顺德容桂工业地出售:Asterisk内核框架

来源:百度文库 编辑:九乡新闻网 时间:2023/01/27 09:24:42

本文主要从三个层面来描述asterisk内核,即asterisk内核模块、内核启动过程、基本呼叫流程。

  1. PBX Switching Core
    PBX交換核心 pbx.c
  2. Scheduler and I/O Manager
    排序與I/O層 channel.c  io.c
  3. Application Launcher
    應用程式層
  4. Codec Translator
    編碼轉換核心 Translate.c
  5. Dynamic Module Loader
    彈性模組載入器 Module.h
  6. CDR Core
    帳務核心 Cdr.c

一、             asterisk内核模块

Asterisk由内部核心和外围动态可加载模块组成。内部核心由以下六个部分组成:PBX交换核心模块(PBX Switching Core)、调度和I/O管理模块(Scheduler and I/O Manager)、应用调用模块(Application Launcher)、编解码转换模块(Codec Translator)、动态模块加载器模块(Dynamic Module Loader)和CDR生成模块(CDR Core)。

外围动态可加载模块包括以App_开始的Applications、以Func_开始的Functions、以Res_开始的Resources、以Chan_开始的channels、以Codec_开始的codec编解码模块等。

1.         内核模块

1)        PBX交换核心模块(PBX Switching Core):

l         pbx.c

pbx.c是asterisk的核心模块,每路呼叫都需要经过它调度。pbx实现了builtin applications,也就是内置的应用,比如最常见的Answer,Hangup, Background,Wait等等。

struct ast_app是一个关键数据结构,它定义了注册builtin applications的结构。

load_pbx函数用来注册builtin applications和一些命令行CLI命令(每个模块都有些CLI命令)。该函数在系统启动时被调用。

pbx_exec是Answer/BackGround/Busy/Goto/GotoIf/Hangup/Set等builtin applications的执行入口函数,它被pbx_extension_helper调用。

ast_pbx_start函数是每路呼叫的起点。

2)        调度和I/O管理模块(Scheduler and I/O Manager):

l         Channel.c:

Channel.c/channel.h定义了channel操作的结构体和接口函数。

struct ast_channel_tech结构体是所有channel都要用到的关键结构体,它定义channel操作的一系列回调函数指针,如call、hangup、answer等。每个channel模块都会定义ast_channel_tech的实体,并将各自的回调函数赋值给它。例如chan_sip.c中定义如下:

/*! \brief Definition of this channel for PBX channel registration */

static const struct ast_channel_tech sip_tech = {

       .type = "SIP",

       .description = "Session Initiation Protocol (SIP)",

       .capabilities = ((AST_FORMAT_MAX_AUDIO << 1) - 1),

       .properties = AST_CHAN_TP_WANTSJITTER | AST_CHAN_TP_CREATESJITTER,

       .requester = sip_request_call,

       .devicestate = sip_devicestate,

       .call = sip_call,

       .hangup = sip_hangup,

       .answer = sip_answer,

       .read = sip_read,

       .write = sip_write,

       .write_video = sip_write,

       .indicate = sip_indicate,

       .transfer = sip_transfer,

       .fixup = sip_fixup,

       .send_digit_begin = sip_senddigit_begin,

       .send_digit_end = sip_senddigit_end,

       .bridge = ast_rtp_bridge,

       .send_text = sip_sendtext,

       .func_channel_read = acf_channel_read,

};

ast_call、ast_hangup、ast_answer等函数分别实现ast_channel_tech中的call、hangup、answer等回调函数的调用。

struct ast_channel结构体定义了channel的上下文参数,它是每个参与呼叫的channel必不可少的,都会调用ast_channel_alloc来申请ast_channel。

l         io.c

io.c实现了asterisk跟外部交互时的I/O管理,如chan_sip为了从外部接收SIP信令,调用ast_io_add添加IO接口,并调用ast_io_wait实现外部消息接收。

3)        应用调用模块(Application Launcher):

在pbx.c中定义了一系列的应用调用接口。

applications模块定义了application回调函数并注册后,在pbx.c中通过应用调用接口回调执行。

应用调用接口的关键函数是pbx_extension_helper,它执行dialplan,在cli上打印“Executing ……”,并抛出ami event事件,同时调用pbx_exec执行application回调函数。

4)        编解码转换模块(Codec Translator):

Translate.c:

struct ast_translator:编码转换描述结构体,它定义了编码转换的名称、回调函数、运行时选项。

struct ast_trans_pvt:编码转换上下文描述结构体。

ast_register_translator:编码转换注册接口函数,供各编码模块调用,注册struct ast_translator类型的结构体变量。

ast_unregister_translator:编码转换注销函数

ast_translate:编码转换的执行函数。

codec_gsm.c/codec_...:对应各种编码的编解码执行模块,如g.711alaw/g.711ulaw/gsm等。

5)        动态模块加载器模块(Dynamic Module Loader):

该模块主要是Module.h。

Module.h中定义了struct ast_module_info结构,用来保存各模块的注册、注销回调函数,以及模块描述信息。

load_module、unload_module,每个应用模块的注册、注销函数,由各个模块自行定义为static函数。

AST_MODULE_INFO_STANDARD:注册接口、注销接口、模块描述信息等模块信息的登记接口。它是一个宏定义,动态模块调用它时,首先定义类型为ast_module_info的__mod_info静态结构变量,保存模块信息,并定义__attribute__ ((constructor)) __reg_module和__attribute__ ((destructor)) __unreg_module,在程序启动和退出时调用。

6)        CDR生成模块(CDR Core):

Cdr.c:

ast_cdr_register:cdr driver注册,供cdr_mysql等调用,注册话单保存的回调函数。

ast_cdr_engine_init:CDR模块初始化,注册cdr status、加载cdr.conf、启动CDR线程。

ast_cdr_detach:产生话单的接口函数,呼叫结束时被调用。

2.         外围可加载模块:

1)        Applications

以app_开始的模块,如app_dial.c、app_db.c、app_queue.c、app_record.c、app_meetme.c等,代码保存在apps目录中。每个application模块都定义了load_module函数和unload_module函数,分别用来注册和注销application。

load_module函数调用ast_register_application函数,注册application命令,例如app_dial模块注册Dial:res = ast_register_application(app, dial_exec, synopsis, descrip)。

unload_module函数调用ast_unregister_application函数,注销application命令。

每个application模块都会使用AST_MODULE_INFO_STANDARD宏来登记模块信息__mod_info。AST_MODULE_INFO_STANDARD将load_module和unload_module注册为回调函数,供module load/unload/reload调用。

2)        Channel

以chan_开始的模块,如chan_sip.c、chan_h323.c、chan_mgcp.c 、chan_iax2.c、 chan_zap.c等,对应代码保存在channels目录中。

channel注册、注销过程和application基本类似。由于每个channel需要和外部交互,都会在load_module中启用do_monitor线程来侦听外部tcp/udp端口,接收外部消息。

每个channel也定义了各自的cli命令和Function命令,例如chan_sip定义了sip debug/history/no/notify/prune/ reload/set/show等cli命令和SIP_HEADER、CHECKSIPDOMAIN、SIPPEER、SIPCHANINFO等Function命令。

3)        Functions

以Fun_开始的模块,例如Fun_db.c、func_moh.c、func_cdr.c等,对应代码保存在funcs目录中。

Function注册、注销过程也和application类似。

每个Function模块也定义了各自的Function命令,例如Fun_db.c就定义了DB、DB_EXISTS、DB_DELETE等Function命令。

二、             asterisk启动过程

主要就main函数讲解asterisk的启动过程:

int main(int argc, char *argv[])

{

       int c;

       char filename[80] = "";

       char hostname[MAXHOSTNAMELEN] = "";

       char tmp[80];

       char * xarg = NULL;

       int x;

       FILE *f;

       sigset_t sigs;

       int num;

       int isroot = 1;

       char *buf;

       char *runuser = NULL, *rungroup = NULL;

/*保存命令行参数(argv[]->_argv[]),以便程序重启时使用*/

       /* Remember original args for restart */

       if (argc > sizeof(_argv) / sizeof(_argv[0]) - 1) {

              fprintf(stderr, "Truncating argument size to %d\n", (int)(sizeof(_argv) / sizeof(_argv[0])) - 1);

              argc = sizeof(_argv) / sizeof(_argv[0]) - 1;

       }

       for (x=0; x

              _argv[x] = argv[x];

       _argv[x] = NULL;

       if (geteuid() != 0)

              isroot = 0;

/*命令如果是rasterisk,设置AST_OPT_FLAG_NO_FORK和AST_OPT_FLAG_REMOTE标志位*/

       /* if the progname is rasterisk consider it a remote console */

       if (argv[0] && (strstr(argv[0], "rasterisk")) != NULL) {

              ast_set_flag(&ast_options, AST_OPT_FLAG_NO_FORK | AST_OPT_FLAG_REMOTE);

       }

/*得到当前主机名,在启动时打印出来*/

       if (gethostname(hostname, sizeof(hostname)-1))

              ast_copy_string(hostname, "", sizeof(hostname));

/*获取当前的进程标识*/

       ast_mainpid = getpid();

/*建立mu-law和a-law转换表*/

       ast_ulaw_init();

       ast_alaw_init();

/*为FFT逆变换(傅立叶逆变换)做一些初始化,用于在zaptel里进行callerid的DTMF检测*/

       callerid_init();

/*初始化内置命令的_full_cmd字符串,并注册常用命令,ast_builtins_init() -> ast_cli_register_multiple() -> ast_cli_register() -> __ast_cli_register() */

       ast_builtins_init();

/*初始化base64转换*/

       ast_utils_init();

/* tty/tdd初始化*/

       tdd_init();

/*设置用户历史命令的保存路径*/

       if (getenv("HOME"))

              snprintf(filename, sizeof(filename), "%s/.asterisk_history", getenv("HOME"));

       /* Check for options */

/*检查命令行的输入参数,匹配参数范围是“mtThfFdvVqprRgciInx:U:G:C:L:M:”,不同的参数输入走到不同的case分支处理。有几个v,verbose级别就增加几*/

       while ((c = getopt(argc, argv, "mtThfFdvVqprRgciInx:U:G:C:L:M:")) != -1) {

              switch (c) {

#if HAVE_WORKING_FORK

              case 'F':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_ALWAYS_FORK);

                     break;

              case 'f':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_NO_FORK);

                     break;

#endif

              case 'd':

                     option_debug++;

                     ast_set_flag(&ast_options, AST_OPT_FLAG_NO_FORK);

                     break;

              case 'c':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_NO_FORK | AST_OPT_FLAG_CONSOLE);

                     break;

              case 'n':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_NO_COLOR);

                     break;

              case 'r':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_NO_FORK | AST_OPT_FLAG_REMOTE);

                     break;

              case 'R':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_NO_FORK | AST_OPT_FLAG_REMOTE | AST_OPT_FLAG_RECONNECT);

                     break;

              case 'p':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_HIGH_PRIORITY);

                     break;

              case 'v':

                     option_verbose++;

                     ast_set_flag(&ast_options, AST_OPT_FLAG_NO_FORK);

                     break;

              case 'm':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_MUTE);

                     break;

              case 'M':

                     if ((sscanf(optarg, "%d", &option_maxcalls) != 1) || (option_maxcalls < 0))

                            option_maxcalls = 0;

                     break;

              case 'L':

                     if ((sscanf(optarg, "%lf", &option_maxload) != 1) || (option_maxload < 0.0))

                            option_maxload = 0.0;

                     break;

              case 'q':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_QUIET);

                     break;

              case 't':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_CACHE_RECORD_FILES);

                     break;

              case 'T':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_TIMESTAMP);

                     break;

              case 'x':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_EXEC);

                     xarg = ast_strdupa(optarg);

                     break;

              case 'C':

                     ast_copy_string(ast_config_AST_CONFIG_FILE, optarg, sizeof(ast_config_AST_CONFIG_FILE));

                     ast_set_flag(&ast_options, AST_OPT_FLAG_OVERRIDE_CONFIG);

                     break;

              case 'I':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_INTERNAL_TIMING);

                     break;

              case 'i':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_INIT_KEYS);

                     break;

              case 'g':

                     ast_set_flag(&ast_options, AST_OPT_FLAG_DUMP_CORE);

                     break;

              case 'h':

                     show_cli_help();

                     exit(0);

              case 'V':

                     show_version();

                     exit(0);

              case 'U':

                     runuser = ast_strdupa(optarg);

                     break;

              case 'G':

                     rungroup = ast_strdupa(optarg);

                     break;

              case '?':

                     exit(1);

              }

       }

/*如果用了-c或者-v或者-r并且没有-x cmd参数,则打印欢迎信息*/

       if (ast_opt_console || option_verbose || (ast_opt_remote && !ast_opt_exec)) {

              ast_register_verbose(console_verboser);

              WELCOME_MESSAGE;

       }

/*如果没有开调试则简单打印Booting... */

       if (ast_opt_console && !option_verbose)

              ast_verbose("[ Booting...\n");

/*显示控制台时,不论是本地还是远程,都不能使用-F参数,否则无效*/

       if (ast_opt_always_fork && (ast_opt_remote || ast_opt_console)) {

              ast_log(LOG_WARNING, "'alwaysfork' is not compatible with console or remote console mode; ignored\n");

              ast_clear_flag(&ast_options, AST_OPT_FLAG_ALWAYS_FORK);

       }

       /* For remote connections, change the name of the remote connection.

        * We do this for the benefit of init scripts (which need to know if/when

        * the main asterisk process has died yet). */

       if (ast_opt_remote) {

              strcpy(argv[0], "rasterisk");

              for (x = 1; x < argc; x++) {

                     argv[x] = argv[0] + 10;

              }

       }

/*读取主配置文件,主配置文件是由make menuselect配置的*/

       if (ast_opt_console && !option_verbose)

              ast_verbose("[ Reading Master Configuration ]\n");

       ast_readconfig();

/*如果启动加了-g,取消core dump文件的大小限制*/

       if (ast_opt_dump_core) {

              struct rlimit l;

              memset(&l, 0, sizeof(l));

              l.rlim_cur = RLIM_INFINITY;

              l.rlim_max = RLIM_INFINITY;

              if (setrlimit(RLIMIT_CORE, &l)) {

                     ast_log(LOG_WARNING, "Unable to disable core size resource limit: %s\n", strerror(errno));

              }

       }

/*修改用户和组权限*/

       if ((!rungroup) && !ast_strlen_zero(ast_config_AST_RUN_GROUP))

              rungroup = ast_config_AST_RUN_GROUP;

       if ((!runuser) && !ast_strlen_zero(ast_config_AST_RUN_USER))

              runuser = ast_config_AST_RUN_USER;

#ifndef __CYGWIN__

       if (isroot)

              ast_set_priority(ast_opt_high_priority);

       if (isroot && rungroup) {

              struct group *gr;

              gr = getgrnam(rungroup);

              if (!gr) {

                     ast_log(LOG_WARNING, "No such group '%s'!\n", rungroup);

                     exit(1);

              }

              if (setgid(gr->gr_gid)) {

                     ast_log(LOG_WARNING, "Unable to setgid to %d (%s)\n", (int)gr->gr_gid, rungroup);

                     exit(1);

              }

              if (setgroups(0, NULL)) {

                     ast_log(LOG_WARNING, "Unable to drop unneeded groups\n");

                     exit(1);

              }

              if (option_verbose)

                     ast_verbose("Running as group '%s'\n", rungroup);

       }

       if (runuser && !ast_test_flag(&ast_options, AST_OPT_FLAG_REMOTE)) {

#ifdef HAVE_CAP

              int has_cap = 1;

#endif /* HAVE_CAP */

              struct passwd *pw;

              pw = getpwnam(runuser);

              if (!pw) {

                     ast_log(LOG_WARNING, "No such user '%s'!\n", runuser);

                     exit(1);

              }

#ifdef HAVE_CAP

              if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0)) {

                     ast_log(LOG_WARNING, "Unable to keep capabilities.\n");

                     has_cap = 0;

              }

#endif /* HAVE_CAP */

              if (!isroot && pw->pw_uid != geteuid()) {

                     ast_log(LOG_ERROR, "Asterisk started as nonroot, but runuser '%s' requested.\n", runuser);

                     exit(1);

              }

              if (!rungroup) {

                     if (setgid(pw->pw_gid)) {

                            ast_log(LOG_WARNING, "Unable to setgid to %d!\n", (int)pw->pw_gid);

                            exit(1);

                     }

                     if (isroot && initgroups(pw->pw_name, pw->pw_gid)) {

                            ast_log(LOG_WARNING, "Unable to init groups for '%s'\n", runuser);

                            exit(1);

                     }

              }

              if (setuid(pw->pw_uid)) {

                     ast_log(LOG_WARNING, "Unable to setuid to %d (%s)\n", (int)pw->pw_uid, runuser);

                     exit(1);

              }

              if (option_verbose)

                     ast_verbose("Running as user '%s'\n", runuser);

#ifdef HAVE_CAP

              if (has_cap) {

                     cap_t cap;

                     cap = cap_from_text("cap_net_admin=ep");

                     if (cap_set_proc(cap))

                            ast_log(LOG_WARNING, "Unable to install capabilities.\n");

                     if (cap_free(cap))

                            ast_log(LOG_WARNING, "Unable to drop capabilities.\n");

              }

#endif /* HAVE_CAP */

       }

#endif /* __CYGWIN__ */

#ifdef linux

       if (geteuid() && ast_opt_dump_core) {

              if (prctl(PR_SET_DUMPABLE, 1, 0, 0, 0) < 0) {

                     ast_log(LOG_WARNING, "Unable to set the process for core dumps after changing to a non-root user. %s\n", strerror(errno));

              }   

       }

#endif

/*初始化模拟终端ast_term_init(),默认是VT100*/

       ast_term_init();

       printf(term_end());

       fflush(stdout);

       if (ast_opt_console && !option_verbose)

              ast_verbose("[ Initializing Custom Configuration Options ]\n");

       /* custom config setup */

/*注册命令core show config mappings*/

       register_config_cli();

/*配置文件的映射和绑定*/

       read_config_maps();

       if (ast_opt_console) {

              if (el_hist == NULL || el == NULL)

                     ast_el_initialize();

              if (!ast_strlen_zero(filename))

                     ast_el_read_history(filename);

       }

/*设置和检查本地或远程终端的连接*/

       if (ast_tryconnect()) {

              /* One is already running */

              if (ast_opt_remote) {

                     if (ast_opt_exec) {

                            ast_remotecontrol(xarg);

                            quit_handler(0, 0, 0, 0);

                            exit(0);

                     }

                     printf(term_quit());

                     ast_remotecontrol(NULL);

                     quit_handler(0, 0, 0, 0);

                     exit(0);

              } else {

                     ast_log(LOG_ERROR, "Asterisk already running on %s.  Use 'asterisk -r' to connect.\n", ast_config_AST_SOCKET);

                     printf(term_quit());

                     exit(1);

              }

       } else if (ast_opt_remote || ast_opt_exec) {

              ast_log(LOG_ERROR, "Unable to connect to remote asterisk (does %s exist?)\n", ast_config_AST_SOCKET);

              printf(term_quit());

              exit(1);

       }

       /* Blindly write pid file since we couldn't connect */

       unlink(ast_config_AST_PID);

       f = fopen(ast_config_AST_PID, "w");

       if (f) {

              fprintf(f, "%ld\n", (long)getpid());

              fclose(f);

       } else

              ast_log(LOG_WARNING, "Unable to open pid file '%s': %s\n", ast_config_AST_PID, strerror(errno));

#if HAVE_WORKING_FORK

       if (ast_opt_always_fork || !ast_opt_no_fork) {

#ifndef HAVE_SBIN_LAUNCHD

              daemon(1, 0);

              ast_mainpid = getpid();

              /* Blindly re-write pid file since we are forking */

              unlink(ast_config_AST_PID);

              f = fopen(ast_config_AST_PID, "w");

              if (f) {

                     fprintf(f, "%ld\n", (long)ast_mainpid);

                     fclose(f);

              } else

                     ast_log(LOG_WARNING, "Unable to open pid file '%s': %s\n", ast_config_AST_PID, strerror(errno));

#else

              ast_log(LOG_WARNING, "Mac OS X detected.  Use '/sbin/launchd -d' to launch with the nofork option.\n");

#endif

       }

#endif

       /* Test recursive mutex locking. */

/*测试线程安全,避免出现死锁*/

       if (test_for_thread_safety())

              ast_verbose("Warning! Asterisk is not thread safe.\n");

/*创建用于和控制台交互的服务器端socket接口*/

       ast_makesocket();

/*加入信号集,设置掩码,以及注册信号的相应handler */

       sigemptyset(&sigs);

       sigaddset(&sigs, SIGHUP);

       sigaddset(&sigs, SIGTERM);

       sigaddset(&sigs, SIGINT);

       sigaddset(&sigs, SIGPIPE);

       sigaddset(&sigs, SIGWINCH);

       pthread_sigmask(SIG_BLOCK, &sigs, NULL);

       signal(SIGURG, urg_handler);

       signal(SIGINT, __quit_handler);

       signal(SIGTERM, __quit_handler);

       signal(SIGHUP, hup_handler);

       signal(SIGCHLD, child_handler);

       signal(SIGPIPE, SIG_IGN);

       /* ensure that the random number generators are seeded with a different value every time

          Asterisk is started

       */

/*设置种子并初始化随机数发生器*/

       srand((unsigned int) getpid() + (unsigned int) time(NULL));

       initstate((unsigned int) getpid() * 65536 + (unsigned int) time(NULL), randompool, sizeof(randompool));

/*初始化日志模块*/

       if (init_logger()) {

              printf(term_quit());

              exit(1);

       }

#ifdef HAVE_ZAPTEL

       {

              int fd;

              int x = 160;

              fd = open("/dev/zap/timer", O_RDWR);

              if (fd >= 0) {

                     if (ioctl(fd, ZT_TIMERCONFIG, &x)) {

                            ast_log(LOG_ERROR, "You have Zaptel built and drivers loaded, but the Zaptel timer test failed to set ZT_TIMERCONFIG to %d.\n", x);

                            exit(1);

                     }

                     if ((x = ast_wait_for_input(fd, 300)) < 0) {

                            ast_log(LOG_ERROR, "You have Zaptel built and drivers loaded, but the Zaptel timer could not be polled during the Zaptel timer test.\n");

                            exit(1);

                     }

                     if (!x) {

                            const char zaptel_timer_error[] = {

                                   "Asterisk has detected a problem with your Zaptel configuration and will shutdown for your protection.  You have options:"

                                   "\n\t1. You only have to compile Zaptel support into Asterisk if you need it.  One option is to recompile without Zaptel support."

                                   "\n\t2. You only have to load Zaptel drivers if you want to take advantage of Zaptel services.  One option is to unload zaptel modules if you don't need them."

                                   "\n\t3. If you need Zaptel services, you must correctly configure Zaptel."

                            };

                            ast_log(LOG_ERROR, "%s\n", zaptel_timer_error);

                            exit(1);

                     }

                     close(fd);

              }

       }

#endif

/*注册threadstorage show allocations和threadstorage show summary这两个命令*/

       threadstorage_init();

       astobj2_init();

       ast_autoservice_init();

/*加载配置文件/etc/asterisk/modules.conf中标记为preload的模块,再去掉标记为noload的模块*/

       if (load_modules(1)) {

              printf(term_quit());

              exit(1);

       }

/* DNS manager的初始化*/

       if (dnsmgr_init()) {

              printf(term_quit());

              exit(1);

       }

/*配置http服务器*/

       ast_http_init();

/*注册两个命令core show channeltypes和core show channeltype */

       ast_channels_init();

/*注册管理命令*/

       if (init_manager()) {

              printf(term_quit());

              exit(1);

       }

/*用来创建一个调度上下文以及注册相应的命令,然后用do_reload来读取配置文件cdr.conf和创建后台线程do_cdr */

       if (ast_cdr_engine_init()) {

              printf(term_quit());

              exit(1);

       }

/*用来创建一个后台线程轮巡设备的状态,如果发生变化则及时通告*/

       if (ast_device_state_engine_init()) {

              printf(term_quit());

              exit(1);

       }

/*注册rtp,rtcp,stun相关的CLI命令,然后调用ast_rtp_reload()读取配置文件rtp.conf,设置相关参数*/

       ast_rtp_init();

/*注册udptl相关的CLI命令,然后调用ast_udptl_reload()读取配置文件udptl.conf,设置相关参数*/

       ast_udptl_init();

/*注册core show image formats */

       if (ast_image_init()) {

              printf(term_quit());

              exit(1);

       }

/*注册core show file formats */

       if (ast_file_init()) {

              printf(term_quit());

              exit(1);

       }

/*注册dialplan相关的CLI命令,然后调用ast_register_application来注册所有的app */

       if (load_pbx()) {

              printf(term_quit());

              exit(1);

       }

/*注册与codec相关的CLI命令*/

       if (init_framer()) {

              printf(term_quit());

              exit(1);

       }

/*注册与database相关的CLI命令,然后再注册两个管理命令DBGet和DBPut */

       if (astdb_init()) {

              printf(term_quit());

              exit(1);

       }

/*读取配置文件enum.conf,初始化支持ENUM(e164)的子系统*/

       if (ast_enum_init()) {

              printf(term_quit());

              exit(1);

       }

/* load_modules(0)加载所有其它需要加载的动态链接库*/

       if (load_modules(0)) {

              printf(term_quit());

              exit(1);

       }

       dnsmgr_start_refresh();

       /* We might have the option of showing a console, but for now just

          do nothing... */

       if (ast_opt_console && !option_verbose)

              ast_verbose(" ]\n");

       if (option_verbose || ast_opt_console)

              ast_verbose(term_color(tmp, "Asterisk Ready.\n", COLOR_BRWHITE, COLOR_BLACK, sizeof(tmp)));

       if (ast_opt_no_fork)

              consolethread = pthread_self();

/*创建管道*/

       if (pipe(sig_alert_pipe))

              sig_alert_pipe[0] = sig_alert_pipe[1] = -1;

       ast_set_flag(&ast_options, AST_OPT_FLAG_FULLY_BOOTED);

       pthread_sigmask(SIG_UNBLOCK, &sigs, NULL);

#ifdef __AST_DEBUG_MALLOC

       __ast_mm_init();

#endif   

       time(&ast_startuptime);

/*注册asterisk相关的命令,比如stop,restart,halt等等*/

       ast_cli_register_multiple(cli_asterisk, sizeof(cli_asterisk) / sizeof(struct ast_cli_entry));

       if (ast_opt_console) {

              /* Console stuff now... */

              /* Register our quit function */

              char title[256];

              pthread_attr_t attr;

              pthread_t dont_care;

/*创建线程,轮询上面创建的sig_alert_pipe管道*/

              pthread_attr_init(&attr);

              pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

              ast_pthread_create(&dont_care, &attr, monitor_sig_flags, NULL);

              pthread_attr_destroy(&attr);

              set_icon("Asterisk");

              snprintf(title, sizeof(title), "Asterisk Console on '%s' (pid %ld)", hostname, (long)ast_mainpid);

              set_title(title);

/*接收和处理控制台命令*/

              for (;;) {

                     buf = (char *)el_gets(el, &num);

                     if (!buf && write(1, "", 1) < 0)

                            goto lostterm;

                     if (buf) {

                            if (buf[strlen(buf)-1] == '\n')

                                   buf[strlen(buf)-1] = '\0';

                            consolehandler((char *)buf);

                     } else if (ast_opt_remote && (write(STDOUT_FILENO, "\nUse EXIT or QUIT to exit the asterisk console\n",

                               strlen("\nUse EXIT or QUIT to exit the asterisk console\n")) < 0)) {

                            /* Whoa, stdout disappeared from under us... Make /dev/null's */

                            int fd;

                            fd = open("/dev/null", O_RDWR);

                            if (fd > -1) {

                                   dup2(fd, STDOUT_FILENO);

                                   dup2(fd, STDIN_FILENO);

                            } else

                                   ast_log(LOG_WARNING, "Failed to open /dev/null to recover from dead console. Bad things will happen!\n");

                            break;

                     }

              }

       }

       monitor_sig_flags(NULL);

lostterm:

       return 0;

}

三、             asterisk基本呼叫流程

从内核的角度去分析问题时,弄清楚呼叫流程是非常关键的,只有理清了呼叫流程,才能从流程的各个环节细节中分析出问题所在。

Asterisk所有功能都是基于函数调用的模式,呼叫流程也不例外。因此如何从一团乱麻似的内核函数调用中理出函数调用执行路线,是解读呼叫流程的关键。

所有呼叫都跟astersisk的channel有关。这路通话都包含一个incoming连接和一个outbound连接。每个电话都是通过对应的channel程序建立起来的,比如Chan_sip,Chan_zap,Chan_iax2等等。每一类的channel,都拥有自己私有的channel数据结构,例如chan_sip的struct sip_pvt结构,这些私有的结构从属于一个通用的Asterisk通道数据结构中,具体定义在channel.h的struct ast_channe中。

下图是asterisk 的呼叫流程图:

我们以sip的呼叫过程为例来描述,其他channel的呼叫过程基本类似。

Astersik下注册的sip用户主动发起一个呼叫的函数调用过程如下:

do_monitor->sipsock_read->handle_request->handle_request_invite->sip_new/ast_pbx_start->pbx_thread->__ast_pbx_run

-> ast_spawn_extension ->pbx_extension_helper->pbx_exec->执行dialplan

当Chan_sip模块被加载时,会启动一个独立的监听线程do_monitor,不断侦听sip端口上的外部消息;

当sip用户拨叫被叫号码后,chan_sip的do_monitor调用sipsock_read函数,在sip端口收到invite消息,然后就调用handle_request和handle_request_invite进行处理。

在handle_request_invite中,首先解析invite消息,对该sip用户的业务属性分析,确认被叫可达,然后就调用sip_new申请channel资源,并调用ast_pbx_start函数启动一个pbx_thread线程来专门处理该呼叫。

pbx_thread线程调用__ast_pbx_run。

__ast_pbx_run是一个衔接dialplan和内核的关键函数,它首先调用ast_exists_extension函数,根据分机号码的context属性,匹配到对应的dialplan;然后进入一个for死循环,逐条执行dialplan对应的context中的语句。

pbx_extension_helper函数调用pbx_extension_helper,在pbx_extension_helper中调用pbx_find_extension找到对应的context后,通过verbose打印dialplan执行语句“Executing ……”,同时调用pbx_exec执行该dialplan。执行到dial语句呼叫被叫。

在等待被叫接通的过程中,完成媒体协商过程,向主叫发送180、200OK消息接通呼叫。

当其他用户呼叫asterisk的sip用户时,函数调用过程如下: Dial->dial_exec->dial_exec_full->ast_request/ast_call/wait_for_answer/ ast_bridge_call

呼叫执行到dial时,pbx_exec调用application dial的接口函数dial_exec,dial_exec调用dial_exec_full。

在dial_exec_full中,首先调用ast_request,在ast_request调用chan_sip对应的回调函数sip_request_call为该被叫sip用户申请channel资源。然后调用ast_call,在ast_call中调用chan_sip对应的回调函数sip_call向被叫发送INVITE消息,呼叫被叫SIP用户。

然后该呼叫线程会调用wait_for_answer等待被叫接通。

在呼叫接通后,也即wait_for_answer函数返回,在dial_exec_full中调用ast_bridge_call桥接媒体,这样呼叫就正式接通了。

当chan_sip的侦听线程接收到BYE消息,则调用handle_request_bye找到相应的channel,执行hangup释放呼叫。