Android 4.1 Netd详细分析（一）概述与应用实例

一.概述
所谓 Netd 就是Network Daemon 的缩写，表示Network守护进程，类似的命名还有很多，例如 Vold（Volumn Deamon），Rild（Radio Interface Layer Deamon）

Netd负责跟一些涉及网络的配置，操作，管理，查询等相关的功能实现，比如，例如带宽控制（Bandwidth），流量统计，带宽控制，网络地址转换（NAT），个人局域网（pan），PPP链接，soft-ap，共享上网（Tether），配置路由表，interface配置管理，等等……

通过netlink，虚拟文件系统，等linux内核提供的用户接口，通信内核,或者直接执行系统模块，管理网络相关部分。

涉及主要源码位置：

Netd:

/System/netd/*

lib：

/system/core/libsysutils/src

Framework:

/frameworks/base/services/java/com/android/server/NetworkManagementService.java

/frameworks/base/services/java/com/android/server/NativeDaemonConnector.java

框架图~

很不规范，会意即可：


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二.ndc

理解一个模块最好方法就是实际应用。netd最为一个deamon，为开发者提供了一个用于管理的接口。就是ndc (nativedeamonconnector)，通过adb可以直接使用CommandListener中定义的各类命令。相似的framework层的NativeDeamonConnector是为上层提供的接口。下面是4.2中ndc可用的命令集合：

可用命令表：

例如： leo@leo-weng:~$ adb shell ndc interface list

interface	list
readrxcounter| readtxcounter
getthrottle<iface><”rx|tx”>
setthrottle<iface><rx_kbps|tx_kbps>
driver<iface><cmd><args>
route<add|remove> <iface> <”default|secondary”><dst> <prefix> <gateway>
list_ttys
ipfwd	status
enable|disable
tether	status
start-reverse|stop-reverse
stop<
start<addr_1 addr_2 addr_3 addr_4 [addr_2n]>
interface<add|remove|list>
dnslist
dnsset <addr_1> < addr_2>
nat	<enable|disable><iface><extface><addrcnt><nated-ipaddr/prelength>
pppd	attach<tty> <addr_local> <add_remote> <dns_1><dns_2>
detach<tty>
softap	startap|stopap
fwreload<iface> <AP|P2P>
clients
status
set<iface> <SSID> <wpa-psk|wpa2-psk|open> [<key><channel> <preamble><max SCB>]
resolver	setdefaultif<iface>
setifdns<iface><dns_1><dns_2>
flushdefaultif
flushif<iface>
bandwith	enable|disable
removequota|rq
getquota|gq
getiquota|giq<iface>
setquota|sq<bytes> <iface>
removequota|rqs<iface>
removeiiquota|riq<iface>
setiquota|sq<interface><bytes>
addnaughtyapps|ana<appUid>
removenaughtyapps|rna<appUid>
setgolbalalert|sga<bytes>
debugsettetherglobalalert|dstga<iface0><iface1>
setsharedalert|ssa<bytes>
removesharedalert|rsa
setinterfacealert|sia<iface><bytes>
removeinterfacealert|ria<iface>
gettetherstats|gts<iface0><iface1>
idletimer	enable|disable
add|remove<iface><timeout><classLabel>
firewall	enable|disable|is_enabled
set_interface_rule<rmnet0><allow|deny>
set_egress_source_rule<ip_addr><allow|deny>
set_egress_dest_rule<ip_addr><port><allow|deny>
set_uid_rule<uid><allow|deny>
clatd	stop|status|start<iface>

从init.rc文件中可以看到，是系统级的守护进程，手动kill后还会从新启动。

三.基本实例

就拿手机的soft-ap功能来举例吧，以使用 softap(Soft Access Point)为例。softap可以为wlan接入设备共享手机使用的移动网络，笔记本接入softap，可以通过手机的 3g 上网。以htc 中的 WLAN 热点的 app,如下图所示。

1)设置并开启 softap(便携式 WLAN 热点)

在 Setting 选项中进行设置,该设置功能的开启将涉及相关的UI 路径下相关的文件,packages /apps/Settings/src/com/android/settings/wifi 路径下,程序中的 WifiApEnabler. OnPreferenceChange 里, 设置 soft ap 在 wifiApDialog.onClick
里。

2)调用相应的处理函数,通过 socket 向 netd 下发命令

应用层通过ConnectivityManager接口，最终走到
Framework 层的 NetworkManagementService.startAccessPoint 函数。

[java]
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//NetworkManagementService.java
@Override
public void startAccessPoint(
WifiConfiguration wifiConfig, String wlanIface, String softapIface) {
mContext.enforceCallingOrSelfPermission(CONNECTIVITY_INTERNAL, TAG);
try {
wifiFirmwareReload(wlanIface, "AP");
if (wifiConfig == null) {
mConnector.execute("softap", "set", wlanIface, softapIface);
} else {
mConnector.execute("softap", "set", wlanIface, softapIface, wifiConfig.SSID,
getSecurityType(wifiConfig), wifiConfig.preSharedKey);
}
mConnector.execute("softap", "startap");
} catch (NativeDaemonConnectorException e) {
throw e.rethrowAsParcelableException();
}
}

NetworkManagementService 通过NativeDaemonConnector, 这里用来和系统的 netd 守护进程通过 socket 进行通信，发送命令。

3) netd 接受命令并进行处理,并将处理结果反馈给 Framework 层。

Netd 中 softap 控制的功能在/system/netd/SoftapController.{h,cpp}里, 具体的执行是通过调用网卡驱动的 ap 功能。NetworkManagementService 通过 NativeDaemonConnector 向下通过 socket
向下 softap 相关的字符串命令,NativeDaemonConnector 中维护着与 Netd 中 CommandListener 相关联的内部socket 线程。两者可以通过它相互通信。

[cpp]
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//CommandListener.cpp
int CommandListener::SoftapCmd::runCommand(SocketClient *cli,
int argc, char **argv) {
int rc = 0, flag = 0;
char *retbuf = NULL;

if (argc < 2) {
cli->sendMsg(ResponseCode::CommandSyntaxError, "Softap Missing argument", false);
return 0;
}

if (!strcmp(argv[1], "start")) {
rc = sSoftapCtrl->startDriver(argv[2]);
} else if (!strcmp(argv[1], "stop")) {
rc = sSoftapCtrl->stopDriver(argv[2]);
} else if (!strcmp(argv[1], "startap")) {
rc = sSoftapCtrl->startSoftap();
} else if (!strcmp(argv[1], "stopap")) {
rc = sSoftapCtrl->stopSoftap();
} else if (!strcmp(argv[1], "fwreload")) {
rc = sSoftapCtrl->fwReloadSoftap(argc, argv);
} else if (!strcmp(argv[1], "clients")) {
rc = sSoftapCtrl->clientsSoftap(&retbuf);
if (!rc) {
cli->sendMsg(ResponseCode::CommandOkay, retbuf, false);
free(retbuf);
return 0;
}
} else if (!strcmp(argv[1], "status")) {

……
……

4) Framework 受到回馈的信息,并通知 UI 处理结果,呈现给用户。

相关的 Log 实例:

D/NetworkManagementService( 1760): ===================startAccessPoint

commandLine=softap set wlan0 wlan0 "HTC Portable Hotspot E2D4" "wpa2-psk" *** 0 0 5 0

D/NetdConnector( 1760): SND -> {softap set wlan0 wlan0 "HTC Portable Hotspot E2D4""wpa2-psk" "3FF8F7531FBB9" 0 0 5 0} {null}

D/NetdConnector( 1760): already send Command (Wait Response)

D/NetdConnector( 1760): listenToSocket read--: (31,0)

D/NetdConnector( 1760): RCV <- {200 Softap operation succeeded}

D/NetdConnector( 1760): RSP <- {200 Softap operation succeeded}

D/NetdConnector( 1760): No Resp times=0

D/NetdConnector( 1760): finish send Command (complete)

D/NetdConnector( 1760): SND -> {softap startap} {null}

D/NetdConnector( 1760): already send Command (Wait Response)

D/NetdConnector( 1760): listenToSocket read--: (31,0)

D/NetdConnector( 1760): RCV <- {600 Iface linkstate wlan0 down}

D/NetdConnector( 1760): listenToSocket read--: (24,0)

D/NetdConnector( 1760): RCV <- {600 Iface added m.wlan0}

D/NetdConnector( 1760): listenToSocket read--: (33,0)

D/NetdConnector( 1760): RCV <- {600 Iface linkstate m.wlan0 down}

D/NetdConnector( 1760): listenToSocket read--: (31,0)

D/NetdConnector( 1760): RCV <- {600 Iface linkstate m.wlan0 up}

D/NetdConnector( 1760): listenToSocket read--: (31,0)

D/NetdConnector( 1760): RCV <- {200 Softap operation succeeded}

D/NetdConnector( 1760): RSP <- {200 Softap operation succeeded}

D/NetdConnector( 1760): No Resp times=0

D/NetdConnector( 1760): finish send Command (complete)

D/NetdConnector( 1760): SND -> {softap setMaxConns 5} {null}

D/NetdConnector( 1760): already send Command (Wait Response)

D/NetdConnector( 1760): listenToSocket read--: (31,0)

D/NetdConnector( 1760): RCV <- {200 Softap operation succeeded}

D/NetdConnector( 1760): RSP <- {200 Softap operation succeeded}

D/NetdConnector( 1760): No Resp times=0

D/NetdConnector( 1760): finish send Command (complete)

D/NetdConnector( 1760): listenToSocket read--: (29,0)

D/NetdConnector( 1760): RCV <- {600 Iface linkstate wlan0 up}

D/NetdConnector( 1760): listenToSocket read--: (29,0)

D/NetdConnector( 1760): RCV <- {600 Iface linkstate wlan0 up}

D/NetdConnector( 1760): listenToSocket read--: (29,0)

D/NetdConnector( 1760): RCV <- {600 Iface linkstate wlan0 up}

D/NetdConnector( 1760): SND -> {interface getcfg wlan0} {null}

D/NetdConnector( 1760): listenToSocket read--: (65,0)

D/NetdConnector( 1760): already send Command (Wait Response)

D/NetdConnector( 1760): RCV <- {213 1c:b0:94:36:bf:cb 0.0.0.0 0 [up broadcast running multicast]}

D/NetdConnector( 1760): RSP <- {213 1c:b0:94:36:bf:cb 0.0.0.0 0 [up broadcast runningmulticast]}

D/NetworkManagementService( 1760): rsp <213 1c:b0:94:36:bf:cb 0.0.0.0 0 [up broadcast running multicast]>

D/NetworkManagementService( 1760): flags <[up broadcast running multicast]>

D/NetdConnector( 1760): SND -> {interface setcfg wlan0 192.168.1.1 24 [up]} {null}

D/NetdConnector( 1760): listenToSocket read--: (32,0)

D/NetdConnector( 1760): RCV <- {200 Interface configuration set}

D/NetdConnector( 1760): already send Command (Wait Response)

D/NetdConnector( 1760): RSP <- {200 Interface configuration set}

D/NetdConnector( 1760): No Resp times=0

D/NetdConnector( 1760): finish send Command (complete)

E/NetworkManagementService( 1760): DEBUG softap setmaclist: softap setmaclist 0 "" ""

D/NetdConnector( 1760): SND -> {softap setmaclist 0 "" ""} {null}

D/NetdConnector( 1760): already send Command (Wait Response)

D/NetdConnector( 1760): listenToSocket read--: (31,0)

D/NetdConnector( 1760): RCV <- {200 Softap operation succeeded}

D/NetdConnector( 1760): RSP <- {200 Softap operation succeeded}

D/NetdConnector( 1760): No Resp times=0

D/NetdConnector( 1760): finish send Command (complete)

D/NetdConnector( 1760): SND -> {tether interface add wlan0} {null}

D/NetdConnector( 1760): already send Command (Wait Response)

D/NetdConnector( 1760): listenToSocket read--: (31,0)

D/NetdConnector( 1760): RCV <- {200 Tether operation succeeded}

D/NetdConnector( 1760): RSP <- {200 Tether operation succeeded}

D/NetdConnector( 1760): No Resp times=0

D/NetdConnector( 1760): finish send Command (complete)

D/NetdConnector( 1760): SND -> {softap getassoclist} {null}

D/NetdConnector( 1760): already send Command (Wait Response)

D/NetdConnector( 1760): listenToSocket read--: (7,0)

D/NetdConnector( 1760): RCV <- {222 0|}

D/NetdConnector( 1760): RSP <- {222 0|}

D/NetdConnector( 1760): No Resp times=0

D/NetdConnector( 1760): finish send Command (complete)

E/NetworkManagementService( 1760): DEBUG softap getassoclist: 0|

D/NetdConnector( 1760): SND -> {ipfwd enable} {null}

D/NetdConnector( 1760): already send Command (Wait Response)

D/NetdConnector( 1760): listenToSocket read--: (30,0)

D/NetdConnector( 1760): RCV <- {200 ipfwd operation succeeded}

D/NetdConnector( 1760): RSP <- {200 ipfwd operation succeeded}

D/NetdConnector( 1760): No Resp times=0

D/NetdConnector( 1760): finish send Command (complete)

D/NetworkManagementService( 1760): stopTethering

D/NetdConnector( 1760): SND -> {tether status} {null}

D/NetdConnector( 1760): listenToSocket read--: (31,0)

……

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