[dns] Add support for resolving IPv6 addresses via AAAA records

Our policy is to prefer IPv6 addreses to IPv4 addresses, but to
request IPv6 addresses only if we have an IPv6 address for the name
server itself.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/dhcpv6.h

 #define DHCPV6_USER_CLASS 15
 
 /** DHCPv6 DNS recursive name server option */
-#define DHCPV6_DNS_SERVER 23
+#define DHCPV6_DNS_SERVERS 23
 
 /** DHCPv6 domain search list option */
-#define DHCPV6_DOMAIN_SEARCH 24
+#define DHCPV6_DOMAIN_LIST 24
 
 /**
  * Any DHCPv6 option

src/include/ipxe/dns.h

 
 #define DNS_TYPE_A		1
 #define DNS_TYPE_CNAME		5
+#define DNS_TYPE_AAAA		28
 #define DNS_TYPE_ANY		255
 
 #define DNS_CLASS_IN		1
 	struct in_addr in_addr;
 } __attribute__ (( packed ));
 
+struct dns_rr_info_aaaa {
+	struct dns_rr_info_common common;
+	struct in6_addr in6_addr;
+} __attribute__ (( packed ));
+
 struct dns_rr_info_cname {
 	struct dns_rr_info_common common;
 	char cname[0];
 union dns_rr_info {
 	struct dns_rr_info_common common;
 	struct dns_rr_info_a a;
+	struct dns_rr_info_aaaa aaaa;
 	struct dns_rr_info_cname cname;
 };
 

src/net/udp/dhcpv6.c

 
 /** Options to be requested */
 static uint16_t dhcpv6_requested_options[] = {
-	htons ( DHCPV6_DNS_SERVER ), htons ( DHCPV6_DOMAIN_SEARCH ),
+	htons ( DHCPV6_DNS_SERVERS ), htons ( DHCPV6_DOMAIN_LIST ),
 };
 
 /**

src/net/udp/dns.c

 #include <ipxe/tcpip.h>
 #include <ipxe/settings.h>
 #include <ipxe/features.h>
+#include <ipxe/dhcp.h>
+#include <ipxe/dhcpv6.h>
 #include <ipxe/dns.h>
 
 /** @file
 	__einfo_uniqify ( EINFO_ENXIO, 0x02, "No DNS servers available" )
 
 /** The DNS server */
-static struct sockaddr_tcpip nameserver = {
-	.st_port = htons ( DNS_PORT ),
+static union {
+	struct sockaddr sa;
+	struct sockaddr_tcpip st;
+	struct sockaddr_in sin;
+	struct sockaddr_in6 sin6;
+} nameserver = {
+	.st = {
+		.st_port = htons ( DNS_PORT ),
+	},
 };
 
 /** The local domain */
 	struct retry_timer timer;
 
 	/** Socket address to fill in with resolved address */
-	struct sockaddr sa;
+	union {
+		struct sockaddr sa;
+		struct sockaddr_in sin;
+		struct sockaddr_in6 sin6;
+	} address;
+	/** Initial query type */
+	uint16_t qtype;
 	/** Current query packet */
 	struct dns_query query;
 	/** Location of query info structure within current packet
 	intf_shutdown ( &dns->resolv, rc );
 }
 
+/**
+ * Mark DNS request as resolved and complete
+ *
+ * @v dns		DNS request
+ * @v rc		Return status code
+ */
+static void dns_resolved ( struct dns_request *dns ) {
+
+	DBGC ( dns, "DNS %p found address %s\n",
+	       dns, sock_ntoa ( &dns->address.sa ) );
+
+	/* Return resolved address */
+	resolv_done ( &dns->resolv, &dns->address.sa );
+
+	/* Mark operation as complete */
+	dns_done ( dns, 0 );
+}
+
 /**
  * Compare DNS reply name against the query name from the original request
  *
 			      struct xfer_metadata *meta __unused ) {
 	const struct dns_header *reply = iobuf->data;
 	union dns_rr_info *rr_info;
-	struct sockaddr_in *sin;
 	unsigned int qtype = dns->qinfo->qtype;
 	int rc;
 
 	while ( ( rr_info = dns_find_rr ( dns, reply ) ) ) {
 		switch ( rr_info->common.type ) {
 
-		case htons ( DNS_TYPE_A ):
+		case htons ( DNS_TYPE_AAAA ):
 
-			/* Found the target A record */
-			DBGC ( dns, "DNS %p found address %s\n",
-			       dns, inet_ntoa ( rr_info->a.in_addr ) );
-			sin = ( struct sockaddr_in * ) &dns->sa;
-			sin->sin_family = AF_INET;
-			sin->sin_addr = rr_info->a.in_addr;
+			/* Found the target AAAA record */
+			dns->address.sin6.sin6_family = AF_INET6;
+			memcpy ( &dns->address.sin6.sin6_addr,
+				 &rr_info->aaaa.in6_addr,
+				 sizeof ( dns->address.sin6.sin6_addr ) );
+			dns_resolved ( dns );
+			rc = 0;
+			goto done;
 
-			/* Return resolved address */
-			resolv_done ( &dns->resolv, &dns->sa );
+		case htons ( DNS_TYPE_A ):
 
-			/* Mark operation as complete */
-			dns_done ( dns, 0 );
+			/* Found the target A record */
+			dns->address.sin.sin_family = AF_INET;
+			dns->address.sin.sin_addr = rr_info->a.in_addr;
+			dns_resolved ( dns );
 			rc = 0;
 			goto done;
 
 			dns->qinfo = ( void * ) dns_decompress_name ( reply,
 							 rr_info->cname.cname,
 							 dns->query.payload );
-			dns->qinfo->qtype = htons ( DNS_TYPE_A );
+			dns->qinfo->qtype = dns->qtype;
 			dns->qinfo->qclass = htons ( DNS_CLASS_IN );
 			
 			/* Terminate the operation if we recurse too far */
 	 */
 	switch ( qtype ) {
 
+	case htons ( DNS_TYPE_AAAA ):
+		/* We asked for an AAAA record and got nothing; try
+		 * the A.
+		 */
+		DBGC ( dns, "DNS %p found no AAAA record; trying A\n", dns );
+		dns->qinfo->qtype = htons ( DNS_TYPE_A );
+		dns_send_packet ( dns );
+		rc = 0;
+		goto done;
+
 	case htons ( DNS_TYPE_A ):
 		/* We asked for an A record and got nothing;
 		 * try the CNAME.
 		 * (i.e. if the next A query is already set up), then
 		 * issue it, otherwise abort.
 		 */
-		if ( dns->qinfo->qtype == htons ( DNS_TYPE_A ) ) {
+		if ( dns->qinfo->qtype == dns->qtype ) {
 			dns_send_packet ( dns );
 			rc = 0;
 			goto done;
 	int rc;
 
 	/* Fail immediately if no DNS servers */
-	if ( ! nameserver.st_family ) {
+	if ( ! nameserver.sa.sa_family ) {
 		DBG ( "DNS not attempting to resolve \"%s\": "
 		      "no DNS servers\n", name );
 		rc = -ENXIO_NO_NAMESERVER;
 	intf_init ( &dns->resolv, &dns_resolv_desc, &dns->refcnt );
 	intf_init ( &dns->socket, &dns_socket_desc, &dns->refcnt );
 	timer_init ( &dns->timer, dns_timer_expired, &dns->refcnt );
-	memcpy ( &dns->sa, sa, sizeof ( dns->sa ) );
+	memcpy ( &dns->address.sa, sa, sizeof ( dns->address.sa ) );
+
+	/* Determine initial query type */
+	switch ( nameserver.sa.sa_family ) {
+	case AF_INET:
+		dns->qtype = htons ( DNS_TYPE_A );
+		break;
+	case AF_INET6:
+		dns->qtype = htons ( DNS_TYPE_AAAA );
+		break;
+	default:
+		rc = -ENOTSUP;
+		goto err_qtype;
+	}
 
 	/* Create query */
 	dns->query.dns.flags = htons ( DNS_FLAG_QUERY | DNS_FLAG_OPCODE_QUERY |
 				       DNS_FLAG_RD );
 	dns->query.dns.qdcount = htons ( 1 );
 	dns->qinfo = ( void * ) dns_make_name ( fqdn, dns->query.payload );
-	dns->qinfo->qtype = htons ( DNS_TYPE_A );
+	dns->qinfo->qtype = dns->qtype;
 	dns->qinfo->qclass = htons ( DNS_CLASS_IN );
 
 	/* Open UDP connection */
 	if ( ( rc = xfer_open_socket ( &dns->socket, SOCK_DGRAM,
-				       ( struct sockaddr * ) &nameserver,
-				       NULL ) ) != 0 ) {
+				       &nameserver.sa, NULL ) ) != 0 ) {
 		DBGC ( dns, "DNS %p could not open socket: %s\n",
 		       dns, strerror ( rc ) );
 		goto err_open_socket;
 	return 0;	
 
  err_open_socket:
- err_alloc_dns:
+ err_qtype:
 	ref_put ( &dns->refcnt );
- err_qualify_name:
+ err_alloc_dns:
 	free ( fqdn );
+ err_qualify_name:
  err_no_nameserver:
 	return rc;
 }
  ******************************************************************************
  */
 
-/** DNS server setting */
+/** IPv4 DNS server setting */
 const struct setting dns_setting __setting ( SETTING_IPv4_EXTRA ) = {
 	.name = "dns",
 	.description = "DNS server",
 	.type = &setting_type_ipv4,
 };
 
+/** IPv6 DNS server setting */
+const struct setting dns6_setting __setting ( SETTING_IPv6_EXTRA ) = {
+	.name = "dns6",
+	.description = "DNS server",
+	.tag = DHCPV6_DNS_SERVERS,
+	.type = &setting_type_ipv6,
+	.scope = &ipv6_scope,
+};
+
 /**
  * Apply DNS settings
  *
  * @ret rc		Return status code
  */
 static int apply_dns_settings ( void ) {
-	struct sockaddr_in *sin_nameserver =
-		( struct sockaddr_in * ) &nameserver;
-	int len;
 
 	/* Fetch DNS server address */
-	nameserver.st_family = 0;
-	if ( ( len = fetch_ipv4_setting ( NULL, &dns_setting,
-					  &sin_nameserver->sin_addr ) ) >= 0 ){
-		nameserver.st_family = AF_INET;
+	nameserver.sa.sa_family = 0;
+	if ( fetch_ipv6_setting ( NULL, &dns6_setting,
+				  &nameserver.sin6.sin6_addr ) >= 0 ) {
+		nameserver.sin6.sin6_family = AF_INET6;
+	} else if ( fetch_ipv4_setting ( NULL, &dns_setting,
+					 &nameserver.sin.sin_addr ) >= 0 ) {
+		nameserver.sin.sin_family = AF_INET;
+	}
+	if ( nameserver.sa.sa_family ) {
 		DBG ( "DNS using nameserver %s\n",
-		      inet_ntoa ( sin_nameserver->sin_addr ) );
+		      sock_ntoa ( &nameserver.sa ) );
 	}
 
 	/* Get local domain DHCP option */