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| 浅析linux开发工具adb具体实现//===============================adb启动shell用到的命令export ADBHOST=192.168.100.2adb kill-serveradb start-server11:31:27adb shell //===============================让我们来分析一下对应的代码adb start-server==>main==>adb_commandline==>do_cmd==>adb_connect("host:start-server");如果是adb start-server命令==>fd = _adb_connect("host:version"); _adb_connect fd = socket_loopback_client(ADB_PORT, SOCK_STREAM);//尝试连接127.0.0.1本机ip地址对应的ADB_PORT端口server 如果fd小于0,那么函数返回-2,否则在ADB_PORT端口打开server成功, snprintf(tmp, sizeof tmp, "%04x", len); if (writex(fd, tmp, 4) || writex(fd, service, len)) //先将4字节长度发送给server,然后发送命令数据"host:start-server" adb_status(fd); readx(fd, buf, 4);//读取server对该命令的反馈信息 if (!memcmp(buf, "OKAY", 4))//server成功处理 if (memcmp(buf, "FAIL", 4))//server返回了非FAIL值,那么说明server出现协议数据异常,直接退出==>如果没有启动server,那么fd将等于-2 if(fd == -2) { fprintf(stdout,"* daemon not running. starting it now */n"); start_server: if(launch_server(0)) { fprintf(stderr,"* failed to start daemon */n"); return -1; } else { fprintf(stdout,"* daemon started successfully */n"); } /* give the server some time to start properly and detect devices */ adb_sleep_ms(2000); // fall through to _adb_connect }==>launch_server==> pipe(fd); pid_t pid = fork(); if (pid == 0) { //子线程[luther.gliethttp] adb_close(fd[0]); dup2(fd[1], STDERR_FILENO);//将pipe[1]的描述符dup2到stderr上, //因为execl操作只会装入新的执行程序代码,然后取代调用execl的child子进程继续在用户空间执行, //并不会改变内核空间的fd_tables[],所以execl运行的程序送往stderr上的数据就是送到parent的pipe[0]管道. adb_close(fd[1]); int result = execl(path, "adb", "fork-server", "server", NULL); // this should not return //永远不会返回到这里,因为位于用户空间的这里的代码,已经被execl操作替换成adb fork-server server程序了, //这里的代码已经被覆盖,不存在了,所以当然不会返回到这里了[luther.gliethttp] fprintf(stderr, "OOPS! execl returned %d, errno: %d/n", result, errno); } else { char temp[3]; temp[0] = 'A'; temp[1] = 'B'; temp[2] = 'C'; // wait for the "OK/n" message adb_close(fd[1]); int ret = adb_read(fd[0], temp, 3);//等待管道数据的到来 /* static __inline__ int adb_read(int fd, void* buf, size_t len) { return read(fd, buf, len); } */ adb_close(fd[0]); if (ret < 0) { fprintf(stderr, "could not read ok from ADB Server, errno = %d/n", errno); return -1; } if (ret != 3 || temp[0] != 'O' || temp[1] != 'K' || temp[2] != '/n') { fprintf(stderr, "ADB server didn't ACK/n" ); return -1; } // run a program in a new session setsid();//之前parent和child运行在同一个session里,而且parent是session头,所以, //所以作为session头的parent如果exit结束执行的话,那么会话session组中的所有进程将都被杀死, //所以执行setsid()之后,parent将重新获得一个新的会话session组id,child将仍持有原有的会话session组, //这时parent退出之后,将不会影响到child了[luther.gliethttp]. }来看看fork之后execl执行的过程[luther.gliethttp]adb fork-server server==>main==>adb_commandline if (!strcmp(argv[0], "fork-server")) { /* this is a special flag used only when the ADB client launches the ADB Server */ is_daemon = 1; } if ((argc > 0) && (!strcmp(argv[0],"server"))) { if (no_daemon || is_daemon) { r = adb_main(is_daemon);//完成daemon启动 } else { r = launch_server(); } if(r) { fprintf(stderr,"* could not start server */n"); } return r; }==>adb_main init_transport_registration HOST = 1; usb_init(); local_init(); if(install_listener("tcp:5037", "*smartsocket*", NULL)) { exit(1); } if (is_daemon) { fprintf(stderr, "OK/n");//将OK传递给上面parent执行adb_read(fd[0], temp, 3);管道接收函数. start_logging();//打开log文件,然后dup2到stdout和stderr, } fdevent_loop(); usb_cleanup();//================================void start_logging(void){ int fd; fd = unix_open("/dev/null", O_RDONLY); dup2(fd, 0);//取消输入通道stdin fd = unix_open("/tmp/adb.log", O_WRONLY | O_CREAT | O_APPEND, 0640);//创建/tmp/adb.log文件 if(fd < 0) { fd = unix_open("/dev/null", O_WRONLY);//如果不成功,那么执行/dev/null } dup2(fd, 1);//将文件句柄dup2到stdout dup2(fd, 2);//将文件句柄dup2到stderr fprintf(stderr,"--- adb starting (pid %d) ---/n", getpid());//向/tmp/adb.log文件写入log数据[luther.gliethttp]}//================================void fdevent_loop(){ fdevent *fde; for(;;) { fdevent_process(); while((fde = fdevent_plist_dequeue())) { unsigned events = fde->events; fde->events = 0; fde->state &= (~FDE_PENDING); dump_fde(fde, "callback"); fde->func(fde->fd, events, fde->arg); } }}//==================================>install_listener fdevent_install(&l->fde, l->fd, ss_listener_event_func, l);==>fdevent_install fde->func = func; fdevent_connect(fde);==>ss_listener_event_func==>connect_to_smartsocket asocket *ss = create_smart_socket(smart_socket_action);==>create_smart_socket s->enqueue = smart_socket_enqueue;==>smart_socket_enqueue==>handle_host_request==>local_connect ... fd = socket_loopback_client(port, SOCK_STREAM);#if ADB_HOST if(fd < 0) { const char *host = getenv("ADBHOST"); if(host) { fd = socket_network_client(host, port, SOCK_STREAM); } }#endif//================================init_transport_registrationvoid init_transport_registration(void){ int s[2]; if(adb_socketpair(s)){ //创建一对unix通信socket fatal_errno("cannot open transport registration socketpair"); } transport_registration_send = s[0];//用来发送 transport_registration_recv = s[1];//用来接收 fdevent_install(&transport_registration_fde, transport_registration_recv,//注册接收socket作为epoll等待信息来源 transport_registration_func,//对接收到的数据执行处理操作的func 0); fdevent_set(&transport_registration_fde, FDE_READ);//登记为READ类型}fdevent_install==>fdevent_register==>fd_table[fde->fd] = fde;//这里fd_table是模拟kernel实现方式,因为fde->fd由内核获取,所以可以保证其值的唯一性.==>fde->state |= FDE_ACTIVE;//置state为激活fdevent_set(&transport_registration_fde, FDE_READ);==>void fdevent_set(fdevent *fde, unsigned events){ ... if(fde->state & FDE_ACTIVE) { fdevent_update(fde, events);//刷新该fde->fd到epoll中 dump_fde(fde, "update"); } fde->state = (fde->state & FDE_STATEMASK) | events;//保存信息 ...}static void fdevent_update(fdevent *fde, unsigned events){ struct epoll_event ev; int active; active = (fde->state & FDE_EVENTMASK) != 0; memset(&ev, 0, sizeof(ev)); ev.events = 0;//清0 ev.data.ptr = fde;//置数据指针 if(events & FDE_READ) ev.events |= EPOLLIN;//置in事件 if(events & FDE_WRITE) ev.events |= EPOLLOUT;//置out事件 if(events & FDE_ERROR) ev.events |= (EPOLLERR | EPOLLHUP); fde->state = (fde->state & FDE_STATEMASK) | events; if(active) { ... } else { /* we're not active. if we're watching events, we need ** to add, otherwise we can just do nothing */ if(ev.events) { if(epoll_ctl(epoll_fd, EPOLL_CTL_ADD, fde->fd, &ev)) { //添加到epoll_fd中 perror("epoll_ctl() failed/n"); exit(1); } } }}static int epoll_fd = -1;static void fdevent_init(){ /* XXX: what's a good size for the passed in hint? */ epoll_fd = epoll_create(256); if(epoll_fd < 0) { perror("epoll_create() failed"); exit(1); } /* mark for close-on-exec */ fcntl(epoll_fd, F_SETFD, FD_CLOEXEC);}static void fdevent_process(){ struct epoll_event events[256]; fdevent *fde; int i, n; n = epoll_wait(epoll_fd, events, 256, -1);//等待添加到epoll_fd中的各个fd对应event事件发生[luther.gliethttp] ... for(i = 0; i < n; i++) { struct epoll_event *ev = events + i; fde = ev->data.ptr; if(ev->events & EPOLLIN) { fde->events |= FDE_READ; } if(ev->events & EPOLLOUT) { fde->events |= FDE_WRITE; } if(ev->events & (EPOLLERR | EPOLLHUP)) { fde->events |= FDE_ERROR; } if(fde->events) { if(fde->state & FDE_PENDING) continue;//正在处理前一条信息 fde->state |= FDE_PENDING; fdevent_plist_enqueue(fde);//放入待处理的list链表上 } }}static void fdevent_plist_enqueue(fdevent *node){ fdevent *list = &list_pending;//需要处理所有pending任务的链表 node->next = list; node->prev = list->prev; node->prev->next = node; list->prev = node;}static fdevent *fdevent_plist_dequeue(void)//从pending任务链表摘下一个node来处理{ fdevent *list = &list_pending; fdevent *node = list->next; if(node == list) return 0; list->next = node->next; list->next->prev = list; node->next = 0; node->prev = 0; return node;}void fdevent_loop(){ fdevent *fde; for(;;) { fdevent_process(); while((fde = fdevent_plist_dequeue())) { unsigned events = fde->events; fde->events = 0;//复位成0 fde->state &= (~FDE_PENDING);//事件检查和前期处理完成,之后将执行事件对应的func,所以清除pending标志,允许该sock接受下一个event的添加[luther.gliethttp] dump_fde(fde, "callback"); fde->func(fde->fd, events, fde->arg); } }}adb_main==>init_transport_registration==>usb_init adb_thread_create(&tid, device_poll_thread, NULL)//创建thread==>local_init adb_thread_create(&thr, client_socket_thread, 0)//host对应的处理函数,对于client,对应server_socket_threadtransport_registration_send === transport_registration_recv [FDE_READ]=== transport_registration_func"tcp:5037" === local_name_to_fd("tcp:5037") [FDE_READ]=== ss_listener_event_func //处理来自loopback端口5037的sock数据 === 尝试连接到"tcp:5037"上的client们 === local_socket_event_func并将"tcp:5037"这个sock添加到listener_list链表上好了,我们的server已经成功起来了,来看一个命令交互:adb shell1.本地执行adb shelladb shell==>main==>adb_commandline==>interactive_shell==>fd = adb_connect("shell:"); int fd = _adb_connect("host:version");//因为server在上面已经打开,所以将成功链接 fd = socket_loopback_client(ADB_PORT, SOCK_STREAM);//打开127.0.0.1本地机tcp:5037端口 //对于server端,fdevent_process()==>epoll_wait(epoll_fd, events, 256, -1);将返回,触发server启动时install_listener("tcp:5037", "*smartsocket*", NULL);注册登记的 //回调函数ss_listener_event_func在fdevent_loop中被执行. if (memcmp(service,"host",4) != 0 && switch_socket_transport(fd))//非host命令,//发送"host:transport-any"命令给server adb_status(fd);//读取"host:version"命令的返回,对于host就是调用 //handle_host_request()==> //#define ADB_SERVER_VERSION 20 //if (!strcmp(service, "version")) { // char version[12]; // snprintf(version, sizeof version, "%04x", ADB_SERVER_VERSION); // snprintf(buf, sizeof buf, "OKAY%04x%s", (unsigned)strlen(version), version); // writex(reply_fd, buf, strlen(buf)); // return 0; //} //在OKAY00040014switch_socket_transport对于server端来说对应==>==>handle_host_request if (!strncmp(service, "transport", strlen("transport"))) { ... } else if (!strncmp(service, "transport-any", strlen("transport-any"))) { type = kTransportAny; } ... transport = acquire_one_transport(CS_ANY, type, serial, &error_string);//就是从transport_list链表上摘下一个登记了的transport,对于我们分析的adb shell就是//init_transport_registration==>transport_registration_func==>会追加transport_list链表//fdevent_install(&transport_registration_fde,// transport_registration_recv,// transport_registration_func,// 0); if (transport) { s->transport = transport; adb_write(reply_fd, "OKAY", 4); }int adb_status(int fd){ unsigned char buf[5]; unsigned len; if(readx(fd, buf, 4)) { strcpy(__adb_error, "protocol fault (no status)"); return -1; } if(!memcmp(buf, "OKAY", 4)) { return 0;//ok,server正常返回数据,退出,进一步处理 } if(memcmp(buf, "FAIL", 4)) { sprintf(__adb_error, "protocol fault (status %02x %02x %02x %02x?!)", buf[0], buf[1], buf[2], buf[3]); return -1; } if(readx(fd, buf, 4)) { //错误：读取返回数据长度 strcpy(__adb_error, "protocol fault (status len)"); return -1; } buf[4] = 0; len = strtoul((char*)buf, 0, 16);//错误：转换长度数据 if(len > 255) len = 255; if(readx(fd, __adb_error, len)) { //错误：读取数据 strcpy(__adb_error, "protocol fault (status read)"); return -1; } __adb_error[len] = 0; return -1;} |
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