Don't flush DNS cache on route changes.

Since Lollipop, routes are isolated within Networks.  Flushing a
Network's DNS cache whenever that same Network's routes are updated
doesn't provide any benefit.  Any system components depending on this
behaviour need to uncovered and fixed.

Additionally, clean up no-longer-used flushNetworkDnsCache().  This
should be replaced, when needed, by a proper binder interface to netd.

Change-Id: I34bf79e4839da014d466058a876d754209d0c007

core/java/android/os/INetworkManagementService.aidl

@@ -328,11 +328,6 @@ interface INetworkManagementService
      */
     void setDnsServersForNetwork(int netId, in String[] servers, String domains);
 
-    /**
-     * Flush the DNS cache associated with the specified network.
-     */
-    void flushNetworkDnsCache(int netId);
-
     void setFirewallEnabled(boolean enabled);
     boolean isFirewallEnabled();
     void setFirewallInterfaceRule(String iface, boolean allow);

services/core/java/com/android/server/ConnectivityService.java

@@ -4134,8 +4134,8 @@ public class ConnectivityService extends IConnectivityManager.Stub
 //        }
         updateTcpBufferSizes(networkAgent);
 
-        final boolean flushDns = updateRoutes(newLp, oldLp, netId);
+        updateRoutes(newLp, oldLp, netId);
-        updateDnses(newLp, oldLp, netId, flushDns);
+        updateDnses(newLp, oldLp, netId);
 
         updateClat(newLp, oldLp, networkAgent);
         if (isDefaultNetwork(networkAgent)) {
@@ -4238,14 +4238,16 @@ public class ConnectivityService extends IConnectivityManager.Stub
         return !routeDiff.added.isEmpty() || !routeDiff.removed.isEmpty();
     }
 
-    private void updateDnses(LinkProperties newLp, LinkProperties oldLp, int netId,
+    private void updateDnses(LinkProperties newLp, LinkProperties oldLp, int netId) {
-                             boolean flush) {
+        if (oldLp != null && newLp.isIdenticalDnses(oldLp)) {
-        if (oldLp == null || (newLp.isIdenticalDnses(oldLp) == false)) {
+            return;  // no updating necessary
+        }
+
         Collection<InetAddress> dnses = newLp.getDnsServers();
         if (DBG) log("Setting Dns servers for network " + netId + " to " + dnses);
         try {
-                mNetd.setDnsServersForNetwork(netId, NetworkUtils.makeStrings(dnses),
+            mNetd.setDnsServersForNetwork(
-                    newLp.getDomains());
+                    netId, NetworkUtils.makeStrings(dnses), newLp.getDomains());
         } catch (Exception e) {
             loge("Exception in setDnsServersForNetwork: " + e);
         }
@@ -4254,14 +4256,6 @@ public class ConnectivityService extends IConnectivityManager.Stub
             setDefaultDnsSystemProperties(dnses);
         }
         flushVmDnsCache();
-        } else if (flush) {
-            try {
-                mNetd.flushNetworkDnsCache(netId);
-            } catch (Exception e) {
-                loge("Exception in flushNetworkDnsCache: " + e);
-            }
-            flushVmDnsCache();
-        }
     }
 
     private void setDefaultDnsSystemProperties(Collection<InetAddress> dnses) {

services/core/java/com/android/server/NetworkManagementService.java

@@ -1936,16 +1936,6 @@ public class NetworkManagementService extends INetworkManagementService.Stub
         }
     }
 
-    @Override
-    public void flushNetworkDnsCache(int netId) {
-        mContext.enforceCallingOrSelfPermission(CONNECTIVITY_INTERNAL, TAG);
-        try {
-            mConnector.execute("resolver", "flushnet", netId);
-        } catch (NativeDaemonConnectorException e) {
-            throw e.rethrowAsParcelableException();
-        }
-    }
-
     @Override
     public void setFirewallEnabled(boolean enabled) {
         enforceSystemUid();