd = bwr.read_buffer = BR_TRANSACTION
return -EFAULT; 即bwr.read_buffer = BR_TRANSACTION
ptr += sizeof(uint32_t);
if (copy_to_user(ptr, &tr, sizeof(tr)))
return -EFAULT;
ptr += sizeof(tr);
}
return 0;
}
int binder_parse(struct binder_state *bs, struct binder_io *bio,
uintptr_t ptr, size_t size, binder_handler func)
{
int r = 1;
uintptr_t end = ptr + (uintptr_t) size;
while (ptr < end) {
uint32_t cmd = *(uint32_t *) ptr; //读取cmd = ptr = readbuf = bwr.read_buffer = BR_TRANSACTION
ptr += sizeof(uint32_t);
switch(cmd) {
...
case BR_TRANSACTION: {
struct binder_transaction_data *txn = (struct binder_transaction_data *) ptr; //由ptr构造binder_transaction_data结构体txn
if ((end - ptr) < sizeof(*txn)) {
ALOGE("parse: txn too small!\n");
return -1;
}
binder_dump_txn(txn);
if (func) { //func为binder_handler函数指针
unsigned rdata[256/4];
struct binder_io msg;
struct binder_io reply;
int res;
bio_init(&reply, rdata, sizeof(rdata), 4); //接收到数据之后，构造一个binder_io结构体reply
bio_init_from_txn(&msg, txn); //由txn构造一个binder_io结构体msg
res = func(bs, txn, &msg, &reply); //调用处理函数 --- 由binder_loop(bs, svcmgr_handler)第二个参数可知func是函数指针binder_handler,这个函数指针指向了svcmgr_handler函数
//其中txn.code = SVC_MGR_ADD_SERVICE，msg保存服务名"window"和new WindowManagerService(...)服务的handle
binder_send_reply(bs, &reply, txn->data.ptr.buffer, res); //如果res为0，表示注册成功，代码0写入binder_io结构体reply中
}
ptr += sizeof(*txn);
break;
}
}
return r;
}
frameworks/native/cmds/servicemanager/Service_manager.c：
int svcmgr_handler(struct binder_state *bs,
struct binder_transaction_data *txn,
struct binder_io *msg,
struct binder_io *reply)
{
struct svcinfo *si;
uint16_t *s;
size_t len;
uint32_t handle;
uint32_t strict_policy;
int allow_isolated;
if (txn->target.handle != svcmgr_handle) //txn->target为NULL，svcmgr_handle为NULL(void* (0))
return -1;
if (txn->code == PING_TRANSACTION)
return 0;
strict_policy = bio_get_uint32(msg);
s = bio_get_string16(msg, &len); //返回bio->data
if (s == NULL) {
return -1;
}
if ((len != (sizeof(svcmgr_id) / 2)) ||
memcmp(svcmgr_id, s, sizeof(svcmgr_id))) {
fprintf(stderr,"invalid id %s\n", str8(s, len));
return -1;
}
if (sehandle && selinux_status_updated() > 0) {
struct selabel_handle *tmp_sehandle = selinux_android_service_context_handle();
if (tmp_sehandle) {
selabel_close(sehandle);
sehandle = tmp_sehandle;
}
}
switch(txn->code) {
...
case SVC_MGR_ADD_SERVICE:
s = bio_get_string16(msg, &len); //由msg获得s = "window"
if (s == NULL) {
return -1;
}
handle = bio_get_ref(msg); //由msg获得new WindowManagerService(...)服务的handle
allow_isolated = bio_get_uint32(msg) ? 1 : 0;
if (do_add_service(bs, s, len, handle, txn->sender_euid, //执行do_add_service
allow_isolated, txn->sender_pid))
return -1;
break;
}
bio_put_uint32(reply, 0); //将注册成功代码0写入binder_io结构体reply中
return 0;
}
int do_add_service(struct binder_state *bs,
const uint16_t *s, size_t len,
uint32_t handle, uid_t uid, int allow_isolated,
pid_t spid)
{
struct svcinfo *si;
if (!handle || (len == 0) || (len > 127))
return -1;
if (!svc_can_register(s, len, spid)) { //检查用户ID为uid的进程是否有权限请求Service Manager注册一个名称为s的Service组件
return -1;
}
si = find_svc(s, len); //来检查服务名称s是否被已经注册了的Service组件使用了
if (si) {
if (si->handle) {
svcinfo_death(bs, si);
}
si->handle = handle;
} else {
si = malloc(sizeof(*si) + (len + 1) * sizeof(uint16_t)); //分配svn_info结构体内存
if (!si) {
return -1;
}
si->handle = handle; //重要：si->handle对应new WindowManagerService(...)的服务端
si->len = len;
memcpy(si->name, s, (len + 1) * sizeof(uint16_t)); //重要：si->name = "window"，s表示要注册的Service组件的名称"window"
si->name[len] = '\0';
si->death.func = (void*) svcinfo_death; //死亡通知
si->death.ptr = si;
si->allow_isolated = allow_isolated;
si->next = svclist; //si->next = svclist;和svclist = si;形成链表，将创建的svcinfo结构体放入链表，注意是从右向左放，即先创建的svcinfo在链表最右边
svclist = si;
}
binder_acquire(bs, handle); //增加相对应的Binder引用对象的引用计数值，避免它过早地被销毁
binder_link_to_death(bs, handle, &si->death); //向Binder驱动程序注册一个Binder本地对象死亡接受通知
return 0;
}
struct svcinfo
{
struct svcinfo *next; //用于形成链表
uint32_t handle;
struct binder_death death;
int allow_isolated;
size_t len;
uint16_t name[0]; //用于保存注册的Service组件的名称
};总结：
ServiceManager 注册服务过程
例如ServiceManager.addService(“window”, new WindowManagerService(…));
a. 创建一个binder_node结构体，binder_node.cookie = new WindowManagerService(…)的服务端
b. 向ServiceManager的todo队列里面添加一条注册服务”window”的事务
c. 创建一个svcinfo结构体放入链表，且svcinfo.handle对应new WindowManagerService(…)的服务端，svcinfo.name保存服务的名称”window”
3. ServiceManager 获取服务
frameworks/base/services/core/java/com/android/server/InputMethodManagerService.java：
ServiceManager.getService(Context.WINDOW_SERVICE);
等价：ServiceManager.getService(“window”);
frameworks/base/core/java/android/os/ServiceManager.java：
public static IBinder getService(String name) {
try {
IBinder service = sCache.get(name);
if (service != null) {
return service;
} else {
return getIServiceManager().getService(name);
}
} catch (RemoteException e) {
Log.e(TAG, "error in getService", e);
}
return null;
}getIServiceManager().getService(name)
等价：ServiceManagerProxy.getService(“window”) //ServiceManagerProxy.mRemote = new BinderProxy()
//frameworks/base/core/java/android/os/ServiceManagerNative.java：
class ServiceManagerProxy implements IServiceManager {
public IBinder getService(String name) throws RemoteException {
Parcel data = Parcel.obtain(); //创建一个Parcel对象
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IServiceManager.descriptor);
data.writeString(name); //向Parcel中写入需要向ServiceManager查询的服务名称"window"
mRemote.transact(GET_SERVICE_TRANSACTION, data, reply, 0);
IBinder binder = reply.readStrongBinder();
reply.recycle();
data.recycle();
return binder;
}
}a. Parcel.obtain(); //1. 创建一个Parcel对象
b. data.writeString(“window”); //2. 向Parcel中写入需要跨进程传输的数据
c. mRemote.transact(GET_SERVICE_TRANSACTION, data, reply, 0); //传入参数data（保存Proxy向native发送的数据），reply（保存native向Proxy返回的数据）
3.1 分析mRemote.transact(GET_SERVICE_TRANSACTION, data, reply, 0);
由前面的分析可知：mRemote = new BinderProxy()
最终会调用：
frameworks/native/libs/binder/IPCThreadState.cpp：
status_t IPCThreadState::transact(int32_t handle,
uint32_t code, const Parcel& data,
Parcel* reply, uint32_t flags) //code = GET_SERVICE_TRANSACTION
{
status_t err = data.errorCheck();
err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL); //打包数据成Binder驱动规定的格式，code = GET_SERVICE_TRANSACTION，data的地址mData保存"window"
err = waitForResponse(reply);
return err;
}
status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags,
int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer) //cmd = BC_TRANSACTION，code = GET_SERVICE_TRANSACTION，data的地址mData保存"window"
{
binder_transaction_data tr; //由输入数据Parcel构造binder_transaction_data结构体
tr.target.ptr = 0;
tr.target.handle = handle; //binder_transaction_data.target.handle = BpBinder.mHandle
tr.code = code; //binder_transaction_data.code = GET_SERVICE_TRANSACTION
tr.flags = binderFlags;
tr.cookie = 0;
tr.sender_pid = 0;
tr.sender_euid = 0;
tr.data_size = data.ipcDataSize();
tr.data.ptr.buffer = data.ipcData(); //tr.data.ptr.buffer = data.ipcData() = mData = "window"，写入数据到Parcel时mDataPos = 0，故Parcel数据的起始地址为mData
tr.offsets_size = data.ipcObjectsCount()*sizeof(binder_size_t);
tr.data.ptr.offsets = data.ipcObjects();
mOut.writeInt32(cmd); //向IPCThreadState.mOut中写入cmd = BC_TRANSACTION
mOut.write(&tr, sizeof(tr)); //向IPCThreadState.mOut中写入tr = binder_transaction_data，其中binder_transaction_data.code = GET_SERVICE_TRANSACTION，binder_transaction_data.data.ptr.buffer = "window"
return NO_ERROR;
}
status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{
int32_t cmd;
int32_t err;
while (1) { //死循环等待，直到talkWithDriver返回NO_ERROR
if ((err=talkWithDriver()) < NO_ERROR) break; //把数据发送给binder驱动
err = mIn.errorCheck();
if (err < NO_ERROR) break;
if (mIn.dataAvail() == 0) continue;
cmd = mIn.readInt32(); //读取cmd = BC_TRANSACTION
switch (cmd) {
...
default: //cmd == BC_TRANSACTION时会执行default
err = executeCommand(cmd);
}
}
}
status_t IPCThreadState::talkWithDriver(bool doReceive)
{
binder_write_read bwr;
const bool needRead = mIn.dataPosition() >= mIn.dataSize(); //needRead = true，doReceive = false
const size_t outAvail = (!doReceive || needRead) ? mOut.dataSize() : 0;
bwr.write_size = outAvail;
bwr.write_buffer = (uintptr_t)mOut.data(); //binder_write_read.write_buffer = mOut，mOut保存binder_transaction_data，其中binder_transaction_data.code = GET_SERVICE_TRANSACTION，binder_transaction_data.data.ptr.buffer = "window"
if (doReceive && needRead) {
bwr.read_size = mIn.dataCapacity();
bwr.read_buffer = (uintptr_t)mIn.data();
} else {
bwr.read_size = 0;
bwr.read_buffer = 0; //binder_write_read.read_buffer = 0
}
if ((bwr.write_size == 0) && (bwr.read_size == 0)) return NO_ERROR;
bwr.write_consumed = 0; //binder_write_read.write_consumed = 0
bwr.read_consumed = 0; //binder_write_read.read_consumed = 0
status_t err;
do {
if (ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) >= 0) //fd = mProcess->mDriverFD为/dev/binder文件句柄（表示调用Binder驱动的ioctl），binder_write_read.write_buffer保存binder_transaction_data，其中binder_transaction_data.code = GET_SERVICE_TRANSACTION，binder_transaction_data.data.ptr.buffer = "window"
err = NO_ERROR;
else
err = -errno;
...
} while (err == -EINTR);
...
return err;
}
drivers/staging/android/binder.c
static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) //cmd = BINDER_WRITE_READ，arg = binder_write_read，binder_write_read.write_buffer保存binder_transaction_data，其中binder_transaction_data.code = GET_SERVICE_TRANSACTION
{
int ret;
struct binder_proc *proc = filp->private_data; //获得binder_proc --- 从打开文件file的私有数据成员变量private_data中获取binder_proc
struct binder_thread *thread;
unsigned int size = _IOC_SIZE(cmd);
void __user *ubuf = (void __user *)arg;
ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret)
return ret;
thread = binder_get_thread(proc); //获得当前线程的信息binder_thread --- binder_proc所在的线程（即ServiceManager所在线程）信息
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))) { //读取执行ioctl传进的参数ubuf = arg并保存到本地对象binder_write_read中
ret = -EFAULT;
goto err;
}
if (bwr.write_size > 0) { //binder_write_read.write_buffer = mOut，mOut保存binder_transaction_data，其中binder_transaction_data.code = GET_SERVICE_TRANSACTION，binder_transaction_data.data.ptr.buffer = "window"
ret = binder_thread_write(proc, thread, (void __user *)bwr.write_buffer, bwr.write_size, &bwr.write_consumed); //参数binder_proc、binder_thread、binder_write_read
if (ret < 0) {
bwr.read_consumed = 0;
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
ret = -EFAULT;
goto err;
}
}
if (bwr.read_size > 0) { //bwr.read_size = 0
ret = binder_thread_read(proc, thread, (void __user *)bwr.Read_Buffer, bwr.read_size, &bwr.read_consumed, filp->f_flags & O_NONBLOCK);
...
}
if (copy_to_user(ubuf, &bwr, sizeof(bwr))) { //将操作结果bwr返回到用户空间ubuf
ret = -EFAULT;
goto err;
}
break;
}
...
}
ret = 0;
err:
...
return ret;
}
//创建binder_node结构体，binder_node.cookie = new WindowManagerService(...)的服务端
int binder_thread_write(struct binder_proc *proc, struct binder_thread *thread, //参数binder_proc、binder_thread、binder_write_read
void __user *buffer, int size, signed long *consumed) //buffer = binder_write_read.write_buffer，binder_write_read.write_buffer = mOut，mOut保存binder_transaction_data，其中binder_transaction_data.code = GET_SERVICE_TRANSACTION，binder_transaction_data.data.ptr.buffer = "window"
{
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)) //在IPCThreadState::writeTransactionData执行mOut.writeInt32(cmd);向IPCThreadState.mOut中写入cmd = BC_TRANSACTION，可知获得用户输入命令cmd = BC_TRANSACTION
//*ptr = *buffer + *consumed = bwr.write_buffer + bwr.write_consumed = bwr.write_buffer = mOut，mOut保存binder_transaction_data，其中binder_transaction_data.code = GET_SERVICE_TRANSACTION，binder_transaction_data.data.ptr.buffer = "window"
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) { //cmd = BC_TRANSACTION
case BC_TRANSACTION:
case BC_REPLY: {
struct binder_transaction_data tr;
if (copy_from_user(&tr, ptr, sizeof(tr))) //读取用户空间ptr的数据，保存到tr
return -EFAULT;
ptr += sizeof(tr);
binder_transaction(proc, thread, &tr, cmd); //cmd = BC_TRANSACTION，tr保存bwr.write_buffer = mOut，mOut保存binder_transaction_data，其中binder_transaction_data.code = GET_SERVICE_TRANSACTION，binder_transaction_data.data.ptr.buffer = "window"
break;
}
}
return 0;
}
static void binder_transaction(struct binder_proc *proc,
struct binder_thread *thread,
struct binder_transaction_data *tr, int reply) //reply = BC_TRANSACTION，tr保存bwr.write_buffer = mOut，mOut保存binder_transaction_data，其中binder_transaction_data.code = GET_SERVICE_TRANSACTION，binder_transaction_data.data.ptr.buffer = "window"
{
struct binder_transaction *t; //binder_transaction结构体
struct binder_work *tcomplete;
size_t *offp, *off_end;
size_t off_min;
struct binder_proc *target_proc; //3个关键结构体binder_proc、binder_thread、binder_node
struct binder_thread *target_thread = NULL;
struct binder_node *target_node = NULL;
struct list_head *target_list; //list_head
wait_queue_head_t *target_wait;
struct binder_transaction *in_reply_to = NULL;
struct binder_transaction_log_entry *e;
uint32_t return_error = BR_OK;
struct binder_ref *ref;
ref = binder_get_ref(proc, tr->target.handle);
target_node = ref->node; //binder_node = binder_ref.node
target_proc = target_node->proc; //binder_proc = binder_node.proc，创建binder_node保存到binder_proc中
if (!reply && !(tr->flags & TF_ONE_WAY))
t->from = thread;
else
t->from = NULL;
/*由binder_transaction_data结构体tr构造binder_transaction结构体t*/
t->sender_euid = proc->tsk->cred->euid;
t->to_proc = target_proc;
t->to_thread = target_thread;
t->code = tr->code; //重点：binder_transaction.code = binder_transaction_data.code = GET_SERVICE_TRANSACTION
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));
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)) { //重点：binder_transaction.buffer.data = binder_transaction_data.data.ptr.buffer = "window"
...
}
if (copy_from_user(offp, tr->data.ptr.offsets, tr->offsets_size)) { //offp = tr->data.ptr.offsets = NULL，因为在执行getService时未写入Object
...
}
off_end = (void *)offp + tr->offsets_size;
for (; offp < off_end; offp++) { //offp为空故不进入for循环
...
}
if (reply) {
binder_pop_transaction(target_thread, in_reply_to);
} else if (!(t->flags & TF_ONE_WAY)) {
t->need_reply = 1;
t->from_parent = thread->transaction_stack;
thread->transaction_stack = t; //把binder_transaction结构体t保存到thread->transaction_stack，表示ServiceManager线程还有任务未完成
}
t->work.type = BINDER_WORK_TRANSACTION; //重点：binder_transaction->work.type = BINDER_WORK_TRANSACTION
list_add_tail(&t->work.entry, target_list); //重点：将binder_transaction放入ServiceManager进程的todo链表中，其中binder_transaction.code = binder_transaction_data.code = GET_SERVICE_TRANSACTION
tcomplete->type = BINDER_WORK_TRANSACTION_COMPLETE; binder_transaction.buffer.data = binder_transaction_data.data.ptr.buffer = "window"
list_add_tail(&tcomplete->entry, &thread->todo);
if (target_wait)
wake_up_interruptible(target_wait); //唤醒ServiceManager线程，ServiceManager线程执行waitForResponse，直到talkWithDriver返回NO_ERROR
return;
}总结：分析mRemote.transact(GET_SERVICE_TRANSACTION, data, reply, 0);可知
在ServiceManager进程的todo链表中保存着一个binder_transaction结构体，其中
binder_transaction.code = binder_transaction_data.code = GET_SERVICE_TRANSACTION
binder_transaction.buffer.data = binder_transaction_data.data.ptr.buffer = “window”
3.2 分析Binder_Loop
ServiceManager线程的thread->todo队列保存着binder_transaction结构体t，t->buffer->data = tr->data.ptr.buffer = “window”
frameworks/native/cmds/servicemanager/Binder.c：
void Binder_Loop(struct binder_state *bs, binder_handler func) //开启for循环，充当Server的角色，等待Client连接
{
int res;
struct binder_write_read bwr;
uint32_t readbuf[32];
bwr.write_size = 0;
bwr.write_consumed = 0;
bwr.write_buffer = 0;
readbuf[0] = BC_ENTER_LOOPER;
binder_write(bs, readbuf, sizeof(uint32_t));
for (;;) {
bwr.read_size = sizeof(readbuf);
bwr.read_consumed = 0;
bwr.read_buffer = (uintptr_t) readbuf;
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr); //bs->fd记录/dev/binder文件句柄，因此调用binder驱动的ioctl函数，传入参数BINDER_WRITE_READ
...
res = binder_parse(bs, 0, (uintptr_t) readbuf, bwr.read_consumed, func);
}
}3.2.1 分析res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);
static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) //cmd = BINDER_WRITE_READ
{
int ret;
struct binder_proc *proc = filp->private_data; //获得Service_manager进程的binder_proc，从打开文件file的私有数据成员变量private_data中获取binder_proc
struct binder_thread *thread;
unsigned int size = _IOC_SIZE(cmd);
void __user *ubuf = (void __user *)arg;
ret = wait_event_interruptible(binder_user_error_wait, binder_stop_on_user_error < 2);
if (ret)
return ret;
binder_lock(__func__);
thread = binder_get_thread(proc); //获得proc对应进程(Service_manager进程)下的所有线程中和当前线程pid相等的binder_thread
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))) { //把用户传递进来的参数转换成binder_write_read结构体，并保存在本地变量bwr中，bwr.read_buffer = BC_ENTER_LOOPER
ret = -EFAULT; bwr.write_buffer = 0
goto err;
}
if (bwr.write_size > 0) { //开始为0
...
}
if (bwr.read_size > 0) { //由binder_loop函数可知bwr.read_buffer = BC_ENTER_LOOPER
/*读取binder_thread->todo的事物，并处理，执行完后bwr.read_buffer = BR_TRANSACTION*/
ret = binder_thread_read(proc, thread, (void __user *)bwr.read_buffer, bwr.read_size, &bwr.read_consumed, filp->f_flags & O_NONBLOCK); //proc和thread分别发起传输动作的进程和线程
if (!list_empty(&proc->todo))
wake_up_interruptible(&proc->wait);
if (ret < 0) {
if (copy_to_user(ubuf, &bwr, sizeof(bwr)))
ret = -EFAULT;
goto err;
}
}
if (copy_to_user(ubuf, &bwr, sizeof(bwr))) { //将bwr返回到用户空间
ret = -EFAULT;
goto err;
}
break;
}
ret = 0;
...
return ret;
}
static int binder_thread_read(struct binder_proc *proc,
struct binder_thread *thread,
void __user *buffer, int size, //buffer = bwr.read_buffer = BC_ENTER_LOOPER，consumed = 0
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)) //把BR_NOOP写回到用户传进来的缓冲区ptr = *buffer + *consumed = bwr.read_buffer + bwr.read_consumed = bwr.read_buffer，即ptr = bwr.read_buffer = BR_NOOP
return -EFAULT; 即bwr.read_buffer = BR_NOOP
ptr += sizeof(uint32_t);
}
...
while (1) {
uint32_t cmd;
struct binder_transaction_data tr;
struct binder_work *w;
struct binder_transaction *t = NULL;
/*在3.1 分析mRemote.transact执行binder_transaction时，向ServiceManager进程的todo链表插入类型BINDER_WORK_TRANSACTION的事项*/
if (!list_empty(&thread->todo))
w = list_first_entry(&thread->todo, struct binder_work, entry); //从thread->todo队列中取出待处理的事项，事项类型BINDER_WORK_TRANSACTION
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) { //由待处理事项的type分类处理，w->type = BINDER_WORK_TRANSACTION
...
case BINDER_WORK_TRANSACTION: {
t = container_of(w, struct binder_transaction, work);
} break;
}
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;
t->saved_priority = task_nice(current);
if (t->priority < target_node->min_priority &&
!(t->flags & TF_ONE_WAY))
binder_set_nice(t->priority);
else if (!(t->flags & TF_ONE_WAY) ||
t->saved_priority > target_node->min_priority)
binder_set_nice(target_node->min_priority);
cmd = BR_TRANSACTION; //cmd = BR_TRANSACTION
} else {
tr.target.ptr = NULL;
tr.cookie = NULL;
cmd = BR_REPLY;
}
...
if (put_user(cmd, (uint32_t __user *)ptr)) //把cmd = BR_TRANSACTION写回到用户传进来的缓冲区ptr = bwr.read_buffer，故执行完binder_thread_read后cmd = bwr.read_buffer = BR_TRANSACTION
return -EFAULT; 即bwr.read_buffer = BR_TRANSACTION
ptr += sizeof(uint32_t);
if (copy_to_user(ptr, &tr, sizeof(tr)))
return -EFAULT;
ptr += sizeof(tr);
}
return 0;
}总结：分析res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);可知 bwr.read_buffer = BR_TRANSACTION
3.2.2 分析res = binder_parse(bs, 0, (uintptr_t) readbuf, bwr.read_consumed, func);
int binder_parse(struct binder_state *bs, struct binder_io *bio,
uintptr_t ptr, size_t size, binder_handler func)
{
int r = 1;
uintptr_t end = ptr + (uintptr_t) size;
while (ptr < end) {
uint32_t cmd = *(uint32_t *) ptr;
ptr += sizeof(uint32_t);
switch(cmd) {
...
case BR_TRANSACTION: {
struct binder_transaction_data *txn = (struct binder_transaction_data *) ptr; //由ptr构造binder_transaction_data结构体txn
if ((end - ptr) < sizeof(*txn)) {
ALOGE("parse: txn too small!\n");
return -1;
}
binder_dump_txn(txn);
if (func) { //func为binder_handler函数指针
unsigned rdata[256/4];
struct binder_io msg;
struct binder_io reply;
int res;
bio_init(&reply, rdata, sizeof(rdata), 4); //接收到数据之后，构造一个binder_io结构体reply
bio_init_from_txn(&msg, txn); //由txn构造一个binder_io结构体msg
res = func(bs, txn, &msg, &reply); //调用处理函数 --- 由binder_loop(bs, svcmgr_handler)第二个参数可知func是函数指针binder_handler,这个函数指针指向了svcmgr_handler函数
binder_send_reply(bs, &reply, txn->data.ptr.buffer, res); //如果res为0，表示注册成功，代码0写入binder_io结构体reply中
}
ptr += sizeof(*txn);
break;
}
}
return r;
}
struct binder_io{
char *data //从binder读取或者写入到binder中的内容指针
binder_size_t *offs;
char *data0; //内容起始位置，用作基准值
...
}
void bio_init(struct binder_io *bio, void *data,
size_t maxdata, size_t maxoffs)
{
size_t n = maxoffs * sizeof(size_t); //偏移数组所占的大小
if (n > maxdata) { //偏移数组所占的大小不能大于最大能分配大小
bio->flags = BIO_F_OVERFLOW;
bio->data_avail = 0;
bio->offs_avail = 0;
return;
}
bio->data = bio->data0 = (char *) data + n; //bio->data
bio->offs = bio->offs0 = data; //开始是偏移数组
bio->data_avail = maxdata - n; //数据缓冲区大小
bio->offs_avail = maxoffs; //偏移数组大小
bio->flags = 0;
}
void bio_init_from_txn(struct binder_io *bio, struct binder_transaction_data *txn)
{
bio->data = bio->data0 = (char *)(intptr_t)txn->data.ptr.buffer;
bio->offs = bio->offs0 = (binder_size_t *)(intptr_t)txn->data.ptr.offsets;
bio->data_avail = txn->data_size;
bio->offs_avail = txn->offsets_size / sizeof(size_t);
bio->flags = BIO_F_SHARED;
}
frameworks/native/cmds/servicemanager/Service_manager.c：
int svcmgr_handler(struct binder_state *bs,
struct binder_transaction_data *txn,
struct binder_io *msg,
struct binder_io *reply)
{
struct svcinfo *si;
uint16_t *s;
size_t len;
uint32_t handle;
uint32_t strict_policy;
int allow_isolated;
if (txn->target.handle != svcmgr_handle) //txn->target为NULL，svcmgr_handle为NULL(void* (0))
return -1;
if (txn->code == PING_TRANSACTION)
return 0;
strict_policy = bio_get_uint32(msg);
s = bio_get_string16(msg, &len); //返回s = bio->data = "window"
if (s == NULL) {
return -1;
}
if ((len != (sizeof(svcmgr_id) / 2)) ||
memcmp(svcmgr_id, s, sizeof(svcmgr_id))) {
fprintf(stderr,"invalid id %s\n", str8(s, len));
return -1;
}
if (sehandle && selinux_status_updated() > 0) {
struct selabel_handle *tmp_sehandle = selinux_android_service_context_handle();
if (tmp_sehandle) {
selabel_close(sehandle);
sehandle = tmp_sehandle;
}
}
switch(txn->code) {
case SVC_MGR_GET_SERVICE:
case SVC_MGR_CHECK_SERVICE:
s = bio_get_string16(msg, &len); //s = "window"
if (s == NULL) {
return -1;
}
handle = do_find_service(bs, s, len, txn->sender_euid, txn->sender_pid);
if (!handle)
break;
bio_put_ref(reply, handle);
return 0;
}
bio_put_uint32(reply, 0); //将注册成功代码0写入binder_io结构体reply中
return 0;
}
uint32_t do_find_service(struct binder_state *bs, const uint16_t *s, size_t len, uid_t uid, pid_t spid) //s = "window"
{
struct svcinfo *si;
if (!svc_can_find(s, len, spid)) {
return 0;
}
si = find_svc(s, len); //从svclist链表中寻找name = "window"的svcinfo并返回
if (si && si->handle) {
if (!si->allow_isolated) {
uid_t appid = uid % AID_USER;
if (appid >= AID_ISOLATED_START && appid <= AID_ISOLATED_END) {
return 0;
}
}
return si->handle; //返回svcinfo.handle即为name = "window"对应的new WindowManagerService(...)的服务端
} else {
return 0;
}
}
struct svcinfo *find_svc(const uint16_t *s16, size_t len) //s16 = "window"
{
struct svcinfo *si;
for (si = svclist; si; si = si->next) { //从svclist链表中寻找name = "window"的svcinfo并返回
if ((len == si->len) &&
!memcmp(s16, si->name, len * sizeof(uint16_t))) {
return si;
}
}
return NULL;
}
struct svcinfo
{
struct svcinfo *next; //用于形成链表
uint32_t handle;
struct binder_death death;
int allow_isolated;
size_t len;
uint16_t name[0]; //用于保存注册的Service组件的名称
};总结：
ServiceManager 服务获得过程
例如ServiceManager.getService(“window”);
a. 向ServiceManager的todo队列里面添加一条获得服务”window”的事务
b. ServiceManager从svclist链表中寻找name = “window”的svcinfo并返回，最终返回svcinfo.handle即为name = “window”对应的new WindowManagerService(…)的服务端
文章最后总结：
(1)ServiceManager 启动流程
a. 打开Binder驱动，建立128K = 128*1024内存映射
b. 设置自己（ServiceManager）为Binder的大管家
c. 开启for循环，充当Server的角色，等待Client连接
在Binder驱动程序中为ServiceManager建立了三个结构体：binder_proc、binder_thread、binder_node
binder_node.proc保存binder_proc，进程间通信的数据会发送到binder_proc的todo链表
binder_proc进程里有很多线程，每个线程对应一个binder_thread，每个binder_thread用来处理一个Client的跨进程通信的请求
(2)ServiceManager 注册服务过程
例如ServiceManager.addService(“window”, new WindowManagerService(…));
a. 创建一个binder_node结构体，binder_node.cookie = new WindowManagerService(…)的服务端
b. 向ServiceManager的todo队列里面添加一条注册服务”window”的事务
c. 创建一个svcinfo结构体放入链表，且svcinfo.handle对应new WindowManagerService(…)的服务端
svcinfo.name保存服务的名称”window”
(3)ServiceManager 获取服务过程
例如ServiceManager.getService(“window”);
a. 向ServiceManager的todo队列里面添加一条获得服务”window”的事务
b. ServiceManager从svclist链表中寻找name = “window”的svcinfo并返回，最终返回svcinfo.handle即为name = “window”对应的new WindowManagerService(…)的服务端
(4)进程A如何和进程B通信？
进程B向ServiceManager注册服务”window”，进程A由向ServceManager查询服务”window”的handle
由服务”window”的handle找到binder_ref，由binder_ref.node找到binder_node，由binder_node.proc找到目标进程的binder_proc
进程A将数据发送到进程B对应binder_proc的todo链表，进程B从todo链表取出数据即可
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