netdev - [PATCH net-next v4 5/5] net-timestamp: ACK timestamp for bytestreams

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Date:	Wed, 30 Jul 2014 11:48:48 -0400
From:	Willem de Bruijn <willemb@...gle.com>
To:	netdev@...r.kernel.org
Cc:	davem@...emloft.net, eric.dumazet@...il.com,
	richardcochran@...il.com, Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH net-next v4 5/5] net-timestamp: ACK timestamp for bytestreams

Add SOF_TIMESTAMPING_TX_ACK, a request for a tstamp when the last byte
in the send() call is acknowledged. It implements the feature for TCP.

The timestamp is generated when the TCP socket cumulative ACK is moved
beyond the tracked seqno for the first time. The feature ignores SACK
and FACK, because those acknowledge the specific byte, but not
necessarily the entire contents of the buffer up to that byte.

Signed-off-by: Willem de Bruijn <willemb@...gle.com>
---
 include/linux/skbuff.h          | 7 ++++++-
 include/uapi/linux/errqueue.h   | 1 +
 include/uapi/linux/net_tstamp.h | 3 ++-
 net/ipv4/tcp_input.c            | 4 ++++
 net/socket.c                    | 2 ++
 5 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index faa7ebe..17b0df7 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -250,9 +250,14 @@ enum {
 
 	/* generate software time stamp when queueing packing in TC */
 	SKBTX_ENQ_TSTAMP = 1 << 6,
+
+	/* generate software timestamp on peer data acknowledgment */
+	SKBTX_ACK_TSTAMP = 1 << 7,
 };
 
-#define SKBTX_ANY_SW_TSTAMP	(SKBTX_SW_TSTAMP | SKBTX_ENQ_TSTAMP)
+#define SKBTX_ANY_SW_TSTAMP	(SKBTX_SW_TSTAMP  | \
+				 SKBTX_ENQ_TSTAMP | \
+				 SKBTX_ACK_TSTAMP)
 #define SKBTX_ANY_TSTAMP	(SKBTX_HW_TSTAMP | SKBTX_ANY_SW_TSTAMP)
 
 /*
diff --git a/include/uapi/linux/errqueue.h b/include/uapi/linux/errqueue.h
index d37e5c7..81639bc 100644
--- a/include/uapi/linux/errqueue.h
+++ b/include/uapi/linux/errqueue.h
@@ -37,6 +37,7 @@ struct scm_timestamping {
 enum {
 	SCM_TSTAMP_SND = 1,	/* driver passed skb to NIC */
 	SCM_TSTAMP_ENQ,		/* data enqueued in traffic shaping layer */
+	SCM_TSTAMP_ACK,		/* data acknowledged by peer */
 };
 
 #endif /* _UAPI_LINUX_ERRQUEUE_H */
diff --git a/include/uapi/linux/net_tstamp.h b/include/uapi/linux/net_tstamp.h
index 99c2035..bf9f338 100644
--- a/include/uapi/linux/net_tstamp.h
+++ b/include/uapi/linux/net_tstamp.h
@@ -21,8 +21,9 @@ enum {
 	SOF_TIMESTAMPING_SYS_HARDWARE = (1<<5),
 	SOF_TIMESTAMPING_RAW_HARDWARE = (1<<6),
 	SOF_TIMESTAMPING_TX_ENQ = (1<<7),
+	SOF_TIMESTAMPING_TX_ACK = (1<<8),
 
-	SOF_TIMESTAMPING_LAST = SOF_TIMESTAMPING_TX_ENQ,
+	SOF_TIMESTAMPING_LAST = SOF_TIMESTAMPING_TX_ACK,
 	SOF_TIMESTAMPING_MASK = (SOF_TIMESTAMPING_LAST - 1) |
 				 SOF_TIMESTAMPING_LAST
 };
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 7832d94..f52f159 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -74,6 +74,7 @@
 #include <linux/ipsec.h>
 #include <asm/unaligned.h>
 #include <net/netdma.h>
+#include <linux/errqueue.h>
 
 int sysctl_tcp_timestamps __read_mostly = 1;
 int sysctl_tcp_window_scaling __read_mostly = 1;
@@ -3102,6 +3103,9 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 		if (!fully_acked)
 			break;
 
+		if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_ACK_TSTAMP))
+			__skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
+
 		tcp_unlink_write_queue(skb, sk);
 		sk_wmem_free_skb(sk, skb);
 		if (skb == tp->retransmit_skb_hint)
diff --git a/net/socket.c b/net/socket.c
index c2849ba..340098a 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -619,6 +619,8 @@ void sock_tx_timestamp(struct sock *sk, __u8 *tx_flags)
 		*tx_flags |= SKBTX_SW_TSTAMP;
 	if (sk->sk_tsflags & SOF_TIMESTAMPING_TX_ENQ)
 		*tx_flags |= SKBTX_ENQ_TSTAMP;
+	if (sk->sk_tsflags & SOF_TIMESTAMPING_TX_ACK)
+		*tx_flags |= SKBTX_ACK_TSTAMP;
 
 	if (sock_flag(sk, SOCK_WIFI_STATUS))
 		*tx_flags |= SKBTX_WIFI_STATUS;
-- 
2.0.0.526.g5318336

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