Re: [PATCH v2 net-next] ipv6: sit: Add ipip6_tunnel_dst_find() for cleanup

[Yue Haibing <yuehaibing@huawei.com>]

On 2025/8/29 23:46, Alexander Lobakin wrote:
> From: Yue Haibing <yuehaibing@huawei.com>
> Date: Fri, 29 Aug 2025 18:09:46 +0800
> 
>> Extract the dst lookup logic from ipip6_tunnel_xmit() into new helper
>> ipip6_tunnel_dst_find() to reduce code duplication and enhance readability.
>> No functional change intended.
> 
> Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> 
>>
>> On a x86_64, with allmodconfig object size is also reduced:
>>
>> ./scripts/bloat-o-meter net/ipv6/sit.o net/ipv6/sit-new.o
>> add/remove: 5/3 grow/shrink: 3/4 up/down: 1841/-2275 (-434)
>> Function                                     old     new   delta
>> ipip6_tunnel_dst_find                          -    1697   +1697
>> __pfx_ipip6_tunnel_dst_find                    -      64     +64
>> __UNIQUE_ID_modinfo2094                        -      43     +43
>> ipip6_tunnel_xmit.isra.cold                   79      88      +9
>> __UNIQUE_ID_modinfo2096                       12      20      +8
>> __UNIQUE_ID___addressable_init_module2092       -       8      +8
>> __UNIQUE_ID___addressable_cleanup_module2093       -       8      +8
>> __func__                                      55      59      +4
>> __UNIQUE_ID_modinfo2097                       20      18      -2
>> __UNIQUE_ID___addressable_init_module2093       8       -      -8
>> __UNIQUE_ID___addressable_cleanup_module2094       8       -      -8
>> __UNIQUE_ID_modinfo2098                       18       -     -18
>> __UNIQUE_ID_modinfo2095                       43      12     -31
>> descriptor                                   112      56     -56
>> ipip6_tunnel_xmit.isra                      9910    7758   -2152
>> Total: Before=72537, After=72103, chg -0.60%
>>
>> Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
>> ---
>> v2: add newlines before return in ipip6_tunnel_dst_find()
>>     add bloat-o-meter info in commit log
>> ---
>>  net/ipv6/sit.c | 95 ++++++++++++++++++++++++--------------------------
>>  1 file changed, 45 insertions(+), 50 deletions(-)
>>
>> diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
>> index 12496ba1b7d4..60bd7f01fa09 100644
>> --- a/net/ipv6/sit.c
>> +++ b/net/ipv6/sit.c
>> @@ -848,6 +848,49 @@ static inline __be32 try_6rd(struct ip_tunnel *tunnel,
>>  	return dst;
>>  }
>>  
>> +static bool ipip6_tunnel_dst_find(struct sk_buff *skb, __be32 *dst,
>> +				  bool is_isatap)
>> +{
>> +	const struct ipv6hdr *iph6 = ipv6_hdr(skb);
>> +	struct neighbour *neigh = NULL;
>> +	const struct in6_addr *addr6;
>> +	bool found = false;
>> +	int addr_type;
>> +
>> +	if (skb_dst(skb))
>> +		neigh = dst_neigh_lookup(skb_dst(skb), &iph6->daddr);
>> +
>> +	if (!neigh) {
>> +		net_dbg_ratelimited("nexthop == NULL\n");
>> +		return false;
>> +	}
>> +
>> +	addr6 = (const struct in6_addr *)&neigh->primary_key;
>> +	addr_type = ipv6_addr_type(addr6);
>> +
>> +	if (is_isatap) {
>> +		if ((addr_type & IPV6_ADDR_UNICAST) &&
>> +		    ipv6_addr_is_isatap(addr6)) {
>> +			*dst = addr6->s6_addr32[3];
>> +			found = true;
>> +		}
>> +	} else {
>> +		if (addr_type == IPV6_ADDR_ANY) {
>> +			addr6 = &ipv6_hdr(skb)->daddr;
>> +			addr_type = ipv6_addr_type(addr6);
>> +		}
>> +
>> +		if ((addr_type & IPV6_ADDR_COMPATv4) != 0) {
>> +			*dst = addr6->s6_addr32[3];
>> +			found = true;
>> +		}
>> +	}
>> +
>> +	neigh_release(neigh);
>> +
>> +	return found;
>> +}
>> +
>>  /*
>>   *	This function assumes it is being called from dev_queue_xmit()
>>   *	and that skb is filled properly by that function.
>> @@ -867,8 +910,6 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
>>  	__be32 dst = tiph->daddr;
>>  	struct flowi4 fl4;
>>  	int    mtu;
>> -	const struct in6_addr *addr6;
>> -	int addr_type;
>>  	u8 ttl;
>>  	u8 protocol = IPPROTO_IPV6;
>>  	int t_hlen = tunnel->hlen + sizeof(struct iphdr);
>> @@ -878,28 +919,7 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
>>  
>>  	/* ISATAP (RFC4214) - must come before 6to4 */
>>  	if (dev->priv_flags & IFF_ISATAP) {
>> -		struct neighbour *neigh = NULL;
>> -		bool do_tx_error = false;
>> -
>> -		if (skb_dst(skb))
>> -			neigh = dst_neigh_lookup(skb_dst(skb), &iph6->daddr);
>> -
>> -		if (!neigh) {
>> -			net_dbg_ratelimited("nexthop == NULL\n");
>> -			goto tx_error;
>> -		}
>> -
>> -		addr6 = (const struct in6_addr *)&neigh->primary_key;
>> -		addr_type = ipv6_addr_type(addr6);
>> -
>> -		if ((addr_type & IPV6_ADDR_UNICAST) &&
>> -		     ipv6_addr_is_isatap(addr6))
>> -			dst = addr6->s6_addr32[3];
>> -		else
>> -			do_tx_error = true;
>> -
>> -		neigh_release(neigh);
>> -		if (do_tx_error)
>> +		if (!ipip6_tunnel_dst_find(skb, &dst, true))
>>  			goto tx_error;
>>  	}
> 
> Ooops, sorry that I didn't notice that before.
> You can flatten the conditions now:

Sorry for miss this, will resend with proposed changes, thanks.
> 
> 	if ((dev->priv_flags & IFF_ISATAP) &&
> 	    !ipip6_tunnel_dst_find(skb, &dst, true))
> 		goto tx_error;
> 
>>  
>> @@ -907,32 +927,7 @@ static netdev_tx_t ipip6_tunnel_xmit(struct sk_buff *skb,
>>  		dst = try_6rd(tunnel, &iph6->daddr);
>>  
>>  	if (!dst) {
>> -		struct neighbour *neigh = NULL;
>> -		bool do_tx_error = false;
>> -
>> -		if (skb_dst(skb))
>> -			neigh = dst_neigh_lookup(skb_dst(skb), &iph6->daddr);
>> -
>> -		if (!neigh) {
>> -			net_dbg_ratelimited("nexthop == NULL\n");
>> -			goto tx_error;
>> -		}
>> -
>> -		addr6 = (const struct in6_addr *)&neigh->primary_key;
>> -		addr_type = ipv6_addr_type(addr6);
>> -
>> -		if (addr_type == IPV6_ADDR_ANY) {
>> -			addr6 = &ipv6_hdr(skb)->daddr;
>> -			addr_type = ipv6_addr_type(addr6);
>> -		}
>> -
>> -		if ((addr_type & IPV6_ADDR_COMPATv4) != 0)
>> -			dst = addr6->s6_addr32[3];
>> -		else
>> -			do_tx_error = true;
>> -
>> -		neigh_release(neigh);
>> -		if (do_tx_error)
>> +		if (!ipip6_tunnel_dst_find(skb, &dst, false))
>>  			goto tx_error;
>>  	}
> 
> Same here:
> 
> 	if (!dst && !ipip6_tunnel_dst_find(skb, &dst, false))
> 		goto tx_error;
> 
> Thanks,
> Olek
>