net: dns: Initialize DNS resolver if DNS servers are set

If the config file contains DNS server addresses, then
configure the DNS resolver to use them.

Change-Id: Ie7f2bdcf7ac4bb7ee0ecf7fb5b7bd2df3379cdc3
Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

include/net/dns_resolve.h

@@ -223,6 +223,25 @@ int dns_resolve_name(struct dns_resolve_context *ctx,
 		     void *user_data,
 		     int32_t timeout);
 
+/**
+ * @brief Get default DNS context.
+ *
+ * @detail The system level DNS context uses DNS servers that are
+ * defined in project config file. If no DNS servers are defined by the
+ * user, then resolving DNS names using default DNS context will do nothing.
+ * The configuration options are described in subsys/net/lib/dns/Kconfig file.
+ *
+ * @return Default DNS context.
+ */
+struct dns_resolve_context *dns_resolve_get_default(void);
+
+/**
+ * @brief Initialize DNS subsystem.
+ */
+void dns_init_resolver(void);
+
+#else
+#define dns_init_resolver(...)
 #endif /* CONFIG_DNS_RESOLVER */
 
 #endif /* _DNS_RESOLVE_H */

subsys/net/ip/net_core.c

@@ -28,6 +28,7 @@
 #include <net/arp.h>
 #include <net/nbuf.h>
 #include <net/net_core.h>
+#include <net/dns_resolve.h>
 
 #include "net_private.h"
 #include "net_shell.h"
@@ -766,6 +767,8 @@ static inline void l3_init(void)
 
 	net_route_init();
 
+	dns_init_resolver();
+
 	NET_DBG("Network L3 init done");
 }
 

subsys/net/lib/dns/Kconfig

@@ -36,19 +36,71 @@ config DNS_RESOLVER_ADDITIONAL_QUERIES
 
 config DNS_RESOLVER_MAX_SERVERS
 	int "Number of DNS server addresses"
-	default 1
-	help
-	Max number of DNS servers that we can connect to. Normally one
-	DNS server is enough.
-
-config DNS_NUM_CONCUR_QUERIES
-	int "Number of simultaneous DNS queries per one DNS context"
 	range 1 NET_MAX_CONTEXTS
 	default 1
 	help
+	Max number of DNS servers that we can connect to. Normally one
+	DNS server is enough. Each connection to DNS server will use one
+	network context.
+
+menuconfig DNS_SERVER_IP_ADDRESSES
+	bool "Set DNS server IP addresses"
+	default n
+	help
+	Allow DNS IP addresses to be set in config file for
+	networking applications.
+
+if DNS_SERVER_IP_ADDRESSES
+
+config DNS_SERVER1
+	string "DNS server 1"
+	default ""
+	help
+	DNS server IP address 1. The address can be either IPv4 or IPv6
+	address. An optional port number can be given.
+	Following syntax is supported:
+	192.0.2.1
+	192.0.2.1:5353
+	2001:db8::1
+	[2001:db8::1]:5353
+	It is not mandatory to use this Kconfig option at all.
+	The one calling dns_resolve_init() can use this option or not
+	to populate the server list. If the DNS server addresses are
+	set here, then we automatically create default DNS context
+	for the user.
+
+config DNS_SERVER2
+	string "DNS server 2"
+	default ""
+	help
+	See help in "DNS server 1" option.
+
+config DNS_SERVER3
+	string "DNS server 3"
+	default ""
+	help
+	See help in "DNS server 1" option.
+
+config DNS_SERVER4
+	string "DNS server 4"
+	default ""
+	help
+	See help in "DNS server 1" option.
+
+config DNS_SERVER5
+	string "DNS server 5"
+	default ""
+	help
+	See help in "DNS server 1" option.
+
+endif # DNS_SERVER_IP_ADDRESSES
+
+config DNS_NUM_CONCUR_QUERIES
+	int "Number of simultaneous DNS queries per one DNS context"
+	default 1
+	help
 	This defines how many concurrent DNS queries can be generated using
-	same DNS context. Normally 1 is a good default value. Each query
+	same DNS context. Normally 1 is a good default value.
-	will use one network context.
 
 config NET_DEBUG_DNS_RESOLVE
 	bool "Debug DNS resolver"

subsys/net/lib/dns/resolve.c

@@ -69,6 +69,8 @@ NET_BUF_POOL_DEFINE(dns_msg_pool, DNS_RESOLVER_BUF_CTR,
 NET_BUF_POOL_DEFINE(dns_qname_pool, DNS_RESOLVER_BUF_CTR, DNS_MAX_NAME_LEN,
 		    0, NULL);
 
+static struct dns_resolve_context dns_default_ctx;
+
 int dns_resolve_init(struct dns_resolve_context *ctx, const char *servers[])
 {
 #if defined(CONFIG_NET_IPV6)
@@ -858,3 +860,48 @@ int dns_resolve_close(struct dns_resolve_context *ctx)
 
 	return 0;
 }
+
+struct dns_resolve_context *dns_resolve_get_default(void)
+{
+	return &dns_default_ctx;
+}
+
+void dns_init_resolver(void)
+{
+#if defined(CONFIG_DNS_SERVER_IP_ADDRESSES)
+	static const char *dns_servers[CONFIG_DNS_RESOLVER_MAX_SERVERS + 1];
+	int count = CONFIG_DNS_RESOLVER_MAX_SERVERS;
+	int ret;
+
+	if (count > 5) {
+		count = 5;
+	}
+
+	switch (count) {
+	case 5:
+		dns_servers[4] = CONFIG_DNS_SERVER5;
+		/* fallthrough */
+	case 4:
+		dns_servers[3] = CONFIG_DNS_SERVER4;
+		/* fallthrough */
+	case 3:
+		dns_servers[2] = CONFIG_DNS_SERVER3;
+		/* fallthrough */
+	case 2:
+		dns_servers[1] = CONFIG_DNS_SERVER2;
+		/* fallthrough */
+	case 1:
+		dns_servers[0] = CONFIG_DNS_SERVER1;
+		/* fallthrough */
+	case 0:
+		break;
+	}
+
+	dns_servers[CONFIG_DNS_RESOLVER_MAX_SERVERS] = NULL;
+
+	ret = dns_resolve_init(dns_resolve_get_default(), dns_servers);
+	if (ret < 0) {
+		NET_WARN("Cannot initialize DNS resolver (%d)", ret);
+	}
+#endif
+}