Don't try to send grants for not realized windows

We rely on composite redirect mode of the X server to get per window
pixmaps. Those are setup/teared-down in compRealizeWindow/
compUnrealizeWindow (via compCheckRedirect).

So not realized windows don't have a per window pixmap. Sending grant
refs for them was always broken since we didn't send the offset into the
screen pixmap in those cases. But with the recent change to not allocate
grant refs for the screen pixmap this leads to a noticable error
message.

So don't try to send grant refs for not realized windows. This means
that the configure before mapping will not contiain grant refs.

We rely here very much on implementation details of the X server. In
particular we require that a damage event is generated after the windows
is realized. Note that the map event is generated before realization.
Additionally we require that no damage event is delivered between the
map notification the window being realized.

Based on experimentation and code reading that seems to hold (what
exactly triggers the first damage event after map depends on background
settings and cursor position). This matches also that we so far haven't
had problems even though this bug has been present for a long time.

Author: HW42

gui-agent/vmside.c

@@ -150,6 +150,7 @@ struct window_data {
     int support_delete_window;
     int support_take_focus;
     int window_dump_pending; /* send MSG_WINDOW_DUMP at next damage notification */
+    int mapped;
 };
 
 struct embeder_data {
@@ -492,6 +493,7 @@ static void process_xevent_createnotify(Ghandles * g, XCreateWindowEvent * ev)
     wd->support_delete_window = False;
     wd->support_take_focus = False;
     wd->window_dump_pending = False;
+    wd->mapped = False;
     list_insert(windows_list, ev->window, wd);
 
     if (attr.border_width > 0) {
@@ -911,6 +913,7 @@ static void process_xevent_map(Ghandles * g, XID window)
 
     if (g->log_level > 1)
         fprintf(stderr, "MAP for window 0x%lx\n", window);
+    wd->mapped = True;
     wd->window_dump_pending = True;
     send_window_state(g, window);
     XGetWindowAttributes(g->display, window, &attr);
@@ -935,13 +938,19 @@ static void process_xevent_map(Ghandles * g, XID window)
 static void process_xevent_unmap(Ghandles * g, XID window)
 {
     struct msg_hdr hdr;
+    struct genlist *l;
+    struct window_data *wd;
 
-    if (!lookup_window(g, windows_list, window, __func__)) {
+    l = lookup_window(g, windows_list, window, __func__);
+    if (!l) {
         return;
     }
 
+    wd = l->data;
+
     if (g->log_level > 1)
         fprintf(stderr, "UNMAP for window 0x%lx\n", window);
+    wd->mapped = False;
     hdr.type = MSG_UNMAP;
     hdr.window = window;
     hdr.untrusted_len = 0;
@@ -989,21 +998,25 @@ static void process_xevent_configure(Ghandles * g, XID window,
     struct msg_configure conf;
     struct genlist *l;
     struct window_data *wd = NULL;
+    int mapped = False;
 
     l = lookup_window(g, windows_list, window, NULL);
     if (l) {
         wd = l->data;
+        mapped = wd->mapped;
     } else {
         /* if not real managed window, check if this is embeder for another window */
         struct genlist *e = lookup_window(g, embeder_list, window, NULL);
         if (e) {
+            struct genlist *i;
             window = ((struct embeder_data*)e->data)->icon_window;
-            if (!list_lookup(windows_list, window))
+            if (!(i = list_lookup(windows_list, window)))
                 /* probably icon window have just destroyed, so ignore message */
                 return;
             /* l and wd not updated intentionally - when configure notify comes
              * from the embeder, it should be passed to dom0 (in most cases as
              * ACK for earlier configure request) */
+            mapped = ((struct window_data*)i->data)->mapped;
         } else {
             /* ignore not managed windows */
             log_unmanaged_window(g, __func__, window);
@@ -1047,7 +1060,10 @@ static void process_xevent_configure(Ghandles * g, XID window,
     conf.height = ev->height;
     conf.override_redirect = ev->override_redirect;
     write_message(g->vchan, hdr, conf);
-    send_pixmap_grant_refs(g, window);
+    if (mapped) {
+        // see comment in dump_window_grant_refs in the xdriver
+        send_pixmap_grant_refs(g, window);
+    }
 }
 
 static void send_clipboard_data(libvchan_t *vchan, XID window, char *data, uint32_t len, int protocol_version)

xf86-input-mfndev/src/qubes.c

@@ -604,6 +604,19 @@ static void dump_window_grant_refs(int window_id, int fd)
         // the window is destroyed before the driver sees the req
         goto send_response;
 
+    if (!x_window->realized) {
+        // Composite redirect is setup/teared-down during Realize-/Unrealize-
+        // Window (called when a window gets mapped/unmapped). So if the window
+        // is not realized we don't have a per window pixmap we can send.
+        //
+        // This means that the configure of a window before mapping will not
+        // send grants. This should be fine since when compRealizeWindow
+        // replaces the pixmap it will trigger a damage event and we will send
+        // the grants then.
+        xf86Msg(X_ERROR, "can't dump not realized window\n");
+        goto send_response;
+    }
+
     screen = x_window->drawable.pScreen;
     pixmap = (*screen->GetWindowPixmap) (x_window);