migrate, tcp: Migrate RFC 7323 timestamp

Currently our migration of the state of TCP sockets omits the RFC 7323
timestamp.  In some circumstances that can result in data sent from the
target machine not being received, because it is discarded on the peer due
to PAWS checking.

Add code to dump and restore the timestamp across migration.

Link: https://bugs.passt.top/show_bug.cgi?id=115
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
[sbrivio: Minor style fixes]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

2 files changed, 61 insertions, 0 deletions

diff --git a/tcp.c b/tcp.c
index 43ee76b..68af43d 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2861,6 +2861,57 @@ static int tcp_flow_dump_mss(const struct tcp_tap_conn *conn,
 	return 0;
 }
 
+
+/**
+ * tcp_flow_dump_timestamp() - Dump RFC 7323 timestamp via TCP_TIMESTAMP
+ * @conn:	Pointer to the TCP connection structure
+ * @t:		Extended migration data (tcpi_options must be populated)
+ *
+ * Return: 0 on success, negative error code on failure
+ */
+static int tcp_flow_dump_timestamp(const struct tcp_tap_conn *conn,
+				   struct tcp_tap_transfer_ext *t)
+{
+	int val = 0;
+
+	if (t->tcpi_options & TCPI_OPT_TIMESTAMPS) {
+		socklen_t sl = sizeof(val);
+
+		if (getsockopt(conn->sock, SOL_TCP, TCP_TIMESTAMP, &val, &sl)) {
+			int rc = -errno;
+			flow_perror(conn, "Getting RFC 7323 timestamp");
+			return rc;
+		}
+	}
+
+	t->timestamp = (uint32_t)val;
+	return 0;
+}
+
+/**
+ * tcp_flow_repair_timestamp() - Restore RFC 7323 timestamp via TCP_TIMESTAMP
+ * @conn:	Pointer to the TCP connection structure
+ * @t:		Extended migration data
+ *
+ * Return: 0 on success, negative error code on failure
+ */
+static int tcp_flow_repair_timestamp(const struct tcp_tap_conn *conn,
+				   const struct tcp_tap_transfer_ext *t)
+{
+	int val = (int)t->timestamp;
+
+	if (t->tcpi_options & TCPI_OPT_TIMESTAMPS) {
+		if (setsockopt(conn->sock, SOL_TCP, TCP_TIMESTAMP,
+			       &val, sizeof(val))) {
+			int rc = -errno;
+			flow_perror(conn, "Setting RFC 7323 timestamp");
+			return rc;
+		}
+	}
+
+	return 0;
+}
+
 /**
  * tcp_flow_dump_wnd() - Dump current tcp_repair_window parameters
  * @conn:	Pointer to the TCP connection structure
@@ -3260,6 +3311,9 @@ int tcp_flow_migrate_source_ext(int fd, const struct tcp_tap_conn *conn)
 	if ((rc = tcp_flow_dump_mss(conn, t)))
 		goto fail;
 
+	if ((rc = tcp_flow_dump_timestamp(conn, t)))
+		goto fail;
+
 	if ((rc = tcp_flow_dump_wnd(conn, t)))
 		goto fail;
 
@@ -3305,6 +3359,7 @@ int tcp_flow_migrate_source_ext(int fd, const struct tcp_tap_conn *conn)
 	t->notsent	= htonl(t->notsent);
 	t->rcvq		= htonl(t->rcvq);
 	t->mss		= htonl(t->mss);
+	t->timestamp	= htonl(t->timestamp);
 
 	t->snd_wl1	= htonl(t->snd_wl1);
 	t->snd_wnd	= htonl(t->snd_wnd);
@@ -3519,6 +3574,7 @@ int tcp_flow_migrate_target_ext(struct ctx *c, struct tcp_tap_conn *conn, int fd
 	t.notsent	= ntohl(t.notsent);
 	t.rcvq		= ntohl(t.rcvq);
 	t.mss		= ntohl(t.mss);
+	t.timestamp	= ntohl(t.timestamp);
 
 	t.snd_wl1	= ntohl(t.snd_wl1);
 	t.snd_wnd	= ntohl(t.snd_wnd);
@@ -3561,6 +3617,9 @@ int tcp_flow_migrate_target_ext(struct ctx *c, struct tcp_tap_conn *conn, int fd
 		/* We weren't able to create the socket, discard flow */
 		goto fail;
 
+	if (tcp_flow_repair_timestamp(conn, &t))
+		goto fail;
+
 	if (tcp_flow_select_queue(conn, TCP_SEND_QUEUE))
 		goto fail;
 
diff --git a/tcp_conn.h b/tcp_conn.h
index 9126a36..35d813d 100644
--- a/tcp_conn.h
+++ b/tcp_conn.h
@@ -152,6 +152,7 @@ struct tcp_tap_transfer {
  * @notsent:		Part of pending send queue that wasn't sent out yet
  * @rcvq:		Length of pending receive queue
  * @mss:		Socket-side MSS clamp
+ * @timestamp:		RFC 7323 timestamp
  * @snd_wl1:		Next sequence used in window probe (next sequence - 1)
  * @snd_wnd:		Socket-side sending window
  * @max_window:		Window clamp
@@ -171,6 +172,7 @@ struct tcp_tap_transfer_ext {
 	uint32_t	rcvq;
 
 	uint32_t	mss;
+	uint32_t	timestamp;
 
 	/* We can't just use struct tcp_repair_window: we need network order */
 	uint32_t	snd_wl1;