NMB packets are so similar to DNS packets; we may as well add NMB as a

name resolution method.

src/include/nmb.h

@@ -0,0 +1,22 @@
+#ifndef NMB_H
+#define NMB_H
+
+#include "dns.h"
+
+/*
+ * NetBIOS name query packets are basically the same as DNS packets,
+ * though the resource record format is different.
+ *
+ */
+
+#define DNS_TYPE_NB		0x20
+#define DNS_FLAG_BROADCAST	( 0x01 << 4 )
+#define NBNS_UDP_PORT		137
+
+struct dns_rr_info_nb {
+	struct dns_rr_info;
+	uint16_t	nb_flags;
+	struct in_addr	nb_address;
+} __attribute__ (( packed ));
+
+#endif /* NMB_H */

src/proto/nmb.c

@@ -0,0 +1,103 @@
+#include "resolv.h"
+#include "string.h"
+#include "dns.h"
+#include "nic.h"
+#include "nmb.h"
+
+/*
+ * Convert a standard NUL-terminated string to an NBNS query name.
+ *
+ * Returns a pointer to the character following the constructed NBNS
+ * query name.
+ *
+ */
+static inline char * nbns_make_name ( char *dest, const char *name ) {
+	char nb_name[16];
+	char c;
+	int i;
+
+	*(dest++) = 32; /* Length is always 32 */
+
+	/* Name encoding is as follows: pad the name with spaces to
+	 * length 15, and add a NUL.  Take this 16-byte string, split
+	 * it into nibbles and add 0x41 to each nibble to form a byte
+	 * of the resulting name string.
+	 */
+	memset ( nb_name, ' ', 15 );
+	nb_name[15] = '\0';
+	memcpy ( nb_name, name, strlen ( name ) ); /* Do not copy NUL */
+	for ( i = 0 ; i < 16 ; i++ ) {
+		c = nb_name[i];
+		*( ( ( uint16_t * ) dest ) ++ ) = 
+			htons ( ( ( c | ( c << 4 ) ) & 0x0f0f ) + 0x4141 );
+	}
+
+	*(dest++) = 0; /* Terminating 0-length name component */
+	return dest;
+}
+
+/*
+ * Resolve a name using NMB
+ *
+ */
+static int nmb_resolv ( struct in_addr *addr, const char *name ) {
+	struct dns_query query;
+	struct dns_query_info *query_info;
+	struct dns_header *reply;
+	struct dns_rr_info *rr_info;
+	struct dns_rr_info_nb *rr_info_nb;
+	struct sockaddr_in nameserver;
+
+	DBG ( "NMB resolving %s\n", name );
+
+	/* Set up the query data */
+	nameserver.sin_addr.s_addr = IP_BROADCAST;
+	nameserver.sin_port = NBNS_UDP_PORT;
+	memset ( &query, 0, sizeof ( query ) );
+	query.dns.id = htons ( 1 );
+	query.dns.flags = htons ( DNS_FLAG_QUERY | DNS_FLAG_OPCODE_QUERY |
+				  DNS_FLAG_RD | DNS_FLAG_BROADCAST );
+	query.dns.qdcount = htons ( 1 );
+	query_info = ( void * )	nbns_make_name ( query.payload, name );
+	query_info->qtype = htons ( DNS_TYPE_NB );
+	query_info->qclass = htons ( DNS_CLASS_IN );
+
+	/* Issue query, wait for reply */
+	reply = dns_query ( &query,
+			    ( ( ( char * ) query_info )
+			      + sizeof ( *query_info )
+			      - ( ( char * ) &query ) ),
+			    &nameserver );
+	if ( ! reply ) {
+		DBG ( "NMB got no response via %@ (port %d)\n",
+		      nameserver.sin_addr.s_addr,
+		      nameserver.sin_port );
+		return 0;
+	}
+
+	/* Search through response for useful answers. */
+	rr_info = dns_find_rr ( &query, reply );
+	if ( ! rr_info ) {
+		DBG ( "NMB got invalid response\n" );
+		return 0;
+	}
+
+	/* Check type of response */
+	if ( ntohs ( rr_info->type ) != DNS_TYPE_NB ) {
+		DBG ( "NMB got answer type %hx (wanted %hx)\n",
+		      ntohs ( rr_info->type ), DNS_TYPE_NB );
+		return 0;
+	}
+
+	/* Read response */
+	rr_info_nb = ( struct dns_rr_info_nb * ) rr_info;
+	*addr = rr_info_nb->nb_address;
+	DBG ( "NMB found address %@\n", addr->s_addr );
+
+	return 1;
+}
+
+static struct resolver nmb_resolver __resolver = {
+	.name = "NMB",
+	.resolv = nmb_resolv,
+};