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：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 |
|
| setthrottle |
|
| driver |
|
| route |
|
| list_ttys | |
| ipfwd | status |
| enable|disable | |
| tether | status |
| start-reverse|stop-reverse | |
| stop< | |
| start |
|
| interface |
|
| dnslist | |
| dnsset |
|
| nat | |
| pppd | attach |
| detach |
|
| softap | startap|stopap |
| fwreload |
|
| clients | |
| status | |
| set |
|
| resolver | setdefaultif |
| setifdns |
|
| flushdefaultif | |
| flushif |
|
| bandwith | enable|disable |
| removequota|rq | |
| getquota|gq | |
| getiquota|giq |
|
| setquota|sq |
|
| removequota|rqs |
|
| removeiiquota|riq |
|
| setiquota|sq |
|
| addnaughtyapps|ana |
|
| removenaughtyapps|rna |
|
| setgolbalalert|sga |
|
| debugsettetherglobalalert|dstga |
|
| setsharedalert|ssa |
|
| removesharedalert|rsa | |
| setinterfacealert|sia |
|
| removeinterfacealert|ria |
|
| gettetherstats|gts |
|
| idletimer | enable|disable |
| add|remove |
|
| firewall | enable|disable|is_enabled |
| set_interface_rule |
|
| set_egress_source_rule |
|
| set_egress_dest_rule |
|
| set_uid_rule |
|
| clatd | stop|status|start |
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。
//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。
//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)
…………