[Spice-devel] [spice-gtk v3 3/3] gtk-session: clipboard: x11: do not request data while on focus

[Victor Toso]

From: Victor Toso <me at victortoso.com>

If SpiceGtkSession is holding the keyboard, that's huge indication
that the client should not be requesting guest's clipboard data yet.

This patch adds a check in clipboard_get() callback, to avoid such
requests. In Linux, this only happens with X11 backend.

This patch helps to handle a possible state race between who owns the
grab between client and agent which could lead to agent clipboard
failing or getting stuck, see:

The way to reproduce the race might depend on guest system and
applications but it is connected to amount of VDAGENTD_CLIPBOARD_GRAB
sent by the agent which depends on the amount of clipboard changes in
the guest. Simple example is on RHEL 6.10, with Gedit, select a text
char by char; Client receives VDAGENTD_CLIPBOARD_GRAB every time a new
char is selected instead of once when the full message is selected.

v2 -> v3:
* Split the fix in two patches while adding some info in a 3rd patch;
* Kept the "clipboard_clear" as it was (Jakub)
* Added a "clipboard_grab" log in clipboard_grab() function;

Related: https://gitlab.freedesktop.org/spice/win32/vd_agent/issues/6
Related: https://gitlab.freedesktop.org/spice/linux/vd_agent/issues/9
Related: https://bugzilla.redhat.com/show_bug.cgi?id=1594876

Signed-off-by: Victor Toso <victortoso at redhat.com>
---
 src/spice-gtk-session.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/spice-gtk-session.c b/src/spice-gtk-session.c
index 85d5880..f5959f7 100644
--- a/src/spice-gtk-session.c
+++ b/src/spice-gtk-session.c
@@ -763,6 +763,19 @@ static void clipboard_get(GtkClipboard *clipboard,
 
     SPICE_DEBUG("clipboard get");
 
+#ifdef GDK_WINDOWING_X11
+    /* Do not request clipboard data while we are still interacting with the
+     * Guest; Clipboard data could change shortly and this request would just
+     * be wasteful. */
+    if (GDK_IS_X11_DISPLAY(gdk_display_get_default()) &&
+        spice_gtk_session_get_keyboard_has_focus(self)) {
+        SPICE_DEBUG("clipboard get: not requesting data while holding focus");
+        return;
+    }
+#endif
+    SPICE_DEBUG("clipboard get: has-foucus=%d",
+                spice_gtk_session_get_keyboard_has_focus(self));
+
     selection = get_selection_from_clipboard(s, clipboard);
     g_return_if_fail(selection != -1);
     g_return_if_fail(info < SPICE_N_ELEMENTS(atom2agent));
@@ -818,6 +831,8 @@ static gboolean clipboard_grab(SpiceMainChannel *main, guint selection,
                                guint32* types, guint32 ntypes,
                                gpointer user_data)
 {
+    SPICE_DEBUG("clipboard_grab");
+
     g_return_val_if_fail(SPICE_IS_GTK_SESSION(user_data), FALSE);
 
     SpiceGtkSession *self = user_data;
-- 
2.20.1