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.

See also added inline comment and #236

Author: HW42

gui-agent/Makefile

@@ -23,9 +23,9 @@ CC ?= gcc
 CFLAGS += -I../include/ `pkg-config --cflags vchan` -g -Wall -Wextra -Werror -fPIC \
 	  -Wmissing-prototypes -Wstrict-prototypes -Wold-style-declaration \
 	  -Wold-style-definition
-OBJS = vmside.o txrx-vchan.o error.o list.o encoding.o
+OBJS = vmside.o txrx-vchan.o error.o list.o encoding.o video-ext-client.o
 LIBS = -lX11 -lXdamage -lXcomposite -lXfixes `pkg-config --libs vchan` -lqubesdb \
-	   -lunistring
+	   -lunistring -lXext
 
 
 all: qubes-gui qubes-gui-runuser

gui-agent/video-ext-client.c

@@ -0,0 +1,117 @@
+/*
+ * The Qubes OS Project, https://www.qubes-os.org/
+ *
+ * Copyright (C) 2025  Simon Gaiser <simon@invisiblethingslab.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "video-ext-client.h"
+
+#include <X11/Xlibint.h>
+#include <X11/extensions/Xext.h>
+#include <X11/extensions/extutil.h>
+
+static int close_display(Display *dpy, XExtCodes *codes);
+static Bool wire_to_event(Display *dpy, XEvent *libEv, xEvent *wireEv);
+
+static XExtensionHooks ext_hooks = {
+    NULL,          // create_gc
+    NULL,          // copy_gc
+    NULL,          // flush_gc
+    NULL,          // free_gc
+    NULL,          // create_font
+    NULL,          // free_font
+    close_display, // close_display
+    wire_to_event, // wire_to_event
+    NULL,          // event_to_wire (we don't need SendEvent)
+    NULL,          // error
+    NULL,          // error_string
+};
+
+static XExtensionInfo _ext_info;
+static XExtensionInfo *ext_info = &_ext_info;
+static const char * ext_name = QVE_NAME;
+
+#define QVECheckExtension(dpy, info, val) \
+    XextCheckExtension(dpy, info, ext_name, val)
+
+static XEXT_GENERATE_FIND_DISPLAY(find_display,
+                                  ext_info,
+                                  ext_name,
+                                  &ext_hooks,
+                                  QVENumberEvents,
+                                  NULL);
+
+static XEXT_GENERATE_CLOSE_DISPLAY(close_display, ext_info);
+
+static Bool
+wire_to_event(Display *dpy, XEvent *libEv, xEvent *wireEv)
+{
+    XExtDisplayInfo *info = find_display(dpy);
+
+    QVECheckExtension(dpy, info, False);
+
+    BYTE type = wireEv->u.u.type;
+    if ((type & 0x7f) != info->codes->first_event + QVEWindowRealized) {
+        return False;
+    }
+
+    XQVEWindowRealizedEvent *qLibEv = (XQVEWindowRealizedEvent *)libEv;
+    xQVEWindowRealizedEvent *qWireEv = (xQVEWindowRealizedEvent *)wireEv;
+
+    qLibEv->type = type & 0x7f;
+    qLibEv->serial = _XSetLastRequestRead(dpy, (xGenericReply *)wireEv);
+    qLibEv->send_event = (type & 0x80) != 0;
+    qLibEv->display = dpy;
+    qLibEv->window = qWireEv->window;
+    qLibEv->unrealized =
+        (qWireEv->detail & QVEWindowRealizedDetailUnrealized) != 0;
+
+    return True;
+}
+
+Bool
+XQVEQueryExtension(Display *dpy, int *event_base)
+{
+    XExtDisplayInfo *info = find_display(dpy);
+
+    if (!XextHasExtension(info)) {
+        return False;
+    }
+
+    *event_base = info->codes->first_event;
+    return True;
+}
+
+Bool
+XQVERegister(Display *dpy)
+{
+    XExtDisplayInfo *info = find_display(dpy);
+
+    QVECheckExtension(dpy, info, False);
+
+    LockDisplay(dpy);
+    xQVEReq *req;
+#define X_QVE X_QVERegister
+    GetReq(QVE, req);
+#undef X_QVE
+    req->reqType = info->codes->major_opcode;
+    req->QVEReqType = X_QVERegister;
+    UnlockDisplay(dpy);
+    SyncHandle();
+
+    return True;
+}

gui-agent/video-ext-client.h

@@ -0,0 +1,36 @@
+/*
+ * The Qubes OS Project, https://www.qubes-os.org/
+ *
+ * Copyright (C) 2025  Simon Gaiser <simon@invisiblethingslab.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#pragma once
+
+#include "qubes-video-ext.h"
+#include <X11/Xlib.h>
+
+typedef struct {
+    int type;
+    unsigned long serial;
+    Bool send_event;
+    Display *display;
+    Window window;
+    Bool unrealized;
+} XQVEWindowRealizedEvent;
+
+Bool XQVERegister(Display *dpy);
+Bool XQVEQueryExtension(Display *dpy, int *event_base);