[PATCH v3 12/14] fwd: Remap ports based directly on forwarding rule

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

Currently we remap port numbers based on the legacy delta[] array, which
is indexed only by original port number, not the listening address.  Now
that we look up a forwarding rule entry in flow_target(), we can use this
entry to directly determine the correct remapped port.  Implement this,
and remove the old delta[] array.

Link: https://bugs.passt.top/show_bug.cgi?id=187

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 flow.c |  7 ++++---
 fwd.c  | 21 +++++++--------------
 fwd.h  |  7 +++----
 3 files changed, 14 insertions(+), 21 deletions(-)

diff --git a/flow.c b/flow.c
index 045e9712..38f88732 100644
--- a/flow.c
+++ b/flow.c
@@ -493,6 +493,7 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow,
 	struct flow_common *f = &flow->f;
 	const struct flowside *ini = &f->side[INISIDE];
 	struct flowside *tgt = &f->side[TGTSIDE];
+	const struct fwd_rule *rule = NULL;
 	uint8_t tgtpif = PIF_NONE;
 
 	ASSERT(flow_new_entry == flow && f->state == FLOW_STATE_INI);
@@ -514,7 +515,7 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow,
 		else
 			goto nofwd;
 
-		if (!fwd_rule_search(fwd, ini)) {
+		if (!(rule = fwd_rule_search(fwd, ini))) {
 			/* This shouldn't happen, because if there's no rule for
 			 * it we should have no listening socket that would let
 			 * us get here
@@ -531,11 +532,11 @@ struct flowside *flow_target(const struct ctx *c, union flow *flow,
 		break;
 
 	case PIF_SPLICE:
-		tgtpif = fwd_nat_from_splice(c, proto, ini, tgt);
+		tgtpif = fwd_nat_from_splice(rule, proto, ini, tgt);
 		break;
 
 	case PIF_HOST:
-		tgtpif = fwd_nat_from_host(c, proto, ini, tgt);
+		tgtpif = fwd_nat_from_host(c, rule, proto, ini, tgt);
 		fwd_neigh_mac_get(c, &tgt->oaddr, f->tap_omac);
 		break;
 	default:
diff --git a/fwd.c b/fwd.c
index 633ba5db..7c4575ff 100644
--- a/fwd.c
+++ b/fwd.c
@@ -405,7 +405,6 @@ void fwd_rule_add(struct fwd_ports *fwd, uint8_t flags,
 		/* Fill in the legacy forwarding data structures to match the table */
 		if (!(new->flags & FWD_SCAN))
 			bitmap_set(fwd->map, port);
-		fwd->delta[port] = new->to - new->first;
 	}
 }
 
@@ -978,7 +977,7 @@ uint8_t fwd_nat_from_tap(const struct ctx *c, uint8_t proto,
 
 /**
  * fwd_nat_from_splice() - Determine to forward a flow from the splice interface
- * @c:		Execution context
+ * @rule:	Forwarding rule to apply
  * @proto:	Protocol (IP L4 protocol number)
  * @ini:	Flow address information of the initiating side
  * @tgt:	Flow address information on the target side (updated)
@@ -986,7 +985,7 @@ uint8_t fwd_nat_from_tap(const struct ctx *c, uint8_t proto,
  * Return: pif of the target interface to forward the flow to, PIF_NONE if the
  *         flow cannot or should not be forwarded at all.
  */
-uint8_t fwd_nat_from_splice(const struct ctx *c, uint8_t proto,
+uint8_t fwd_nat_from_splice(const struct fwd_rule *rule, uint8_t proto,
 			    const struct flowside *ini, struct flowside *tgt)
 {
 	if (!inany_is_loopback(&ini->eaddr) ||
@@ -1010,11 +1009,7 @@ uint8_t fwd_nat_from_splice(const struct ctx *c, uint8_t proto,
 		/* But for UDP preserve the source port */
 		tgt->oport = ini->eport;
 
-	tgt->eport = ini->oport;
-	if (proto == IPPROTO_TCP)
-		tgt->eport += c->tcp.fwd_out.delta[tgt->eport];
-	else if (proto == IPPROTO_UDP)
-		tgt->eport += c->udp.fwd_out.delta[tgt->eport];
+	tgt->eport = ini->oport - rule->first + rule->to;
 
 	return PIF_HOST;
 }
@@ -1058,6 +1053,7 @@ bool nat_inbound(const struct ctx *c, const union inany_addr *addr,
 /**
  * fwd_nat_from_host() - Determine to forward a flow from the host interface
  * @c:		Execution context
+ * @rule:	Forwarding rule to apply
  * @proto:	Protocol (IP L4 protocol number)
  * @ini:	Flow address information of the initiating side
  * @tgt:	Flow address information on the target side (updated)
@@ -1065,15 +1061,12 @@ bool nat_inbound(const struct ctx *c, const union inany_addr *addr,
  * Return: pif of the target interface to forward the flow to, PIF_NONE if the
  *         flow cannot or should not be forwarded at all.
  */
-uint8_t fwd_nat_from_host(const struct ctx *c, uint8_t proto,
+uint8_t fwd_nat_from_host(const struct ctx *c,
+			  const struct fwd_rule *rule, uint8_t proto,
 			  const struct flowside *ini, struct flowside *tgt)
 {
 	/* Common for spliced and non-spliced cases */
-	tgt->eport = ini->oport;
-	if (proto == IPPROTO_TCP)
-		tgt->eport += c->tcp.fwd_in.delta[tgt->eport];
-	else if (proto == IPPROTO_UDP)
-		tgt->eport += c->udp.fwd_in.delta[tgt->eport];
+	tgt->eport = ini->oport - rule->first + rule->to;
 
 	if (!c->no_splice && inany_is_loopback(&ini->eaddr) &&
 	    (proto == IPPROTO_TCP || proto == IPPROTO_UDP)) {
diff --git a/fwd.h b/fwd.h
index a10bdbb4..cfe9ed46 100644
--- a/fwd.h
+++ b/fwd.h
@@ -82,7 +82,6 @@ enum fwd_ports_mode {
  * @count:	Number of forwarding rules
  * @rules:	Array of forwarding rules
  * @map:	Bitmap describing which ports are forwarded
- * @delta:	Offset between the original destination and mapped port number
  * @listen_sock_count: Number of entries used in @listen_socks
  * @listen_socks: Listening sockets for forwarding
  */
@@ -93,7 +92,6 @@ struct fwd_ports {
 	unsigned count;
 	struct fwd_rule rules[MAX_FWD_RULES];
 	uint8_t map[PORT_BITMAP_SIZE];
-	in_port_t delta[NUM_PORTS];
 	unsigned listen_sock_count;
 	int listen_socks[MAX_LISTEN_SOCKS];
 };
@@ -117,9 +115,10 @@ bool nat_inbound(const struct ctx *c, const union inany_addr *addr,
 		 union inany_addr *translated);
 uint8_t fwd_nat_from_tap(const struct ctx *c, uint8_t proto,
 			 const struct flowside *ini, struct flowside *tgt);
-uint8_t fwd_nat_from_splice(const struct ctx *c, uint8_t proto,
+uint8_t fwd_nat_from_splice(const struct fwd_rule *rule, uint8_t proto,
 			    const struct flowside *ini, struct flowside *tgt);
-uint8_t fwd_nat_from_host(const struct ctx *c, uint8_t proto,
+uint8_t fwd_nat_from_host(const struct ctx *c,
+			  const struct fwd_rule *rule, uint8_t proto,
 			  const struct flowside *ini, struct flowside *tgt);
 void fwd_neigh_table_update(const struct ctx *c, const union inany_addr *addr,
 			    const uint8_t *mac, bool permanent);
-- 
2.52.0