l2 tap queue entries are currently initialized at system start, and
reused with preset headers through its whole life time. The only
fields we need to update per message are things like payload size
and checksums.

If we want to reuse these entries between ipv4 and ipv6 messages we
will need to set the pointer to the right header on the fly per
message, since the header type may differ between entries in the same
queue.

The same needs to be done for the ethernet header.

We do these changes here.

Signed-off-by: Jon Maloy <jmaloy(a)redhat.com>

---
v2: Setting pointers to pre-initialized IP and MAC headers instead of
    copying them in on the fly.
v3: Adapted to D. Gibson's recent commit eliminitaing overlapping memcpy()
---
 tcp_buf.c | 54 ++++++++++++++++++++++++++++++------------------------
 1 file changed, 30 insertions(+), 24 deletions(-)

diff --git a/tcp_buf.c b/tcp_buf.c
index ffbff5e..c56fb9c 100644
--- a/tcp_buf.c
+++ b/tcp_buf.c
@@ -159,8 +159,7 @@ void tcp_sock4_iov_init(const struct ctx *c)
 		iov = tcp4_l2_iov[i];
 
 		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp4_payload_tap_hdr[i]);
-		iov[TCP_IOV_ETH] = IOV_OF_LVALUE(tcp4_eth_src);
-		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp4_payload_ip[i]);
+		iov[TCP_IOV_ETH].iov_len = sizeof(struct ethhdr);
 		iov[TCP_IOV_PAYLOAD].iov_base = &tcp4_payload[i];
 	}
 
@@ -202,8 +201,7 @@ void tcp_sock6_iov_init(const struct ctx *c)
 		iov = tcp6_l2_iov[i];
 
 		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp6_payload_tap_hdr[i]);
-		iov[TCP_IOV_ETH] = IOV_OF_LVALUE(tcp6_eth_src);
-		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp6_payload_ip[i]);
+		iov[TCP_IOV_ETH].iov_len = sizeof(struct ethhdr);
 		iov[TCP_IOV_PAYLOAD].iov_base = &tcp6_payload[i];
 	}
 
@@ -302,11 +300,17 @@ int tcp_buf_send_flag(const struct ctx *c, struct tcp_tap_conn
*conn, int flags)
 	uint32_t seq;
 	int ret;
 
-	if (CONN_V4(conn))
-		iov = tcp4_l2_flags_iov[tcp4_flags_used++];
-	else
-		iov = tcp6_l2_flags_iov[tcp6_flags_used++];
-
+	if (CONN_V4(conn)) {
+		iov = tcp4_l2_flags_iov[tcp4_flags_used];
+		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp4_flags_ip[tcp4_flags_used]);
+		iov[TCP_IOV_ETH].iov_base = &tcp4_eth_src;
+		tcp4_flags_used++;
+	} else {
+		iov = tcp6_l2_flags_iov[tcp6_flags_used];
+		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp6_flags_ip[tcp6_flags_used]);
+		iov[TCP_IOV_ETH].iov_base = &tcp6_eth_src;
+		tcp6_flags_used++;
+	}
 	payload = iov[TCP_IOV_PAYLOAD].iov_base;
 
 	seq = conn->seq_to_tap;
@@ -325,21 +329,19 @@ int tcp_buf_send_flag(const struct ctx *c, struct tcp_tap_conn
*conn, int flags)
 
 	if (flags & DUP_ACK) {
 		struct iovec *dup_iov;
-		int i;
 
 		if (CONN_V4(conn))
 			dup_iov = tcp4_l2_flags_iov[tcp4_flags_used++];
 		else
-			dup_iov = tcp6_l2_flags_iov[tcp6_flags_used++];
-
-		for (i = 0; i < TCP_NUM_IOVS; i++) {
-			/* All frames share the same ethernet header buffer */
-			if (i != TCP_IOV_ETH) {
-				memcpy(dup_iov[i].iov_base, iov[i].iov_base,
-				       iov[i].iov_len);
-			}
-		}
-		dup_iov[TCP_IOV_PAYLOAD].iov_len = iov[TCP_IOV_PAYLOAD].iov_len;
+			dup_iov = tcp4_l2_flags_iov[tcp6_flags_used++];
+
+		memcpy(dup_iov[TCP_IOV_TAP].iov_base, iov[TCP_IOV_TAP].iov_base,
+		       iov[TCP_IOV_TAP].iov_len);
+		dup_iov[TCP_IOV_ETH].iov_base = iov[TCP_IOV_ETH].iov_base;
+		dup_iov[TCP_IOV_IP] = IOV_OF_LVALUE(iov[TCP_IOV_IP]);
+		memcpy(dup_iov[TCP_IOV_PAYLOAD].iov_base,
+		       iov[TCP_IOV_PAYLOAD].iov_base, l4len);
+		dup_iov[TCP_IOV_PAYLOAD].iov_len = l4len;
 	}
 
 	if (CONN_V4(conn)) {
@@ -379,8 +381,10 @@ static void tcp_data_to_tap(const struct ctx *c, struct tcp_tap_conn
*conn,
 		}
 
 		tcp4_frame_conns[tcp4_payload_used] = conn;
-
-		iov = tcp4_l2_iov[tcp4_payload_used++];
+		iov = tcp4_l2_iov[tcp4_payload_used];
+		iov[TCP_IOV_IP] =
+			IOV_OF_LVALUE(tcp4_payload_ip[tcp4_payload_used++]);
+		iov[TCP_IOV_ETH].iov_base = &tcp4_eth_src;
 		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, check, seq,
 						false);
 		iov[TCP_IOV_PAYLOAD].iov_len = l4len;
@@ -388,8 +392,10 @@ static void tcp_data_to_tap(const struct ctx *c, struct tcp_tap_conn
*conn,
 			tcp_payload_flush(c);
 	} else if (CONN_V6(conn)) {
 		tcp6_frame_conns[tcp6_payload_used] = conn;
-
-		iov = tcp6_l2_iov[tcp6_payload_used++];
+		iov = tcp6_l2_iov[tcp6_payload_used];
+		iov[TCP_IOV_IP] =
+			IOV_OF_LVALUE(tcp6_payload_ip[tcp6_payload_used++]);
+		iov[TCP_IOV_ETH].iov_base = &tcp6_eth_src;
 		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, NULL, seq,
 						false);
 		iov[TCP_IOV_PAYLOAD].iov_len = l4len;
-- 
2.45.2

Following the preparations in the previous commit, we can now remove
the payload and flag queues dedicated for TCPv6 and TCPv4 and move all
traffic into common queues handling both protocol types.

Apart from reducing code and memory footprint, this change reduces
a potential risk for TCPv4 traffic starving out TCPv6 traffic.
Since we always flush out the TCPv4 frame queue before the TCPv6 queue,
the latter will never be handled if the former fails to send all its
frames.

Tests with iperf3 shows no measurable change in performance after this
change.

Signed-off-by: Jon Maloy <jmaloy(a)redhat.com>

---
v2: Merged previous patch #3, where the tcp4_ prefix was changed to
    tcp_ into this patch.
v3: Fixes based on feedback from D. Gibson
---
 tcp.c     |   6 +-
 tcp_buf.c | 245 ++++++++++++++++--------------------------------------
 tcp_buf.h |   3 +-
 3 files changed, 74 insertions(+), 180 deletions(-)

diff --git a/tcp.c b/tcp.c
index 1962fcc..12e864f 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2547,11 +2547,7 @@ int tcp_init(struct ctx *c)
 {
 	ASSERT(!c->no_tcp);
 
-	if (c->ifi4)
-		tcp_sock4_iov_init(c);
-
-	if (c->ifi6)
-		tcp_sock6_iov_init(c);
+	tcp_sock_iov_init(c);
 
 	memset(init_sock_pool4,		0xff,	sizeof(init_sock_pool4));
 	memset(init_sock_pool6,		0xff,	sizeof(init_sock_pool6));
diff --git a/tcp_buf.c b/tcp_buf.c
index c56fb9c..625c29c 100644
--- a/tcp_buf.c
+++ b/tcp_buf.c
@@ -67,59 +67,43 @@ struct tcp_flags_t {
 } __attribute__ ((packed, aligned(__alignof__(unsigned int))));
 #endif
 
-/* Ethernet header for IPv4 frames */
+/* Ethernet header for IPv4 and IPv6 frames */
 static struct ethhdr		tcp4_eth_src;
+static struct ethhdr		tcp6_eth_src;
+
+static struct tap_hdr		tcp_payload_tap_hdr[TCP_FRAMES_MEM];
 
-static struct tap_hdr		tcp4_payload_tap_hdr[TCP_FRAMES_MEM];
-/* IPv4 headers */
-static struct iphdr		tcp4_payload_ip[TCP_FRAMES_MEM];
-/* TCP segments with payload for IPv4 frames */
-static struct tcp_payload_t	tcp4_payload[TCP_FRAMES_MEM];
+/* IP headers for IPv4 and IPv6 */
+struct iphdr		tcp4_payload_ip[TCP_FRAMES_MEM];
+struct ipv6hdr		tcp6_payload_ip[TCP_FRAMES_MEM];
 
-static_assert(MSS4 <= sizeof(tcp4_payload[0].data), "MSS4 is greater than
65516");
+/* TCP segments with payload for IPv4 and IPv6 frames */
+static struct tcp_payload_t	tcp_payload[TCP_FRAMES_MEM];
+
+static_assert(MSS4 <= sizeof(tcp_payload[0].data), "MSS4 is greater than
65516");
+static_assert(MSS6 <= sizeof(tcp_payload[0].data), "MSS6 is greater than
65516");
 
 /* References tracking the owner connection of frames in the tap outqueue */
-static struct tcp_tap_conn *tcp4_frame_conns[TCP_FRAMES_MEM];
-static unsigned int tcp4_payload_used;
+static struct tcp_tap_conn *tcp_frame_conns[TCP_FRAMES_MEM];
+static unsigned int tcp_payload_used;
 
-static struct tap_hdr		tcp4_flags_tap_hdr[TCP_FRAMES_MEM];
+static struct tap_hdr		tcp_flags_tap_hdr[TCP_FRAMES_MEM];
 /* IPv4 headers for TCP segment without payload */
 static struct iphdr		tcp4_flags_ip[TCP_FRAMES_MEM];
 /* TCP segments without payload for IPv4 frames */
-static struct tcp_flags_t	tcp4_flags[TCP_FRAMES_MEM];
-
-static unsigned int tcp4_flags_used;
+static struct tcp_flags_t	tcp_flags[TCP_FRAMES_MEM];
 
-/* Ethernet header for IPv6 frames */
-static struct ethhdr		tcp6_eth_src;
-
-static struct tap_hdr		tcp6_payload_tap_hdr[TCP_FRAMES_MEM];
-/* IPv6 headers */
-static struct ipv6hdr		tcp6_payload_ip[TCP_FRAMES_MEM];
-/* TCP headers and data for IPv6 frames */
-static struct tcp_payload_t	tcp6_payload[TCP_FRAMES_MEM];
+static unsigned int tcp_flags_used;
 
-static_assert(MSS6 <= sizeof(tcp6_payload[0].data), "MSS6 is greater than
65516");
-
-/* References tracking the owner connection of frames in the tap outqueue */
-static struct tcp_tap_conn *tcp6_frame_conns[TCP_FRAMES_MEM];
-static unsigned int tcp6_payload_used;
-
-static struct tap_hdr		tcp6_flags_tap_hdr[TCP_FRAMES_MEM];
 /* IPv6 headers for TCP segment without payload */
 static struct ipv6hdr		tcp6_flags_ip[TCP_FRAMES_MEM];
-/* TCP segment without payload for IPv6 frames */
-static struct tcp_flags_t	tcp6_flags[TCP_FRAMES_MEM];
-
-static unsigned int tcp6_flags_used;
 
 /* recvmsg()/sendmsg() data for tap */
 static struct iovec	iov_sock		[TCP_FRAMES_MEM + 1];
 
-static struct iovec	tcp4_l2_iov		[TCP_FRAMES_MEM][TCP_NUM_IOVS];
-static struct iovec	tcp6_l2_iov		[TCP_FRAMES_MEM][TCP_NUM_IOVS];
-static struct iovec	tcp4_l2_flags_iov	[TCP_FRAMES_MEM][TCP_NUM_IOVS];
-static struct iovec	tcp6_l2_flags_iov	[TCP_FRAMES_MEM][TCP_NUM_IOVS];
+static struct iovec	tcp_l2_iov[TCP_FRAMES_MEM][TCP_NUM_IOVS];
+static struct iovec	tcp_l2_flags_iov[TCP_FRAMES_MEM][TCP_NUM_IOVS];
+
 /**
  * tcp_update_l2_buf() - Update Ethernet header buffers with addresses
  * @eth_d:	Ethernet destination address, NULL if unchanged
@@ -132,86 +116,46 @@ void tcp_update_l2_buf(const unsigned char *eth_d, const unsigned
char *eth_s)
 }
 
 /**
- * tcp_sock4_iov_init() - Initialise scatter-gather L2 buffers for IPv4 sockets
+ * tcp_sock_iov_init() - Initialise scatter-gather L2 buffers for IPv4 sockets
  * @c:		Execution context
  */
-void tcp_sock4_iov_init(const struct ctx *c)
+void tcp_sock_iov_init(const struct ctx *c)
 {
+	struct ipv6hdr ip6 = L2_BUF_IP6_INIT(IPPROTO_TCP);
 	struct iphdr iph = L2_BUF_IP4_INIT(IPPROTO_TCP);
-	struct iovec *iov;
 	int i;
 
+	tcp6_eth_src.h_proto = htons_constant(ETH_P_IPV6);
 	tcp4_eth_src.h_proto = htons_constant(ETH_P_IP);
 
-	for (i = 0; i < ARRAY_SIZE(tcp4_payload); i++) {
+	for (i = 0; i < ARRAY_SIZE(tcp_payload); i++) {
+		tcp6_payload_ip[i] = ip6;
 		tcp4_payload_ip[i] = iph;
-		tcp4_payload[i].th.doff = sizeof(struct tcphdr) / 4;
-		tcp4_payload[i].th.ack = 1;
+		tcp_payload[i].th.doff = sizeof(struct tcphdr) / 4;
+		tcp_payload[i].th.ack = 1;
 	}
 
-	for (i = 0; i < ARRAY_SIZE(tcp4_flags); i++) {
+	for (i = 0; i < ARRAY_SIZE(tcp_flags); i++) {
+		tcp6_flags_ip[i] = ip6;
 		tcp4_flags_ip[i] = iph;
-		tcp4_flags[i].th.doff = sizeof(struct tcphdr) / 4;
-		tcp4_flags[i].th.ack = 1;
+		tcp_flags[i].th.doff = sizeof(struct tcphdr) / 4;
+		tcp_flags[i].th.ack = 1;
 	}
 
 	for (i = 0; i < TCP_FRAMES_MEM; i++) {
-		iov = tcp4_l2_iov[i];
+		struct iovec *iov = tcp_l2_iov[i];
 
-		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp4_payload_tap_hdr[i]);
+		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp_payload_tap_hdr[i]);
 		iov[TCP_IOV_ETH].iov_len = sizeof(struct ethhdr);
-		iov[TCP_IOV_PAYLOAD].iov_base = &tcp4_payload[i];
+		iov[TCP_IOV_PAYLOAD].iov_base = &tcp_payload[i];
 	}
 
 	for (i = 0; i < TCP_FRAMES_MEM; i++) {
-		iov = tcp4_l2_flags_iov[i];
-
-		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp4_flags_tap_hdr[i]);
-		iov[TCP_IOV_ETH] = IOV_OF_LVALUE(tcp4_eth_src);
-		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp4_flags_ip[i]);
-		iov[TCP_IOV_PAYLOAD].iov_base = &tcp4_flags[i];
-	}
-}
-
-/**
- * tcp_sock6_iov_init() - Initialise scatter-gather L2 buffers for IPv6 sockets
- * @c:		Execution context
- */
-void tcp_sock6_iov_init(const struct ctx *c)
-{
-	struct ipv6hdr ip6 = L2_BUF_IP6_INIT(IPPROTO_TCP);
-	struct iovec *iov;
-	int i;
-
-	tcp6_eth_src.h_proto = htons_constant(ETH_P_IPV6);
+		struct iovec *iov = tcp_l2_flags_iov[i];
 
-	for (i = 0; i < ARRAY_SIZE(tcp6_payload); i++) {
-		tcp6_payload_ip[i] = ip6;
-		tcp6_payload[i].th.doff = sizeof(struct tcphdr) / 4;
-		tcp6_payload[i].th.ack = 1;
-	}
-
-	for (i = 0; i < ARRAY_SIZE(tcp6_flags); i++) {
-		tcp6_flags_ip[i] = ip6;
-		tcp6_flags[i].th.doff = sizeof(struct tcphdr) / 4;
-		tcp6_flags[i].th .ack = 1;
-	}
-
-	for (i = 0; i < TCP_FRAMES_MEM; i++) {
-		iov = tcp6_l2_iov[i];
-
-		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp6_payload_tap_hdr[i]);
+		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp_flags_tap_hdr[i]);
 		iov[TCP_IOV_ETH].iov_len = sizeof(struct ethhdr);
-		iov[TCP_IOV_PAYLOAD].iov_base = &tcp6_payload[i];
-	}
-
-	for (i = 0; i < TCP_FRAMES_MEM; i++) {
-		iov = tcp6_l2_flags_iov[i];
-
-		iov[TCP_IOV_TAP] = tap_hdr_iov(c, &tcp6_flags_tap_hdr[i]);
-		iov[TCP_IOV_ETH] = IOV_OF_LVALUE(tcp6_eth_src);
-		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp6_flags_ip[i]);
-		iov[TCP_IOV_PAYLOAD].iov_base = &tcp6_flags[i];
+		iov[TCP_IOV_PAYLOAD].iov_base = &tcp_flags[i];
 	}
 }
 
@@ -221,13 +165,9 @@ void tcp_sock6_iov_init(const struct ctx *c)
  */
 void tcp_flags_flush(const struct ctx *c)
 {
-	tap_send_frames(c, &tcp6_l2_flags_iov[0][0], TCP_NUM_IOVS,
-			tcp6_flags_used);
-	tcp6_flags_used = 0;
-
-	tap_send_frames(c, &tcp4_l2_flags_iov[0][0], TCP_NUM_IOVS,
-			tcp4_flags_used);
-	tcp4_flags_used = 0;
+	tap_send_frames(c, &tcp_l2_flags_iov[0][0], TCP_NUM_IOVS,
+			tcp_flags_used);
+	tcp_flags_used = 0;
 }
 
 /**
@@ -266,21 +206,13 @@ void tcp_payload_flush(const struct ctx *c)
 {
 	size_t m;
 
-	m = tap_send_frames(c, &tcp6_l2_iov[0][0], TCP_NUM_IOVS,
-			    tcp6_payload_used);
-	if (m != tcp6_payload_used) {
-		tcp_revert_seq(c, &tcp6_frame_conns[m], &tcp6_l2_iov[m],
-			       tcp6_payload_used - m);
-	}
-	tcp6_payload_used = 0;
-
-	m = tap_send_frames(c, &tcp4_l2_iov[0][0], TCP_NUM_IOVS,
-			    tcp4_payload_used);
-	if (m != tcp4_payload_used) {
-		tcp_revert_seq(c, &tcp4_frame_conns[m], &tcp4_l2_iov[m],
-			       tcp4_payload_used - m);
+	m = tap_send_frames(c, &tcp_l2_iov[0][0], TCP_NUM_IOVS,
+			    tcp_payload_used);
+	if (m != tcp_payload_used) {
+		tcp_revert_seq(c, &tcp_frame_conns[m], &tcp_l2_iov[m],
+			       tcp_payload_used - m);
 	}
-	tcp4_payload_used = 0;
+	tcp_payload_used = 0;
 }
 
 /**
@@ -300,41 +232,30 @@ int tcp_buf_send_flag(const struct ctx *c, struct tcp_tap_conn
*conn, int flags)
 	uint32_t seq;
 	int ret;
 
+	iov = tcp_l2_flags_iov[tcp_flags_used];
 	if (CONN_V4(conn)) {
-		iov = tcp4_l2_flags_iov[tcp4_flags_used];
-		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp4_flags_ip[tcp4_flags_used]);
+		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp4_flags_ip[tcp_flags_used]);
 		iov[TCP_IOV_ETH].iov_base = &tcp4_eth_src;
-		tcp4_flags_used++;
 	} else {
-		iov = tcp6_l2_flags_iov[tcp6_flags_used];
-		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp6_flags_ip[tcp6_flags_used]);
+		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp6_flags_ip[tcp_flags_used]);
 		iov[TCP_IOV_ETH].iov_base = &tcp6_eth_src;
-		tcp6_flags_used++;
 	}
-	payload = iov[TCP_IOV_PAYLOAD].iov_base;
 
+	payload = iov[TCP_IOV_PAYLOAD].iov_base;
 	seq = conn->seq_to_tap;
 	ret = tcp_prepare_flags(c, conn, flags, &payload->th,
 				payload->opts, &optlen);
-	if (ret <= 0) {
-		if (CONN_V4(conn))
-			tcp4_flags_used--;
-		else
-			tcp6_flags_used--;
+	if (ret <= 0)
 		return ret;
-	}
 
+	tcp_flags_used++;
 	l4len = tcp_l2_buf_fill_headers(conn, iov, optlen, NULL, seq, false);
 	iov[TCP_IOV_PAYLOAD].iov_len = l4len;
 
 	if (flags & DUP_ACK) {
 		struct iovec *dup_iov;
 
-		if (CONN_V4(conn))
-			dup_iov = tcp4_l2_flags_iov[tcp4_flags_used++];
-		else
-			dup_iov = tcp4_l2_flags_iov[tcp6_flags_used++];
-
+		dup_iov = tcp_l2_flags_iov[tcp_flags_used++];
 		memcpy(dup_iov[TCP_IOV_TAP].iov_base, iov[TCP_IOV_TAP].iov_base,
 		       iov[TCP_IOV_TAP].iov_len);
 		dup_iov[TCP_IOV_ETH].iov_base = iov[TCP_IOV_ETH].iov_base;
@@ -344,13 +265,8 @@ int tcp_buf_send_flag(const struct ctx *c, struct tcp_tap_conn *conn,
int flags)
 		dup_iov[TCP_IOV_PAYLOAD].iov_len = l4len;
 	}
 
-	if (CONN_V4(conn)) {
-		if (tcp4_flags_used > TCP_FRAMES_MEM - 2)
-			tcp_flags_flush(c);
-	} else {
-		if (tcp6_flags_used > TCP_FRAMES_MEM - 2)
-			tcp_flags_flush(c);
-	}
+	if (tcp_flags_used > TCP_FRAMES_MEM - 2)
+		tcp_flags_flush(c);
 
 	return 0;
 }
@@ -366,42 +282,30 @@ int tcp_buf_send_flag(const struct ctx *c, struct tcp_tap_conn
*conn, int flags)
 static void tcp_data_to_tap(const struct ctx *c, struct tcp_tap_conn *conn,
 			    ssize_t dlen, int no_csum, uint32_t seq)
 {
+	const uint16_t *check = NULL;
 	struct iovec *iov;
 	size_t l4len;
 
 	conn->seq_to_tap = seq + dlen;
-
+	tcp_frame_conns[tcp_payload_used] = conn;
+	iov = tcp_l2_iov[tcp_payload_used];
 	if (CONN_V4(conn)) {
-		struct iovec *iov_prev = tcp4_l2_iov[tcp4_payload_used - 1];
-		const uint16_t *check = NULL;
-
 		if (no_csum) {
+			struct iovec *iov_prev = tcp_l2_iov[tcp_payload_used - 1];
 			struct iphdr *iph = iov_prev[TCP_IOV_IP].iov_base;
+
 			check = &iph->check;
 		}
-
-		tcp4_frame_conns[tcp4_payload_used] = conn;
-		iov = tcp4_l2_iov[tcp4_payload_used];
-		iov[TCP_IOV_IP] =
-			IOV_OF_LVALUE(tcp4_payload_ip[tcp4_payload_used++]);
+		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp4_payload_ip[tcp_payload_used]);
 		iov[TCP_IOV_ETH].iov_base = &tcp4_eth_src;
-		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, check, seq,
-						false);
-		iov[TCP_IOV_PAYLOAD].iov_len = l4len;
-		if (tcp4_payload_used > TCP_FRAMES_MEM - 1)
-			tcp_payload_flush(c);
 	} else if (CONN_V6(conn)) {
-		tcp6_frame_conns[tcp6_payload_used] = conn;
-		iov = tcp6_l2_iov[tcp6_payload_used];
-		iov[TCP_IOV_IP] =
-			IOV_OF_LVALUE(tcp6_payload_ip[tcp6_payload_used++]);
+		iov[TCP_IOV_IP] = IOV_OF_LVALUE(tcp6_payload_ip[tcp_payload_used]);
 		iov[TCP_IOV_ETH].iov_base = &tcp6_eth_src;
-		l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, NULL, seq,
-						false);
-		iov[TCP_IOV_PAYLOAD].iov_len = l4len;
-		if (tcp6_payload_used > TCP_FRAMES_MEM - 1)
-			tcp_payload_flush(c);
 	}
+	l4len = tcp_l2_buf_fill_headers(conn, iov, dlen, check, seq, false);
+	iov[TCP_IOV_PAYLOAD].iov_len = l4len;
+	if (++tcp_payload_used > TCP_FRAMES_MEM - 1)
+		tcp_payload_flush(c);
 }
 
 /**
@@ -417,8 +321,7 @@ int tcp_buf_data_from_sock(const struct ctx *c, struct tcp_tap_conn
*conn)
 {
 	uint32_t wnd_scaled = conn->wnd_from_tap << conn->ws_from_tap;
 	int fill_bufs, send_bufs = 0, last_len, iov_rem = 0;
-	int sendlen, len, dlen, v4 = CONN_V4(conn);
-	int s = conn->sock, i, ret = 0;
+	int sendlen, len, dlen, i, s = conn->sock, ret = 0;
 	struct msghdr mh_sock = { 0 };
 	uint16_t mss = MSS_GET(conn);
 	uint32_t already_sent, seq;
@@ -465,19 +368,15 @@ int tcp_buf_data_from_sock(const struct ctx *c, struct tcp_tap_conn
*conn)
 		mh_sock.msg_iovlen = fill_bufs;
 	}
 
-	if (( v4 && tcp4_payload_used + fill_bufs > TCP_FRAMES_MEM) ||
-	    (!v4 && tcp6_payload_used + fill_bufs > TCP_FRAMES_MEM)) {
+	if (tcp_payload_used + fill_bufs > TCP_FRAMES_MEM) {
 		tcp_payload_flush(c);
 
 		/* Silence Coverity CWE-125 false positive */
-		tcp4_payload_used = tcp6_payload_used = 0;
+		tcp_payload_used = 0;
 	}
 
 	for (i = 0, iov = iov_sock + 1; i < fill_bufs; i++, iov++) {
-		if (v4)
-			iov->iov_base = &tcp4_payload[tcp4_payload_used + i].data;
-		else
-			iov->iov_base = &tcp6_payload[tcp6_payload_used + i].data;
+		iov->iov_base = &tcp_payload[tcp_payload_used + i].data;
 		iov->iov_len = mss;
 	}
 	if (iov_rem)
@@ -525,7 +424,7 @@ int tcp_buf_data_from_sock(const struct ctx *c, struct tcp_tap_conn
*conn)
 	dlen = mss;
 	seq = conn->seq_to_tap;
 	for (i = 0; i < send_bufs; i++) {
-		int no_csum = i && i != send_bufs - 1 && tcp4_payload_used;
+		int no_csum = i && i != send_bufs - 1 && tcp_payload_used;
 
 		if (i == send_bufs - 1)
 			dlen = last_len;
diff --git a/tcp_buf.h b/tcp_buf.h
index 8d4b615..49c04d4 100644
--- a/tcp_buf.h
+++ b/tcp_buf.h
@@ -6,8 +6,7 @@
 #ifndef TCP_BUF_H
 #define TCP_BUF_H
 
-void tcp_sock4_iov_init(const struct ctx *c);
-void tcp_sock6_iov_init(const struct ctx *c);
+void tcp_sock_iov_init(const struct ctx *c);
 void tcp_flags_flush(const struct ctx *c);
 void tcp_payload_flush(const struct ctx *c);
 int tcp_buf_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn);
-- 
2.45.2

On Thu, 19 Sep 2024 14:44:07 -0400
Jon Maloy <jmaloy(a)redhat.com> wrote:

...
  This should save us some memory and code.
 
 ---
 v2: - Setting pointers to pre-set IP and MAC headers on the fly
       instead of copying them.
     - Merged patch #2 and #3 from v1
 v3: - Changes based on feedback from team 
Sorry for the delay, now tests go a bit further but I have a similar
problem as I had on v2: guest to host, IPv6, with 65520 bytes MTU only
(perf/passt_tcp case), the iperf3 server fails to receive results, test
suite output:

=== perf/passt_tcp
...
  passt: throughput and latency 
Throughput in
Gbps, latency in µs, 4 threads at 3.6 GHz
                                        MTU: |  256B  |  576B  |  1280B |  1500B |  9000B
| 65520B |
                                            
|--------|--------|--------|--------|--------|--------|
   TCP throughput over IPv6: guest to host   |      - |      - |    5.8 |    6.5 |   18.1
|

and matching iperf3 server output:

- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate
[  6]   0.00-1.01   sec   568 MBytes  4.74 Gbits/sec                  receiver
[  9]   0.00-1.01   sec   621 MBytes  5.18 Gbits/sec                  receiver
[ 11]   0.00-1.01   sec   569 MBytes  4.75 Gbits/sec                  receiver
[ 13]   0.00-1.01   sec   675 MBytes  5.63 Gbits/sec                  receiver
[SUM]   0.00-1.01   sec  2.38 GBytes  20.3 Gbits/sec                  receiver
iperf3: error - unable to receive results: Bad file descriptor

after that, connectivity from the guest seems to be pretty much gone.
I didn't debug further.

-- 
Stefano