Asterisk内核.docx

Asterisk 内核简介：/5dteam/archive/2010/09/16/1828087.htmlAsterisk是一个开源的pbx系统，在公开的资料中，很难找到asterisk内核系统的详细描述。因此，很有必要写一篇内核框架的描述文档，作为内部培训文档，相互学习提高。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。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.cpbx.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 _argv)，以便程序重启时使用*/ /* Remember original args for restart */ if (argc sizeof(_argv) / sizeof(_argv0) - 1) fprintf(stderr, Truncating argument size to %dn, (int)(sizeof(_argv) / sizeof(_argv0) - 1); argc = sizeof(_argv) / sizeof(_argv0) - 1; for (x=0; xargc; x+) _argvx = argvx; _argvx = 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 (argv0 & (strstr(argv0, 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; ignoredn); 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(argv0, rasterisk); for (x = 1; x 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 groupsn); exit(1); if (option_verbose) ast_verbose(Running as group %sn, 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 %sn, runuse