Add support for Linux eventfd(7) in the UNIX event loop

eventfd(7) uses less resources than a pipe, as it only needs to store a
single 64-bit integer, as opposed to a full buffer.

It was introduced first on Linux version 2.6.22 and glibc 2.7. However,
both the configure-time test and the runtime usage require the use of
EFD_CLOEXEC for thread-safety, so this code will be enabled only for
Linux 2.6.27 and up as well as glibc 2.9 and up.

Change-Id: Ic7e10b28d7b1d4ca24be614ed84055c4429a68e4
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

2 files changed, 54 insertions, 0 deletions

diff --git a/config.tests/unix/eventfd/eventfd.pro b/config.tests/unix/eventfd/eventfd.pro
new file mode 100644
index 0000000000..c41204f49f
--- /dev/null
+++ b/config.tests/unix/eventfd/eventfd.pro
@@ -0,0 +1,3 @@
+SOURCES = main.cpp
+CONFIG -= qt dylib
+mac:CONFIG -= app_bundle
diff --git a/config.tests/unix/eventfd/main.cpp b/config.tests/unix/eventfd/main.cpp
new file mode 100644
index 0000000000..0523ee0320
--- /dev/null
+++ b/config.tests/unix/eventfd/main.cpp
@@ -0,0 +1,51 @@
+/****************************************************************************
+**
+** Copyright (C) 2012 Intel Corporation
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the config.tests of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <sys/eventfd.h>
+
+int main()
+{
+    eventfd_t value;
+    int fd = eventfd(0, EFD_CLOEXEC);
+    eventfd_read(fd, &value);
+    eventfd_write(fd, value);
+    return 0;
+}