+// ========== User Data ==============
+XBT_PUBLIC(void*) sg_host_user(sg_host_t host);
+XBT_PUBLIC(void) sg_host_user_set(sg_host_t host, void* userdata);
+XBT_PUBLIC(void) sg_host_user_destroy(sg_host_t host);
+
+// ========== MSG Layer ==============
+typedef struct s_msg_host_priv *msg_host_priv_t;
+msg_host_priv_t sg_host_msg(sg_host_t host);
+XBT_PUBLIC(void) sg_host_msg_set(sg_host_t host, msg_host_priv_t priv);
+
+// ========== Simix layer =============
+typedef struct s_smx_host_priv *smx_host_priv_t;