ipv6: use skb_expand_head in ip6_finish_output2

Unlike skb_realloc_headroom, new helper skb_expand_head does not allocate
a new skb if possible.

Additionally this patch replaces commonly used dereferencing with variables.

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index d72347c..3fa5891 100644 (file)
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -60,46 +60,29 @@ static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *
 {
        struct dst_entry *dst = skb_dst(skb);
        struct net_device *dev = dst->dev;
+       struct inet6_dev *idev = ip6_dst_idev(dst);
        unsigned int hh_len = LL_RESERVED_SPACE(dev);
-       int delta = hh_len - skb_headroom(skb);
-       const struct in6_addr *nexthop;
+       const struct in6_addr *daddr, *nexthop;
+       struct ipv6hdr *hdr;
        struct neighbour *neigh;
        int ret;
 
        /* Be paranoid, rather than too clever. */
-       if (unlikely(delta > 0) && dev->header_ops) {
-               /* pskb_expand_head() might crash, if skb is shared */
-               if (skb_shared(skb)) {
-                       struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
-
-                       if (likely(nskb)) {
-                               if (skb->sk)
-                                       skb_set_owner_w(nskb, skb->sk);
-                               consume_skb(skb);
-                       } else {
-                               kfree_skb(skb);
-                       }
-                       skb = nskb;
-               }
-               if (skb &&
-                   pskb_expand_head(skb, SKB_DATA_ALIGN(delta), 0, GFP_ATOMIC)) {
-                       kfree_skb(skb);
-                       skb = NULL;
-               }
+       if (unlikely(hh_len > skb_headroom(skb)) && dev->header_ops) {
+               skb = skb_expand_head(skb, hh_len);
                if (!skb) {
-                       IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTDISCARDS);
+                       IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTDISCARDS);
                        return -ENOMEM;
                }
        }
 
-       if (ipv6_addr_is_multicast(&ipv6_hdr(skb)->daddr)) {
-               struct inet6_dev *idev = ip6_dst_idev(skb_dst(skb));
-
+       hdr = ipv6_hdr(skb);
+       daddr = &hdr->daddr;
+       if (ipv6_addr_is_multicast(daddr)) {
                if (!(dev->flags & IFF_LOOPBACK) && sk_mc_loop(sk) &&
                    ((mroute6_is_socket(net, skb) &&
                     !(IP6CB(skb)->flags & IP6SKB_FORWARDED)) ||
-                    ipv6_chk_mcast_addr(dev, &ipv6_hdr(skb)->daddr,
-                                        &ipv6_hdr(skb)->saddr))) {
+                    ipv6_chk_mcast_addr(dev, daddr, &hdr->saddr))) {
                        struct sk_buff *newskb = skb_clone(skb, GFP_ATOMIC);
 
                        /* Do not check for IFF_ALLMULTI; multicast routing
@@ -110,7 +93,7 @@ static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *
                                        net, sk, newskb, NULL, newskb->dev,
                                        dev_loopback_xmit);
 
-                       if (ipv6_hdr(skb)->hop_limit == 0) {
+                       if (hdr->hop_limit == 0) {
                                IP6_INC_STATS(net, idev,
                                              IPSTATS_MIB_OUTDISCARDS);
                                kfree_skb(skb);
@@ -119,9 +102,7 @@ static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *
                }
 
                IP6_UPD_PO_STATS(net, idev, IPSTATS_MIB_OUTMCAST, skb->len);
-
-               if (IPV6_ADDR_MC_SCOPE(&ipv6_hdr(skb)->daddr) <=
-                   IPV6_ADDR_SCOPE_NODELOCAL &&
+               if (IPV6_ADDR_MC_SCOPE(daddr) <= IPV6_ADDR_SCOPE_NODELOCAL &&
                    !(dev->flags & IFF_LOOPBACK)) {
                        kfree_skb(skb);
                        return 0;
@@ -136,10 +117,10 @@ static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *
        }
 
        rcu_read_lock_bh();
-       nexthop = rt6_nexthop((struct rt6_info *)dst, &ipv6_hdr(skb)->daddr);
-       neigh = __ipv6_neigh_lookup_noref(dst->dev, nexthop);
+       nexthop = rt6_nexthop((struct rt6_info *)dst, daddr);
+       neigh = __ipv6_neigh_lookup_noref(dev, nexthop);
        if (unlikely(!neigh))
-               neigh = __neigh_create(&nd_tbl, nexthop, dst->dev, false);
+               neigh = __neigh_create(&nd_tbl, nexthop, dev, false);
        if (!IS_ERR(neigh)) {
                sock_confirm_neigh(skb, neigh);
                ret = neigh_output(neigh, skb, false);
@@ -148,7 +129,7 @@ static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *
        }
        rcu_read_unlock_bh();
 
-       IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_OUTNOROUTES);
+       IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTNOROUTES);
        kfree_skb(skb);
        return -EINVAL;
 }