udp: Consistently use -1 to indicate un-opened sockets in maps

udp uses the udp_tap_map, udp_splice_ns and udp_splice_init tables to keep
track of already opened sockets bound to specific ports.  We need a way to
indicate entries where a socket hasn't been opened, but the code isn't
consistent if this is indicated by a 0 or a -1:
  * udp_splice_sendfrom() and udp_tap_handler() assume that 0 indicates
    an unopened socket
  * udp_sock_init() fills in -1 for a failure to open a socket
  * udp_timer_one() is somewhere in between, treating only strictly
    positive fds as valid

-1 (or, at least, negative) is really the correct choice here, since 0 is
a theoretically valid fd value (if very unlikely in practice).  Change to
use that consistently throughout.

The table does need to be initialised to all -1 values before any calls to
udp_sock_init() which can happen from conf_ports().  Because C doesn't make
it easy to statically initialise non zero values in large tables, this does
require a somewhat awkward call to initialise the table from conf().  This
is the best approach I could see for the short term, with any luck it will
go away at some point when those socket tables are replaced by a unified
flow table.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

conf.c

@@ -1675,6 +1675,7 @@ void conf(struct ctx *c, int argc, char **argv)
 		c->no_map_gw = 1;
 
 	/* Inbound port options can be parsed now (after IPv4/IPv6 settings) */
+	udp_portmap_clear();
 	optind = 1;
 	do {
 		name = getopt_long(argc, argv, optstring, options, NULL);

udp.c

@@ -238,6 +238,20 @@ static struct sockaddr_in6 udp6_localname = {
 static struct mmsghdr	udp4_mh_splice		[UDP_MAX_FRAMES];
 static struct mmsghdr	udp6_mh_splice		[UDP_MAX_FRAMES];
 
+/**
+ * udp_portmap_clear() - Clear UDP port map before configuration
+ */
+void udp_portmap_clear(void)
+{
+	unsigned i;
+
+	for (i = 0; i < NUM_PORTS; i++) {
+		udp_tap_map[V4][i].sock = udp_tap_map[V6][i].sock = -1;
+		udp_splice_ns[V4][i].sock = udp_splice_ns[V6][i].sock = -1;
+		udp_splice_init[V4][i].sock = udp_splice_init[V6][i].sock = -1;
+	}
+}
+
 /**
  * udp_invert_portmap() - Compute reverse port translations for return packets
  * @fwd:	Port forwarding configuration to compute reverse map for
@@ -522,7 +536,7 @@ static void udp_splice_sendfrom(const struct ctx *c, unsigned start, unsigned n,
 	if (from_pif == PIF_SPLICE) {
 		src += c->udp.fwd_in.rdelta[src];
 		s = udp_splice_init[v6][src].sock;
-		if (!s && allow_new)
+		if (s < 0 && allow_new)
 			s = udp_splice_new(c, v6, src, false);
 
 		if (s < 0)
@@ -534,7 +548,7 @@ static void udp_splice_sendfrom(const struct ctx *c, unsigned start, unsigned n,
 		ASSERT(from_pif == PIF_HOST);
 		src += c->udp.fwd_out.rdelta[src];
 		s = udp_splice_ns[v6][src].sock;
-		if (!s && allow_new) {
+		if (s < 0 && allow_new) {
 			struct udp_splice_new_ns_arg arg = {
 				c, v6, src, -1,
 			};
@@ -849,7 +863,9 @@ int udp_tap_handler(struct ctx *c, uint8_t pif,
 				s_in.sin_addr = c->ip4.addr_seen;
 		}
 
-		if (!(s = udp_tap_map[V4][src].sock)) {
+		debug("UDP from tap src=%hu dst=%hu, s=%d",
+		      src, dst, udp_tap_map[V4][src].sock);
+		if ((s = udp_tap_map[V4][src].sock) < 0) {
 			union udp_epoll_ref uref = { .port = src };
 			in_addr_t bind_addr = { 0 };
 			const char *bind_if = NULL;
@@ -899,7 +915,7 @@ int udp_tap_handler(struct ctx *c, uint8_t pif,
 			bind_addr = &c->ip6.addr_ll;
 		}
 
-		if (!(s = udp_tap_map[V6][src].sock)) {
+		if ((s = udp_tap_map[V6][src].sock) < 0) {
 			union udp_epoll_ref uref = { .v6 = 1, .port = src };
 			const char *bind_if = NULL;
 
@@ -1161,7 +1177,7 @@ static void udp_timer_one(struct ctx *c, int v6, enum udp_act_type type,
 		return;
 	}
 
-	if (s > 0) {
+	if (s >= 0) {
 		epoll_ctl(c->epollfd, EPOLL_CTL_DEL, s, NULL);
 		close(s);
 		bitmap_clear(udp_act[v6 ? V6 : V4][type], port);

udp.h

@@ -8,6 +8,7 @@
 
 #define UDP_TIMER_INTERVAL		1000 /* ms */
 
+void udp_portmap_clear(void);
 void udp_sock_handler(const struct ctx *c, union epoll_ref ref, uint32_t events,
 		      const struct timespec *now);
 int udp_tap_handler(struct ctx *c, uint8_t pif, int af,