Android的RIL机制中的 reference-ril.c 即为厂商提供的驱动接口。这个驱动源代码各个厂商都是有提供的，网上也有下载。我如今用的就是huawei wcdma的。最后编译成libreference-ril.so。关于这个接口驱动在RIL中所扮演的角色可參考 Android——RIL 机制源代码分析

android 4.2自带pppd源代码在/external/ppp/pppd中.相同，kernel中也是须要打开对point-to-point 的支持，在network support里面.

                                              撰写不易,转载请注明出处：http://blog.csdn.net/jscese/article/details/40340665

一.requestSetupDataCall:         

      这个就是在reference-ril.c 中的数据流量的request，上层的接口通过onRequest 的RIL_REQUEST_SETUP_DATA_CALL请求。这些在上面说到的源代码分析里有具体分析，这里就仅仅从拨号连接分析。

static void requestSetupDataCall(void *data, size_t datalen, RIL_Token t)
{
    const char *apn;
    char *cmd;
    int err;
    ATResponse *p_response = NULL;

    char ppp_dnses[(PROPERTY_VALUE_MAX * 2) + 3] = {‘\0‘}; //初始化属性数组。用于暂时存储拨号的属性变量
    char ppp_local_ip[PROPERTY_VALUE_MAX] = {‘\0‘};
    char ril_pppd_tty[PROPERTY_VALUE_MAX] = {‘\0‘};
    char ppp_dns1[PROPERTY_VALUE_MAX] = {‘\0‘};
    char ppp_dns2[PROPERTY_VALUE_MAX] = {‘\0‘};
    char ppp_gw[PROPERTY_VALUE_MAX] = {‘\0‘};

    char exit_code[PROPERTY_VALUE_MAX] = {‘\0‘};

    int n = 1;
    RIL_Data_Call_Response_v6 *responses = alloca(n * sizeof(RIL_Data_Call_Response_v6)); //使用的是ipv6

    apn = ((const char **)data)[2]; //取传进来的接入点 apn
    /*    ALOGD("jscese display in reference  APN == ‘%s‘ \n",apn);
     apn ="3gnet";*/
    ALOGD("[%s] jscese display in reference  APN ‘%s‘ ", __func__, apn);

#ifdef USE_TI_COMMANDS
    // Config for multislot class 10 (probably default anyway eh?
)
    err = at_send_command("AT%CPRIM=\"GMM\",\"CONFIG MULTISLOT_CLASS=<10>\"",
            NULL);

    err = at_send_command("AT%DATA=http://www.mamicode.com/2,/"UART\",1,,\"SER\",\"UART\",0", NULL);
#endif /* USE_TI_COMMANDS */

    int fd, qmistatus;
    size_t cur = 0;
    size_t len;
    ssize_t written, rlen;
    char status[32] = {0};
    int retry = 10;
    const char *pdp_type;

    ALOGD("requesting data connection to APN ‘%s‘", apn);

    pdp_type = "IP"; // jscese add for dial

    asprintf(&cmd, "AT+CGDCONT=1,\"%s\",\"%s\",,0,0", pdp_type, apn);
    //FIXME check for error here
    err = at_send_command(cmd, NULL); //发送接入点的AT指令
    free(cmd);
#if 0
    // Set required QoS params to default
    err = at_send_command("AT+CGQREQ=1", NULL);

    // Set minimum QoS params to default
    err = at_send_command("AT+CGQMIN=1", NULL);

    // packet-domain event reporting
    err = at_send_command("AT+CGEREP=1,0", NULL);

    // Hangup anything that‘s happening there now
    err = at_send_command("AT+CGACT=1,0", NULL);

#endif
    // Start data on PDP context 1
    if (strcmp(apn, "3gnet") == 0)
    {
        ALOGD("jscese display in reference  is 3gnet \n");
        err = at_send_command("ATD*99***1#", &p_response);  //这个就是联通3G上网须要拨的号码 ATD*99***1# 获取连接

    }
    else if (strcmp(apn, "ctnet") == 0)
    {
        ALOGD("jscese display in reference  is ctnet \n");
        err = at_send_command("ATD#777", &p_response);
    }

    if (err < 0 || p_response->success == 0)
    {
        goto error;
    }
    at_response_free(p_response);

    sleep(1); //Wait for the modem to finish

    property_set("net.ppp1.local-ip", "");
    property_set("net.gprs.ppp-exit", "");
    property_set("ctl.start", "pppd_gprs"); //假设上面的拨号AT指令成功返回，这里就启用之前定义好的一个pppd service 调用脚本去拨号获取IP 等网络參数

    // Dialup
    sleep(3);


    /*jscese add try 5 times to get ip*/
    int iRetry = 5;
    while (iRetry > 0)
    {
        property_get("net.gprs.ppp-exit", exit_code, "");

        if (strcmp(exit_code, "0") != 0)
        {
            ALOGE("PPPd exit with code %s", exit_code);
            iRetry = 0;
            break;
        }

        ALOGI("Waiting For Property");
        if (wait_for_property("net.ppp1.local-ip", NULL, 10) < 0) //监測 ip 地址的属性值。这个值我放在 pppd拨号脚本里面来进行设置，假设成功这里就能监測到
        {
            ALOGE("[%s]: wait for IP from ppp link at %d\n", __func__, iRetry);
        }
        else
        {
            ALOGI("[%s]: got IP from ppp link\r\n", __func__);
            break;
        }
        iRetry--;
    }

    if (iRetry <= 0)
    {
        ALOGE("[%s]: fail to get IP\r\n", __func__);
        goto error;
    }

    /*    if (wait_for_property("net.ppp1.local-ip", NULL, 10) < 0) {
     ALOGE("Timeout waiting net.ppp1.local-ip - giving up!\n");
     goto error;
     }*/

    property_get("net.ppp1.local-ip", ppp_local_ip, NULL);
    property_get("net.ppp1.dns1", ppp_dns1, NULL);
    property_get("net.ppp1.dns2", ppp_dns2, NULL);
    property_get("net.ppp1.gw", ppp_gw, NULL);
    sprintf(ppp_dnses, "%s %s", ppp_dns1, ppp_dns2);

    ALOGI("Got net.ppp1.local-ip: %s\n", ppp_local_ip);

    responses[0].status = 0;
    responses[0].suggestedRetryTime = -1;
    responses[0].cid = 1;
    responses[0].active = 2;
    responses[0].type = "PPP";
    responses[0].ifname = PPP_TTY_PATH;
    responses[0].addresses = ppp_local_ip;
    responses[0].dnses = ppp_dnses;
    responses[0].gateways = ppp_gw;  //通过获取到的 网络属性 设置这个responses 提供给上层

    RIL_onRequestComplete(t, RIL_E_SUCCESS, responses, n * sizeof(RIL_Data_Call_Response_v6));
    return;
    error: RIL_onRequestComplete(t, RIL_E_GENERIC_FAILURE, NULL, 0);
    at_response_free(p_response);

}

二.pppd

     在上面 requestSetupDataCall 中启动一个服务来调用pppd拨号，先在init.rc中加入：

 #jscese add for usb_switch service when 3G dongle add for serial

service ril-daemon /system/bin/rild -l /system/lib/libreference-ril.so -- -d /dev/ttyUSB2
    class main
    socket rild stream 660 root radio
    socket rild-debug stream 660 radio system
    user root
    group radio cache inet misc audio log


service pppd_gprs /system/etc/ppp/init.gprs-pppd /dev/ttyUSB0
    user root
    group radio cache inet misc
    disabled
    oneshot
## end

上面的服务是用来开机启动rild的，载入libreference-ril动态库，

而且指定了通信port为串口 -d /dev/ttyUSB2，另外还有 -s 代表是socket设备 -p 代表回环接口

以下的就是pppd拨号的脚本服务了，用来启动拨号脚本，而且指定数据port.

这个pppd_gprs 服务须要设置权限。由于我是在reference-ril里面通过属性启动的 在/system/core/init/property_service.c中加入例如以下：

struct {
    const char *service;
    unsigned int uid;
    unsigned int gid;
} control_perms[] = {
    { "dumpstate",AID_SHELL, AID_LOG },
    { "ril-daemon",AID_RADIO, AID_RADIO },
/*jscese add for pppd 3G*/
    { "pppd_gprs",AID_RADIO, AID_LOG },
/*end*/
     {NULL, 0, 0 }
};

struct {
    const char *prefix;
    unsigned int uid;
    unsigned int gid;
} property_perms[] = {

...

/*jscese add  pppd for 3G*/
    { "net.ppp1.",AID_RADIO,0 },
/*end*/

    { NULL, 0, 0 }
};

init.gprs-pppd 设置运行权限，/system/core/include/private/android_filesystem_config.h中：

static struct fs_path_config android_files[] = {

...

/*jscese add for pppd */
    { 00777, AID_ROOT,      AID_SHELL,    "system/etc/init.gprs-pppd" },
/*    end*/

...

}

init.gprs-pppd：

贴出拨号脚本

#!/system/bin/sh
 
PPPD_PID=
 
USER=`/system/bin/getprop net.gprs.user`
PASSWORD=`/system/bin/getprop net.gprs.password`
 
/system/bin/setprop "net.gprs.ppp-exit" ""

 
/system/bin/pppd $1 115200 linkname datakey unit 1 crtscts usepeerdns noauth defaultroute noipdefault ipcp-accept-local ipcp-accept-remote ipcp-max-failure 30 lcp-echo-interval 5 lcp-echo-failure 30 modem dump debug kdebug 8

PPPD_EXIT=$?
PPPD_PID=$!
 
/system/bin/log -t pppd "pppd exited with $PPPD_EXIT"
 
/system/bin/setprop "net.gprs.ppp-exit" "$PPPD_EXIT"

另外在这个拨号脚本同文件夹下 /system/etc/ppp/ 须要设置和注销ip等參数的脚本。一个在拨号成功时调用。一个在断开网络时调用：

ip-up-datakey：

#!/system/bin/sh
case $1 in
    ppp1)
        /android/bin/iptables --flush;
        /android/bin/iptables --table nat --flush;
        /android/bin/iptables --delete-chain;
        /android/bin/iptables --table nat --append POSTROUTING --out-interface ppp0 -j MASQUERADE;
        /android/bin/iptables --append FORWARD --in-interface ppp1 -j ACCEPT;
        echo 0 > /proc/sys/net/ipv4/ip_forward;
        echo 1 > /proc/sys/net/ipv4/ip_forward;
        ;;
    ppp0)
    /system/bin/setprop "net.interfaces.defaultroute" "ppp1";
    ;;
esac
 
/system/bin/setprop "net.ppp1.dns1" "$DNS1"
/system/bin/setprop "net.ppp1.dns2" "$DNS2"
/system/bin/setprop "net.ppp1.local-ip" "$IPLOCAL"
/system/bin/setprop "net.ppp1.remote-ip" "$IPREMOTE"
/system/bin/setprop "net.ppp1.gw" "$IPREMOTE"
/system/bin/setprop "net.ppp1.if" "$IFNAME"

ip-down-datakey：

#!/system/bin/sh
case $1 in
    ppp1)
        echo 0 > /proc/sys/net/ipv4/ip_forward;
        ;;
esac
 
/system/bin/setprop "net.ppp1.dns1" ""
/system/bin/setprop "net.ppp1.dns2" ""
/system/bin/setprop "net.ppp1.local-ip" ""
/system/bin/setprop "net.ppp1.remote-ip" ""
/system/bin/setprop "net.ppp1.gw" ""
/system/bin/setprop "net.ppp1.if" ""

贴张联通apn为 3gnet 的拨号log：