conf: Use array indices rather than pointers for DNS array slots

Currently add_dns[46]() take a somewhat awkward double pointer to the
entry in the c->ip[46].dns array to update.  It turns out to be easier to
work with indices into that array instead.

This diff does add some lines, but it's comments, and will allow some
future code reductions.

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

1 files changed, 41 insertions, 32 deletions

diff --git a/conf.c b/conf.c
index 9b05afe..2a52bc3 100644
--- a/conf.c
+++ b/conf.c
@@ -354,54 +354,65 @@ bind_all_fail:
  * add_dns4() - Possibly add the IPv4 address of a DNS resolver to configuration
  * @c:		Execution context
  * @addr:	Address found in /etc/resolv.conf
- * @conf:	Pointer to reference of current entry in array of IPv4 resolvers
+ * @idx:	Index of free entry in array of IPv4 resolvers
+ *
+ * Return: Number of entries added (0 or 1)
  */
-static void add_dns4(struct ctx *c, const struct in_addr *addr,
-		     struct in_addr **conf)
+static unsigned add_dns4(struct ctx *c, const struct in_addr *addr,
+			 unsigned idx)
 {
+	unsigned added = 0;
+
 	/* Guest or container can only access local addresses via redirect */
 	if (IN4_IS_ADDR_LOOPBACK(addr)) {
 		if (!c->no_map_gw) {
-			**conf = c->ip4.gw;
-			(*conf)++;
+			c->ip4.dns[idx] = c->ip4.gw;
+			added++;
 
 			if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns_match))
 				c->ip4.dns_match = c->ip4.gw;
 		}
 	} else {
-		**conf = *addr;
-		(*conf)++;
+		c->ip4.dns[idx] = *addr;
+		added++;
 	}
 
 	if (IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns_host))
 		c->ip4.dns_host = *addr;
+
+	return added;
 }
 
 /**
  * add_dns6() - Possibly add the IPv6 address of a DNS resolver to configuration
  * @c:		Execution context
  * @addr:	Address found in /etc/resolv.conf
- * @conf:	Pointer to reference of current entry in array of IPv6 resolvers
+ * @idx:	Index of free entry in array of IPv6 resolvers
+ *
+ * Return: Number of entries added (0 or 1)
  */
-static void add_dns6(struct ctx *c,
-		     struct in6_addr *addr, struct in6_addr **conf)
+static unsigned add_dns6(struct ctx *c, struct in6_addr *addr, unsigned idx)
 {
+	unsigned added = 0;
+
 	/* Guest or container can only access local addresses via redirect */
 	if (IN6_IS_ADDR_LOOPBACK(addr)) {
 		if (!c->no_map_gw) {
-			**conf = c->ip6.gw;
-			(*conf)++;
+			c->ip6.dns[idx] = c->ip6.gw;
+			added++;
 
 			if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_match))
 				c->ip6.dns_match = *addr;
 		}
 	} else {
-		**conf = *addr;
-		(*conf)++;
+		c->ip6.dns[idx] = *addr;
+		added++;
 	}
 
 	if (IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns_host))
 		c->ip6.dns_host = *addr;
+
+	return added;
 }
 
 /**
@@ -410,18 +421,19 @@ static void add_dns6(struct ctx *c,
  */
 static void get_dns(struct ctx *c)
 {
-	struct in6_addr *dns6 = &c->ip6.dns[0], dns6_tmp;
-	struct in_addr *dns4 = &c->ip4.dns[0], dns4_tmp;
 	int dns4_set, dns6_set, dnss_set, dns_set, fd;
+	unsigned dns4_idx = 0, dns6_idx = 0;
 	struct fqdn *s = c->dns_search;
 	struct lineread resolvconf;
+	struct in6_addr dns6_tmp;
+	struct in_addr dns4_tmp;
 	unsigned int added = 0;
 	ssize_t line_len;
 	char *line, *end;
 	const char *p;
 
-	dns4_set = !c->ifi4 || !IN4_IS_ADDR_UNSPECIFIED(dns4);
-	dns6_set = !c->ifi6 || !IN6_IS_ADDR_UNSPECIFIED(dns6);
+	dns4_set = !c->ifi4 || !IN4_IS_ADDR_UNSPECIFIED(&c->ip4.dns[0]);
+	dns6_set = !c->ifi6 || !IN6_IS_ADDR_UNSPECIFIED(&c->ip6.dns[0]);
 	dnss_set = !!*s->n || c->no_dns_search;
 	dns_set = (dns4_set && dns6_set) || c->no_dns;
 
@@ -442,17 +454,15 @@ static void get_dns(struct ctx *c)
 			if (end)
 				*end = 0;
 
-			if (!dns4_set &&
-			    dns4 - &c->ip4.dns[0] < ARRAY_SIZE(c->ip4.dns) - 1
+			if (!dns4_set && dns4_idx < ARRAY_SIZE(c->ip4.dns) - 1
 			    && inet_pton(AF_INET, p + 1, &dns4_tmp)) {
-				add_dns4(c, &dns4_tmp, &dns4);
+				dns4_idx += add_dns4(c, &dns4_tmp, dns4_idx);
 				added++;
 			}
 
-			if (!dns6_set &&
-			    dns6 - &c->ip6.dns[0] < ARRAY_SIZE(c->ip6.dns) - 1
+			if (!dns6_set && dns6_idx < ARRAY_SIZE(c->ip6.dns) - 1
 			    && inet_pton(AF_INET6, p + 1, &dns6_tmp)) {
-				add_dns6(c, &dns6_tmp, &dns6);
+				dns6_idx += add_dns6(c, &dns6_tmp, dns6_idx);
 				added++;
 			}
 		} else if (!dnss_set && strstr(line, "search ") == line &&
@@ -1236,8 +1246,7 @@ void conf(struct ctx *c, int argc, char **argv)
 	bool copy_addrs_opt = false, copy_routes_opt = false;
 	enum fwd_ports_mode fwd_default = FWD_NONE;
 	bool v4_only = false, v6_only = false;
-	struct in6_addr *dns6 = c->ip6.dns;
-	struct in_addr *dns4 = c->ip4.dns;
+	unsigned dns4_idx = 0, dns6_idx = 0;
 	struct fqdn *dnss = c->dns_search;
 	unsigned int ifi4 = 0, ifi6 = 0;
 	const char *logfile = NULL;
@@ -1662,13 +1671,13 @@ void conf(struct ctx *c, int argc, char **argv)
 			if (!strcmp(optarg, "none")) {
 				c->no_dns = 1;
 
-				dns4 = &c->ip4.dns[0];
+				dns4_idx = 0;
 				memset(c->ip4.dns, 0, sizeof(c->ip4.dns));
 				c->ip4.dns[0]    = (struct in_addr){ 0 };
 				c->ip4.dns_match = (struct in_addr){ 0 };
 				c->ip4.dns_host  = (struct in_addr){ 0 };
 
-				dns6 = &c->ip6.dns[0];
+				dns6_idx = 0;
 				memset(c->ip6.dns, 0, sizeof(c->ip6.dns));
 				c->ip6.dns_match = (struct in6_addr){ 0 };
 				c->ip6.dns_host  = (struct in6_addr){ 0 };
@@ -1678,15 +1687,15 @@ void conf(struct ctx *c, int argc, char **argv)
 
 			c->no_dns = 0;
 
-			if (dns4 - &c->ip4.dns[0] < ARRAY_SIZE(c->ip4.dns) &&
+			if (dns4_idx < ARRAY_SIZE(c->ip4.dns) &&
 			    inet_pton(AF_INET, optarg, &dns4_tmp)) {
-				add_dns4(c, &dns4_tmp, &dns4);
+				dns4_idx += add_dns4(c, &dns4_tmp, dns4_idx);
 				continue;
 			}
 
-			if (dns6 - &c->ip6.dns[0] < ARRAY_SIZE(c->ip6.dns) &&
+			if (dns6_idx < ARRAY_SIZE(c->ip6.dns) &&
 			    inet_pton(AF_INET6, optarg, &dns6_tmp)) {
-				add_dns6(c, &dns6_tmp, &dns6);
+				dns6_idx += add_dns6(c, &dns6_tmp, dns6_idx);
 				continue;
 			}