一. 概述
这里只讲下binder的实现原理，不牵扯到android的java层是如何调用;
涉及到的会有ServiceManager,led_control_server和test_client的代码,这些都是用c写的.其中led_control_server和test_client是
仿照bctest.c写的; 在linux平台下运行binder更容易分析binder机制实现的原理(可以增加大量的log,进行分析);
在Linux运行时.先运行ServiceManager,再运行led_control_server最后运行test_client;
1.1 Binder通信模型
Binder通信采用C/S架构，从组件视角来说，包含Client、Server、ServiceManager以及binder驱动，其中ServiceManager用于管理系统中的各种服务。
1.2 运行环境
本文中的代码运行环境是在imx6ul上跑的，运行的是linux系统，内核版本4.10(非android环境分析);
1.3 文章代码
文章所有代码已上传
https://github.com/SourceLink...
二. ServiceManager
涉及到的源码地址:
frameworks/native/cmds/servicemanager/sevice_manager.c
frameworks/native/cmds/servicemanager/binder.c
frameworks/native/cmds/servicemanager/bctest.c
ServiceManager相当于binder通信过程中的守护进程，本身也是个binder服务、好比一个root管理员一样;
主要功能是查询和注册服务;接下来结合代码从main开始分析下serviceManager的服务过程;
2.1 main
源码中的sevice_manager.c中主函数中使用了selinux，为了在我板子的linux环境中运行，把这些代码屏蔽，删减后如下：
int main(int argc, char **argv)
{
struct binder_state *bs;
bs = binder_open(128*1024); ①
if (!bs) {
ALOGE("failed to open binder driver\n");
return -1;
}
if (binder_become_context_manager(bs)) { ②
ALOGE("cannot become context manager (%s)\n", strerror(errno));
return -1;
}
svcmgr_handle = BINDER_SERVICE_MANAGER;
binder_loop(bs, svcmgr_handler); ③
return 0;
}
①: 打开binder驱动(详见2.2.1)
②: 注册为管理员(详见2.2.2)
③: 进入循环，处理消息(详见2.2.3)
从主函数的启动流程就能看出sevice_manager的工作流程并不是特别复杂;
其实client和server的启动流程和manager的启动类似，后面再详细分析;
2.2 binder_open
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); ①
if (bs->fd < 0) {
fprintf(stderr,"binder: cannot open device (%s)\n",
strerror(errno));
goto fail_open;
}
if ((ioctl(bs->fd, BINDER_VERSION, &vers) == -1) || ②
(vers.protocol_version != BINDER_CURRENT_PROTOCOL_VERSION)) {
fprintf(stderr, "binder: driver version differs from user space\n");
goto fail_open;
}
bs->mapsize = mapsize;
bs->mapped = mmap(NULL, mapsize, PROT_READ, MAP_PRIVATE, bs->fd, 0); ③
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;
}①: 打开binder设备
②: 通过ioctl获取binder版本号
③: mmp内存映射
这里说明下为什么binder驱动是用ioctl来操作，是因为ioctl可以同时进行读和写操作；
2.2 binder_become_context_manager
int binder_become_context_manager(struct binder_state *bs)
{
return ioctl(bs->fd, BINDER_SET_CONTEXT_MGR, 0);
}还是通过ioctl请求类型BINDER_SET_CONTEXT_MGR注册成manager;
2.3 binder_loop
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;
binder_write(bs, readbuf, sizeof(uint32_t)); ①
for (;;) {
bwr.read_size = sizeof(readbuf);
bwr.read_consumed = 0;
bwr.read_buffer = (uintptr_t) readbuf;
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr); ②
if (res < 0) {
ALOGE("binder_loop: ioctl failed (%s)\n", strerror(errno));
break;
}
res = binder_parse(bs, 0, (uintptr_t) readbuf, bwr.read_consumed, func); ③
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;
}
}
}①: 写入命令BC_ENTER_LOOPER通知驱动该线程已经进入主循环，可以接收数据;
②: 先读一次数据，因为刚才写过一次;
③: 然后解析读出来的数据(详见2.2.4);
binder_loop函数的主要流程如下:
2.4 binder_parse
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);
#if TRACE
fprintf(stderr,"%s:\n", cmd_name(cmd));
#endif
switch(cmd) {
case BR_NOOP:
break;
case BR_TRANSACTION_COMPLETE:
/* check服务 */
break;
case BR_INCREFS:
case BR_ACQUIRE:
case BR_RELEASE:
case BR_DECREFS:
#if TRACE
fprintf(stderr," %p, %p\n", (void *)ptr, (void *)(ptr + sizeof(void *)));
#endif
ptr += sizeof(struct binder_ptr_cookie);
break;
case BR_SPAWN_LOOPER: {
/* create new thread */
//if (fork() == 0) {
//}
pthread_t thread;
struct binder_thread_desc btd;
btd.bs = bs;
btd.func = func;
pthread_create(&thread, NULL, binder_thread_routine, &btd);
/* in new thread: ioctl(BC_ENTER_LOOPER), enter binder_looper */
break;
}
case BR_TRANSACTION: {
struct binder_transaction_data *txn = (struct binder_transaction_data *) ptr;
if ((end - ptr) < sizeof(*txn)) {
ALOGE("parse: txn too small!\n");
return -1;
}
if (func) {
unsigned rdata[256/4];
struct binder_io msg;
struct binder_io reply;
int res;
bio_init(&reply, rdata, sizeof(rdata), 4); ①
bio_init_from_txn(&msg, txn);
res = func(bs, txn, &msg, &reply); ②
binder_send_reply(bs, &reply, txn->data.ptr.buffer, res); ③
}
ptr += sizeof(*txn);
break;
}
case BR_REPLY: {
struct binder_transaction_data *txn = (struct binder_transaction_data *) ptr;
if ((end - ptr) < sizeof(*txn)) {
ALOGE("parse: reply too small!\n");
return -1;
}
binder_dump_txn(txn);
if (bio) {
bio_init_from_txn(bio, txn);
bio = 0;
} else {
/* todo FREE BUFFER */
}
ptr += sizeof(*txn);
r = 0;
break;
}
case BR_DEAD_BINDER: {
struct binder_death *death = (struct binder_death *)(uintptr_t) *(binder_uintptr_t *)ptr;
ptr += sizeof(binder_uintptr_t);
death->func(bs, death->ptr);
break;
}
case BR_FAILED_REPLY:
r = -1;
break;
case BR_DEAD_REPLY:
r = -1;
break;
default:
ALOGE("parse: OOPS %d\n", cmd);
return -1;
}
}
return r;
}①: 按照一定的格式初始化rdata数据,请注意这里rdata是在用户空间创建的buf;
②: 调用设置进来的处理函数svcmgr_handler(详见2.2.5);
③: 发送回复信息;
这个函数我们只重点关注下BR_TRANSACTION其他的命令含义可以参考表格A;
2.5 svcmgr_handler
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;
//ALOGI("target=%x code=%d pid=%d uid=%d\n",
// txn->target.handle, txn->code, txn->sender_pid, txn->sender_euid);
if (txn->target.handle != svcmgr_handle)
return -1;
if (txn->code == PING_TRANSACTION)
return 0;
// Equivalent to Parcel::enforceInterface(), reading the RPC
// header with the strict mode policy mask and the interface name.
// Note that we ignore the strict_policy and don't propagate it
// further (since we do no outbound RPCs anyway).
strict_policy = bio_get_uint32(msg); ①
s = bio_get_string16(msg, &len);
if (s == NULL) {
return -1;
}
if ((len != (sizeof(svcmgr_id) / 2)) || ②
memcmp(svcmgr_id, s, sizeof(svcmgr_id))) {
fprintf(stderr,"invalid id %s\n", str8(s, len));
return -1;
}
switch(txn->code) { ③
case SVC_MGR_GET_SERVICE:
case SVC_MGR_CHECK_SERVICE:
s = bio_get_string16(msg, &len);
if (s == NULL) {
return -1;
}
handle = do_find_service(bs, s, len, txn->sender_euid, txn->sender_pid); ④
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;
if (do_add_service(bs, s, len, handle, txn->sender_euid, ⑤
allow_isolated, txn->sender_pid))
return -1;
break;
case SVC_MGR_LIST_SERVICES: {
uint32_t n = bio_get_uint32(msg);
if (!svc_can_list(txn->sender_pid)) {
ALOGE("list_service() uid=%d - PERMISSION DENIED\n",
txn->sender_euid);
return -1;
}
si = svclist;
while ((n-- > 0) && si) ⑥
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;
}①: 获取帧头数据,一般为0，因为发送方发送数据时都会在数据最前方填充4个字节0数据(分配数据空间的最小单位4字节);
②: 对比svcmgr_id是否和我们原来定义相同#define SVC_MGR_NAME "linux.os.ServiceManager"(我改写了);
③: 根据code做对应的事情,就想到与根据编码去执行对应的fun(client请求服务后去执行服务，service也是根据不同的code来执行。接下来会举例说明);、
④: 从服务名在server链表中查找对应的服务，并返回handle(详见2.2.6);
⑤: 添加服务，一般都是service发起的请求。将handle和服务名添加到服务链表中(这里的handle是由binder驱动分配);
⑥: 查找server_manager中链表中第n个服务的名字(该数值由查询端决定);
2.6 do_find_service
uint32_t do_find_service(struct binder_state *bs, const uint16_t *s, size_t len, uid_t uid, pid_t spid)
{
struct svcinfo *si;
if (!svc_can_find(s, len, spid)) { ①
ALOGE("find_service('%s') uid=%d - PERMISSION DENIED\n",
str8(s, len), uid);
return 0;
}
si = find_svc(s, len); ②
//ALOGI("check_service('%s') handle = %x\n", str8(s, len), si ? si->handle : 0);
if (si && si->handle) {
if (!si->allow_isolated) { ③
// If this service doesn't allow access from isolated processes,
// then check the uid to see if it is isolated.
uid_t appid = uid % AID_USER;
if (appid >= AID_ISOLATED_START && appid <= AID_ISOLATED_END) {
return 0;
}
}
return si->handle; ④
} else {
return 0;
}
}①: 检测调用进程是否有权限请求服务(这里用selinux管理权限,为了让代码可以方便允许,这里面的代码有做删减);
②: 遍历server_manager服务链表;
③: 如果binder服务不允许服务从沙箱中访问,则执行下面检查;
④: 返回查询到handle;
do_find_service函数主要工作是搜索服务链表,返回查找到的服务
2.7 do_add_service
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;
//ALOGI("add_service('%s',%x,%s) uid=%d\n", str8(s, len), handle,
// allow_isolated ? "allow_isolated" : "!allow_isolated", uid);
if (!handle || (len == 0) || (len > 127))
return -1;
if (!svc_can_register(s, len, spid)) { ①
ALOGE("add_service('%s',%x) uid=%d - PERMISSION DENIED\n",
str8(s, len), handle, uid);
return -1;
}
si = find_svc(s, len); ②
if (si) {
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 { ③
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->next = svclist;
svclist = si;
}
ALOGI("add_service('%s'), handle = %d\n", str8(s, len), handle);
binder_acquire(bs, handle); ④
binder_link_to_death(bs, handle, &si->death); ⑤
return 0;
}①: 判断请求进程是否有权限注册服务;
②: 查找ServiceManager的服务链表中是否已经注册了该服务,如果有则通知驱动杀死原先的binder服务,然后更新最新的binder服务;
③: 如果原来没有创建该binder服务,则进行一系列的赋值,再插入到服务链表的表头;
④: 增加binder服务的引用计数;
⑤: 告诉驱动接收服务的死亡通知;
2.8 调用时序图
从上面分析,可以知道ServiceManager的主要工作流程如下:
三. led_control_server
3.1 main
int main(int argc, char **argv)
{
int fd;
struct binder_state *bs;
uint32_t svcmgr = BINDER_SERVICE_MANAGER;
uint32_t handle;
int ret;
struct register_server led_control[3] = { ①
[0] = {
.code = 1,
.fun = led_on
} ,
[1] = {
.code = 2,
.fun = led_off
}
};
bs = binder_open(128*1024); ②
if (!bs) {
ALOGE("failed to open binder driver\n");
return -1;
}
ret = svcmgr_publish(bs, svcmgr, LED_CONTROL_SERVER_NAME, led_control); ③
if (ret) {
ALOGE("failed to publish %s service\n", LED_CONTROL_SERVER_NAME);
return -1;
}
binder_set_maxthreads(bs, 10); ④
binder_loop(bs, led_control_server_handler); ⑤
return 0;
}①:led_control_server提供的服务函数;
②: 初始化binder组件( 详见2.2);
③: 注册服务,svcmgr是发送的目标,LED_CONTROL_SERVER_NAME注册的服务名,led_control注册的binder实体;
④: 设置创建线程最大数(详见3.5);
⑤: 进入线程循环(详见2.3);
3.2 svcmgr_publish
int svcmgr_publish(struct binder_state *bs, uint32_t target, const char *name, void *ptr)
{
int status;
unsigned iodata[512/4];
struct binder_io msg, reply;
bio_init(&msg, iodata, sizeof(iodata), 4); ①
bio_put_uint32(&msg, 0); // strict mode header
bio_put_string16_x(&msg, SVC_MGR_NAME);
bio_put_string16_x(&msg, name);
bio_put_obj(&msg, ptr);
if (binder_call(bs, &msg, &reply, target, SVC_MGR_ADD_SERVICE)) ②
return -1;
status = bio_get_uint32(&reply); ③
binder_done(bs, &msg, &reply); ④
return status;
}①: 初始化用户空间的数据iodata,设置了四个字节的offs,接着按一定格式往buf里面填充数据;
②: 调用ServiceManager服务的SVC_MGR_ADD_SERVICE功能;
③: 获取ServiceManager回复数据,成功返回0;
④: 结束注册过程,释放内核中刚才交互分配的buf;
3.2.1 bio_init
void bio_init(struct binder_io *bio, void *data,
size_t maxdata, size_t maxoffs)
{
size_t n = maxoffs * sizeof(size_t);
if (n > maxdata) {
bio->flags = BIO_F_OVERFLOW;
bio->data_avail = 0;
bio->offs_avail = 0;
return;
}
bio->data = bio->data0 = (char *) data + n; ①
bio->offs = bio->offs0 = data; ②
bio->data_avail = maxdata - n; ③
bio->offs_avail = maxoffs; ④
bio->flags = 0; ⑤
}①: 根据传进来的参数,留下一定长度的offs数据空间, data指针则从data + n开始;
②: offs指针则从data开始,则offs可使用的数据空间只有n个字节;
③: 可使用的data空间计数;
④: 可使用的offs空间计数;
⑤: 清除buf的flag;
init后此时buf空间的分配情况如下图:
3.2.2 bio_put_uint32
void bio_put_uint32(struct binder_io *bio, uint32_t n)
{
uint32_t *ptr = bio_alloc(bio, sizeof(n));
if (ptr)
*ptr = n;
}这个函数往buf里面填充一个uint32的数据,这个数据的最小单位为4个字节;
前面svcmgr_publish调用bio_put_uint32(&msg, 0);,实质buf中的数据是00 00 00 00 ;
3.2.3 bio_alloc
static void *bio_alloc(struct binder_io *bio, size_t size)
{
size = (size + 3) & (~3);
if (size > bio->data_avail) {
bio->flags |= BIO_F_OVERFLOW;
return NULL;
} else {
void *ptr = bio->data;
bio->data += size;
bio->data_avail -= size;
return ptr;
}
}这个函数分配的数据宽度为4的倍数,先判断当前可使用的数据宽度是否小于待分配的宽度;
如果小于则置标志BIO_F_OVERFLOW否则分配数据,并对data往后偏移size个字节,可使用数据宽度data_avail减去size个字节;
3.2.4 bio_put_string16_x
void bio_put_string16_x(struct binder_io *bio, const char *_str)
{
unsigned char *str = (unsigned char*) _str;
size_t len;
uint16_t *ptr;
if (!str) { ①
bio_put_uint32(bio, 0xffffffff);
return;
}
len = strlen(_str);
if (len >= (MAX_BIO_SIZE / sizeof(uint16_t))) {
bio_put_uint32(bio, 0xffffffff);
return;
}
/* Note: The payload will carry 32bit size instead of size_t */
bio_put_uint32(bio, len); ②
ptr = bio_alloc(bio, (len + 1) * sizeof(uint16_t));
if (!ptr)
return;
while (*str) ③
*ptr++ = *str++;
*ptr++ = 0;
}①: 这里到bio_alloc前都是为了计算和判断自己串的长度再填充到buf中;
②: 填充字符串前会填充字符串的长度;
③: 填充字符串到buf中,一个字符占两个字节,注意uint16_t *ptr;;
3.2.5 bio_put_obj
void bio_put_obj(struct binder_io *bio, void *ptr)
{
struct flat_binder_object *obj;
obj = bio_alloc_obj(bio); ①
if (!obj)
return;
obj->flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS;
obj->type = BINDER_TYPE_BINDER; ②
obj->binder = (uintptr_t)ptr; ③
obj->cookie = 0;
}struct flat_binder_object {
/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
__u32 type;
__u32 flags;
union {
binder_uintptr_t binder;
/* WARNING: DO NOT EDIT, AUTO-GENERATED CODE - SEE TOP FOR INSTRUCTIONS */
__u32 handle;
};
binder_uintptr_t cookie;
};①: 分配一个flat_binder_object大小的空间(详见3.2.6);
②: type的类型为BINDER_TYPE_BINDER时则type传入的是binder实体,一般是服务端注册服务时传入;
type的类型为BINDER_TYPE_HANDLE时则type传入的为handle,一般由客户端请求服务时;
③:obj->binder值,跟随type改变;
3.2.6 bio_alloc_obj
static struct flat_binder_object *bio_alloc_obj(struct binder_io *bio)
{
struct flat_binder_object *obj;
obj = bio_alloc(bio, sizeof(*obj)); ①
if (obj && bio->offs_avail) {
bio->offs_avail--;
*bio->offs++ = ((char*) obj) - ((char*) bio->data0); ②
return obj;
}
bio->flags |= BIO_F_OVERFLOW;
return NULL;
}①: 在data后分配struct flat_binder_object长度的空间;
②: bio->offs空间记下此时插入obj,相对于data0的偏移值;
看到这终于知道offs是干嘛的了,原来是用来记录数据中是否有obj类型的数据;
3.2.7 完整数据格式图
综上分析,传输一次完整的数据的格式如下:
3.3 binder_call
int binder_call(struct binder_state *bs,
struct binder_io *msg, struct binder_io *reply,
uint32_t target, uint32_t code)
{
int res;
struct binder_write_read bwr;
struct {
uint32_t cmd;
struct binder_transaction_data txn;
} __attribute__((packed)) writebuf;
unsigned readbuf[32];
if (msg->flags & BIO_F_OVERFLOW) {
fprintf(stderr,"binder: txn buffer overflow\n");
goto fail;
}
writebuf.cmd = BC_TRANSACTION; // binder call transaction
writebuf.txn.target.handle = target; ①
writebuf.txn.code = code; ②
writebuf.txn.flags = 0;
writebuf.txn.data_size = msg->data - msg->data0; ③
writebuf.txn.offsets_size = ((char*) msg->offs) - ((char*) msg->offs0);
writebuf.txn.data.ptr.buffer = (uintptr_t)msg->data0;
writebuf.txn.data.ptr.offsets = (uintptr_t)msg->offs0;
bwr.write_size = sizeof(writebuf); ④
bwr.write_consumed = 0;
bwr.write_buffer = (uintptr_t) &writebuf;
for (;;) {
bwr.read_size = sizeof(readbuf);
bwr.read_consumed = 0;
bwr.read_buffer = (uintptr_t) readbuf;
res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr); ⑤
if (res < 0) {
fprintf(stderr,"binder: ioctl failed (%s)\n", strerror(errno));
goto fail;
}
res = binder_parse(bs, reply, (uintptr_t) readbuf, bwr.read_consumed, 0); ⑥
if (res == 0) return 0;
if (res < 0) goto fail;
}
fail:
memset(reply, 0, sizeof(*reply));
reply->flags |= BIO_F_IOERROR;
return -1;
}①: 这个target就是我们这次请求服务的目标,即ServiceManager;
②: code是我们请求服务的功能码,由服务端提供;
③: 把binder_io数据转化成binder_transaction_data数据;
④: 驱动进行读写是根据这个size来的,分析驱动的时候再详细分析;
⑤: 进行一次读写;
⑥: 解析发送的后返回的数据,判断是否注册成功;
3.4 binder_done
void binder_done(struct binder_state *bs,
struct binder_io *msg,
struct binder_io *reply)
{
struct {
uint32_t cmd;
uintptr_t buffer;
} __attribute__((packed)) data;
if (reply->flags & BIO_F_SHARED) {
data.cmd = BC_FREE_BUFFER;
data.buffer = (uintptr_t) reply->data0;
binder_write(bs, &data, sizeof(data));
reply->flags = 0;
}
}这个函数比较简单发送BC_FREE_BUFFER命令给驱动,让驱动释放内核态由刚才交互分配的buf;
3.5 binder_set_maxthreads
void binder_set_maxthreads(struct binder_state *bs, int threads)
{
ioctl(bs->fd, BINDER_SET_MAX_THREADS, &threads);
}这里主要调用ioctl函数写入命令BINDER_SET_MAX_THREADS进行设置最大线程数;
3.6 调用时序图
led_control_server主要提供led的控制服务,具体的流程如下:
四. test_client
4.1 main
int main(int argc, char **argv)
{
struct binder_state *bs;
uint32_t svcmgr = BINDER_SERVICE_MANAGER;
unsigned int g_led_control_handle;
if (argc < 3) {
ALOGE("Usage:\n");
ALOGE("%s led \n", argv[0]);
return -1;
}
bs = binder_open(128*1024); ①
if (!bs) {
ALOGE("failed to open binder driver\n");
return -1;
}
g_led_control_handle = svcmgr_lookup(bs, svcmgr, LED_CONTROL_SERVER_NAME); ②
if (!g_led_control_handle) {
ALOGE( "failed to get led control service\n");
return -1;
}
ALOGI("Handle for led control service = %d\n", g_led_control_handle);
if (!strcmp(argv[1], "led")) {
if (!strcmp(argv[2], "on")) {
if (interface_led_on(bs, g_led_control_handle, 2) == 0) { ③
ALOGI("led was on\n");
}
} else if (!strcmp(argv[2], "off")) {
if (interface_led_off(bs, g_led_control_handle, 2) == 0) {
ALOGI("led was off\n");
}
}
}
binder_release(bs, g_led_control_handle); ④
return 0;
} ①: 打开binder设备(详见2.2);
②: 根据名字获取led控制服务;
③: 根据获取到的handle,调用led控制服务(详见4.3);
④: 释放服务;
client的流程也很简单,按步骤1.2.3.4读下来就是了;
4.2 svcmgr_lookup
uint32_t svcmgr_lookup(struct binder_state *bs, uint32_t target, const char *name)
{
uint32_t handle;
unsigned iodata[512/4];
struct binder_io msg, reply;
bio_init(&msg, iodata, sizeof(iodata), 4); ①
bio_put_uint32(&msg, 0); // strict mode header
bio_put_string16_x(&msg, SVC_MGR_NAME);
bio_put_string16_x(&msg, name);
if (binder_call(bs, &msg, &reply, target, SVC_MGR_GET_SERVICE)) ②
return 0;
handle = bio_get_ref(&reply); ③
if (handle)
binder_acquire(bs, handle); ④
binder_done(bs, &msg, &reply); ⑤
return handle;
}①: 因为是请求服务,所以这里不用添加binder实体数据,具体的参考3.2,这里就不重复解释了;
②: 向target进程(ServiceManager)请求获取led_control服务(详细参考3.3);
③: 从ServiceManager返回的数据buf中获取led_control服务的handle;
④: 增加该handle的引用计数;
⑤: 释放内核空间buf(详3.4);
4.2.1 bio_get_ref
uint32_t bio_get_ref(struct binder_io *bio)
{
struct flat_binder_object *obj;
obj = _bio_get_obj(bio); ①
if (!obj)
return 0;
if (obj->type == BINDER_TYPE_HANDLE) ②
return obj->handle;
return 0;
}①: 把bio的数据转化成flat_binder_object格式;
②: 判断binder数据类型是否为引用,是则返回获取到的handle;
4.2.2 _bio_get_obj
static struct flat_binder_object *_bio_get_obj(struct binder_io *bio)
{
size_t n;
size_t off = bio->data - bio->data0; ①
/* TODO: be smarter about this? */
for (n = 0; n < bio->offs_avail; n++) {
if (bio->offs[n] == off)
return bio_get(bio, sizeof(struct flat_binder_object)); ②
}
bio->data_avail = 0;
bio->flags |= BIO_F_OVERFLOW;
return NULL;
}①: 一般情况下该值都为0,因为在reply时获取ServiceManager传来的数据,bio->data和bio->data都指向同一个地址;
②: 获取到struct flat_binder_object数据的头指针;
从ServiceManager传来的数据是struct flat_binder_object的数据,格式如下:
4.3 interface_led_on
int interface_led_on(struct binder_state *bs, unsigned int handle, unsigned char led_enum)
{
unsigned iodata[512/4];
struct binder_io msg, reply;
int ret = -1;
int exception;
bio_init(&msg, iodata, sizeof(iodata), 4);
bio_put_uint32(&msg, 0); // strict mode header
bio_put_uint32(&msg, led_enum);
if (binder_call(bs, &msg, &reply, handle, LED_CONTROL_ON))
return ret;
exception = bio_get_uint32(&reply);
if (exception == 0)
ret = bio_get_uint32(&reply);
binder_done(bs, &msg, &reply);
return ret;
}这个流程和前面svcmgr_lookup的请求服务差不多,只是最后是获取led_control_server的返回值.
注意这里为什么获取了两次uint32类型的数据,这是因为服务方在回复数据的时候添加了头帧,这个是可以调节的,非规则;
4.4 binder_release
void binder_release(struct binder_state *bs, uint32_t target)
{
uint32_t cmd[2];
cmd[0] = BC_RELEASE;
cmd[1] = target;
binder_write(bs, cmd, sizeof(cmd));
}通知驱动层减小对target进程的引用,结合驱动讲解就更能明白了;
4.5 调用时序图
test_client的调用时序如下,过程和led_control_server的调用过程相识:
A: 表BR_含义
BR个人理解是缩写为binder reply
| 消息 | 含义 | 参数 |
|---|---|---|
| BR_ERROR | 发生内部错误（如内存分配失败） | --- |
| BR_OK BR_NOOP |
操作完成 | --- |
| BR_SPAWN_LOOPER | 该消息用于接收方线程池管理。当驱动发现接收方所有 线程都处于忙碌状态且线程池里的线程总数没有超过 BINDER_SET_MAX_THREADS设置的最大线程数时， 向接收方发送该命令要求创建更多线程以备接收数据。 |
--- |
| BR_TRANSACTION | 对应发送方的BC_TRANSACTION | binder_transaction_data |
| BR_REPLY | 对应发送方BC_REPLY的回复 | binder_transaction_data |
| BR_ACQUIRE_RESULT BR_FINISHED |
未使用 | --- |
| BR_DEAD_REPLY | 交互时向驱动发送binder调用，如果对方已经死亡，则 驱动回应此命令 |
--- |
| BR_TRANSACTION_COMPLETE | 发送方通过BC_TRANSACTION或BC_REPLY发送 完一个数据包后，都能收到该消息做为成功发送的反馈。 这和BR_REPLY不一样，是驱动告知发送方已经发送成 功，而不是Server端返回请求数据。所以不管 同步还是异步交互接收方都能获得本消息。 |
--- |
| BR_INCREFS BR_ACQUIRE BR_RELEASE BR_DECREFS |
这一组消息用于管理强/弱指针的引用计数。只有 提供Binder实体的进程才能收到这组消息。 |
binder_uintptr_t binder：Binder实体在用户空间中的指针 binder_uintptr_t cookie：与该实体相关的附加数据 |
| BR_DEAD_BINDER |
向获得Binder引用的进程发送Binder实体 死亡通知书；收到死亡通知书的进程接下 来会返回BC_DEAD_BINDER_DONE做确认。 |
--- |
| BR_CLEAR_DEATH_NOTIFICATION_DONE | 回应命令BC_REQUEST_DEATH_NOTIFICATION | --- |
| BR_FAILED_REPLY | 如果发送非法引用号则返回该消息 | --- |
B: 表BC_含义
BC个人理解是缩写为binder call or cmd
| 消息 | 含义 | 参数 |
|---|---|---|
| BC_TRANSACTION BC_REPLY |
BC_TRANSACTION用于Client向Server发送请求数据； BC_REPLY用于Server向Client发送回复（应答）数据。 其后面紧接着一个binder_transaction_data结构体表明要写 入的数据。 |
struct binder_transaction_data |
| BC_ACQUIRE_RESULT BC_ATTEMPT_ACQUIRE |
未使用 | --- |
| BC_FREE_BUFFER | 请求驱动释放调刚在内核空间创建用来保存用户空间数据的内存块 | --- |
| BC_INCREFS BC_ACQUIRE BC_RELEASE BC_DECREFS |
这组命令增加或减少Binder的引用计数，用以实现强指针或 弱指针的功能。 |
--- |
| BC_INCREFS_DONE BC_ACQUIRE_DONE |
第一次增加Binder实体引用计数时，驱动向Binder 实体所在的进程发送BR_INCREFS， BR_ACQUIRE消息； Binder实体所在的进程处理完毕回馈BC_INCREFS_DONE， BC_ACQUIRE_DONE |
--- |
| BC_REGISTER_LOOPER BC_ENTER_LOOPER BC_EXIT_LOOPER |
这组命令同BINDER_SET_MAX_THREADS一道实现Binder驱 动对接收方线程池管理。BC_REGISTER_LOOPER通知驱动线程 池中一个线程已经创建了；BC_ENTER_LOOPER通知驱动该线程 已经进入主循环，可以接收数据；BC_EXIT_LOOPER通知驱动 该线程退出主循环，不再接收数据。 |
--- |
| BC_REQUEST_DEATH_NOTIFICATION | 获得Binder引用的进程通过该命令要求驱动在Binder实体销毁得到 通知。虽说强指针可以确保只要有引用就不会销毁实体，但这毕竟 是个跨进程的引用，谁也无法保证实体由于所在的Server关闭Binder 驱动或异常退出而消失，引用者能做的是要求Server在此刻给出通知。 |
--- |
| BC_DEAD_BINDER_DONE | 收到实体死亡通知书的进程在删除引用后用本命令告知驱动。 | --- |
参考
表格参考博客: