[PATCH 3/8] tcp: More precise terms for addresses and ports

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

In a number of places the comments and variable names we use to describe
addresses and ports are ambiguous.  It's not sufficient to describe a port
as "tap-facing" or "socket-facing", because on both the tap side and the
socket side there are two ports for the two ends of the connection.
Similarly, "local" and "remote" aren't particularly helpful, because it's
not necessarily clear whether we're talking from the point of view of the
guest/namespace, the host, or passt itself.

This patch makes a number of changes to be more precise about this.  It
introduces two new terms in aid of this:
    A "forwarding" address (or port) refers to an address which is local
from the point of view of passt itself.  That is a source address for
traffic sent by passt, whether it's to the guest via the tap interface
or to a host on the internet via a socket.
    The "correspondent" address (or port) is the reverse: a remote address
from passt's point of view, the destination address for traffic sent by
passt.

Between them the "side" (either tap/guest-facing or sock/host-facing) and
forwarding/correspondent unambiguously describes which address or port
we're talking about.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 tcp.c      | 93 +++++++++++++++++++++++++++---------------------------
 tcp_conn.h | 12 +++----
 2 files changed, 53 insertions(+), 52 deletions(-)

diff --git a/tcp.c b/tcp.c
index 482c25b..c1bfc4f 100644
--- a/tcp.c
+++ b/tcp.c
@@ -401,7 +401,7 @@ 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)->addr))
+#define CONN_V4(conn)		(!!inany_v4(&(conn)->faddr))
 #define CONN_V6(conn)		(!CONN_V4(conn))
 #define CONN_IS_CLOSING(conn)						\
 	((conn->events & ESTABLISHED) &&				\
@@ -434,7 +434,9 @@ static const char *tcp_flag_str[] __attribute((__unused__)) = {
 static int tcp_sock_init_ext	[NUM_PORTS][IP_VERSIONS];
 static int tcp_sock_ns		[NUM_PORTS][IP_VERSIONS];
 
-/* Table of destinations with very low RTT (assumed to be local), LRU */
+/* Table of guest side forwarding addresses with very low RTT (assumed
+ * to be local to the host), LRU
+ */
 static union inany_addr low_rtt_dst[LOW_RTT_TABLE_SIZE];
 
 /* Static buffers */
@@ -860,7 +862,7 @@ 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->addr, low_rtt_dst + i))
+		if (inany_equals(&conn->faddr, low_rtt_dst + i))
 			return 1;
 
 	return 0;
@@ -882,7 +884,7 @@ 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->addr, low_rtt_dst + i))
+		if (inany_equals(&conn->faddr, low_rtt_dst + i))
 			return;
 		if (hole == -1 && IN6_IS_ADDR_UNSPECIFIED(low_rtt_dst + i))
 			hole = i;
@@ -894,7 +896,7 @@ static void tcp_rtt_dst_check(const struct tcp_tap_conn *conn,
 	if (hole == -1)
 		return;
 
-	low_rtt_dst[hole++] = conn->addr;
+	low_rtt_dst[hole++] = conn->faddr;
 	if (hole == LOW_RTT_TABLE_SIZE)
 		hole = 0;
 	inany_from_af(low_rtt_dst + hole, AF_INET6, &in6addr_any);
@@ -1164,18 +1166,18 @@ static int tcp_opt_get(const char *opts, size_t len, uint8_t type_find,
 /**
  * tcp_hash_match() - Check if a connection entry matches address and ports
  * @conn:	Connection entry to match against
- * @addr:	Remote address
- * @tap_port:	tap-facing port
- * @sock_port:	Socket-facing port
+ * @faddr:	Guest side forwarding address
+ * @cport:	Guest side correspondent port
+ * @fport:	Guest side forwarding port
  *
  * Return: 1 on match, 0 otherwise
  */
 static int tcp_hash_match(const struct tcp_tap_conn *conn,
-			  const union inany_addr *addr,
-			  in_port_t tap_port, in_port_t sock_port)
+			  const union inany_addr *faddr,
+			  in_port_t cport, in_port_t fport)
 {
-	if (inany_equals(&conn->addr, addr) &&
-	    conn->tap_port == tap_port && conn->sock_port == sock_port)
+	if (inany_equals(&conn->faddr, faddr) &&
+	    conn->cport == cport && conn->fport == fport)
 		return 1;
 
 	return 0;
@@ -1184,21 +1186,21 @@ static int tcp_hash_match(const struct tcp_tap_conn *conn,
 /**
  * tcp_hash() - Calculate hash value for connection given address and ports
  * @c:		Execution context
- * @addr:	Remote address
- * @tap_port:	tap-facing port
- * @sock_port:	Socket-facing port
+ * @faddr:	Guest side forwarding address
+ * @cport:	Guest side correspondent port
+ * @fport:	Guest side forwarding port
  *
  * Return: hash value, already modulo size of the hash table
  */
-static unsigned int tcp_hash(const struct ctx *c, const union inany_addr *addr,
-			     in_port_t tap_port, in_port_t sock_port)
+static unsigned int tcp_hash(const struct ctx *c, const union inany_addr *faddr,
+			     in_port_t cport, in_port_t fport)
 {
 	struct {
-		union inany_addr addr;
-		in_port_t tap_port;
-		in_port_t sock_port;
+		union inany_addr faddr;
+		in_port_t cport;
+		in_port_t fport;
 	} __attribute__((__packed__)) in = {
-		*addr, tap_port, sock_port
+		*faddr, cport, fport
 	};
 	uint64_t b = 0;
 
@@ -1217,7 +1219,7 @@ static unsigned int tcp_hash(const struct ctx *c, const union inany_addr *addr,
 static unsigned int tcp_conn_hash(const struct ctx *c,
 				  const struct tcp_tap_conn *conn)
 {
-	return tcp_hash(c, &conn->addr, conn->tap_port, conn->sock_port);
+	return tcp_hash(c, &conn->faddr, conn->cport, conn->fport);
 }
 
 /**
@@ -1229,7 +1231,7 @@ static void tcp_hash_insert(const struct ctx *c, struct tcp_tap_conn *conn)
 {
 	int b;
 
-	b = tcp_hash(c, &conn->addr, conn->tap_port, conn->sock_port);
+	b = tcp_hash(c, &conn->faddr, conn->cport, conn->fport);
 	conn->next_index = tc_hash[b] ? CONN_IDX(tc_hash[b]) : -1;
 	tc_hash[b] = conn;
 
@@ -1298,25 +1300,24 @@ static void tcp_tap_conn_update(struct ctx *c, struct tcp_tap_conn *old,
  * tcp_hash_lookup() - Look up connection given remote address and ports
  * @c:		Execution context
  * @af:		Address family, AF_INET or AF_INET6
- * @addr:	Remote address, pointer to in_addr or in6_addr
- * @tap_port:	tap-facing port
- * @sock_port:	Socket-facing port
+ * @faddr:	Guest side forwarding address (guest remote address)
+ * @cport:	Guest side correspondent port (guest local port)
+ * @fport:	Guest side forwarding port (guest remote port)
  *
  * Return: connection pointer, if found, -ENOENT otherwise
  */
 static struct tcp_tap_conn *tcp_hash_lookup(const struct ctx *c,
-					    int af, const void *addr,
-					    in_port_t tap_port,
-					    in_port_t sock_port)
+					    int af, const void *faddr,
+					    in_port_t cport, in_port_t fport)
 {
 	union inany_addr aany;
 	struct tcp_tap_conn *conn;
 	int b;
 
-	inany_from_af(&aany, af, addr);
-	b = tcp_hash(c, &aany, tap_port, sock_port);
+	inany_from_af(&aany, af, faddr);
+	b = tcp_hash(c, &aany, cport, fport);
 	for (conn = tc_hash[b]; conn; conn = conn_at_idx(conn->next_index)) {
-		if (tcp_hash_match(conn, &aany, tap_port, sock_port))
+		if (tcp_hash_match(conn, &aany, cport, fport))
 			return conn;
 	}
 
@@ -1449,13 +1450,13 @@ 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->addr);
+	const struct in_addr *a4 = inany_v4(&conn->faddr);
 	size_t ip_len, tlen;
 
 #define SET_TCP_HEADER_COMMON_V4_V6(b, conn, seq)			\
 do {									\
-	b->th.source = htons(conn->sock_port);				\
-	b->th.dest = htons(conn->tap_port);				\
+	b->th.source = htons(conn->fport);				\
+	b->th.dest = htons(conn->cport);				\
 	b->th.seq = htonl(seq);						\
 	b->th.ack_seq = htonl(conn->seq_ack_to_tap);			\
 	if (conn->events & ESTABLISHED)	{				\
@@ -1491,7 +1492,7 @@ do {									\
 		ip_len = plen + sizeof(struct ipv6hdr) + sizeof(struct tcphdr);
 
 		b->ip6h.payload_len = htons(plen + sizeof(struct tcphdr));
-		b->ip6h.saddr = conn->addr.a6;
+		b->ip6h.saddr = conn->faddr.a6;
 		if (IN6_IS_ADDR_LINKLOCAL(&b->ip6h.saddr))
 			b->ip6h.daddr = c->ip6.addr_ll_seen;
 		else
@@ -1844,7 +1845,7 @@ static void tcp_clamp_window(const struct ctx *c, struct tcp_tap_conn *conn,
 /**
  * tcp_seq_init() - Calculate initial sequence number according to RFC 6528
  * @c:		Execution context
- * @conn:	TCP connection, with addr, sock_port and tap_port populated
+ * @conn:	TCP connection, with faddr, fport and cport populated
  * @now:	Current timestamp
  */
 static void tcp_seq_init(const struct ctx *c, struct tcp_tap_conn *conn,
@@ -1857,9 +1858,9 @@ 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->addr,
-		.srcport = conn->tap_port,
-		.dstport = conn->sock_port,
+		.src = conn->faddr,
+		.srcport = conn->cport,
+		.dstport = conn->fport,
 	};
 	uint32_t ns, seq = 0;
 
@@ -2084,7 +2085,7 @@ 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->addr, af, daddr);
+	inany_from_af(&conn->faddr, af, daddr);
 
 	if (af == AF_INET) {
 		sa = (struct sockaddr *)&addr4;
@@ -2094,8 +2095,8 @@ static void tcp_conn_from_tap(struct ctx *c,
 		sl = sizeof(addr6);
 	}
 
-	conn->sock_port = ntohs(th->dest);
-	conn->tap_port = ntohs(th->source);
+	conn->fport = ntohs(th->dest);
+	conn->cport = ntohs(th->source);
 
 	conn->seq_init_from_tap = ntohl(th->seq);
 	conn->seq_from_tap = conn->seq_init_from_tap + 1;
@@ -2754,10 +2755,10 @@ 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->addr, &conn->sock_port, sa);
-	conn->tap_port = ref.r.p.tcp.tcp.index;
+	inany_from_sockaddr(&conn->faddr, &conn->fport, sa);
+	conn->cport = ref.r.p.tcp.tcp.index;
 
-	tcp_snat_inbound(c, &conn->addr);
+	tcp_snat_inbound(c, &conn->faddr);
 
 	tcp_seq_init(c, conn, now);
 	tcp_hash_insert(c, conn);
diff --git a/tcp_conn.h b/tcp_conn.h
index 9e2b1bf..ba2a1ef 100644
--- a/tcp_conn.h
+++ b/tcp_conn.h
@@ -35,9 +35,9 @@ 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
- * @addr:		Remote address (IPv4 or IPv6)
- * @tap_port:		Guest-facing tap port
- * @sock_port:		Remote, socket-facing port
+ * @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)
  * @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
@@ -105,9 +105,9 @@ struct tcp_tap_conn {
 	uint8_t		seq_dup_ack_approx;
 
 
-	union inany_addr addr;
-	in_port_t	tap_port;
-	in_port_t	sock_port;
+	union inany_addr faddr;
+	in_port_t	cport;
+	in_port_t	fport;
 
 	uint16_t	wnd_from_tap;
 	uint16_t	wnd_to_tap;
-- 
@@ -35,9 +35,9 @@ 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
- * @addr:		Remote address (IPv4 or IPv6)
- * @tap_port:		Guest-facing tap port
- * @sock_port:		Remote, socket-facing port
+ * @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)
  * @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
@@ -105,9 +105,9 @@ struct tcp_tap_conn {
 	uint8_t		seq_dup_ack_approx;
 
 
-	union inany_addr addr;
-	in_port_t	tap_port;
-	in_port_t	sock_port;
+	union inany_addr faddr;
+	in_port_t	cport;
+	in_port_t	fport;
 
 	uint16_t	wnd_from_tap;
 	uint16_t	wnd_to_tap;
-- 
2.41.0