Subject: Re: [DISCUSSION] rt6i_genid

From: Fan Du <[email-masked]>
Date: Thu, 18 Jul 2013 17:28:02 +0800

Thanks for replying :)

On 2013年07月18日 17:13, Nicolas Dichtel wrote:
> Le 18/07/2013 05:22, Fan Du a écrit :
>> Hello Nicolas
>>
>> Commit 6f3118b571b8a4c06c7985dc3172c3526cb86253: "ipv6: use net->rt_genid to
>> check dst validity"
>> makes ip6_dst_check to check rt6i_genid against with struct net->rt_genid,
>> As a matter of fact, struct net->rt_genid could only be modified by two places,
>> first is adding/delete IPv4 address, second is inserting new XFRM policy.
>>
>> Is there any other considerations that adding/deleting IPv4 address would
>> invalid all IPv6 dst
>> as well? because I'm working a patch which actually depends on the result of
>> this question.
> No, the goal was to cover the IPsec case, ie invalidate dst entries when an xfrm policy is inserted/deleted.

Ok, then how about we only checking rt6i_genid against rt_genid *only*
when XFRM is enabled for IPv6, because when XFRM is not enabled for IPv6
ip6_dst_check for rt_genid is really not necessary.

So what do you think of below modifications?

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 2a601e7..4ae35fd 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -119,7 +119,9 @@ struct rt6_info {
         struct inet6_dev                *rt6i_idev;
         unsigned long                   _rt6i_peer;

+#ifdef CONFIG_XFRM
         u32                             rt6i_genid;
+#endif

         /* more non-fragment space at head required */
         unsigned short                  rt6i_nfheader_len;
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index bd5fd70..1b64406 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -277,7 +277,9 @@ static inline struct rt6_info *ip6_dst_alloc(struct net *net,

                 memset(dst + 1, 0, sizeof(*rt) - sizeof(*dst));
                 rt6_init_peer(rt, table ? &table->tb6_peers : net->ipv6.peers);
+#ifdef CONFIG_XFRM
                 rt->rt6i_genid = rt_genid(net);
+#endif
                 INIT_LIST_HEAD(&rt->rt6i_siblings);
                 rt->rt6i_nsiblings = 0;
         }
@@ -1041,12 +1043,15 @@ static struct dst_entry *ip6_dst_check(struct dst_entry *dst, u32 cookie)

         rt = (struct rt6_info *) dst;

+#ifdef CONFIG_XFRM
         /* All IPV6 dsts are created with ->obsolete set to the value
          * DST_OBSOLETE_FORCE_CHK which forces validation calls down
          * into this function always.
+        * Note: for IPv6, rt6i_genid is noly used when XFRM enabled.
          */
         if (rt->rt6i_genid != rt_genid(dev_net(rt->dst.dev)))
                 return NULL;
+#endif

         if (rt->rt6i_node && (rt->rt6i_node->fn_sernum == cookie))
                 return dst;

> Regards,
> Nicolas

-- 
浮沉随浪只记今朝笑

--fan