Re: [RFC PATCH v6 net-next 2/4] tcp: refactor struct tcp_skb_cb

[Yuchung Cheng]

On Tue, Aug 25, 2015 at 4:33 PM, Lawrence Brakmo bra...@fb.com wrote:

 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 bra...@fb.com
Acked-by: Yuchung Cheng ych...@google.com

 ---
  include/net/tcp.h | 11 ---
  1 file changed, 8 insertions(+), 3 deletions(-)

 diff --git a/include/net/tcp.h b/include/net/tcp.h
 index 0121529..a086a98 100644
 --- a/include/net/tcp.h
 +++ b/include/net/tcp.h
 @@ -755,11 +755,16 @@ struct tcp_skb_cb {
 /* 1 byte hole */
 __u32   ack_seq;/* Sequence number ACK'd*/
 union {
 -   struct inet_skb_parmh4;
 +   struct {
 +   /* There is space for up to 20 bytes */
 +   } tx;   /* only used for outgoing skbs */
 +   union {
 +   struct inet_skb_parmh4;
  #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]))
 --
 1.8.1

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[RFC PATCH v6 net-next 2/4] tcp: refactor struct tcp_skb_cb

[Lawrence Brakmo]

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 bra...@fb.com
---
 include/net/tcp.h | 11 ---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 0121529..a086a98 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -755,11 +755,16 @@ struct tcp_skb_cb {
/* 1 byte hole */
__u32   ack_seq;/* Sequence number ACK'd*/
union {
-   struct inet_skb_parmh4;
+   struct {
+   /* There is space for up to 20 bytes */
+   } tx;   /* only used for outgoing skbs */
+   union {
+   struct inet_skb_parmh4;
 #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]))
-- 
1.8.1

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