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

5 files changed, 17 insertions, 2 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 50e1e9b3a5a5..11c270551d25 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -250,9 +250,14 @@ enum {
 
         /* generate software time stamp when entering packet scheduling */
         SKBTX_SCHED_TSTAMP = 1 << 6,
+
+        /* generate software timestamp on peer data acknowledgment */
+        SKBTX_ACK_TSTAMP = 1 << 7,
 };
 
-#define SKBTX_ANY_SW_TSTAMP     (SKBTX_SW_TSTAMP | SKBTX_SCHED_TSTAMP)
+#define SKBTX_ANY_SW_TSTAMP     (SKBTX_SW_TSTAMP    | \
+                                 SKBTX_SCHED_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 17437cf297b7..07bdce1f444a 100644
--- a/include/uapi/linux/errqueue.h
+++ b/include/uapi/linux/errqueue.h
@@ -40,6 +40,7 @@ struct scm_timestamping {
 enum {
         SCM_TSTAMP_SND,         /* driver passed skb to NIC, or HW */
         SCM_TSTAMP_SCHED,       /* data entered the packet scheduler */
+        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 60733845fcdd..ff354021bb69 100644
--- a/include/uapi/linux/net_tstamp.h
+++ b/include/uapi/linux/net_tstamp.h
@@ -22,8 +22,9 @@ enum {
         SOF_TIMESTAMPING_RAW_HARDWARE = (1<<6),
         SOF_TIMESTAMPING_OPT_ID = (1<<7),
         SOF_TIMESTAMPING_TX_SCHED = (1<<8),
+        SOF_TIMESTAMPING_TX_ACK = (1<<9),
 
-        SOF_TIMESTAMPING_LAST = SOF_TIMESTAMPING_TX_SCHED,
+        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 6a2984507755..a3d47af01906 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;
@@ -3106,6 +3107,11 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
                         tp->retrans_stamp = 0;
                 }
 
+                if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_ACK_TSTAMP) &&
+                    between(skb_shinfo(skb)->tskey, prior_snd_una,
+                            tp->snd_una + 1))
+                        __skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
+
                 if (!fully_acked)
                         break;
 
diff --git a/net/socket.c b/net/socket.c
index 3a2778d71631..ae89569a2db5 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_SCHED)
                 *tx_flags |= SKBTX_SCHED_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;