[Spice-devel] [spice-gtk v3 2/3] gtk-session: clipboard: x11: owner-change improvement

[Victor Toso]

From: Victor Toso <me at victortoso.com>

While interacting within the guest the VD_AGENT_CLIPBOARD_GRAB message
will be sent by the guest agent to notify that agent is holding some
clipboard data. When this clipboard data changes, the agent will send
VD_AGENT_CLIPBOARD_RELEASE to simply notify that previous clipboard
data is not available anymore and a new VD_AGENT_CLIPBOARD_GRAB
follows up with the current clipboard data being hold by agent.

This patch helps in fixing a state race, in X11, between who is
'holding' the clipboard grab.

The bug happens because gtk_clipboard_clear() will set owner to none,
making the rest of the code path consider that clipboard data has
changed in the *client* and ends up requesting the metadata with
gtk_clipboard_request_targets(), handled by clipboard_get_targets().

It is possible to have clipboard_get_targets() being called between
one VD_AGENT_CLIPBOARD_RELEASE and other VD_AGENT_CLIPBOARD_GRAB.

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>
Tested-by: James Harvey @jamespharvey20
---
 src/spice-gtk-session.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/src/spice-gtk-session.c b/src/spice-gtk-session.c
index adc72a2..85d5880 100644
--- a/src/spice-gtk-session.c
+++ b/src/spice-gtk-session.c
@@ -27,6 +27,9 @@
 #include <X11/Xlib.h>
 #include <gdk/gdkx.h>
 #endif
+#ifdef GDK_WINDOWING_WAYLAND
+#include <gdk/gdkwayland.h>
+#endif
 #ifdef G_OS_WIN32
 #include <windows.h>
 #include <gdk/gdkwin32.h>
@@ -674,6 +677,19 @@ static void clipboard_owner_change(GtkClipboard        *clipboard,
         return;
     }
 
+#ifdef GDK_WINDOWING_X11
+    /* In X11, while holding the keyboard-grab we are not interested in this
+     * event as it either came by grab or release messages from agent.  */
+    if (GDK_IS_X11_DISPLAY(gdk_display_get_default()) &&
+        spice_gtk_session_get_keyboard_has_focus(self)) {
+        SPICE_DEBUG("clipboard: owner-changed event: not requesting client's target "
+                    "while holding focus");
+        return;
+    }
+#endif
+    SPICE_DEBUG("clipboard: owner-changed event: has-foucus=%d",
+                spice_gtk_session_get_keyboard_has_focus(self));
+
     s->clipboard_by_guest[selection] = FALSE;
     s->clip_hasdata[selection] = TRUE;
     if (s->auto_clipboard_enable && !read_only(self))
-- 
2.20.1