Moving logic from Qt4 for grabbing the X server

Basically you don't want to grab the X server while your debugging.
Also added an environment variable which lets you force to not grab
the X server

Change-Id: Iba03f11c8f486ce71c55fac7716bffcb7cc8cb98
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>

src/plugins/platforms/xcb/qxcbconnection.cpp

@@ -242,8 +242,9 @@ void QXcbConnection::updateScreens()
             ((QXcbIntegration*)QGuiApplicationPrivate::platformIntegration())->screenAdded(screen);
 }
 
-QXcbConnection::QXcbConnection(QXcbNativeInterface *nativeInterface, const char *displayName)
+QXcbConnection::QXcbConnection(QXcbNativeInterface *nativeInterface, bool canGrabServer, const char *displayName)
     : m_connection(0)
+    , m_canGrabServer(canGrabServer)
     , m_primaryScreen(0)
     , m_displayName(displayName ? QByteArray(displayName) : qgetenv("DISPLAY"))
     , m_nativeInterface(nativeInterface)
@@ -952,6 +953,18 @@ void QXcbConnection::setFocusWindow(QXcbWindow *w)
     m_focusWindow = w;
 }
 
+void QXcbConnection::grabServer()
+{
+    if (m_canGrabServer)
+        xcb_grab_server(m_connection);
+}
+
+void QXcbConnection::ungrabServer()
+{
+    if (m_canGrabServer)
+        xcb_ungrab_server(m_connection);
+}
+
 void QXcbConnection::sendConnectionEvent(QXcbAtom::Atom a, uint id)
 {
     xcb_client_message_event_t event;

src/plugins/platforms/xcb/qxcbconnection.h

@@ -306,7 +306,7 @@ class QXcbConnection : public QObject
 {
     Q_OBJECT
 public:
-    QXcbConnection(QXcbNativeInterface *nativeInterface, const char *displayName = 0);
+    QXcbConnection(QXcbNativeInterface *nativeInterface, bool canGrabServer, const char *displayName = 0);
     ~QXcbConnection();
 
     QXcbConnection *connection() const { return const_cast<QXcbConnection *>(this); }
@@ -391,6 +391,8 @@ public:
     QByteArray startupId() const { return m_startupId; }
     void clearStartupId() { m_startupId.clear(); }
 
+    void grabServer();
+    void ungrabServer();
 private slots:
     void processXcbEvents();
 
@@ -454,6 +456,7 @@ private:
 
     xcb_connection_t *m_connection;
     const xcb_setup_t *m_setup;
+    bool m_canGrabServer;
 
     QList<QXcbScreen *> m_screens;
     int m_primaryScreen;

src/plugins/platforms/xcb/qxcbdrag.cpp

@@ -1160,7 +1160,7 @@ bool QXcbDrag::dndEnable(QXcbWindow *w, bool on)
             if (desktop_proxy) // *WE* already have one.
                 return false;
 
-            xcb_grab_server(xcb_connection());
+            connection()->grabServer();
 
             // As per Xdnd4, use XdndProxy
             xcb_window_t proxy_id = xdndProxy(connection(), w->xcb_window());
@@ -1176,7 +1176,7 @@ bool QXcbDrag::dndEnable(QXcbWindow *w, bool on)
                                     XCB_ATOM_WINDOW, 32, 1, &proxy_id);
             }
 
-            xcb_ungrab_server(xcb_connection());
+            connection()->ungrabServer();
         } else {
             xdnd_widget = w;
         }

src/plugins/platforms/xcb/qxcbintegration.cpp

@@ -91,8 +91,34 @@
 #endif
 #endif
 
+#include <QtCore/QFileInfo>
+
 QT_BEGIN_NAMESPACE
 
+#if defined(QT_DEBUG) && defined(Q_OS_LINUX)
+// Find out if our parent process is gdb by looking at the 'exe' symlink under /proc,.
+// or, for older Linuxes, read out 'cmdline'.
+static bool runningUnderDebugger()
+{
+    const QString parentProc = QLatin1String("/proc/") + QString::number(getppid());
+    const QFileInfo parentProcExe(parentProc + QLatin1String("/exe"));
+    if (parentProcExe.isSymLink())
+        return parentProcExe.symLinkTarget().endsWith(QLatin1String("/gdb"));
+    QFile f(parentProc + QLatin1String("/cmdline"));
+    if (!f.open(QIODevice::ReadOnly))
+        return false;
+    QByteArray s;
+    char c;
+    while (f.getChar(&c) && c) {
+        if (c == '/')
+            s.clear();
+        else
+            s += c;
+    }
+    return s == "gdb";
+}
+#endif
+
 QXcbIntegration::QXcbIntegration(const QStringList &parameters)
     : m_eventDispatcher(createUnixEventDispatcher())
     ,  m_services(new QGenericUnixServices)
@@ -104,7 +130,15 @@ QXcbIntegration::QXcbIntegration(const QStringList &parameters)
 #endif
     m_nativeInterface.reset(new QXcbNativeInterface);
 
-    m_connections << new QXcbConnection(m_nativeInterface.data());
+    bool canGrab = true;
+    #if defined(QT_DEBUG) && defined(Q_OS_LINUX)
+    canGrab = !runningUnderDebugger();
+    #endif
+    static bool canNotGrabEnv = qgetenv("QT_XCB_NO_GRAB_SERVER").length();
+    if (canNotGrabEnv)
+        canGrab = false;
+
+    m_connections << new QXcbConnection(m_nativeInterface.data(), canGrab);
 
     for (int i = 0; i < parameters.size() - 1; i += 2) {
 #ifdef Q_XCB_DEBUG