深入浅出asterisk(五):pbx.c代码分析

pbx.c主要实现了builtin applications，也就是内置的应用，比如最常见的Answer,Hangup, Background,Wait等等。

在/main/asterisk.c中有一段代码调用load_pbx()负责加载builtin applications。

02895    if (load_pbx()) {

02896       printf(term_quit());

02897       exit(1);

02898    }

这个load_pbx()函数就是实现在pbx.c中，它的主要任务是遍历全局数组builtins中每个application信息，调用ast_register_application()注册application的各自入口函数。

06046    /* Register builtin applications */

06047    for (x=0; x<sizeof(builtins) / sizeof(struct pbx_builtin); x++) {

06048       if (option_verbose)

06049          ast_verbose( VERBOSE_PREFIX_1 "[%s]\n", builtins[x].name);

06050       if (ast_register_application(builtins[x].name, builtins[x].execute, builtins[x].synopsis, builtins[x].description)) {

06051          ast_log(LOG_ERROR, "Unable to register builtin application '%s'\n", builtins[x].name);

06052          return -1;

06053       }

06054    }

比如Hangup应用的入口函数就是pbx_builtin_hangup()

00364    { "Hangup", pbx_builtin_hangup,

00365    "Hang up the calling channel",

00366    "  Hangup([causecode]): This application will hang up the calling channel.\n"

00367    "If a causecode is given the channel's hangup cause will be set to the given\n"

00368    "value.\n"

00369    },

 

 

下面我们分析一下pbx_builtin_hangup()函数，这个函数查看参数data调用ast_str2cause()获取挂断码，如果没有获取到，则设置chan->hangupcause为

AST_CAUSE_NORMAL_CLEARING，也就是0。

05448 /*!

05449  * \ingroup applications

05450  */

05451 static int pbx_builtin_hangup(struct ast_channel *chan, void *data)

05452 {

05453    if (!ast_strlen_zero(data)) {

05454       int cause;

05455       char *endptr;

05456 

05457       if ((cause = ast_str2cause(data)) > -1) {

05458          chan->hangupcause = cause;

05459          return -1;

05460       }

05461       

05462       cause = strtol((const char *) data, &endptr, 10);

05463       if (cause != 0 || (data != endptr)) {

05464          chan->hangupcause = cause;

05465          return -1;

05466       }

05467          

05468       ast_log(LOG_NOTICE, "Invalid cause given to Hangup(): \"%s\"\n", (char *) data);

05469    }

05470 

05471    if (!chan->hangupcause) {

05472       chan->hangupcause = AST_CAUSE_NORMAL_CLEARING;

05473    }

05474 

05475    return -1;

05476 }

看看pbx_exec()函数，这个函数是所有application被调用的入口处。它首先保存channel的两个变量，appl和data，分别表示正在调用的application名和参数。然后调用app->execute(c, data)进入真正的处理，完后恢复appl和data的值，有点像堆栈的管理

00507 /*

00508    \note This function is special. It saves the stack so that no matter

00509    how many times it is called, it returns to the same place */

00510 int pbx_exec(struct ast_channel *c,       /*!< Channel */

00511         struct ast_app *app,     /*!< Application */

00512         void *data)        /*!< Data for execution */

00513 {

00514    int res;

00515 

00516    const char *saved_c_appl;

00517    const char *saved_c_data;

00518 

00519    if (c->cdr &&  !ast_check_hangup(c))

00520       ast_cdr_setapp(c->cdr, app->name, data);

00521 

00522    /* save channel values */

00523    saved_c_appl= c->appl;

00524    saved_c_data= c->data;

00525 

00526    c->appl = app->name;

00527    c->data = data;

00528    /* XXX remember what to to when we have linked apps to modules */

00529    if (app->module) {

00530       /* XXX LOCAL_USER_ADD(app->module) */

00531    }

00532    res = app->execute(c, data);

00533    if (app->module) {

00534       /* XXX LOCAL_USER_REMOVE(app->module) */

00535    }

00536    /* restore channel values */

00537    c->appl = saved_c_appl;

00538    c->data = saved_c_data;

00539    return res;

00540 }