xnest: use own dev-privates key for per-screen cursor

Since it's storing an locally defined (ddx-internal) struct, it's better
not to abuse some globally defined key for this.

It just happened to work before, since CursorScreenKey is only used by DDX
(and there's only one DDX per executable) and they currently (!) have the
same size (pointer) - but that's a fragile programming style, so clean it up.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1342>
(cherry picked from commit 49d139344d)

hw/xnest/Cursor.c

@@ -21,7 +21,6 @@ is" without express or implied warranty.
 #include "screenint.h"
 #include "input.h"
 #include "misc.h"
-#include "cursor.h"
 #include "cursorstr.h"
 #include "scrnintstr.h"
 #include "servermd.h"

hw/xnest/Screen.c

@@ -45,6 +45,7 @@ is" without express or implied warranty.
 Window xnestDefaultWindows[MAXSCREENS];
 Window xnestScreenSaverWindows[MAXSCREENS];
 DevPrivateKeyRec xnestScreenCursorFuncKeyRec;
+DevScreenPrivateKeyRec xnestScreenCursorPrivKeyRec;
 
 ScreenPtr
 xnestScreen(Window window)
@@ -158,6 +159,10 @@ xnestOpenScreen(ScreenPtr pScreen, int argc, char *argv[])
     if (!dixRegisterPrivateKey(&xnestScreenCursorFuncKeyRec, PRIVATE_SCREEN, 0))
         return FALSE;
 
+    if (!dixRegisterScreenPrivateKey(&xnestScreenCursorPrivKeyRec, pScreen,
+                                     PRIVATE_CURSOR, 0))
+        return FALSE;
+
     visuals = xallocarray(xnestNumVisuals, sizeof(VisualRec));
     numVisuals = 0;
 

hw/xnest/XNCursor.h

@@ -30,11 +30,16 @@ typedef struct {
     Cursor cursor;
 } xnestPrivCursor;
 
+// stores xnestPrivCursor per screen's cursor
+extern DevScreenPrivateKeyRec xnestScreenCursorPrivKeyRec;
+
 #define xnestGetCursorPriv(pCursor, pScreen) ((xnestPrivCursor *) \
-    dixLookupScreenPrivate(&(pCursor)->devPrivates, CursorScreenKey, pScreen))
+    dixLookupScreenPrivate(&(pCursor)->devPrivates, \
+                           &xnestScreenCursorPrivKeyRec, pScreen))
 
 #define xnestSetCursorPriv(pCursor, pScreen, v) \
-    dixSetScreenPrivate(&(pCursor)->devPrivates, CursorScreenKey, pScreen, v)
+    dixSetScreenPrivate(&(pCursor)->devPrivates, \
+                        &xnestScreenCursorPrivKeyRec, pScreen, v)
 
 #define xnestCursor(pCursor, pScreen) \
   (xnestGetCursorPriv(pCursor, pScreen)->cursor)