[IPSEC]: Kill obsolete get_mss function

Now that we've switched over to storing MTUs in the xfrm_dst entries,
we no longer need the dst's get_mss methods.  This patch gets rid of
them.

It also documents the fact that our MTU calculation is not optimal
for ESP.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>

include/net/dst.h

@@ -94,7 +94,6 @@ struct dst_ops
 	struct dst_entry *	(*negative_advice)(struct dst_entry *);
 	void			(*link_failure)(struct sk_buff *);
 	void			(*update_pmtu)(struct dst_entry *dst, u32 mtu);
-	int			(*get_mss)(struct dst_entry *dst, u32 mtu);
 	int			entry_size;
 
 	atomic_t		entries;

net/xfrm/xfrm_policy.c

@@ -1192,46 +1192,6 @@ int xfrm_bundle_ok(struct xfrm_dst *first, struct flowi *fl, int family)
 
 EXPORT_SYMBOL(xfrm_bundle_ok);
 
-/* Well... that's _TASK_. We need to scan through transformation
- * list and figure out what mss tcp should generate in order to
- * final datagram fit to mtu. Mama mia... :-)
- *
- * Apparently, some easy way exists, but we used to choose the most
- * bizarre ones. :-) So, raising Kalashnikov... tra-ta-ta.
- *
- * Consider this function as something like dark humour. :-)
- */
-static int xfrm_get_mss(struct dst_entry *dst, u32 mtu)
-{
-	int res = mtu - dst->header_len;
-
-	for (;;) {
-		struct dst_entry *d = dst;
-		int m = res;
-
-		do {
-			struct xfrm_state *x = d->xfrm;
-			if (x) {
-				spin_lock_bh(&x->lock);
-				if (x->km.state == XFRM_STATE_VALID &&
-				    x->type && x->type->get_max_size)
-					m = x->type->get_max_size(d->xfrm, m);
-				else
-					m += x->props.header_len;
-				spin_unlock_bh(&x->lock);
-			}
-		} while ((d = d->child) != NULL);
-
-		if (m <= mtu)
-			break;
-		res -= (m - mtu);
-		if (res < 88)
-			return mtu;
-	}
-
-	return res + dst->header_len;
-}
-
 int xfrm_policy_register_afinfo(struct xfrm_policy_afinfo *afinfo)
 {
 	int err = 0;
@@ -1252,8 +1212,6 @@ int xfrm_policy_register_afinfo(struct xfrm_policy_afinfo *afinfo)
 			dst_ops->negative_advice = xfrm_negative_advice;
 		if (likely(dst_ops->link_failure == NULL))
 			dst_ops->link_failure = xfrm_link_failure;
-		if (likely(dst_ops->get_mss == NULL))
-			dst_ops->get_mss = xfrm_get_mss;
 		if (likely(afinfo->garbage_collect == NULL))
 			afinfo->garbage_collect = __xfrm_garbage_collect;
 		xfrm_policy_afinfo[afinfo->family] = afinfo;
@@ -1281,7 +1239,6 @@ int xfrm_policy_unregister_afinfo(struct xfrm_policy_afinfo *afinfo)
 			dst_ops->check = NULL;
 			dst_ops->negative_advice = NULL;
 			dst_ops->link_failure = NULL;
-			dst_ops->get_mss = NULL;
 			afinfo->garbage_collect = NULL;
 		}
 	}

net/xfrm/xfrm_state.c

@@ -1026,6 +1026,12 @@ void xfrm_state_delete_tunnel(struct xfrm_state *x)
 }
 EXPORT_SYMBOL(xfrm_state_delete_tunnel);
 
+/*
+ * This function is NOT optimal.  For example, with ESP it will give an
+ * MTU that's usually two bytes short of being optimal.  However, it will
+ * usually give an answer that's a multiple of 4 provided the input is
+ * also a multiple of 4.
+ */
 int xfrm_state_mtu(struct xfrm_state *x, int mtu)
 {
 	int res = mtu;