dix: add getter for display name

Xrdp needs to know the current display name (for setting up it's
own server sockets accordingly). Instead of exporting an internal
field, adding a little getter for this.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1783>

dix/display.c

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: MIT OR X11
+ *
+ * Copyright © 2024 Enrico Weigelt, metux IT consult <info@metux.net>
+ */
+#include <dix-config.h>
+
+#include "dix/dix_priv.h"
+#include "include/dix.h"
+#include "include/screenint.h"
+
+const char *display = "0";
+int displayfd = -1;
+
+const char *dixGetDisplayName(ScreenPtr *pScreen)
+{
+    // pScreen currently is ignored as the value is global,
+    // but this might perhaps change in the future.
+    return display;
+}

dix/globals.c

@@ -116,7 +116,5 @@ TimeStamp currentTime;
 int defaultColorVisualClass = -1;
 int monitorResolution = 0;
 
-const char *display;
-int displayfd = -1;
 Bool explicit_display = FALSE;
 char *ConnectionInfo;

dix/meson.build

@@ -5,6 +5,7 @@ srcs_dix = [
     'cursor.c',
     'devices.c',
     'dispatch.c',
+    'display.c',
     'dixfonts.c',
     'main.c',
     'dixutils.c',

include/dix.h

@@ -407,4 +407,15 @@ IsFloating(DeviceIntPtr dev);
 
 extern _X_EXPORT void *lastGLContext;
 
+/**
+ * @brief get display string for given screen
+ *
+ * Entry point for drivers/modules that really need to know what
+ * display ID we're running on (eg. xrdp).
+ *
+ * @param pScreen pointer to ScreenRec to query.
+ * @return pointer to string, valid as long as the pScreen is, owned by DIX.
+ */
+_X_EXPORT const char *dixGetDisplayName(ScreenPtr *pScreen);
+
 #endif                          /* DIX_H */