netdev - [PATCH v2] net: tcp: fixes commit 98aaa913b4ed ("tcp: Extend SOF_TIMESTAMPING_RX

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Message-Id: <20200508005021.9998-1-kelly@onechronos.com>
Date:   Fri,  8 May 2020 00:50:21 +0000
From:   Kelly Littlepage <kelly@...chronos.com>
To:     willemdebruijn.kernel@...il.com
Cc:     davem@...emloft.net, edumazet@...gle.com, iris@...chronos.com,
        kelly@...chronos.com, kuba@...nel.org, kuznet@....inr.ac.ru,
        maloney@...gle.com, netdev@...r.kernel.org, soheil@...gle.com,
        yoshfuji@...ux-ipv6.org
Subject: [PATCH v2] net: tcp: fixes commit 98aaa913b4ed ("tcp: Extend SOF_TIMESTAMPING_RX_SOFTWARE to TCP recvmsg")

The stated intent of the original commit is to is to "return the timestamp
corresponding to the highest sequence number data returned." The current
implementation returns the timestamp for the last byte of the last fully
read skb, which is not necessarily the last byte in the recv buffer. This
patch converts behavior to the original definition, and to the behavior of
the previous draft versions of commit 98aaa913b4ed ("tcp: Extend
SOF_TIMESTAMPING_RX_SOFTWARE to TCP recvmsg") which also match this
behavior.

Co-developed-by: Iris Liu <iris@...chronos.com>
Signed-off-by: Iris Liu <iris@...chronos.com>
Signed-off-by: Kelly Littlepage <kelly@...chronos.com>
---
Thanks and credit to Willem de Bruijn for the revised commit language

 net/ipv4/tcp.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 6d87de434377..e72bd651d21a 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2154,13 +2154,15 @@ int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
 			tp->urg_data = 0;
 			tcp_fast_path_check(sk);
 		}
-		if (used + offset < skb->len)
-			continue;
 
 		if (TCP_SKB_CB(skb)->has_rxtstamp) {
 			tcp_update_recv_tstamps(skb, &tss);
 			cmsg_flags |= 2;
 		}
+
+		if (used + offset < skb->len)
+			continue;
+
 		if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
 			goto found_fin_ok;
 		if (!(flags & MSG_PEEK))
-- 
2.26.2


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