QLocalSocket: always open outer QIODevice in unbuffered mode

The actual buffering is performed either in the inner socket (Unix),
or in the pipeReader (Windows). To avoid unnecessary copying of data
between buffers, enforce unbuffered mode for all implementations,
which slightly improves read performance.

Change-Id: Idb2a09f35823b9945c71231710290be12d9930f7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

src/network/socket/qlocalsocket.cpp

@@ -396,6 +396,8 @@ QLocalSocket::QLocalSocket(QObject * parent)
     : QIODevice(*new QLocalSocketPrivate, parent)
 {
     Q_D(QLocalSocket);
+
+    d->readBufferChunkSize = 0; // force QIODevice unbuffered mode
     d->init();
 }
 

src/network/socket/qlocalsocket_unix.cpp

@@ -357,7 +357,7 @@ void QLocalSocketPrivate::_q_connectToSocket()
     fullServerName = connectingPathName;
     if (unixSocket.setSocketDescriptor(connectingSocket,
         QAbstractSocket::ConnectedState, connectingOpenMode)) {
-        q->QIODevice::open(connectingOpenMode | QIODevice::Unbuffered);
+        q->QIODevice::open(connectingOpenMode);
         q->emit connected();
     } else {
         QString function = QLatin1String("QLocalSocket::connectToServer");