Currently TCP connections use a 1-bit selector, 'spliced', to determine the
rest of the contents of the structure.  We want to generalise the TCP
connection table to other types of flows in other protocols.  Make a start
on this by replacing the tcp_conn_common structure with a new flow_common
structure with an enum rather than a simple boolean indicating the type of
flow.

Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
 Makefile     |  8 +++----
 flow.c       | 16 +++++++++++++
 flow.h       | 36 ++++++++++++++++++++++++++++++
 tcp.c        | 63 +++++++++++++++++++++++++++++++++++++---------------
 tcp_conn.h   | 24 ++++++--------------
 tcp_splice.c |  3 ++-
 6 files changed, 110 insertions(+), 40 deletions(-)
 create mode 100644 flow.c
 create mode 100644 flow.h

diff --git a/Makefile b/Makefile
index 6c53695..e2970e3 100644
--- a/Makefile
+++ b/Makefile
@@ -44,15 +44,15 @@ FLAGS += -DARCH=\"$(TARGET_ARCH)\"
 FLAGS += -DVERSION=\"$(VERSION)\"
 FLAGS += -DDUAL_STACK_SOCKETS=$(DUAL_STACK_SOCKETS)
 
-PASST_SRCS = arch.c arp.c checksum.c conf.c dhcp.c dhcpv6.c icmp.c igmp.c \
-	isolation.c lineread.c log.c mld.c ndp.c netlink.c packet.c passt.c \
-	pasta.c pcap.c port_fwd.c tap.c tcp.c tcp_splice.c udp.c util.c
+PASST_SRCS = arch.c arp.c checksum.c conf.c dhcp.c dhcpv6.c flow.c icmp.c \
+	igmp.c isolation.c lineread.c log.c mld.c ndp.c netlink.c packet.c \
+	passt.c pasta.c pcap.c port_fwd.c tap.c tcp.c tcp_splice.c udp.c util.c
 QRAP_SRCS = qrap.c
 SRCS = $(PASST_SRCS) $(QRAP_SRCS)
 
 MANPAGES = passt.1 pasta.1 qrap.1
 
-PASST_HEADERS = arch.h arp.h checksum.h conf.h dhcp.h dhcpv6.h icmp.h \
+PASST_HEADERS = arch.h arp.h checksum.h conf.h dhcp.h dhcpv6.h flow.h icmp.h \
 	inany.h isolation.h lineread.h log.h ndp.h netlink.h packet.h passt.h \
 	pasta.h pcap.h pif.h port_fwd.h siphash.h tap.h tcp.h tcp_conn.h \
 	tcp_splice.h udp.h util.h
diff --git a/flow.c b/flow.c
new file mode 100644
index 0000000..7c3603c
--- /dev/null
+++ b/flow.c
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: David Gibson <david(a)gibson.dropbear.id.au>
+ *
+ * Tracking for logical "flows" of packets.
+ */
+
+#include <stdint.h>
+
+#include "flow.h"
+
+const char *flow_type_str[] = {
+	[FLOW_TYPE_NONE]	= "<none>",
+	[FLOW_TCP]		= "TCP connection",
+	[FLOW_TCP_SPLICE]	= "TCP connection (spliced)",
+};
diff --git a/flow.h b/flow.h
new file mode 100644
index 0000000..88e6f0b
--- /dev/null
+++ b/flow.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: David Gibson &lt;david(a)gibson.dropbear.id.au&gt;
+ *
+ * Tracking for logical "flows" of packets.
+ */
+#ifndef FLOW_H
+#define FLOW_H
+
+/**
+ * enum flow_type - Different types of packet flows we track
+ */
+enum flow_type {
+	/* Represents an invalid or unused flow */
+	FLOW_TYPE_NONE = 0,
+	/* A TCP connection between a socket and tap interface */
+	FLOW_TCP,
+	/* A TCP connection between a host socket and ns socket */
+	FLOW_TCP_SPLICE,
+
+	FLOW_TYPE_MAX = FLOW_TCP_SPLICE,
+};
+
+extern const char *flow_type_str[];
+#define FLOW_TYPE(f)							\
+        ((f)->type <= FLOW_TYPE_MAX ? flow_type_str[(f)->type] : "?")
+
+/**
+ * struct flow_common - Common fields for packet flows
+ * @type:	Type of packet flow
+ */
+struct flow_common {
+	uint8_t		type;
+};
+
+#endif /* FLOW_H */
diff --git a/tcp.c b/tcp.c
index 40e3dec..1c25032 100644
--- a/tcp.c
+++ b/tcp.c
@@ -299,6 +299,7 @@
 #include "tcp_splice.h"
 #include "log.h"
 #include "inany.h"
+#include "flow.h"
 
 #include "tcp_conn.h"
 
@@ -584,7 +585,7 @@ static inline struct tcp_tap_conn *conn_at_idx(int idx)
 {
 	if ((idx < 0) || (idx >= TCP_MAX_CONNS))
 		return NULL;
-	ASSERT(!(CONN(idx)->c.spliced));
+	ASSERT(CONN(idx)->f.type == FLOW_TCP);
 	return CONN(idx);
 }
 
@@ -1319,14 +1320,21 @@ void tcp_table_compact(struct ctx *c, union tcp_conn *hole)
 	from = tc + c->tcp.conn_count;
 	memcpy(hole, from, sizeof(*hole));
 
-	if (from->c.spliced)
-		tcp_splice_conn_update(c, &hole->splice);
-	else
+	switch (from->f.type) {
+	case FLOW_TCP:
 		tcp_tap_conn_update(c, &from->tap, &hole->tap);
+		break;
+	case FLOW_TCP_SPLICE:
+		tcp_splice_conn_update(c, &hole->splice);
+		break;
+	default:
+		die("Unexpected %s in tcp_table_compact()",
+		    FLOW_TYPE(&from->f));
+	}
 
-	debug("TCP: table compaction (spliced=%d): old index %li, new index %li, "
+	debug("TCP: table compaction (%s): old index %li, new index %li, "
 	      "from: %p, to: %p",
-	      from->c.spliced, CONN_IDX(from), CONN_IDX(hole),
+	      FLOW_TYPE(&from->f), CONN_IDX(from), CONN_IDX(hole),
 	      (void *)from, (void *)hole);
 
 	memset(from, 0, sizeof(*from));
@@ -1402,12 +1410,18 @@ void tcp_defer_handler(struct ctx *c)
 	tcp_l2_data_buf_flush(c);
 
 	for (conn = tc + c->tcp.conn_count - 1; conn >= tc; conn--) {
-		if (conn->c.spliced) {
-			if (conn->splice.flags & CLOSING)
-				tcp_splice_destroy(c, conn);
-		} else {
+		switch (conn->f.type) {
+		case FLOW_TCP:
 			if (conn->tap.events == CLOSED)
 				tcp_conn_destroy(c, conn);
+			break;
+		case FLOW_TCP_SPLICE:
+			if (conn->splice.flags & CLOSING)
+				tcp_splice_destroy(c, conn);
+			break;
+		default:
+			die("Unexpected %s in tcp_defer_handler()",
+			    FLOW_TYPE(&conn->f));
 		}
 	}
 }
@@ -2017,7 +2031,7 @@ static void tcp_conn_from_tap(struct ctx *c,
 	}
 
 	conn = CONN(c->tcp.conn_count++);
-	conn->c.spliced = false;
+	conn->f.type = FLOW_TCP;
 	conn->sock = s;
 	conn->timer = -1;
 	conn_event(c, conn, TAP_SYN_RCVD);
@@ -2726,7 +2740,7 @@ static void tcp_tap_conn_from_sock(struct ctx *c,
 				   const struct sockaddr *sa,
 				   const struct timespec *now)
 {
-	conn->c.spliced = false;
+	conn->f.type = FLOW_TCP;
 	conn->sock = s;
 	conn->timer = -1;
 	conn->ws_to_tap = conn->ws_from_tap = 0;
@@ -2909,10 +2923,17 @@ void tcp_sock_handler(struct ctx *c, union epoll_ref ref, uint32_t
events)
 {
 	union tcp_conn *conn = tc + ref.tcp.index;
 
-	if (conn->c.spliced)
-		tcp_splice_sock_handler(c, &conn->splice, ref.fd, events);
-	else
+	switch (conn->f.type) {
+	case FLOW_TCP:
 		tcp_tap_sock_handler(c, &conn->tap, events);
+		break;
+	case FLOW_TCP_SPLICE:
+		tcp_splice_sock_handler(c, &conn->splice, ref.fd, events);
+		break;
+	default:
+		die("Unexpected %s in tcp_sock_handler_compact()",
+		    FLOW_TYPE(&conn->f));
+	}
 }
 
 /**
@@ -3244,11 +3265,17 @@ void tcp_timer(struct ctx *c, const struct timespec *ts)
 	}
 
 	for (conn = tc + c->tcp.conn_count - 1; conn >= tc; conn--) {
-		if (conn->c.spliced) {
-			tcp_splice_timer(c, conn);
-		} else {
+		switch (conn->f.type) {
+		case FLOW_TCP:
 			if (conn->tap.events == CLOSED)
 				tcp_conn_destroy(c, conn);
+			break;
+		case FLOW_TCP_SPLICE:
+			tcp_splice_timer(c, conn);
+			break;
+		default:
+			die("Unexpected %s in tcp_timer()",
+			    FLOW_TYPE(&conn->f));
 		}
 	}
 
diff --git a/tcp_conn.h b/tcp_conn.h
index 0c6a35b..136f8da 100644
--- a/tcp_conn.h
+++ b/tcp_conn.h
@@ -9,19 +9,9 @@
 #ifndef TCP_CONN_H
 #define TCP_CONN_H
 
-/**
- * struct tcp_conn_common - Common fields for spliced and non-spliced
- * @spliced:		Is this a spliced connection?
- */
-struct tcp_conn_common {
-	bool spliced	:1;
-};
-
-extern const char *tcp_common_flag_str[];
-
 /**
  * struct tcp_tap_conn - Descriptor for a TCP connection (not spliced)
- * @c:			Fields common with tcp_splice_conn
+ * @f:			Generic flow information
  * @in_epoll:		Is the connection in the epoll set?
  * @next_index:		Connection index of next item in hash chain, -1 for none
  * @tap_mss:		MSS advertised by tap/guest, rounded to 2 ^ TCP_MSS_BITS
@@ -46,8 +36,8 @@ extern const char *tcp_common_flag_str[];
  * @seq_init_from_tap:	Initial sequence number from tap
  */
 struct tcp_tap_conn {
-	/* Must be first element to match tcp_splice_conn */
-	struct tcp_conn_common c;
+	/* Must be first element */
+	struct flow_common f;
 
 	bool		in_epoll	:1;
 	int	 	next_index	:TCP_CONN_INDEX_BITS + 2;
@@ -121,7 +111,7 @@ struct tcp_tap_conn {
 #define SIDES			2
 /**
  * struct tcp_splice_conn - Descriptor for a spliced TCP connection
- * @c:			Fields common with tcp_tap_conn
+ * @f:			Generic flow information
  * @in_epoll:		Is the connection in the epoll set?
  * @s:			File descriptor for sockets
  * @pipe:		File descriptors for pipes
@@ -131,8 +121,8 @@ struct tcp_tap_conn {
  * @written:		Bytes written (not fully written from one other side read)
 */
 struct tcp_splice_conn {
-	/* Must be first element to match tcp_tap_conn */
-	struct tcp_conn_common c;
+	/* Must be first element */
+	struct flow_common f;
 
 	bool in_epoll	:1;
 	int s[SIDES];
@@ -168,7 +158,7 @@ struct tcp_splice_conn {
  * @splice:		Fields specific to spliced connections
 */
 union tcp_conn {
-	struct tcp_conn_common c;
+	struct flow_common f;
 	struct tcp_tap_conn tap;
 	struct tcp_splice_conn splice;
 };
diff --git a/tcp_splice.c b/tcp_splice.c
index a5c1332..bfd2bd1 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -54,6 +54,7 @@
 #include "tcp_splice.h"
 #include "siphash.h"
 #include "inany.h"
+#include "flow.h"
 
 #include "tcp_conn.h"
 
@@ -476,7 +477,7 @@ bool tcp_splice_conn_from_sock(const struct ctx *c,
 	if (setsockopt(s, SOL_TCP, TCP_QUICKACK, &((int){ 1 }), sizeof(int)))
 		trace("TCP (spliced): failed to set TCP_QUICKACK on %i", s);
 
-	conn->c.spliced = true;
+	conn->f.type = FLOW_TCP_SPLICE;
 	conn->s[0] = s;
 
 	if (tcp_splice_new(c, conn, ref.port, ref.pif))
-- 
2.43.0

Both tcp.c and tcp_splice.c define CONN_IDX() variants to find the index
of their connection structures in the connection table, now become the
unified flow table.  We can easily combine these into a common helper.
While we're there, add some trickery for some additional type safety.

They also define their own CONN() versions, which aren't so easily combined
since they need to return different types, but we can have them use a
common helper.

In the process, we standardise on always using an unsigned type to store
the connection / flow index, which makes more sense.  tcp.c's conn_at_idx()
remains for now, but we change its parameter to unsigned to match.  That in
turn means we can remove a check for negative values from it.

Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
 flow_table.h | 25 ++++++++++++++++++++
 tcp.c        | 65 ++++++++++++++++++++++++++--------------------------
 tcp_conn.h   |  2 +-
 tcp_splice.c | 21 ++++++++---------
 4 files changed, 68 insertions(+), 45 deletions(-)

diff --git a/flow_table.h b/flow_table.h
index c4c646b..5e897bd 100644
--- a/flow_table.h
+++ b/flow_table.h
@@ -22,4 +22,29 @@ union flow {
 /* Global Flow Table */
 extern union flow flowtab[];
 
+
+/** flow_idx - Index of flow from common structure
+ * @f:	Common flow fields pointer
+ *
+ * Return: index of @f in the flow table
+ */
+static inline unsigned flow_idx(const struct flow_common *f)
+{
+	return (union flow *)f - flowtab;
+}
+
+/** FLOW_IDX - Find the index of a flow
+ * @f_:	Flow pointer, either union flow * or protocol specific
+ *
+ * Return: index of @f in the flow table
+ */
+#define FLOW_IDX(f_)		(flow_idx(&(f_)->f))
+
+/** FLOW - Flow entry at a given index
+ * @idx:	Flow index
+ *
+ * Return: pointer to entry @idx in the flow table
+ */
+#define FLOW(idx)		(&flowtab[(idx)])
+
 #endif /* FLOW_TABLE_H */
diff --git a/tcp.c b/tcp.c
index 0119bd3..859df6f 100644
--- a/tcp.c
+++ b/tcp.c
@@ -570,17 +570,16 @@ tcp6_l2_flags_buf[TCP_FRAMES_MEM];
 
 static unsigned int tcp6_l2_flags_buf_used;
 
-#define CONN(idx)		(&flowtab[(idx)].tcp)
-#define CONN_IDX(conn)		((union flow *)(conn) - flowtab)
+#define CONN(idx)		(&(FLOW(idx)->tcp))
 
 /** conn_at_idx() - Find a connection by index, if present
  * @idx:	Index of connection to lookup
  *
  * Return: pointer to connection, or NULL if @idx is out of bounds
  */
-static inline struct tcp_tap_conn *conn_at_idx(int idx)
+static inline struct tcp_tap_conn *conn_at_idx(unsigned idx)
 {
-	if ((idx < 0) || (idx >= FLOW_MAX))
+	if (idx >= FLOW_MAX)
 		return NULL;
 	ASSERT(CONN(idx)->f.type == FLOW_TCP);
 	return CONN(idx);
@@ -640,7 +639,7 @@ static int tcp_epoll_ctl(const struct ctx *c, struct tcp_tap_conn
*conn)
 {
 	int m = conn->in_epoll ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
 	union epoll_ref ref = { .type = EPOLL_TYPE_TCP, .fd = conn->sock,
-				.tcp.index = CONN_IDX(conn) };
+				.tcp.index = FLOW_IDX(conn) };
 	struct epoll_event ev = { .data.u64 = ref.u64 };
 
 	if (conn->events == CLOSED) {
@@ -661,7 +660,7 @@ static int tcp_epoll_ctl(const struct ctx *c, struct tcp_tap_conn
*conn)
 	if (conn->timer != -1) {
 		union epoll_ref ref_t = { .type = EPOLL_TYPE_TCP_TIMER,
 					  .fd = conn->sock,
-					  .tcp.index = CONN_IDX(conn) };
+					  .tcp.index = FLOW_IDX(conn) };
 		struct epoll_event ev_t = { .data.u64 = ref_t.u64,
 					    .events = EPOLLIN | EPOLLET };
 
@@ -689,7 +688,7 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_tap_conn
*conn)
 	if (conn->timer == -1) {
 		union epoll_ref ref = { .type = EPOLL_TYPE_TCP_TIMER,
 					.fd = conn->sock,
-					.tcp.index = CONN_IDX(conn) };
+					.tcp.index = FLOW_IDX(conn) };
 		struct epoll_event ev = { .data.u64 = ref.u64,
 					  .events = EPOLLIN | EPOLLET };
 		int fd;
@@ -725,7 +724,7 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_tap_conn
*conn)
 		it.it_value.tv_sec = ACT_TIMEOUT;
 	}
 
-	debug("TCP: index %li, timer expires in %lu.%03lus", CONN_IDX(conn),
+	debug("TCP: index %u, timer expires in %lu.%03lus", FLOW_IDX(conn),
 	      it.it_value.tv_sec, it.it_value.tv_nsec / 1000 / 1000);
 
 	timerfd_settime(conn->timer, 0, &it, NULL);
@@ -748,7 +747,7 @@ static void conn_flag_do(const struct ctx *c, struct tcp_tap_conn
*conn,
 
 		conn->flags &= flag;
 		if (flag_index >= 0) {
-			debug("TCP: index %li: %s dropped", CONN_IDX(conn),
+			debug("TCP: index %u: %s dropped", FLOW_IDX(conn),
 			      tcp_flag_str[flag_index]);
 		}
 	} else {
@@ -769,7 +768,7 @@ static void conn_flag_do(const struct ctx *c, struct tcp_tap_conn
*conn,
 
 		conn->flags |= flag;
 		if (flag_index >= 0) {
-			debug("TCP: index %li: %s", CONN_IDX(conn),
+			debug("TCP: index %u: %s", FLOW_IDX(conn),
 			      tcp_flag_str[flag_index]);
 		}
 	}
@@ -819,12 +818,12 @@ static void conn_event_do(const struct ctx *c, struct tcp_tap_conn
*conn,
 		new += 5;
 
 	if (prev != new) {
-		debug("TCP: index %li, %s: %s -> %s", CONN_IDX(conn),
+		debug("TCP: index %u, %s: %s -> %s", FLOW_IDX(conn),
 		      num == -1 	       ? "CLOSED" : tcp_event_str[num],
 		      prev == -1	       ? "CLOSED" : tcp_state_str[prev],
 		      (new == -1 || num == -1) ? "CLOSED" : tcp_state_str[new]);
 	} else {
-		debug("TCP: index %li, %s", CONN_IDX(conn),
+		debug("TCP: index %u, %s", FLOW_IDX(conn),
 		      num == -1 	       ? "CLOSED" : tcp_event_str[num]);
 	}
 
@@ -1204,11 +1203,11 @@ static void tcp_hash_insert(const struct ctx *c, struct
tcp_tap_conn *conn)
 	int b;
 
 	b = tcp_hash(c, &conn->faddr, conn->eport, conn->fport);
-	conn->next_index = tc_hash[b] ? CONN_IDX(tc_hash[b]) : -1;
+	conn->next_index = tc_hash[b] ? FLOW_IDX(tc_hash[b]) : -1U;
 	tc_hash[b] = conn;
 
-	debug("TCP: hash table insert: index %li, sock %i, bucket: %i, next: "
-	      "%p", CONN_IDX(conn), conn->sock, b,
+	debug("TCP: hash table insert: index %u, sock %i, bucket: %i, next: "
+	      "%p", FLOW_IDX(conn), conn->sock, b,
 	      (void *)conn_at_idx(conn->next_index));
 }
 
@@ -1234,8 +1233,8 @@ static void tcp_hash_remove(const struct ctx *c,
 		}
 	}
 
-	debug("TCP: hash table remove: index %li, sock %i, bucket: %i, new: %p",
-	      CONN_IDX(conn), conn->sock, b,
+	debug("TCP: hash table remove: index %u, sock %i, bucket: %i, new: %p",
+	      FLOW_IDX(conn), conn->sock, b,
 	      (void *)(prev ? conn_at_idx(prev->next_index) : tc_hash[b]));
 }
 
@@ -1255,16 +1254,16 @@ static void tcp_tap_conn_update(const struct ctx *c, struct
tcp_tap_conn *old,
 	     prev = entry, entry = conn_at_idx(entry->next_index)) {
 		if (entry == old) {
 			if (prev)
-				prev->next_index = CONN_IDX(new);
+				prev->next_index = FLOW_IDX(new);
 			else
 				tc_hash[b] = new;
 			break;
 		}
 	}
 
-	debug("TCP: hash table update: old index %li, new index %li, sock %i, "
+	debug("TCP: hash table update: old index %u, new index %u, sock %i, "
 	      "bucket: %i, old: %p, new: %p",
-	      CONN_IDX(old), CONN_IDX(new), new->sock, b,
+	      FLOW_IDX(old), FLOW_IDX(new), new->sock, b,
 	      (void *)old, (void *)new);
 
 	tcp_epoll_ctl(c, new);
@@ -1307,9 +1306,9 @@ void tcp_table_compact(struct ctx *c, union flow *hole)
 {
 	union flow *from;
 
-	if (CONN_IDX(hole) == --c->flow_count) {
-		debug("TCP: table compaction: maximum index was %li (%p)",
-		      CONN_IDX(hole), (void *)hole);
+	if (FLOW_IDX(hole) == --c->flow_count) {
+		debug("TCP: table compaction: maximum index was %u (%p)",
+		      FLOW_IDX(hole), (void *)hole);
 		memset(hole, 0, sizeof(*hole));
 		return;
 	}
@@ -1329,9 +1328,9 @@ void tcp_table_compact(struct ctx *c, union flow *hole)
 		    FLOW_TYPE(&from->f));
 	}
 
-	debug("TCP: table compaction (%s): old index %li, new index %li, "
+	debug("TCP: table compaction (%s): old index %u, new index %u, "
 	      "from: %p, to: %p",
-	      FLOW_TYPE(&from->f), CONN_IDX(from), CONN_IDX(hole),
+	      FLOW_TYPE(&from->f), FLOW_IDX(from), FLOW_IDX(hole),
 	      (void *)from, (void *)hole);
 
 	memset(from, 0, sizeof(*from));
@@ -1357,7 +1356,7 @@ static void tcp_conn_destroy(struct ctx *c, union flow *flow)
 static void tcp_rst_do(struct ctx *c, struct tcp_tap_conn *conn);
 #define tcp_rst(c, conn)						\
 	do {								\
-		debug("TCP: index %li, reset at %s:%i", CONN_IDX(conn), \
+		debug("TCP: index %u, reset at %s:%i", FLOW_IDX(conn),	\
 		      __func__, __LINE__);				\
 		tcp_rst_do(c, conn);					\
 	} while (0)
@@ -2581,7 +2580,7 @@ int tcp_tap_handler(struct ctx *c, uint8_t pif, int af,
 		return 1;
 	}
 
-	trace("TCP: packet length %lu from tap for index %lu", len, CONN_IDX(conn));
+	trace("TCP: packet length %lu from tap for index %u", len, FLOW_IDX(conn));
 
 	if (th->rst) {
 		conn_event(c, conn, CLOSED);
@@ -2821,17 +2820,17 @@ void tcp_timer_handler(struct ctx *c, union epoll_ref ref)
 		tcp_timer_ctl(c, conn);
 	} else if (conn->flags & ACK_FROM_TAP_DUE) {
 		if (!(conn->events & ESTABLISHED)) {
-			debug("TCP: index %li, handshake timeout", CONN_IDX(conn));
+			debug("TCP: index %u, handshake timeout", FLOW_IDX(conn));
 			tcp_rst(c, conn);
 		} else if (CONN_HAS(conn, SOCK_FIN_SENT | TAP_FIN_ACKED)) {
-			debug("TCP: index %li, FIN timeout", CONN_IDX(conn));
+			debug("TCP: index %u, FIN timeout", FLOW_IDX(conn));
 			tcp_rst(c, conn);
 		} else if (conn->retrans == TCP_MAX_RETRANS) {
-			debug("TCP: index %li, retransmissions count exceeded",
-			      CONN_IDX(conn));
+			debug("TCP: index %u, retransmissions count exceeded",
+			      FLOW_IDX(conn));
 			tcp_rst(c, conn);
 		} else {
-			debug("TCP: index %li, ACK timeout, retry", CONN_IDX(conn));
+			debug("TCP: index %u, ACK timeout, retry", FLOW_IDX(conn));
 			conn->retrans++;
 			conn->seq_to_tap = conn->seq_ack_from_tap;
 			tcp_data_from_sock(c, conn);
@@ -2849,7 +2848,7 @@ void tcp_timer_handler(struct ctx *c, union epoll_ref ref)
 		 */
 		timerfd_settime(conn->timer, 0, &new, &old);
 		if (old.it_value.tv_sec == ACT_TIMEOUT) {
-			debug("TCP: index %li, activity timeout", CONN_IDX(conn));
+			debug("TCP: index %u, activity timeout", FLOW_IDX(conn));
 			tcp_rst(c, conn);
 		}
 	}
diff --git a/tcp_conn.h b/tcp_conn.h
index 5a107fc..5a9376e 100644
--- a/tcp_conn.h
+++ b/tcp_conn.h
@@ -40,7 +40,7 @@ struct tcp_tap_conn {
 	struct flow_common f;
 
 	bool		in_epoll	:1;
-	int	 	next_index	:FLOW_INDEX_BITS + 2;
+	unsigned 	next_index	:FLOW_INDEX_BITS + 2;
 
 #define TCP_RETRANS_BITS		3
 	unsigned int	retrans		:TCP_RETRANS_BITS;
diff --git a/tcp_splice.c b/tcp_splice.c
index 9f4831a..3955417 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -76,8 +76,7 @@ static int splice_pipe_pool		[TCP_SPLICE_PIPE_POOL_SIZE][2];
 #define CONN_V6(x)			(x->flags & SPLICE_V6)
 #define CONN_V4(x)			(!CONN_V6(x))
 #define CONN_HAS(conn, set)		((conn->events & (set)) == (set))
-#define CONN(idx)			(&tc[(idx)].splice)
-#define CONN_IDX(conn)			((union flow *)(conn) - flowtab)
+#define CONN(idx)			(&FLOW(idx)->tcp_splice)
 
 /* Display strings for connection events */
 static const char *tcp_splice_event_str[] __attribute((__unused__)) = {
@@ -129,8 +128,8 @@ static int tcp_splice_epoll_ctl(const struct ctx *c,
 {
 	int m = conn->in_epoll ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
 	union epoll_ref ref[SIDES] = {
-		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[0], .tcp.index = CONN_IDX(conn) },
-		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[1], .tcp.index = CONN_IDX(conn) }
+		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[0], .tcp.index = FLOW_IDX(conn) },
+		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[1], .tcp.index = FLOW_IDX(conn) }
 	};
 	struct epoll_event ev[SIDES] = { { .data.u64 = ref[0].u64 },
 					 { .data.u64 = ref[1].u64 } };
@@ -140,8 +139,8 @@ static int tcp_splice_epoll_ctl(const struct ctx *c,
 	if (epoll_ctl(c->epollfd, m, conn->s[0], &ev[0]) ||
 	    epoll_ctl(c->epollfd, m, conn->s[1], &ev[1])) {
 		int ret = -errno;
-		err("TCP (spliced): index %li, ERROR on epoll_ctl(): %s",
-		    CONN_IDX(conn), strerror(errno));
+		err("TCP (spliced): index %u, ERROR on epoll_ctl(): %s",
+		    FLOW_IDX(conn), strerror(errno));
 		return ret;
 	}
 
@@ -167,7 +166,7 @@ static void conn_flag_do(const struct ctx *c, struct tcp_splice_conn
*conn,
 
 		conn->flags &= flag;
 		if (flag_index >= 0) {
-			debug("TCP (spliced): index %li: %s dropped", CONN_IDX(conn),
+			debug("TCP (spliced): index %u: %s dropped", FLOW_IDX(conn),
 			      tcp_splice_flag_str[flag_index]);
 		}
 	} else {
@@ -178,7 +177,7 @@ static void conn_flag_do(const struct ctx *c, struct tcp_splice_conn
*conn,
 
 		conn->flags |= flag;
 		if (flag_index >= 0) {
-			debug("TCP (spliced): index %li: %s", CONN_IDX(conn),
+			debug("TCP (spliced): index %u: %s", FLOW_IDX(conn),
 			      tcp_splice_flag_str[flag_index]);
 		}
 	}
@@ -213,7 +212,7 @@ static void conn_event_do(const struct ctx *c, struct tcp_splice_conn
*conn,
 
 		conn->events &= event;
 		if (flag_index >= 0) {
-			debug("TCP (spliced): index %li, ~%s", CONN_IDX(conn),
+			debug("TCP (spliced): index %u, ~%s", FLOW_IDX(conn),
 			      tcp_splice_event_str[flag_index]);
 		}
 	} else {
@@ -224,7 +223,7 @@ static void conn_event_do(const struct ctx *c, struct tcp_splice_conn
*conn,
 
 		conn->events |= event;
 		if (flag_index >= 0) {
-			debug("TCP (spliced): index %li, %s", CONN_IDX(conn),
+			debug("TCP (spliced): index %u, %s", FLOW_IDX(conn),
 			      tcp_splice_event_str[flag_index]);
 		}
 	}
@@ -282,7 +281,7 @@ void tcp_splice_destroy(struct ctx *c, union flow *flow)
 
 	conn->events = SPLICE_CLOSED;
 	conn->flags = 0;
-	debug("TCP (spliced): index %li, CLOSED", CONN_IDX(conn));
+	debug("TCP (spliced): index %u, CLOSED", FLOW_IDX(conn));
 
 	tcp_table_compact(c, flow);
 }
-- 
2.43.0

tcp_table_compact() will move entries in the connection/flow table to keep
it compact when other entries are removed.  The moved entries need not have
the same type as the flow removed, so it needs to be able to handle moving
any type of flow.  Therefore, move it to flow.c rather than being
purportedly TCP specific.

Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
 flow.c       | 39 +++++++++++++++++++++++++++++++++++++++
 flow.h       |  2 ++
 tcp.c        | 46 ++++------------------------------------------
 tcp_conn.h   |  3 ++-
 tcp_splice.c |  2 +-
 5 files changed, 48 insertions(+), 44 deletions(-)

diff --git a/flow.c b/flow.c
index a9bb8f5..0fff119 100644
--- a/flow.c
+++ b/flow.c
@@ -25,3 +25,42 @@ const char *flow_type_str[] = {
 
 /* Global Flow Table */
 union flow flowtab[FLOW_MAX];
+
+/**
+ * flow_table_compact() - Perform compaction on flow table
+ * @c:		Execution context
+ * @hole:	Pointer to recently closed flow
+ */
+void flow_table_compact(struct ctx *c, union flow *hole)
+{
+	union flow *from;
+
+	if (FLOW_IDX(hole) == --c->flow_count) {
+		debug("flow: table compaction: maximum index was %u (%p)",
+		      FLOW_IDX(hole), (void *)hole);
+		memset(hole, 0, sizeof(*hole));
+		return;
+	}
+
+	from = flowtab + c->flow_count;
+	memcpy(hole, from, sizeof(*hole));
+
+	switch (from->f.type) {
+	case FLOW_TCP:
+		tcp_tap_conn_update(c, &from->tcp, &hole->tcp);
+		break;
+	case FLOW_TCP_SPLICE:
+		tcp_splice_conn_update(c, &hole->tcp_splice);
+		break;
+	default:
+		die("Unexpected %s in tcp_table_compact()",
+		    FLOW_TYPE(&from->f));
+	}
+
+	debug("flow: table compaction (%s): old index %u, new index %u, "
+	      "from: %p, to: %p",
+	      FLOW_TYPE(&from->f), FLOW_IDX(from), FLOW_IDX(hole),
+	      (void *)from, (void *)hole);
+
+	memset(from, 0, sizeof(*from));
+}
diff --git a/flow.h b/flow.h
index 57289a8..9f49195 100644
--- a/flow.h
+++ b/flow.h
@@ -41,4 +41,6 @@ struct flow_common {
 
 union flow;
 
+void flow_table_compact(struct ctx *c, union flow *hole);
+
 #endif /* FLOW_H */
diff --git a/tcp.c b/tcp.c
index 859df6f..6924dd2 100644
--- a/tcp.c
+++ b/tcp.c
@@ -1244,8 +1244,9 @@ static void tcp_hash_remove(const struct ctx *c,
  * @old:	Old location of tcp_tap_conn
  * @new:	New location of tcp_tap_conn
  */
-static void tcp_tap_conn_update(const struct ctx *c, struct tcp_tap_conn *old,
-				struct tcp_tap_conn *new)
+void tcp_tap_conn_update(const struct ctx *c, struct tcp_tap_conn *old,
+			 struct tcp_tap_conn *new)
+
 {
 	struct tcp_tap_conn *entry, *prev = NULL;
 	int b = tcp_conn_hash(c, old);
@@ -1297,45 +1298,6 @@ static struct tcp_tap_conn *tcp_hash_lookup(const struct ctx *c,
 	return NULL;
 }
 
-/**
- * tcp_table_compact() - Perform compaction on connection table
- * @c:		Execution context
- * @hole:	Pointer to recently closed connection
- */
-void tcp_table_compact(struct ctx *c, union flow *hole)
-{
-	union flow *from;
-
-	if (FLOW_IDX(hole) == --c->flow_count) {
-		debug("TCP: table compaction: maximum index was %u (%p)",
-		      FLOW_IDX(hole), (void *)hole);
-		memset(hole, 0, sizeof(*hole));
-		return;
-	}
-
-	from = flowtab + c->flow_count;
-	memcpy(hole, from, sizeof(*hole));
-
-	switch (from->f.type) {
-	case FLOW_TCP:
-		tcp_tap_conn_update(c, &from->tcp, &hole->tcp);
-		break;
-	case FLOW_TCP_SPLICE:
-		tcp_splice_conn_update(c, &hole->tcp_splice);
-		break;
-	default:
-		die("Unexpected %s in tcp_table_compact()",
-		    FLOW_TYPE(&from->f));
-	}
-
-	debug("TCP: table compaction (%s): old index %u, new index %u, "
-	      "from: %p, to: %p",
-	      FLOW_TYPE(&from->f), FLOW_IDX(from), FLOW_IDX(hole),
-	      (void *)from, (void *)hole);
-
-	memset(from, 0, sizeof(*from));
-}
-
 /**
  * tcp_conn_destroy() - Close sockets, trigger hash table removal and compaction
  * @c:		Execution context
@@ -1350,7 +1312,7 @@ static void tcp_conn_destroy(struct ctx *c, union flow *flow)
 		close(conn->timer);
 
 	tcp_hash_remove(c, conn);
-	tcp_table_compact(c, flow);
+	flow_table_compact(c, flow);
 }
 
 static void tcp_rst_do(struct ctx *c, struct tcp_tap_conn *conn);
diff --git a/tcp_conn.h b/tcp_conn.h
index 5a9376e..3900305 100644
--- a/tcp_conn.h
+++ b/tcp_conn.h
@@ -157,8 +157,9 @@ struct tcp_splice_conn {
 extern int init_sock_pool4	[TCP_SOCK_POOL_SIZE];
 extern int init_sock_pool6	[TCP_SOCK_POOL_SIZE];
 
+void tcp_tap_conn_update(const struct ctx *c, struct tcp_tap_conn *old,
+			 struct tcp_tap_conn *new);
 void tcp_splice_conn_update(const struct ctx *c, struct tcp_splice_conn *new);
-void tcp_table_compact(struct ctx *c, union flow *hole);
 void tcp_splice_destroy(struct ctx *c, union flow *flow);
 void tcp_splice_timer(struct ctx *c, union flow *flow);
 int tcp_conn_pool_sock(int pool[]);
diff --git a/tcp_splice.c b/tcp_splice.c
index 3955417..212fe16 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -283,7 +283,7 @@ void tcp_splice_destroy(struct ctx *c, union flow *flow)
 	conn->flags = 0;
 	debug("TCP (spliced): index %u, CLOSED", FLOW_IDX(conn));
 
-	tcp_table_compact(c, flow);
+	flow_table_compact(c, flow);
 }
 
 /**
-- 
2.43.0

In a number of places, we use indices into the flow table to identify a
specific flow.  We also have cases where we need to identify a particular
side of a particular flow, and we expect those to become more common as
we generalise the flow table to cover more things.

To assist with that, introduces flow_sidx_t, an index type which identifies
a specific side of a specific flow in the table.

Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
 flow.h       | 13 +++++++++++++
 flow_table.h | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/flow.h b/flow.h
index b6da516..3c90bbd 100644
--- a/flow.h
+++ b/flow.h
@@ -39,6 +39,19 @@ struct flow_common {
 #define FLOW_TABLE_PRESSURE		30	/* % of FLOW_MAX */
 #define FLOW_FILE_PRESSURE		30	/* % of c->nofile */
 
+/**
+ * struct flow_sidx - ID for one side of a specific flow
+ * @side:	Side referenced (0 or 1)
+ * @flow:	Index of flow referenced
+ */
+typedef struct flow_sidx {
+	int		side :1;
+	unsigned	flow :FLOW_INDEX_BITS;
+} flow_sidx_t;
+static_assert(sizeof(flow_sidx_t) <= sizeof(uint32_t));
+
+#define FLOW_SIDX_NONE ((flow_sidx_t){ .flow = FLOW_MAX })
+
 union flow;
 
 void flow_table_compact(struct ctx *c, union flow *hole);
diff --git a/flow_table.h b/flow_table.h
index 5e897bd..3c68d4a 100644
--- a/flow_table.h
+++ b/flow_table.h
@@ -47,4 +47,40 @@ static inline unsigned flow_idx(const struct flow_common *f)
  */
 #define FLOW(idx)		(&flowtab[(idx)])
 
+/** flow_at_sidx - Flow entry for a given sidx
+ * @sidx:	Flow & side index
+ *
+ * Return: pointer to the corresponding flow entry, or NULL
+ */
+static inline union flow *flow_at_sidx(flow_sidx_t sidx)
+{
+	if (sidx.flow >= FLOW_MAX)
+		return NULL;
+	return FLOW(sidx.flow);
+}
+
+/** flow_sidx_t - Index of one side of a flow from common structure
+ * @f:		Common flow fields pointer
+ * @side:	Which side to refer to (0 or 1)
+ *
+ * Return: index of @f and @side in the flow table
+ */
+static inline flow_sidx_t flow_sidx(const struct flow_common *f,
+				    int side)
+{
+	ASSERT(side == !!side);
+	return (flow_sidx_t){
+		.side = side,
+		.flow = flow_idx(f),
+	};
+}
+
+/** FLOW_SIDX - Find the index of one side of a flow
+ * @f_:		Flow pointer, either union flow * or protocol specific
+ * @side:	Which side to index (0 or 1)
+ *
+ * Return: index of @f and @side in the flow table
+ */
+#define FLOW_SIDX(f_, side)	(flow_sidx(&(f_)->f, (side)))
+
 #endif /* FLOW_TABLE_H */
-- 
2.43.0

TCP uses three different epoll object types: one for connected sockets, one
for timers and one for listening sockets.  Listening sockets really need
information that's specific to TCP, so need their own epoll_ref field.
Timers and connected sockets, however, only need the connection (flow)
they're associated with.  As we expand the use of the flow table, we expect
that to be true for more epoll fds.  So, rename the "TCP" epoll_ref field
to be a "flow" epoll_ref field that can be used both for TCP and for other
future cases.

Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
 passt.h      |  6 +++---
 tcp.c        | 10 +++++-----
 tcp_splice.c |  4 ++--
 3 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/passt.h b/passt.h
index 0fce637..66a819f 100644
--- a/passt.h
+++ b/passt.h
@@ -76,8 +76,8 @@ enum epoll_type {
  * union epoll_ref - Breakdown of reference for epoll fd bookkeeping
  * @type:	Type of fd (tells us what to do with events)
  * @fd:		File descriptor number (implies < 2^24 total descriptors)
- * @tcp:	TCP-specific reference part (connected sockets)
- * @tcp_listen:	TCP-specific reference part (listening sockets)
+ * @flow:	Index of the flow this fd is linked to
+ * @tcp_listen:	TCP-specific reference part for listening sockets
  * @udp:	UDP-specific reference part
  * @icmp:	ICMP-specific reference part
  * @data:	Data handled by protocol handlers
@@ -90,7 +90,7 @@ union epoll_ref {
 #define FD_REF_MAX		((int)MAX_FROM_BITS(FD_REF_BITS))
 		int32_t		fd:FD_REF_BITS;
 		union {
-			union tcp_epoll_ref tcp;
+			uint32_t flow;
 			union tcp_listen_epoll_ref tcp_listen;
 			union udp_epoll_ref udp;
 			union icmp_epoll_ref icmp;
diff --git a/tcp.c b/tcp.c
index 512baf3..e80a6aa 100644
--- a/tcp.c
+++ b/tcp.c
@@ -639,7 +639,7 @@ static int tcp_epoll_ctl(const struct ctx *c, struct tcp_tap_conn
*conn)
 {
 	int m = conn->in_epoll ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
 	union epoll_ref ref = { .type = EPOLL_TYPE_TCP, .fd = conn->sock,
-				.tcp.index = FLOW_IDX(conn) };
+				.flow = FLOW_IDX(conn) };
 	struct epoll_event ev = { .data.u64 = ref.u64 };
 
 	if (conn->events == CLOSED) {
@@ -660,7 +660,7 @@ static int tcp_epoll_ctl(const struct ctx *c, struct tcp_tap_conn
*conn)
 	if (conn->timer != -1) {
 		union epoll_ref ref_t = { .type = EPOLL_TYPE_TCP_TIMER,
 					  .fd = conn->sock,
-					  .tcp.index = FLOW_IDX(conn) };
+					  .flow = FLOW_IDX(conn) };
 		struct epoll_event ev_t = { .data.u64 = ref_t.u64,
 					    .events = EPOLLIN | EPOLLET };
 
@@ -688,7 +688,7 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_tap_conn
*conn)
 	if (conn->timer == -1) {
 		union epoll_ref ref = { .type = EPOLL_TYPE_TCP_TIMER,
 					.fd = conn->sock,
-					.tcp.index = FLOW_IDX(conn) };
+					.flow = FLOW_IDX(conn) };
 		struct epoll_event ev = { .data.u64 = ref.u64,
 					  .events = EPOLLIN | EPOLLET };
 		int fd;
@@ -2760,7 +2760,7 @@ void tcp_listen_handler(struct ctx *c, union epoll_ref ref,
 void tcp_timer_handler(struct ctx *c, union epoll_ref ref)
 {
 	struct itimerspec check_armed = { { 0 }, { 0 } };
-	struct tcp_tap_conn *conn = CONN(ref.tcp.index);
+	struct tcp_tap_conn *conn = CONN(ref.flow);
 
 	if (c->no_tcp)
 		return;
@@ -2874,7 +2874,7 @@ static void tcp_tap_sock_handler(struct ctx *c, struct tcp_tap_conn
*conn,
  */
 void tcp_sock_handler(struct ctx *c, union epoll_ref ref, uint32_t events)
 {
-	union flow *flow = flowtab + ref.tcp.index;
+	union flow *flow = FLOW(ref.flow);
 
 	switch (flow->f.type) {
 	case FLOW_TCP:
diff --git a/tcp_splice.c b/tcp_splice.c
index 28b91e1..5ebc4e5 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -128,8 +128,8 @@ static int tcp_splice_epoll_ctl(const struct ctx *c,
 {
 	int m = conn->in_epoll ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
 	union epoll_ref ref[SIDES] = {
-		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[0], .tcp.index = FLOW_IDX(conn) },
-		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[1], .tcp.index = FLOW_IDX(conn) }
+		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[0], .flow = FLOW_IDX(conn) },
+		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[1], .flow = FLOW_IDX(conn) }
 	};
 	struct epoll_event ev[SIDES] = { { .data.u64 = ref[0].u64 },
 					 { .data.u64 = ref[1].u64 } };
-- 
2.43.0

Currently TCP uses the 'flow' epoll_ref field for both connected
sockets and timers, which consists of just the index of the relevant
flow (connection).

This is just fine for timers, for while it obviously works, it's
subtly incomplete for sockets on spliced connections.  In that case we
want to know which side of the connection the event is occurring on as
well as which connection.  At present, we deduce that information by
looking at the actual fd, and comparing it to the fds of the sockets
on each side.

When we use the flow table for more things, we expect more cases where
something will need to know a specific side of a specific flow for an
event, but nothing more.

Therefore add a new 'flowside' epoll_ref field, with exactly that
information.  We use it for TCP connected sockets.  This allows us to
directly know the side for spliced connections.  For "tap"
connections, it's pretty meaningless, since the side is always the
socket side.  It still makes logical sense though, and it may become
important for future flow table work.

Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
 flow.h       |  2 +-
 passt.h      |  2 ++
 tcp.c        | 11 ++++++++---
 tcp_splice.c | 37 ++++++++++++-------------------------
 tcp_splice.h |  2 +-
 5 files changed, 24 insertions(+), 30 deletions(-)

diff --git a/flow.h b/flow.h
index 3c90bbd..75e2115 100644
--- a/flow.h
+++ b/flow.h
@@ -45,7 +45,7 @@ struct flow_common {
  * @flow:	Index of flow referenced
  */
 typedef struct flow_sidx {
-	int		side :1;
+	unsigned	side :1;
 	unsigned	flow :FLOW_INDEX_BITS;
 } flow_sidx_t;
 static_assert(sizeof(flow_sidx_t) <= sizeof(uint32_t));
diff --git a/passt.h b/passt.h
index 66a819f..33b493f 100644
--- a/passt.h
+++ b/passt.h
@@ -37,6 +37,7 @@ union epoll_ref;
 
 #include "pif.h"
 #include "packet.h"
+#include "flow.h"
 #include "icmp.h"
 #include "port_fwd.h"
 #include "tcp.h"
@@ -91,6 +92,7 @@ union epoll_ref {
 		int32_t		fd:FD_REF_BITS;
 		union {
 			uint32_t flow;
+			flow_sidx_t flowside;
 			union tcp_listen_epoll_ref tcp_listen;
 			union udp_epoll_ref udp;
 			union icmp_epoll_ref icmp;
diff --git a/tcp.c b/tcp.c
index e80a6aa..24aba44 100644
--- a/tcp.c
+++ b/tcp.c
@@ -304,6 +304,10 @@
 #include "tcp_conn.h"
 #include "flow_table.h"
 
+/* Sides of a flow as we use them in "tap" connections */
+#define	SOCKSIDE	0
+#define	TAPSIDE		1
+
 #define TCP_FRAMES_MEM			128
 #define TCP_FRAMES							\
 	(c->mode == MODE_PASST ? TCP_FRAMES_MEM : 1)
@@ -639,7 +643,7 @@ static int tcp_epoll_ctl(const struct ctx *c, struct tcp_tap_conn
*conn)
 {
 	int m = conn->in_epoll ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
 	union epoll_ref ref = { .type = EPOLL_TYPE_TCP, .fd = conn->sock,
-				.flow = FLOW_IDX(conn) };
+				.flowside = FLOW_SIDX(conn, SOCKSIDE) };
 	struct epoll_event ev = { .data.u64 = ref.u64 };
 
 	if (conn->events == CLOSED) {
@@ -2874,14 +2878,15 @@ static void tcp_tap_sock_handler(struct ctx *c, struct
tcp_tap_conn *conn,
  */
 void tcp_sock_handler(struct ctx *c, union epoll_ref ref, uint32_t events)
 {
-	union flow *flow = FLOW(ref.flow);
+	union flow *flow = FLOW(ref.flowside.flow);
 
 	switch (flow->f.type) {
 	case FLOW_TCP:
 		tcp_tap_sock_handler(c, &flow->tcp, events);
 		break;
 	case FLOW_TCP_SPLICE:
-		tcp_splice_sock_handler(c, &flow->tcp_splice, ref.fd, events);
+		tcp_splice_sock_handler(c, &flow->tcp_splice, ref.flowside.side,
+					events);
 		break;
 	default:
 		die("Unexpected %s in tcp_sock_handler_compact()",
diff --git a/tcp_splice.c b/tcp_splice.c
index 9cec9c6..d5c351b 100644
--- a/tcp_splice.c
+++ b/tcp_splice.c
@@ -128,8 +128,10 @@ static int tcp_splice_epoll_ctl(const struct ctx *c,
 {
 	int m = conn->in_epoll ? EPOLL_CTL_MOD : EPOLL_CTL_ADD;
 	union epoll_ref ref[SIDES] = {
-		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[0], .flow = FLOW_IDX(conn) },
-		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[1], .flow = FLOW_IDX(conn) }
+		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[0],
+		  .flowside = FLOW_SIDX(conn, 0) },
+		{ .type = EPOLL_TYPE_TCP, .fd = conn->s[1],
+		  .flowside = FLOW_SIDX(conn, 1) }
 	};
 	struct epoll_event ev[SIDES] = { { .data.u64 = ref[0].u64 },
 					 { .data.u64 = ref[1].u64 } };
@@ -481,13 +483,13 @@ bool tcp_splice_conn_from_sock(const struct ctx *c,
  * tcp_splice_sock_handler() - Handler for socket mapped to spliced connection
  * @c:		Execution context
  * @conn:	Connection state
- * @s:		Socket fd on which an event has occurred
+ * @side:	Side of the connection on which an event has occurred
  * @events:	epoll events bitmap
  *
  * #syscalls:pasta splice
  */
 void tcp_splice_sock_handler(struct ctx *c, struct tcp_splice_conn *conn,
-			     int s, uint32_t events)
+			     int side, uint32_t events)
 {
 	uint8_t lowat_set_flag, lowat_act_flag;
 	int eof, never_read;
@@ -507,30 +509,15 @@ void tcp_splice_sock_handler(struct ctx *c, struct tcp_splice_conn
*conn,
 	}
 
 	if (events & EPOLLOUT) {
-		if (s == conn->s[0]) {
-			conn_event(c, conn, ~OUT_WAIT_0);
-			fromside = 1;
-		} else {
-			conn_event(c, conn, ~OUT_WAIT_1);
-			fromside = 0;
-		}
+		fromside = !side;
+		conn_event(c, conn, side == 0 ? ~OUT_WAIT_0 : ~OUT_WAIT_1);
 	} else {
-		fromside = s == conn->s[0] ? 0 : 1;
-	}
-
-	if (events & EPOLLRDHUP) {
-		if (s == conn->s[0])
-			conn_event(c, conn, FIN_RCVD_0);
-		else
-			conn_event(c, conn, FIN_RCVD_1);
+		fromside = side;
 	}
 
-	if (events & EPOLLHUP) {
-		if (s == conn->s[0])
-			conn_event(c, conn, FIN_SENT_0); /* Fake, but implied */
-		else
-			conn_event(c, conn, FIN_SENT_1);
-	}
+	if (events & EPOLLRDHUP)
+		/* For side 0 this is fake, but implied */
+		conn_event(c, conn, side == 0 ? FIN_RCVD_0 : FIN_RCVD_1);
 
 swap:
 	eof = 0;
diff --git a/tcp_splice.h b/tcp_splice.h
index dc486f1..aa85c7c 100644
--- a/tcp_splice.h
+++ b/tcp_splice.h
@@ -9,7 +9,7 @@
 struct tcp_splice_conn;
 
 void tcp_splice_sock_handler(struct ctx *c, struct tcp_splice_conn *conn,
-			     int s, uint32_t events);
+			     int side, uint32_t events);
 bool tcp_splice_conn_from_sock(const struct ctx *c,
 			       union tcp_listen_epoll_ref ref,
 			       struct tcp_splice_conn *conn, int s,
-- 
2.43.0