Index: sys/kern/uipc_socket.c
===================================================================
--- sys/kern/uipc_socket.c
+++ sys/kern/uipc_socket.c
@@ -1101,6 +1101,8 @@
 drop:
 	if (so->so_proto->pr_usrreqs->pru_close != NULL)
 		(*so->so_proto->pr_usrreqs->pru_close)(so);
+	if (so->so_dtor != NULL)
+		so->so_dtor(so);
 
 	SOCK_LOCK(so);
 	if ((listening = (so->so_options & SO_ACCEPTCONN))) {
Index: sys/sys/socketvar.h
===================================================================
--- sys/sys/socketvar.h
+++ sys/sys/socketvar.h
@@ -111,6 +111,7 @@
 
 	int so_ts_clock;	/* type of the clock used for timestamps */
 	uint32_t so_max_pacing_rate;	/* (f) TX rate limit in bytes/s */
+	void (*so_dtor)(struct socket *so); /* (a) optional destructor */
 	union {
 		/* Regular (data flow) socket. */
 		struct {