[RK3288][Android6.0] WiFi之Autojoin对无线网络的选择机制

Platform: Rockchip

OS: Android 6.0

Kernel: 3.10.92

当有两个或者两个以上的已经保存的无线网络可以连接时，系统通过attemptAutoJoin()来选择一个最优网络。

假设只有两个保存的无线网络，配置文件如下：

root@rk3288:/ # cat /data/misc/wifi/wpa_supplicant.conf

network={
ssid="RD-TA100-2.4G"
psk="Gerrit2All"
key_mgmt=WPA-PSK
priority=2
}

network={
ssid="Kris"
psk="20122008"
key_mgmt=WPA-PSK
priority=3
}

来看attemptAutoJoin()：

boolean attemptAutoJoin()
{
//获取上一次选择的网络配置，我上次选的是ap: "Kris"
String lastSelectedConfiguration = mWifiConfigStore.getLastSelectedConfiguration();
if (lastSelectedConfiguration != null) {
age = 14000;
}
//获取最近配置过的网络，这里会获取到两个，也就是配置文件中的那两个
List<WifiConfiguration> list =
mWifiConfigStore.getRecentConfiguredNetworks(age, false);

for (WifiConfiguration config : list) {
//candidate保存当前网络配置
if (candidate == null) {
candidate = config;
} else {
//循环第二次时就会比较两个网络配置
int order = compareWifiConfigurations(candidate, config);
if (order > 0) {
// Ascending : candidate < config
//经过一番计算后，发现order>0，那么老的candidate网络配置就会被新的代替，
//如果有多余两个保存的无线网络，那么依次计算并且符合条件后替换
candidate = config;
}
}
}
if (mWifiStateMachine.shouldSwitchNetwork(networkDelta)) {      // !!! JNo: Here!
//发送自动连接event给WifiStateMachine
mWifiStateMachine.sendMessage(WifiStateMachine.CMD_AUTO_CONNECT,
candidate.networkId, networkSwitchType, candidate);
found = true;
}
return found;
}

compareWifiConfigurations():

int compareWifiConfigurations(WifiConfiguration a, WifiConfiguration b)
{
int order = 0;
boolean linked = false;

// ephemeral的解释是
// Indicate that a WifiConfiguration is temporary and should not be saved
//nor considered by AutoJoin.
//正常连接时WifiStateMachine在connect的时候设置为false
//当是未信任网络时会设置为true
if (a.ephemeral && b.ephemeral == false) {
return 1; // b is of higher priority - ascending
}
if (b.ephemeral && a.ephemeral == false) {
return -1; // a is of higher priority - descending
}

// Apply RSSI, in the range [-5, +5]
// after band adjustment, +n difference roughly corresponds to +10xn dBm
//通过RSSI也就是信号强度计算得到一个order
order = order + compareWifiConfigurationsRSSI(a, b, mCurrentConfigurationKey);

// If the configurations are not linked, compare by user's choice, only a
// very high RSSI difference can then override the choice
//如果用户上次有选择过某个网络，那么又要根据选择的choice来重新计算最终的order
if (!linked) {
int choice;

choice = getConnectChoice(a, b, false);
if (choice > 0) {
// a is of higher priority - descending
order = order - choice;
if (a.visibility != null) {
a.visibility.lastChoiceBoost = choice;
a.visibility.lastChoiceConfig = b.configKey();
}
}

choice = getConnectChoice(b, a, false);
if (choice > 0) {
// a is of lower priority - ascending
order = order + choice;
if (b.visibility != null) {
b.visibility.lastChoiceBoost = choice;
b.visibility.lastChoiceConfig = a.configKey();
}
}
}

String sorder = " == ";
if (order > 0) {
sorder = " < ";
} else if (order < 0) {
sorder = " > ";
}

return order;
}

调试时可以把debug log打开，对应的log如下:

07-06 15:41:00.357   557   608 D WifiAutoJoinController : attemptAutoJoin() status=wpa_state=SCANNING
07-06 15:41:00.357   557   608 D WifiAutoJoinController : p2p_device_address=b2:f1:ec:49:50:cb
07-06 15:41:00.357   557   608 D WifiAutoJoinController : address=b0:f1:ec:49:50:cb
07-06 15:41:00.357   557   608 D WifiAutoJoinController : uuid=544ae0ce-fa0a-58d2-af21-81be288cb44c
07-06 15:41:00.358   557   608 D WifiAutoJoinController : attemptAutoJoin() num recent config 2 ---> suppNetId=-1
07-06 15:41:00.358   557   608 D WifiAutoJoinController : attemptAutoJoin good candidate seen, bumped hard -> status="Kris"WPA_PSK status=0
07-06 15:41:00.358   557   608 D WifiAutoJoinController : attemptAutoJoin trying id=1 "Kris"WPA_PSK status=0
07-06 15:41:00.359   557   608 D WifiAutoJoinController : attemptAutoJoin good candidate seen, bumped hard -> status="RD-TA100-2.4G"WPA_PSK status=0
07-06 15:41:00.359   557   608 D WifiAutoJoinController : attemptAutoJoin trying id=0 "RD-TA100-2.4G"WPA_PSK status=0 current candidate "Kris"WPA_PSK
07-06 15:41:00.359   557   608 D WifiAutoJoinController : attemptAutoJoin will compare candidate  "Kris"WPA_PSK with "RD-TA100-2.4G"WPA_PSK
07-06 15:41:00.359   557   608 D WifiAutoJoinController :     compareWifiConfigurationsRSSI: "Kris"WPA_PSK rssi=-55,-127 boost=0 "RD-TA100-2.4G"WPA_PSK rssi=-47,-127 boost=0
07-06 15:41:00.359   557   608 D WifiAutoJoinController :         "Kris"WPA_PSK is5=false score=-55 "RD-TA100-2.4G"WPA_PSK is5=false score=-47
07-06 15:41:00.359   557   608 D WifiAutoJoinController :     compareWifiConfigurationsRSSI "Kris"WPA_PSK rssi=(-55,-127) num=(1,0) < "RD-TA100-2.4G"WPA_PSK rssi=(-47,-127) num=(1,0) -> 8
07-06 15:41:00.360   557   608 D WifiAutoJoinController :     compareWifiConfigurations prefers "Kris"WPA_PSK over "RD-TA100-2.4G"WPA_PSK due to user choice of 60 order -> -52
07-06 15:41:00.360   557   608 D WifiAutoJoinController : compareWifiConfigurations: "Kris"WPA_PSK > "RD-TA100-2.4G"WPA_PSK order -52
07-06 15:41:00.360   557   608 D WifiAutoJoinController : attemptAutoJoin compareWifiConfigurations returned -52
07-06 15:41:00.360   557   608 D WifiAutoJoinController : attemptAutoJoin networkSwitching candidate "Kris"WPA_PSK linked=false : delta=1000
07-06 15:41:00.361   557   608 D WifiStateMachine: shouldSwitchNetwork  txSuccessRate=0.00 rxSuccessRate=0.00 delta 1000 -> 1000
07-06 15:41:00.361   557   608 D WifiAutoJoinController : AutoJoin auto connect with netId 1 to "Kris"WPA_PSK
07-06 15:41:00.361   557   608 D WifiAutoJoinController : attemptRoam: "Kris"WPA_PSK Found ee:29:f5:be:c5:6b rssi=-55 freq=2437
07-06 15:41:00.361   557   608 D WifiAutoJoinController : Done attemptAutoJoin status=3

总的来说,评分机制有三种：

1. ephemeral值，即是否是未信任网络

2. RSSI值

3. 用户上次选择，优先级比RSSI高，除非RSSI非常大的情况

参考：

WifiAutoJoinController.java源码解析