Android Binder------ServiceManager启动分析

ServiceManager启动分析

简述：

　　ServiceManager是一个全局的manager、调用了Jni函数，实现addServicew getService checkService listService等函数，

Server进程先注册一些service到SercviceManager中。

Client想获得一些service，就要到Service中去获取该Service。

这样，Server和Client之间就可以进行通讯了，

Server和Client之间的通讯都是通过Binder进行的。

三步走：

1.初始化Binder通讯环境，打开Binder设备，并映射内存。

2.注册自身为上下文管理者（context_manager）

3.进入无限循环的looping！！！

详细过程：

1 ，启动入口一个标准的 main函数！

int main(int argc, char **argv)

{

//记录serviceManager的状态

struct binder_state *bs;

void *svcmgr = BINDER_SERVICE_MANAGER;

//用于打开binder设备 用于打开设备 后把设备映射到内存时申请的内存大小128*1024

bs = binder_open(*);

//注册自身为上下文管理者（context_manager）

if (binder_become_context_manager(bs)) {

ALOGE("cannot become context manager (%s)\n", strerror(errno));

return -;

}

svcmgr_handle = svcmgr;

//loop无线循环，等待接收IPC同请求

binder_loop(bs, svcmgr_handler);

return ;

}

2  bind_open函数。用来打开binder设备。 call

by1

struct binder_state *binder_open(unsigned mapsize)

{

struct binder_state *bs;

bs = malloc(sizeof(*bs));

if (!bs) {

errno = ENOMEM;

return ;

}

bs->fd = open("/dev/binder", O_RDWR);//打开binder设备

if (bs->fd < ) {

fprintf(stderr,"binder: cannot open device (%s)\n",

strerror(errno));

goto fail_open;

}

bs->mapsize = mapsize;//bs是用来保存open 和mmap的返回信息

bs->mapped = mmap(NULL, mapsize, PROT_READ, MAP_PRIVATE, bs->fd, );//进行内存映射，返回的映射区的起始地址给bs->mapped

if (bs->mapped == MAP_FAILED) {//映射失败吹里逻辑

fprintf(stderr,"binder: cannot map device (%s)\n",

strerror(errno));

goto fail_map;

}

/* TODO: check version */

return bs;

fail_map://映射失败的 goto处。

close(bs->fd);

fail_open://打开设备失败的goto处。

free(bs);

return ;

3.设置上下文Manager call by1

int binder_become_context_manager(struct binder_state *bs)

{

return ioctl(bs->fd, BINDER_SET_CONTEXT_MGR, );

//直接用ioctl函数（ 提供了一种获得设备信息和向设备发送控制参数的手段）来让设备Binder设置上下文

}

4.进入loop。 call by 1

void binder_loop(struct binder_state *bs, binder_handler func)

{

int res;

struct binder_write_read bwr;

unsigned readbuf[];

bwr.write_size = ;

bwr.write_consumed = ;

bwr.write_buffer = ;

//设置事务类型，Binder Command 为 BC_ENTER_LOOPER

readbuf[] = BC_ENTER_LOOPER;

//在binder_write中调用了ioctl函数，调用Binder设备的函数，标志serviceManager进入的Loop 状态。

binder_write(bs, readbuf, sizeof(unsigned));

for (;;) {

bwr.read_size = sizeof(readbuf);

bwr.read_consumed = ;

bwr.read_buffer = (unsigned) readbuf;

//每次循环都进入Binder设备的缓冲区中，看看是否有IPC请求。

res = ioctl(bs->fd, BINDER_WRITE_READ, &bwr);

if (res < ) {

ALOGE("binder_loop: ioctl failed (%s)\n", strerror(errno));

break;

}

//对获取的结果进行解析。

res = binder_parse(bs, , readbuf, bwr.read_consumed, func);

if (res == ) {

ALOGE("binder_loop: unexpected reply?!\n");

break;

}

if (res < ) {

ALOGE("binder_loop: io error %d %s\n", res, strerror(errno));

break;

}

}

}

5.把返回的数据进行解析 call by 4

int binder_parse(struct binder_state *bs, struct binder_io *bio,

uint32_t *ptr, uint32_t size, binder_handler func)

{

int r = ;

uint32_t *end = ptr + (size / );

while (ptr < end) {

uint32_t cmd = *ptr++;

#if TRACE

fprintf(stderr,"%s:\n", cmd_name(cmd));

#endif

switch(cmd) {

case BR_NOOP:

break;

case BR_TANSACTION_COMPLETE:

break;R

case BR_INCREFS:

case BR_ACQUIRE:

case BR_RELEASE:

case BR_DECREFS:

#if TRACE

fprintf(stderr," %08x %08x\n", ptr[], ptr[]);

#endif

ptr += ;

break;

case BR_TRANSACTION: {

struct binder_txn *txn = (void *) ptr;

if ((end - ptr) * sizeof(uint32_t) < sizeof(struct binder_txn)) {

ALOGE("parse: txn too small!\n");

return -;

}

binder_dump_txn(txn);

if (func) {

unsigned rdata[/];

struct binder_io msg;//

struct binder_io reply;//回复信息的结构体

int res;

bio_init(&reply, rdata, sizeof(rdata), );//数据的初始化

bio_init_from_txn(&msg, txn);

//fun函数中会进行事务最终的处理，add Service find service 注册 service

res = func(bs, txn, &msg, &reply);

binder_send_reply(bs, &reply, txn->data, res);

}

ptr += sizeof(*txn) / sizeof(uint32_t);

break;

}

case BR_REPLY: {

struct binder_txn *txn = (void*) ptr;

if ((end - ptr) * sizeof(uint32_t) < sizeof(struct binder_txn)) {

ALOGE("parse: reply too small!\n");

return -;

}

binder_dump_txn(txn);

if (bio) {

bio_init_from_txn(bio, txn);

bio = ;

} else {

/* todo FREE BUFFER */

}

ptr += (sizeof(*txn) / sizeof(uint32_t));

r = ;

break;

6 在该函数中会对事务进行相应的出路 callby 5

int svcmgr_handler(struct binder_state *bs,

struct binder_txn *txn,

struct binder_io *msg,

struct binder_io *reply)

{

struct svcinfo *si;

uint16_t *s;

unsigned len;

void *ptr;

uint32_t strict_policy;

int allow_isolated;

// ALOGI("target=%p code=%d pid=%d uid=%d\n",

// txn->target, txn->code, txn->sender_pid, txn->sender_euid);

if (txn->target != svcmgr_handle)

return -;

// Equivalent to Parcel::enforceInterface(), reading the RPC

// header with the strict mode policy mask and the interface name.

// Note that we ignore the strict_policy and don't propagate it

// further (since we do no outbound RPCs anyway).

strict_policy = bio_get_uint32(msg);

s = bio_get_string16(msg, &len);

if ((len != (sizeof(svcmgr_id) / )) ||

memcmp(svcmgr_id, s, sizeof(svcmgr_id))) {

fprintf(stderr,"invalid id %s\n", str8(s));

return -;

}

switch(txn->code) {

case SVC_MGR_GET_SERVICE:

case SVC_MGR_CHECK_SERVICE:

s = bio_get_string16(msg, &len);

//查找相应的service

ptr = do_find_service(bs, s, len, txn->sender_euid);//call 7

if (!ptr)

break;

bio_put_ref(reply, ptr);

return ;

case SVC_MGR_ADD_SERVICE:

s = bio_get_string16(msg, &len);

ptr = bio_get_ref(msg);

allow_isolated = bio_get_uint32(msg) ?  : ;

//add service 进行service的注册。

if (do_add_service(bs, s, len, ptr, txn->sender_euid, allow_isolated))

return -;

break;

case SVC_MGR_LIST_SERVICES: {

unsigned n = bio_get_uint32(msg);

si = svclist;

while ((n-- > ) && si)

si = si->next;

if (si) {

bio_put_string16(reply, si->name);

return ;

}

return -;

}

default:

ALOGE("unknown code %d\n", txn->code);

return -;

}

bio_put_uint32(reply, );

return ;

}

7 查找service call by 6

void *do_find_service(struct binder_state *bs, uint16_t *s, unsigned len, unsigned uid)

{

struct svcinfo *si;

//最终的查找函数了

si = find_svc(s, len);

// ALOGI("check_service('%s') ptr = %p\n", str8(s), si ? si->ptr : 0);

if (si && si->ptr) {

if (!si->allow_isolated) {

// If this service doesn't allow access from isolated processes,

// then check the uid to see if it is isolated.

unsigned appid = uid % AID_USER;

if (appid >= AID_ISOLATED_START && appid <= AID_ISOLATED_END) {

return ;

}

}

return si->ptr;

} else {

return ;

}

}

8 最终的findservice动作是在这里结束    callby

7

struct svcinfo *find_svc(uint16_t *s16, unsigned len)

{

struct svcinfo *si;//svcinfo就是一个链表的node数据结构，存放了service的信息

//svclist存放了所有已经注册的了的 service，这里进行遍历，通过mencmp进行匹配

for (si = svclist; si; si = si->next) {

if ((len == si->len) &&

!memcmp(s16, si->name, len * sizeof(uint16_t))) {

return si;

}

}

return ;

}

9 注册服务   callby

6

int do_add_service(struct binder_state *bs,

uint16_t *s, unsigned len,

void *ptr, unsigned uid, int allow_isolated)

{

struct svcinfo *si;

//ALOGI("add_service('%s',%p,%s) uid=%d\n", str8(s), ptr,

// allow_isolated ? "allow_isolated" : "!allow_isolated", uid);

if (!ptr || (len == ) || (len > ))

return -;

//验证UID是否有添加服务的权限。

if (!svc_can_register(uid, s)) {

ALOGE("add_service('%s',%p) uid=%d - PERMISSION DENIED\n",

str8(s), ptr, uid);

return -;

}

//判断服务是否存在，存在就不进行重复注册了。

si = find_svc(s, len);

if (si) {

if (si->ptr) {

ALOGE("add_service('%s',%p) uid=%d - ALREADY REGISTERED, OVERRIDE\n",

str8(s), ptr, uid);

svcinfo_death(bs, si);

}

si->ptr = ptr;

} else {//不存在则为心注册的服务分配内存

si = malloc(sizeof(*si) + (len + ) * sizeof(uint16_t));

if (!si) {//分配内存失败

ALOGE("add_service('%s',%p) uid=%d - OUT OF MEMORY\n",

str8(s), ptr, uid);

return -;

}

//为注册的服务的 scvinfo 结构体赋值，

si->ptr = ptr;

si->len = len;

memcpy(si->name, s, (len + ) * sizeof(uint16_t));

si->name[len] = '\0';

si->death.func = svcinfo_death;

si->death.ptr = si;

si->allow_isolated = allow_isolated;

//可见list的插入可以头插入法。

si->next = svclist;

svclist = si;

}

binder_acquire(bs, ptr);

binder_link_to_death(bs, ptr, &si->death);

return ;

}

10 判断当前uid是否具有注册service的权限，没有就拒绝 callby9

int svc_can_register(unsigned uid, uint16_t *name)

{

unsigned n;

if ((uid == ) || (uid == AID_SYSTEM))//uid=0为root用户， AID_SYSTEM为系统 service

return ;

//遍历允许注册service的进程数组

for (n = ; n < sizeof(allowed) / sizeof(allowed[]); n++)

if ((uid == allowed[n].uid) && str16eq(name, allowed[n].name))

return ;

return ;

}

允许注册服务的进程列表（如果自定义rom自己增加系统服务，就可以在这里增加以获得权限啦）

static struct {

unsigned uid;

const char *name;

} allowed[] = {

{ AID_MEDIA, "media.audio_flinger" },

{ AID_MEDIA, "media.player" },

{ AID_MEDIA, "media.camera" },

{ AID_MEDIA, "media.audio_policy" },

{ AID_DRM, "drm.drmManager" },

{ AID_NFC, "nfc" },

{ AID_RADIO, "radio.phone" },

{ AID_RADIO, "radio.sms" },

{ AID_RADIO, "radio.phonesubinfo" },

{ AID_RADIO, "radio.simphonebook" },

/* TODO: remove after phone services are updated: */

{ AID_RADIO, "phone" },

{ AID_RADIO, "sip" },

{ AID_RADIO, "isms" },

{ AID_RADIO, "iphonesubinfo" },

{ AID_RADIO, "simphonebook" },

{ AID_MEDIA, "common_time.clock" },

{ AID_MEDIA, "common_time.config" },

};

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Android Binder------ServiceManager启动分析

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