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tcp: refactor struct tcp_skb_cb

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Refactor tcp_skb_cb to create two overlaping areas to store
state for incoming or outgoing skbs based on comments by
Neal Cardwell to tcp_nv patch:

   AFAICT this patch would not require an increase in the size of
   sk_buff cb[] if it were to take advantage of the fact that the
   tcp_skb_cb header.h4 and header.h6 fields are only used in the packet
   reception code path, and this in_flight field is only used on the
   transmit side.

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Lawrence Brakmo 2016-05-06 20:35:35 -07:00 committed by David S. Miller
parent 7d94579675
commit b75803d52a
1 changed files with 8 additions and 3 deletions
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11
include/net/tcp.h
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@ -765,11 +765,16 @@ struct tcp_skb_cb {
unused:6;
__u32 ack_seq; /* Sequence number ACK'd */
union {
struct inet_skb_parm h4;
struct {
/* There is space for up to 20 bytes */
} tx; /* only used for outgoing skbs */
union {
struct inet_skb_parm h4;
#if IS_ENABLED(CONFIG_IPV6)
struct inet6_skb_parm h6;
struct inet6_skb_parm h6;
#endif
} header; /* For incoming frames */
} header; /* For incoming skbs */
};
};
#define TCP_SKB_CB(__skb) ((struct tcp_skb_cb *)&((__skb)->cb[0]))