Compositor: add API for using existing socket fd's

This adds functionality to allow system-level control over handing out
file descriptors for sockets. In particular, it allows writing socket-
activated compositors.

[ChangeLog][Compositor] Added API for installing a socket on which bind()
and listen() have already been called into the event dispatch loop. This
facilitates socket-activated compositors.

Change-Id: I620f5ad0a3c3c5c4ecb937004230dcd024df8f69
Reviewed-by: Johan Helsing <johan.helsing@qt.io>

3 files changed, 66 insertions, 0 deletions

diff --git a/src/compositor/compositor_api/qwaylandcompositor.cpp b/src/compositor/compositor_api/qwaylandcompositor.cpp
index 8c476cf1c..b0e3cbd24 100644
--- a/src/compositor/compositor_api/qwaylandcompositor.cpp
+++ b/src/compositor/compositor_api/qwaylandcompositor.cpp
@@ -193,6 +193,10 @@ void QWaylandCompositorPrivate::init()
         emit q->socketNameChanged(socket_name);
     }
 
+#if WAYLAND_VERSION_MAJOR >= 1 && (WAYLAND_VERSION_MAJOR != 1 || WAYLAND_VERSION_MINOR >= 10)
+    connectToExternalSockets();
+#endif
+
     loop = wl_display_get_event_loop(display);
 
     int fd = wl_event_loop_get_fd(loop);
@@ -274,6 +278,18 @@ void QWaylandCompositorPrivate::addPolishObject(QObject *object)
     }
 }
 
+#if WAYLAND_VERSION_MAJOR >= 1 && (WAYLAND_VERSION_MAJOR != 1 || WAYLAND_VERSION_MINOR >= 10)
+void QWaylandCompositorPrivate::connectToExternalSockets()
+{
+    // Clear out any backlog of user-supplied external socket descriptors
+    for (int fd : qAsConst(externally_added_socket_fds)) {
+        if (wl_display_add_socket_fd(display, fd) != 0)
+            qWarning() << "Failed to integrate user-supplied socket fd into the Wayland event loop";
+    }
+    externally_added_socket_fds.clear();
+}
+#endif
+
 void QWaylandCompositorPrivate::compositor_create_surface(wl_compositor::Resource *resource, uint32_t id)
 {
     Q_Q(QWaylandCompositor);
@@ -552,6 +568,46 @@ QByteArray QWaylandCompositor::socketName() const
 }
 
 /*!
+ * \qmlmethod QtWaylandCompositor::WaylandCompositor::addSocketFd(fd)
+ * \since 5.12
+ *
+ * Listen for client connections on a file descriptor referring to a
+ * server socket already bound and listening.
+ *
+ * Does not take ownership of the file descriptor; it must be closed
+ * explicitly if needed.
+ *
+ * \note This method is only available with libwayland 1.10.0 or
+ * newer. If built against an earlier libwayland runtime, this
+ * method is a noop.
+ */
+
+/*!
+ * Listen for client connections on a file descriptor referring to a
+ * server socket already bound and listening.
+ *
+ * Does not take ownership of the file descriptor; it must be closed
+ * explicitly if needed.
+ *
+ * \note This method is only available with libwayland 1.10.0 or
+ * newer. If built against an earlier libwayland runtime, this
+ * method is a noop.
+ *
+ * \since 5.12
+ */
+void QWaylandCompositor::addSocketFd(int fd)
+{
+#if WAYLAND_VERSION_MAJOR >= 1 && (WAYLAND_VERSION_MAJOR != 1 || WAYLAND_VERSION_MINOR >= 10)
+    Q_D(QWaylandCompositor);
+    d->externally_added_socket_fds.append(fd);
+    if (isCreated())
+        d->connectToExternalSockets();
+#else
+    qWarning() << "QWaylandCompositor::addSocketFd() does nothing on libwayland versions prior to 1.10.0";
+#endif
+}
+
+/*!
  * \internal
  */
 struct wl_display *QWaylandCompositor::display() const
diff --git a/src/compositor/compositor_api/qwaylandcompositor.h b/src/compositor/compositor_api/qwaylandcompositor.h
index 23844d72a..72b8f2d1b 100644
--- a/src/compositor/compositor_api/qwaylandcompositor.h
+++ b/src/compositor/compositor_api/qwaylandcompositor.h
@@ -93,6 +93,8 @@ public:
     void setSocketName(const QByteArray &name);
     QByteArray socketName() const;
 
+    Q_INVOKABLE void addSocketFd(int fd);
+
     ::wl_display *display() const;
     uint32_t nextSerial();
 
diff --git a/src/compositor/compositor_api/qwaylandcompositor_p.h b/src/compositor/compositor_api/qwaylandcompositor_p.h
index 0d259ee84..cdf4be6b4 100644
--- a/src/compositor/compositor_api/qwaylandcompositor_p.h
+++ b/src/compositor/compositor_api/qwaylandcompositor_p.h
@@ -112,6 +112,11 @@ public:
 
     inline void addOutput(QWaylandOutput *output);
     inline void removeOutput(QWaylandOutput *output);
+
+#if WAYLAND_VERSION_MAJOR >= 1 && (WAYLAND_VERSION_MAJOR != 1 || WAYLAND_VERSION_MINOR >= 10)
+    void connectToExternalSockets();
+#endif
+
 protected:
     void compositor_create_surface(wl_compositor::Resource *resource, uint32_t id) override;
     void compositor_create_region(wl_compositor::Resource *resource, uint32_t id) override;
@@ -128,6 +133,9 @@ protected:
     void loadServerBufferIntegration();
 
     QByteArray socket_name;
+#if WAYLAND_VERSION_MAJOR >= 1 && (WAYLAND_VERSION_MAJOR != 1 || WAYLAND_VERSION_MINOR >= 10)
+    QList<int> externally_added_socket_fds;
+#endif
     struct wl_display *display = nullptr;
 
     QList<QWaylandSeat *> seats;