[PATCH 7/8] tcp, flow: Introduce struct demiflow

[David Gibson <david@gibson.dropbear.id.au>]

For TCP tap connections we keep track of both the IP address and port for
each side of a connection as seen by the guest.  We're planning to track
similar information in a number of other places as well.

To assist with this, create a new structure: struct demiflow to track both
sides of a connection or other logical packet flow as seen from a single
"side" of passt.  Also add a small helper function for initializing this
structure.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 flow.h       | 41 ++++++++++++++++++++++++++++++++++++
 tcp.c        | 59 ++++++++++++++++++++++++++--------------------------
 tcp_conn.h   | 11 ++--------
 tcp_splice.c |  1 +
 4 files changed, 74 insertions(+), 38 deletions(-)
 create mode 100644 flow.h

diff --git a/flow.h b/flow.h
new file mode 100644
index 0000000..f7c0981
--- /dev/null
+++ b/flow.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ *
+ * Tracking for logical "flows" of packets.
+ */
+#ifndef FLOW_H
+#define FLOW_H
+
+/**
+ * struct demiflow - Describes a logical packet flow as seen from one "side"
+ * @caddr:		Correspondent address (remote address from passt's PoV)
+ * @faddr:		Forwarding address (local address from passt's PoV)
+ * @cport:		Correspondent port
+ * @fport:		Forwarding port
+ */
+struct demiflow {
+	union inany_addr faddr;
+	union inany_addr caddr;
+	in_port_t fport, cport;
+};
+
+/** demiflow_from_af - Initialize a demiflow from addresses
+ * @df:		demiflow to initialize
+ * @af:		Address family for @faddr and @caddr
+ * @faddr:	Forwarding address (pointer to in_addr or in6_addr)
+ * @fport:	Forwarding port
+ * @caddr:	Correspondent address (pointer to in_addr or in6_addr)
+ * @cport:	Correspondent port
+ */
+static inline void demiflow_from_af(struct demiflow *df, int af,
+				    const void *faddr, in_port_t fport,
+				    const void *caddr, in_port_t cport)
+{
+	inany_from_af(&df->faddr, af, faddr);
+	inany_from_af(&df->caddr, af, caddr);
+	df->fport = fport;
+	df->cport = cport;
+}
+
+#endif /* FLOW_H */
diff --git a/tcp.c b/tcp.c
index 6c4d71e..c1875c3 100644
--- a/tcp.c
+++ b/tcp.c
@@ -302,6 +302,7 @@
 #include "tcp_splice.h"
 #include "log.h"
 #include "inany.h"
+#include "flow.h"
 
 #include "tcp_conn.h"
 
@@ -399,7 +400,7 @@ struct tcp6_l2_head {	/* For MSS6 macro: keep in sync with tcp6_l2_buf_t */
 #define OPT_SACK	5
 #define OPT_TS		8
 
-#define CONN_V4(conn)		(!!inany_v4(&(conn)->faddr))
+#define CONN_V4(conn)		(!!inany_v4(&(conn)->tapflow.faddr))
 #define CONN_V6(conn)		(!CONN_V4(conn))
 #define CONN_IS_CLOSING(conn)						\
 	((conn->events & ESTABLISHED) &&				\
@@ -852,7 +853,7 @@ static int tcp_rtt_dst_low(const struct tcp_tap_conn *conn)
 	int i;
 
 	for (i = 0; i < LOW_RTT_TABLE_SIZE; i++)
-		if (inany_equals(&conn->faddr, low_rtt_dst + i))
+		if (inany_equals(&conn->tapflow.faddr, low_rtt_dst + i))
 			return 1;
 
 	return 0;
@@ -874,7 +875,7 @@ static void tcp_rtt_dst_check(const struct tcp_tap_conn *conn,
 		return;
 
 	for (i = 0; i < LOW_RTT_TABLE_SIZE; i++) {
-		if (inany_equals(&conn->faddr, low_rtt_dst + i))
+		if (inany_equals(&conn->tapflow.faddr, low_rtt_dst + i))
 			return;
 		if (hole == -1 && IN6_IS_ADDR_UNSPECIFIED(low_rtt_dst + i))
 			hole = i;
@@ -886,7 +887,7 @@ static void tcp_rtt_dst_check(const struct tcp_tap_conn *conn,
 	if (hole == -1)
 		return;
 
-	low_rtt_dst[hole++] = conn->faddr;
+	low_rtt_dst[hole++] = conn->tapflow.faddr;
 	if (hole == LOW_RTT_TABLE_SIZE)
 		hole = 0;
 	inany_from_af(low_rtt_dst + hole, AF_INET6, &in6addr_any);
@@ -1151,8 +1152,8 @@ static int tcp_hash_match(const struct tcp_tap_conn *conn,
 			  const union inany_addr *faddr,
 			  in_port_t cport, in_port_t fport)
 {
-	if (inany_equals(&conn->faddr, faddr) &&
-	    conn->cport == cport && conn->fport == fport)
+	if (inany_equals(&conn->tapflow.faddr, faddr) &&
+	    conn->tapflow.cport == cport && conn->tapflow.fport == fport)
 		return 1;
 
 	return 0;
@@ -1194,7 +1195,8 @@ static unsigned int tcp_hash(const struct ctx *c, const union inany_addr *faddr,
 static unsigned int tcp_conn_hash(const struct ctx *c,
 				  const struct tcp_tap_conn *conn)
 {
-	return tcp_hash(c, &conn->faddr, conn->cport, conn->fport);
+	return tcp_hash(c, &conn->tapflow.faddr,
+			conn->tapflow.cport, conn->tapflow.fport);
 }
 
 /**
@@ -1206,7 +1208,8 @@ static void tcp_hash_insert(const struct ctx *c, struct tcp_tap_conn *conn)
 {
 	int b;
 
-	b = tcp_hash(c, &conn->faddr, conn->cport, conn->fport);
+	b = tcp_hash(c, &conn->tapflow.faddr,
+		     conn->tapflow.cport, conn->tapflow.fport);
 	conn->next_index = tc_hash[b] ? CONN_IDX(tc_hash[b]) : -1;
 	tc_hash[b] = conn;
 
@@ -1425,13 +1428,13 @@ static size_t tcp_l2_buf_fill_headers(const struct ctx *c,
 				      void *p, size_t plen,
 				      const uint16_t *check, uint32_t seq)
 {
-	const struct in_addr *a4 = inany_v4(&conn->faddr);
+	const struct in_addr *a4 = inany_v4(&conn->tapflow.faddr);
 	size_t ip_len, tlen;
 
 #define SET_TCP_HEADER_COMMON_V4_V6(b, conn, seq)			\
 do {									\
-	b->th.source = htons(conn->fport);				\
-	b->th.dest = htons(conn->cport);				\
+	b->th.source = htons(conn->tapflow.fport);			\
+	b->th.dest = htons(conn->tapflow.cport);			\
 	b->th.seq = htonl(seq);						\
 	b->th.ack_seq = htonl(conn->seq_ack_to_tap);			\
 	if (conn->events & ESTABLISHED)	{				\
@@ -1449,7 +1452,7 @@ do {									\
 		ip_len = plen + sizeof(struct iphdr) + sizeof(struct tcphdr);
 		b->iph.tot_len = htons(ip_len);
 		b->iph.saddr = a4->s_addr;
-		b->iph.daddr = inany_v4(&conn->caddr)->s_addr;
+		b->iph.daddr = inany_v4(&conn->tapflow.caddr)->s_addr;
 
 		if (check)
 			b->iph.check = *check;
@@ -1467,8 +1470,8 @@ do {									\
 		ip_len = plen + sizeof(struct ipv6hdr) + sizeof(struct tcphdr);
 
 		b->ip6h.payload_len = htons(plen + sizeof(struct tcphdr));
-		b->ip6h.saddr = conn->faddr.a6;
-		b->ip6h.daddr = conn->caddr.a6;
+		b->ip6h.saddr = conn->tapflow.faddr.a6;
+		b->ip6h.daddr = conn->tapflow.caddr.a6;
 
 		memset(b->ip6h.flow_lbl, 0, 3);
 
@@ -1829,10 +1832,10 @@ static void tcp_seq_init(const struct ctx *c, struct tcp_tap_conn *conn,
 		union inany_addr dst;
 		in_port_t dstport;
 	} __attribute__((__packed__)) in = {
-		.src = conn->faddr,
-		.srcport = conn->cport,
-		.dst = conn->caddr,
-		.dstport = conn->fport,
+		.src = conn->tapflow.faddr,
+		.srcport = conn->tapflow.cport,
+		.dst = conn->tapflow.caddr,
+		.dstport = conn->tapflow.fport,
 	};
 	uint32_t ns, seq = 0;
 
@@ -2049,10 +2052,8 @@ static void tcp_conn_from_tap(struct ctx *c,
 	if (!(conn->wnd_from_tap = (htons(th->window) >> conn->ws_from_tap)))
 		conn->wnd_from_tap = 1;
 
-	inany_from_af(&conn->faddr, af, daddr);
-	inany_from_af(&conn->caddr, af, saddr);
-	conn->fport = ntohs(th->dest);
-	conn->cport = ntohs(th->source);
+	demiflow_from_af(&conn->tapflow, af, daddr, ntohs(th->dest),
+			 saddr, ntohs(th->source));
 
 	if (af == AF_INET) {
 		sa = (struct sockaddr *)&addr4;
@@ -2719,18 +2720,18 @@ static void tcp_tap_conn_from_sock(struct ctx *c, union epoll_ref ref,
 	conn->ws_to_tap = conn->ws_from_tap = 0;
 	conn_event(c, conn, SOCK_ACCEPTED);
 
-	inany_from_sockaddr(&conn->faddr, &conn->fport, sa);
-	tcp_snat_inbound(c, &conn->faddr);
+	inany_from_sockaddr(&conn->tapflow.faddr, &conn->tapflow.fport, sa);
+	tcp_snat_inbound(c, &conn->tapflow.faddr);
 
 	if (CONN_V4(conn)) {
-		inany_from_af(&conn->caddr, AF_INET, &c->ip4.addr_seen);
+		inany_from_af(&conn->tapflow.caddr, AF_INET, &c->ip4.addr_seen);
 	} else {
-		if (IN6_IS_ADDR_LINKLOCAL(&conn->faddr.a6))
-			conn->caddr.a6 = c->ip6.addr_ll_seen;
+		if (IN6_IS_ADDR_LINKLOCAL(&conn->tapflow.faddr.a6))
+			conn->tapflow.caddr.a6 = c->ip6.addr_ll_seen;
 		else
-			conn->caddr.a6 = c->ip6.addr_seen;
+			conn->tapflow.caddr.a6 = c->ip6.addr_seen;
 	}
-	conn->cport = ref.r.p.tcp.tcp.index;
+	conn->tapflow.cport = ref.r.p.tcp.tcp.index;
 
 	tcp_seq_init(c, conn, now);
 	tcp_hash_insert(c, conn);
diff --git a/tcp_conn.h b/tcp_conn.h
index 9151c18..92d4637 100644
--- a/tcp_conn.h
+++ b/tcp_conn.h
@@ -35,10 +35,7 @@ extern const char *tcp_common_flag_str[];
  * @ws_to_tap:		Window scaling factor advertised to tap/guest
  * @sndbuf:		Sending buffer in kernel, rounded to 2 ^ SNDBUF_BITS
  * @seq_dup_ack_approx:	Last duplicate ACK number sent to tap
- * @caddr:		Guest side correspondent address (guest's local address)
- * @faddr:		Guest side forwarding address (guest's remote address)
- * @cport:		Guest side correspondent port (guest's local port)
- * @fport:		Guest side forwarding port (guest's remote port)
+ * @tapflow:		Tap(guest)-side demiflow
  * @wnd_from_tap:	Last window size from tap, unscaled (as received)
  * @wnd_to_tap:		Sending window advertised to tap, unscaled (as sent)
  * @seq_to_tap:		Next sequence for packets to tap
@@ -105,11 +102,7 @@ struct tcp_tap_conn {
 
 	uint8_t		seq_dup_ack_approx;
 
-
-	union inany_addr caddr;
-	union inany_addr faddr;
-	in_port_t	cport;
-	in_port_t	fport;
+	struct demiflow	tapflow;
 
 	uint16_t	wnd_from_tap;
 	uint16_t	wnd_to_tap;
diff --git a/tcp_splice.c b/tcp_splice.c
index 71256b0..a1aeff7 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -53,6 +53,7 @@
 #include "log.h"
 #include "tcp_splice.h"
 #include "inany.h"
+#include "flow.h"
 
 #include "tcp_conn.h"
 
-- 
@@ -53,6 +53,7 @@
 #include "log.h"
 #include "tcp_splice.h"
 #include "inany.h"
+#include "flow.h"
 
 #include "tcp_conn.h"
 
-- 
2.41.0