[Spice-devel] [vdagent-linux] x11: invalidate requests for targets on grab from client

[Jakub Janků]

If XSetSelectionOwner() is invoked during the time
we are waiting for the requested clipboard targets,
the targets we eventually receive are no longer valid.

To solve this, ignore the same count of target notifications
as we expected at the time we received grab from the client.

Otherwise we end up in a situation when vdagent holds
the clipboard grab in the guest but cannot provide data to the
apps that request it - this can be observed in the log:

    clipboard: received selection request event for target *, while not owning client clipboard

Signed-off-by: Jakub Janků <jjanku at redhat.com>
---

This addresses the same issue as [0], just in the X11 clipboard implementation.

[0] https://lists.freedesktop.org/archives/spice-devel/2019-February/048075.html

---
 src/vdagent/x11-priv.h |  1 +
 src/vdagent/x11.c      | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/src/vdagent/x11-priv.h b/src/vdagent/x11-priv.h
index e487aa2..99676d2 100644
--- a/src/vdagent/x11-priv.h
+++ b/src/vdagent/x11-priv.h
@@ -92,6 +92,7 @@ struct vdagent_x11 {
     int xfixes_event_base;
     int max_prop_size;
     int expected_targets_notifies[256];
+    int ignore_targets_notifies[256];
     int clipboard_owner[256];
     int clipboard_type_count[256];
     uint32_t clipboard_agent_types[256][256];
diff --git a/src/vdagent/x11.c b/src/vdagent/x11.c
index 484be5e..c2515a8 100644
--- a/src/vdagent/x11.c
+++ b/src/vdagent/x11.c
@@ -945,6 +945,12 @@ static void vdagent_x11_handle_targets_notify(struct vdagent_x11 *x11,
 
     x11->expected_targets_notifies[selection]--;
 
+    if (x11->ignore_targets_notifies[selection] > 0) {
+        x11->ignore_targets_notifies[selection]--;
+        VSELPRINTF("ignoring selection notify TARGETS");
+        return;
+    }
+
     /* If we have more targets_notifies pending, ignore this one, we
        are only interested in the targets list of the current owner
        (which is the last one we've requested a targets list from) */
@@ -1246,6 +1252,11 @@ void vdagent_x11_clipboard_grab(struct vdagent_x11 *x11, uint8_t selection,
                        x11->selection_window, CurrentTime);
     vdagent_x11_set_clipboard_owner(x11, selection, owner_client);
 
+    /* If there're pending requests for targets, ignore the returned
+     * targets as the XSetSelectionOwner() call above made them invalid */
+    x11->ignore_targets_notifies[selection] =
+        x11->expected_targets_notifies[selection];
+
     /* Flush output buffers and consume any pending events */
     vdagent_x11_do_read(x11);
 }
-- 
2.20.1