tcp: allow tcp_sacktag_one() to tag ranges not aligned with skbs

This commit allows callers of tcp_sacktag_one() to pass in sequence
ranges that do not align with skb boundaries, as tcp_shifted_skb()
needs to do in an upcoming fix in this patch series.

In fact, now tcp_sacktag_one() does not need to depend on an input skb
at all, which makes its semantics and dependencies more clear.

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

1 files changed, 22 insertions, 14 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 976034f82320..4e8a81fda65c 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1307,25 +1307,26 @@ static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
         return in_sack;
 }
 
-static u8 tcp_sacktag_one(const struct sk_buff *skb, struct sock *sk,
-                          struct tcp_sacktag_state *state,
+/* Mark the given newly-SACKed range as such, adjusting counters and hints. */
+static u8 tcp_sacktag_one(struct sock *sk,
+                          struct tcp_sacktag_state *state, u8 sacked,
+                          u32 start_seq, u32 end_seq,
                           int dup_sack, int pcount)
 {
         struct tcp_sock *tp = tcp_sk(sk);
-        u8 sacked = TCP_SKB_CB(skb)->sacked;
         int fack_count = state->fack_count;
 
         /* Account D-SACK for retransmitted packet. */
         if (dup_sack && (sacked & TCPCB_RETRANS)) {
                 if (tp->undo_marker && tp->undo_retrans &&
-                    after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
+                    after(end_seq, tp->undo_marker))
                         tp->undo_retrans--;
                 if (sacked & TCPCB_SACKED_ACKED)
                         state->reord = min(fack_count, state->reord);
         }
 
         /* Nothing to do; acked frame is about to be dropped (was ACKed). */
-        if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
+        if (!after(end_seq, tp->snd_una))
                 return sacked;
 
         if (!(sacked & TCPCB_SACKED_ACKED)) {
@@ -1344,13 +1345,13 @@ static u8 tcp_sacktag_one(const struct sk_buff *skb, struct sock *sk,
                                 /* New sack for not retransmitted frame,
                                  * which was in hole. It is reordering.
                                  */
-                                if (before(TCP_SKB_CB(skb)->seq,
+                                if (before(start_seq,
                                            tcp_highest_sack_seq(tp)))
                                         state->reord = min(fack_count,
                                                            state->reord);
 
                                 /* SACK enhanced F-RTO (RFC4138; Appendix B) */
-                                if (!after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark))
+                                if (!after(end_seq, tp->frto_highmark))
                                         state->flag |= FLAG_ONLY_ORIG_SACKED;
                         }
 
@@ -1368,8 +1369,7 @@ static u8 tcp_sacktag_one(const struct sk_buff *skb, struct sock *sk,
 
                 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
                 if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
-                    before(TCP_SKB_CB(skb)->seq,
-                           TCP_SKB_CB(tp->lost_skb_hint)->seq))
+                    before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
                         tp->lost_cnt_hint += pcount;
 
                 if (fack_count > tp->fackets_out)
@@ -1425,7 +1425,11 @@ static int tcp_shifted_skb(struct sock *sk, struct sk_buff *skb,
         }
 
         /* We discard results */
-        tcp_sacktag_one(skb, sk, state, dup_sack, pcount);
+        tcp_sacktag_one(sk, state,
+                        TCP_SKB_CB(skb)->sacked,
+                        TCP_SKB_CB(skb)->seq,
+                        TCP_SKB_CB(skb)->end_seq,
+                        dup_sack, pcount);
 
         /* Difference in this won't matter, both ACKed by the same cumul. ACK */
         TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
@@ -1664,10 +1668,14 @@ static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
                         break;
 
                 if (in_sack) {
-                        TCP_SKB_CB(skb)->sacked = tcp_sacktag_one(skb, sk,
-                                                                  state,
-                                                                  dup_sack,
-                                                                  tcp_skb_pcount(skb));
+                        TCP_SKB_CB(skb)->sacked =
+                                tcp_sacktag_one(sk,
+                                                state,
+                                                TCP_SKB_CB(skb)->sacked,
+                                                TCP_SKB_CB(skb)->seq,
+                                                TCP_SKB_CB(skb)->end_seq,
+                                                dup_sack,
+                                                tcp_skb_pcount(skb));
 
                         if (!before(TCP_SKB_CB(skb)->seq,
                                     tcp_highest_sack_seq(tp)))