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.cServiceManager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(1281024); 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_openstruct 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_managerint 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_loopvoid 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_parseint 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_handlerint 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_serviceuint32_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_serviceint 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_server3.1 mainint 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(1281024); 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_publishint 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_initvoid 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_uint32void 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_allocstatic 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_xvoid 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); ptr = bio_alloc(bio, (len + 1) * sizeof(uint16_t)); if (!ptr) return; while (*str) ② *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: 填充字符串到buf中,一个字符占两个字节,注意 uint16_t *ptr;;3.2.5 bio_put_objvoid 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_objstatic 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_callint 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_donevoid 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_maxthreadsvoid 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_client4.1 mainint 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 <on|off>\n", argv[0]); return -1; } bs = binder_open(1281024); 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_lookupuint32_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_refuint32_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_objstatic 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_onint 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_releasevoid 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_TRANSACTIONbinder_transaction_dataBR_REPLY对应发送方BC_REPLY的回复binder_transaction_dataBR_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_REPLYBC_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_dataBC_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:https://blog.csdn.net/univers…
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