Enhance debug logging of SHM related functions

common/os_calls.c

@@ -3322,12 +3322,12 @@ g_text2bool(const char *s)
 }
 
 /*****************************************************************************/
-/* returns pointer or nil on error */
+/* returns pointer or -1 on error */
 void * APP_CC
 g_shmat(int shmid)
 {
 #if defined(_WIN32)
-    return 0;
+    return -1;
 #else
      return shmat(shmid, 0, 0);
 #endif

xup/xup.c

@@ -32,6 +32,7 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <netdb.h>
+#include <errno.h>
 
 /******************************************************************************/
 /**
@@ -1202,6 +1203,7 @@ process_server_paint_rect_shmem(struct mod *amod, struct stream *s)
             amod->screen_shmem_id = 0;
             amod->screen_shmem_pixels = 0;
             amod->screen_shmem_id_mapped = 0;
+            log_message(LOG_LEVEL_ERROR, "g_shmat() returned error, errno: %d\nIs X11rdp running on the same host as xrdp?\n", errno);
         }
         else
         {
@@ -1313,6 +1315,7 @@ process_server_paint_rect_shmem_ex(struct mod *amod, struct stream *s)
                 amod->screen_shmem_id = 0;
                 amod->screen_shmem_pixels = 0;
                 amod->screen_shmem_id_mapped = 0;
+                log_message(LOG_LEVEL_ERROR, "g_shmat() returned error, errno: %d\nIs X11rdp running on the same host as xrdp?\n", errno);
             }
             else
             {