盒子
盒子
文章目录
  1. ServiceManager
    1. main
  2. binder_open
  3. binder_become_context_manager
  4. binder_loop
    1. binder_write
    2. binder_parse
    3. svcmgr_handler
    4. do_add_service
  5. 项目

Binder: ServiceManager的创建

承接Binder: addService初探这篇文章,我们已经知道Client端通过BpBindertransact方法与service端进行通信,在BpBindertransact方法中又通过IPCThreadStatetransact方法将数据传递到service端。

最终来到IPCThreadStatewriteTransactionData方法

frameworks/native/libs/binder/IPCThreadState.cpp

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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;
// 将数据封装到tr中
tr.target.ptr = 0;
tr.target.handle = handle; // handle = 0, 定位到ServiceManager
tr.code = code; // 操作码 ADD_SERVICE_TRANSACTION
tr.flags = binderFlags;
tr.cookie = 0;
tr.sender_pid = 0;
tr.sender_euid = 0;
const status_t err = data.errorCheck();
if (err == NO_ERROR) {
tr.data_size = data.ipcDataSize();
tr.data.ptr.buffer = data.ipcData();
tr.offsets_size = data.ipcObjectsCount()*sizeof(binder_size_t);
tr.data.ptr.offsets = data.ipcObjects();
} else if (statusBuffer) {
tr.flags |= TF_STATUS_CODE;
*statusBuffer = err;
tr.data_size = sizeof(status_t);
tr.data.ptr.buffer = reinterpret_cast<uintptr_t>(statusBuffer);
tr.offsets_size = 0;
tr.data.ptr.offsets = 0;
} else {
return (mLastError = err);
}
mOut.writeInt32(cmd); // 指令码 BC_TRANSACTION
// 写入数据,进行数据传递
mOut.write(&tr, sizeof(tr));
return NO_ERROR;
}

在传递数据的过程中,通过handle = 0来定位到serviceservice_manager

下面我们来分析一下ServiceManager的创建过程。

ServiceManager

ServiceManager是伴随着Android init 启动一起被创建的,在init.rc文件中进行声明的。

其所对应的可执行程序是/system/bin/servicemanager,所对应的源文件是service_manager.c,进程名为/system/bin/servicemanager

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service servicemanager /system/bin/servicemanager
class core
user system
group system
critical
onrestart restart healthd
onrestart restart zygote
onrestart restart media
onrestart restart surfaceflinger
onrestart restart drm

所以启动ServiceManager的入口在service_manager.cmain方法中

main

frameworks/native/cmds/servicemanager/service_manager.c

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int main(int argc, char** argv)
{
struct binder_state *bs;
union selinux_callback cb;
char *driver;
if (argc > 1) {
driver = argv[1];
} else {
driver = "/dev/binder";
}
// 打开binder驱动
bs = binder_open(driver, 128*1024);
...
// 将ServiceManager设置成binder的守护者
if (binder_become_context_manager(bs)) {
ALOGE("cannot become context manager (%s)\n", strerror(errno));
return -1;
}
...
// 开启binder循环,监听数据的到来
binder_loop(bs, svcmgr_handler);
return 0;
}

main方法中主要做了三件事

  1. 通过binder_open打开binder驱动,申请128kb的内存大小空间
  2. 通过binder_become_context_managerServiceManager设置成binder的守护者
  3. 通过binder_loop开启binder循环,监听数据

binder_open

frameworks/native/cmds/servicemanager/binder.c

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struct binder_state *binder_open(const char* driver, size_t mapsize)
{
struct binder_state *bs;
struct binder_version vers;
bs = malloc(sizeof(*bs));
if (!bs) {
errno = ENOMEM;
return NULL;
}
// 开启binder驱动
bs->fd = open(driver, O_RDWR | O_CLOEXEC);
if (bs->fd < 0) {
fprintf(stderr,"binder: cannot open %s (%s)\n",
driver, strerror(errno));
goto fail_open;
}
// 获取binder版本信息
if ((ioctl(bs->fd, BINDER_VERSION, &vers) == -1) ||
(vers.protocol_version != BINDER_CURRENT_PROTOCOL_VERSION)) {
fprintf(stderr,
"binder: kernel driver version (%d) differs from user space version (%d)\n",
vers.protocol_version, BINDER_CURRENT_PROTOCOL_VERSION);
goto fail_open;
}
// 设置mmap映射大小128kb
bs->mapsize = mapsize;
// 设置内存映射地址
bs->mapped = mmap(NULL, mapsize, PROT_READ, MAP_PRIVATE, bs->fd, 0);
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;
}

这里主要对bs结构体的三个变量进行赋值,它是binder_state类型的结构体

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struct binder_state
{
int fd; // dev/binder 文件描述符
void *mapped; // 映射的内存地址
size_t mapsize; // 映射的大小
};

所以binder_open主要做的事情是

  1. 打开binder驱动
  2. 验证binder版本信息
  3. 设置mmap内存映射大小,默认为128kb
  4. 设置mmap内存映射的地址

binder_become_context_manager

frameworks/native/cmds/servicemanager/binder.c

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int binder_become_context_manager(struct binder_state *bs)
{
struct flat_binder_object obj;
// 初始化obj
memset(&obj, 0, sizeof(obj));
obj.flags = FLAT_BINDER_FLAG_TXN_SECURITY_CTX;
// 与binder驱动进行数据通信
int result = ioctl(bs->fd, BINDER_SET_CONTEXT_MGR_EXT, &obj);
if (result != 0) {
android_errorWriteLog(0x534e4554, "121035042");
// 与binder驱动进行数据通信
result = ioctl(bs->fd, BINDER_SET_CONTEXT_MGR, 0);
}
return result;
}

binder_become_context_manager方法中,通过ioctlbinder驱动进行通信,并传入数据0作为标识,将ServiceManager设置为binder的守护者,用来统一处理binder的数据传输。

binder_loop

frameworks/native/cmds/servicemanager/binder.c

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void binder_loop(struct binder_state *bs, binder_handler func)
{
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;
// 写入数据
binder_write(bs, readbuf, sizeof(uint32_t));
// 开启循环,监听数据的到来
for (;;) {
bwr.read_size = sizeof(readbuf);
bwr.read_consumed = 0;
bwr.read_buffer = (uintptr_t) readbuf;
// 获取binder驱动中的数据
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);
if (res < 0) {
ALOGE("binder_loop: ioctl failed (%s)\n", strerror(errno));
break;
}
// 解析数据
res = binder_parse(bs, 0, (uintptr_t) readbuf, bwr.read_consumed, func);
if (res == 0) {
ALOGE("binder_loop: unexpected reply?!\n");
break;
}
if (res < 0) {
ALOGE("binder_loop: io error %d %s\n", res, strerror(errno));
break;
}
}
}

binder_loop中主要做了三件事:

  1. 首先通过binder_write传递BC_ENTER_LOOPER指令码,告诉binder进入循环
  2. 开启循序,通过ioctl监听并读取数据
  3. 一旦读取到数据,将通过binder_parse来进一步解析

binder_write

frameworks/native/cmds/servicemanager/binder.c

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int binder_write(struct binder_state *bs, void *data, size_t len)
{
struct binder_write_read bwr;
int res;
// 将数据填充到bwr中
bwr.write_size = len;
bwr.write_consumed = 0;
bwr.write_buffer = (uintptr_t) data;
bwr.read_size = 0;
bwr.read_consumed = 0;
bwr.read_buffer = 0;
// 传输数据
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);
if (res < 0) {
fprintf(stderr,"binder_write: ioctl failed (%s)\n",
strerror(errno));
}
return res;
}

这里主要是将数据统一封装到bwr中,bwrbinder_write_read的结构体,当写数据时会将数据写入到write_buffer中,而当读数据时会从read_buffer中读取数据。所以这是一个支持双向读写操作的数据源。以便可以通过ioctlbinder驱动进行读写操作。

由于是首次进入且即将进入循序操作,所以第一次会传递BC_ENTER_LOOPER指令码,通知binder进行循环操作。

所以通过ioctl发送BINDER_WRITE_READ的通信code,将bwr传递给binder驱动。

binder_parse

frameworks/native/cmds/servicemanager/binder.c

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int binder_parse(struct binder_state *bs, struct binder_io *bio,
uintptr_t ptr, size_t size, binder_handler func)
{
int r = 1;
// 获取数据截止位的内存地址
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_secctx 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.transaction_data);
// 调用func,对应的是svcmgr_handler
res = func(bs, &txn, &msg, &reply);
if (txn.transaction_data.flags & TF_ONE_WAY) {
binder_free_buffer(bs, txn.transaction_data.data.ptr.buffer);
} else {
// 发送reply
binder_send_reply(bs, &reply, txn.transaction_data.data.ptr.buffer, res);
}
}
break;
}
...
case BR_REPLY: {
...
break;
}
default:
ALOGE("parse: OOPS %d\n", cmd);
return -1;
}
}
return r;
}

binder_parse中主要是解析binder信息,参数ptr指向BC_ENTER_LOOPERfunc指向svcmgr_handler。所以一旦请求到来,会调用svcmgr_handler,并将处理的结构通过binder_send_reply返回会给client端。这个对应的就是之前文章中说的BC_REPLAY

这个svcmgr_handler是在最外面的binder_loop传递过来的。

svcmgr_handler

frameworks/native/cmds/servicemanager/service_manager.c

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int svcmgr_handler(struct binder_state *bs,
struct binder_transaction_data_secctx *txn_secctx,
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;
uint32_t dumpsys_priority;
struct binder_transaction_data *txn = &txn_secctx->transaction_data;
switch(txn->code) {
case SVC_MGR_GET_SERVICE:
case SVC_MGR_CHECK_SERVICE:
s = bio_get_string16(msg, &len);
if (s == NULL) {
return -1;
}
// 查找service
handle = do_find_service(s, len, txn->sender_euid, txn->sender_pid,
(const char*) txn_secctx->secctx);
if (!handle)
break;
bio_put_ref(reply, handle);
return 0;
case SVC_MGR_ADD_SERVICE:
s = bio_get_string16(msg, &len);
if (s == NULL) {
return -1;
}
handle = bio_get_ref(msg);
allow_isolated = bio_get_uint32(msg) ? 1 : 0;
dumpsys_priority = bio_get_uint32(msg);
// 注册service
if (do_add_service(bs, s, len, handle, txn->sender_euid, allow_isolated, dumpsys_priority,
txn->sender_pid, (const char*) txn_secctx->secctx))
return -1;
break;
case SVC_MGR_LIST_SERVICES: {
uint32_t n = bio_get_uint32(msg);
uint32_t req_dumpsys_priority = bio_get_uint32(msg);
if (!svc_can_list(txn->sender_pid, (const char*) txn_secctx->secctx, txn->sender_euid)) {
ALOGE("list_service() uid=%d - PERMISSION DENIED\n",
txn->sender_euid);
return -1;
}
si = svclist;
// 遍历service
while (si) {
if (si->dumpsys_priority & req_dumpsys_priority) {
if (n == 0) break;
n--;
}
si = si->next;
}
if (si) {
bio_put_string16(reply, si->name);
return 0;
}
return -1;
}
default:
ALOGE("unknown code %d\n", txn->code);
return -1;
}
bio_put_uint32(reply, 0);
return 0;
}

svcmgr_handler主要是对service的操作处理,例如之前文章中提到的addService操作,最终都会在SVC_MGR_ADD_SERVICE中进行处理。

SVC_MGR_ADD_SERVICE中会通过do_add_service方法来注册service

do_add_service

frameworks/native/cmds/servicemanager/service_manager.c

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int do_add_service(struct binder_state *bs, const uint16_t *s, size_t len, uint32_t handle,
uid_t uid, int allow_isolated, uint32_t dumpsys_priority, pid_t spid, const char* sid) {
struct svcinfo *si;
if (!handle || (len == 0) || (len > 127))
return -1;
// 检查是否能够注册该service
if (!svc_can_register(s, len, spid, sid, uid)) {
ALOGE("add_service('%s',%x) uid=%d - PERMISSION DENIED\n",
str8(s, len), handle, uid);
return -1;
}
// 查找是否已经注册了
si = find_svc(s, len);
if (si) { //已经注册
if (si->handle) {
ALOGE("add_service('%s',%x) uid=%d - ALREADY REGISTERED, OVERRIDE\n",
str8(s, len), handle, uid);
svcinfo_death(bs, si);
}
si->handle = handle;
} else { //没有注册
// 申请内存
si = malloc(sizeof(*si) + (len + 1) * sizeof(uint16_t));
if (!si) {
ALOGE("add_service('%s',%x) uid=%d - OUT OF MEMORY\n",
str8(s, len), handle, uid);
return -1;
}
si->handle = handle;
si->len = len;
memcpy(si->name, s, (len + 1) * sizeof(uint16_t));
si->name[len] = '\0';
si->death.func = (void*) svcinfo_death;
si->death.ptr = si;
si->allow_isolated = allow_isolated;
si->dumpsys_priority = dumpsys_priority;
si->next = svclist;
// 保存到svclist表中
svclist = si;
}
binder_acquire(bs, handle);
binder_link_to_death(bs, handle, &si->death);
return 0;
}

do_add_service中首先会检查该注册的service是否能够注册,然后再出查询现有的svclist中是否存在该service;如果不存在就为该service申请内存空间,最后在加入到svclist注册表中。

至此整个ServiceManager的流程就分析完了,我这里做个总结:

  1. 通过binder_open打开binder驱动,并调用mmap分配128kb的内存映射地址空间
  2. 通过binder_become_context_managerServiceManager设置为binder驱动的守护进程,通过0来标识
  3. 通过binder_loop开启循环,等待与监听client端传递过来的数据
  4. 在数据监听的过程中,使用binder_write通知binder进行循环
  5. 通过ioctl来与binder驱动进行数据读写
  6. 通过binder_parse来解析监听到的数据,根据BR_指令码来区别不同的操作,并通过replyBC_指令码的方式回馈给client
  7. 将解析的数据回调给svcmgr_handler进行统一逻辑处理,包括service的注册、查找、验证等操作
  8. 最终ServiceManager会将注册的service保存到svclist注册表中,以便之后的验证与查询

项目

android_startup: 提供一种在应用启动时能够更加简单、高效的方式来初始化组件。开发人员可以使用android-startup来简化启动序列,并显式地设置初始化顺序与组件之间的依赖关系。 与此同时android-startup支持同步与异步等待,并通过有向无环图拓扑排序的方式来保证内部依赖组件的初始化顺序。

AwesomeGithub: 基于Github客户端,纯练习项目,支持组件化开发,支持账户密码与认证登陆。使用Kotlin语言进行开发,项目架构是基于Jetpack&DataBindingMVVM;项目中使用了ArouterRetrofitCoroutineGlideDaggerHilt等流行开源技术。

flutter_github: 基于Flutter的跨平台版本Github客户端,与AwesomeGithub相对应。

android-api-analysis: 结合详细的Demo来全面解析Android相关的知识点, 帮助读者能够更快的掌握与理解所阐述的要点。

daily_algorithm: 算法进阶,由浅入深,欢迎加入一起共勉。

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