tcp: do not copy headers in tcp_collapse()

tcp_collapse() wants to shrink skb so that the overhead is minimal.

Now we store tcp flags into TCP_SKB_CB(skb)->tcp_flags, we no longer
need to keep around full headers.
Whole available space is dedicated to the payload.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 15 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 228bf0c5ff19..ea92f23ffaf1 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4535,26 +4535,13 @@ restart:
                 return;
 
         while (before(start, end)) {
+                int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
                 struct sk_buff *nskb;
-                unsigned int header = skb_headroom(skb);
-                int copy = SKB_MAX_ORDER(header, 0);
 
-                /* Too big header? This can happen with IPv6. */
-                if (copy < 0)
-                        return;
-                if (end - start < copy)
-                        copy = end - start;
-                nskb = alloc_skb(copy + header, GFP_ATOMIC);
+                nskb = alloc_skb(copy, GFP_ATOMIC);
                 if (!nskb)
                         return;
 
-                skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
-                skb_set_network_header(nskb, (skb_network_header(skb) -
-                                              skb->head));
-                skb_set_transport_header(nskb, (skb_transport_header(skb) -
-                                                skb->head));
-                skb_reserve(nskb, header);
-                memcpy(nskb->head, skb->head, header);
                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
                 __skb_queue_before(list, skb, nskb);