tcp: Extend SOF_TIMESTAMPING_RX_SOFTWARE to TCP recvmsg

When SOF_TIMESTAMPING_RX_SOFTWARE is enabled for tcp sockets, return the
timestamp corresponding to the highest sequence number data returned.

Previously the skb->tstamp is overwritten when a TCP packet is placed
in the out of order queue.  While the packet is in the ooo queue, save the
timestamp in the TCB_SKB_CB.  This space is shared with the gso_*
options which are only used on the tx path, and a previously unused 4
byte hole.

When skbs are coalesced either in the sk_receive_queue or the
out_of_order_queue always choose the timestamp of the appended skb to
maintain the invariant of returning the timestamp of the last byte in
the recvmsg buffer.

Signed-off-by: Mike Maloney <maloney@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index d79a1af3252e..abba3bc2a3d9 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1394,6 +1394,8 @@ static void tcp_v6_fill_cb(struct sk_buff *skb, const struct ipv6hdr *hdr,
         TCP_SKB_CB(skb)->tcp_tw_isn = 0;
         TCP_SKB_CB(skb)->ip_dsfield = ipv6_get_dsfield(hdr);
         TCP_SKB_CB(skb)->sacked = 0;
+        TCP_SKB_CB(skb)->has_rxtstamp =
+                        skb->tstamp || skb_hwtstamps(skb)->hwtstamp;
 }
 
 static int tcp_v6_rcv(struct sk_buff *skb)