Add DNS support

On 04 Oct 2008 Pieter posted a dns implementation for U-Boot.

http://www.mail-archive.com/u-boot-users@lists.sourceforge.net/msg10216.html
>
> DNS can be enabled by setting CFG_CMD_DNS. After performing a query,
> the serverip environment var is updated.
>
> Probably there are some cosmetic issues with the patch. Unfortunatly I
> do not have the time to correct these. So if anybody else likes DNS
> support in U-Boot and has the time, feel free to patch it in the main tree.

Here it is again - slightly modified & smaller:
  - update to 2009-06 (Pieter's patch was for U-Boot 1.2.0)
  - README.dns is added
  - syntax is changed (now takes a third option, the env var to store
    the result in)
  - add a random port() function in net.c
  - sort Makefile in ./net/Makefile
  - dns just returns unless a env var is given
  - run through checkpatch, and clean up style issues
  - remove packet from stack
  - cleaned up some comments
  - failure returns much faster (if server responds, don't wait for
    timeout)
  - use built in functions (memcpy) rather than byte copy.

Signed-off-by: Robin Getz <rgetz@blackfin.uclinux.org>
Signed-off-by: Pieter Voorthuijsen <pieter.voorthuijsen@prodrive.nl>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>

common/cmd_net.c

@@ -353,3 +353,52 @@ U_BOOT_CMD(
 	"[NTP server IP]\n"
 );
 #endif
+
+#if defined(CONFIG_CMD_DNS)
+int do_dns(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+{
+	if (argc == 1) {
+		cmd_usage(cmdtp);
+		return -1;
+	}
+
+	/*
+	 * We should check for a valid hostname:
+	 * - Each label must be between 1 and 63 characters long
+	 * - the entire hostname has a maximum of 255 characters
+	 * - only the ASCII letters 'a' through 'z' (case-insensitive),
+	 *   the digits '0' through '9', and the hyphen
+	 * - cannot begin or end with a hyphen
+	 * - no other symbols, punctuation characters, or blank spaces are
+	 *   permitted
+	 * but hey - this is a minimalist implmentation, so only check length
+	 * and let the name server deal with things.
+	 */
+	if (strlen(argv[1]) >= 255) {
+		printf("dns error: hostname too long\n");
+		return 1;
+	}
+
+	NetDNSResolve = argv[1];
+
+	if (argc == 3)
+		NetDNSenvvar = argv[2];
+	else
+		NetDNSenvvar = NULL;
+
+	if (NetLoop(DNS) < 0) {
+		printf("dns lookup of %s failed, check setup\n", argv[1]);
+		return 1;
+	}
+
+	return 0;
+}
+
+U_BOOT_CMD(
+	dns,	3,	1,	do_dns,
+	"lookup the IP of a hostname",
+	"hostname [envvar]"
+);
+
+#endif	/* CONFIG_CMD_DNS */
+

doc/README.dns

@@ -0,0 +1,64 @@
+Domain Name System
+-------------------------------------------
+
+The Domain Name System (DNS) is a hierarchical naming system for computers,
+services, or any resource participating in the Internet. It associates various
+information with domain names assigned to each of the participants. Most
+importantly, it translates domain names meaningful to humans into the numerical
+(binary) identifiers associated with networking equipment for the purpose of
+locating and addressing these devices world-wide. An often used analogy to
+explain the Domain Name System is that it serves as the "phone book" for the
+Internet by translating human-friendly computer hostnames into IP addresses.
+For example, www.example.com translates to 208.77.188.166.
+
+For more information on DNS - http://en.wikipedia.org/wiki/Domain_Name_System
+
+
+
+U-Boot and DNS
+------------------------------------------
+
+CONFIG_CMD_DNS - controls if the 'dns' command is compiled in. If it is, it
+                 will send name lookups to the dns server (env var 'dnsip')
+                 Turning this option on will about abou 1k to U-Boot's size.
+
+                 Example:
+
+bfin> print dnsip
+dnsip=192.168.0.1
+
+bfin> dns www.google.com
+66.102.1.104
+
+                 By default, dns does nothing except print the IP number on
+                 the default console - which by itself, would be pretty
+                 useless. Adding a third argument to the dns command will
+                 use that as the environment variable to be set.
+
+                 Example:
+
+bfin> print googleip
+## Error: "googleip" not defined
+bfin> dns www.google.com googleip
+64.233.161.104
+bfin> print googleip
+googleip=64.233.161.104
+bfin> ping ${googleip}
+Using Blackfin EMAC device
+host 64.233.161.104 is alive
+
+                 In this way, you can lookup, and set many more meaningful
+                 things.
+
+bfin> sntp
+ntpserverip not set
+bfin> dns pool.ntp.org ntpserverip
+72.18.205.156
+bfin> sntp
+Date: 2009-07-18 Time:  4:06:57
+
+                 For some helpful things that can be related to DNS in U-Boot,
+                 look at the top level README for these config options:
+                    CONFIG_CMD_DHCP
+                    CONFIG_BOOTP_DNS
+                    CONFIG_BOOTP_DNS2

include/net.h

@@ -361,6 +361,11 @@ typedef enum { BOOTP, RARP, ARP, TFTP, DHCP, PING, DNS, NFS, CDP, NETCONS, SNTP
 /* from net/net.c */
 extern char	BootFile[128];			/* Boot File name		*/
 
+#if defined(CONFIG_CMD_DNS)
+extern char *NetDNSResolve;		/* The host to resolve  */
+extern char *NetDNSenvvar;		/* the env var to put the ip into */
+#endif
+
 #if defined(CONFIG_CMD_PING)
 extern IPaddr_t	NetPingIP;			/* the ip address to ping		*/
 #endif

net/Makefile

@@ -27,13 +27,14 @@ include $(TOPDIR)/config.mk
 
 LIB	= $(obj)libnet.a
 
-COBJS-y += net.o
-COBJS-y += tftp.o
 COBJS-y += bootp.o
-COBJS-y += rarp.o
+COBJS-$(CONFIG_CMD_DNS)  += dns.o
 COBJS-y += eth.o
+COBJS-y += net.o
 COBJS-y += nfs.o
+COBJS-y += rarp.o
 COBJS-$(CONFIG_CMD_SNTP) += sntp.o
+COBJS-y += tftp.o
 
 COBJS	:= $(COBJS-y)
 SRCS	:= $(COBJS:.o=.c)

net/dns.c

@@ -0,0 +1,211 @@
+/*
+ * DNS support driver
+ *
+ * Copyright (c) 2008 Pieter Voorthuijsen <pieter.voorthuijsen@prodrive.nl>
+ * Copyright (c) 2009 Robin Getz <rgetz@blackfin.uclinux.org>
+ *
+ * This is a simple DNS implementation for U-Boot. It will use the first IP
+ * in the DNS response as NetServerIP. This can then be used for any other
+ * network related activities.
+ *
+ * The packet handling is partly based on TADNS, original copyrights
+ * follow below.
+ *
+ */
+
+/*
+ * Copyright (c) 2004-2005 Sergey Lyubka <valenok@gmail.com>
+ *
+ * "THE BEER-WARE LICENSE" (Revision 42):
+ * Sergey Lyubka wrote this file.  As long as you retain this notice you
+ * can do whatever you want with this stuff. If we meet some day, and you think
+ * this stuff is worth it, you can buy me a beer in return.
+ */
+
+#include <common.h>
+#include <command.h>
+#include <net.h>
+
+#include "dns.h"
+
+char *NetDNSResolve;	/* The host to resolve  */
+char *NetDNSenvvar;	/* The envvar to store the answer in */
+
+static int DnsOurPort;
+
+static void
+DnsSend(void)
+{
+	struct header *header;
+	int n, name_len;
+	uchar *p, *pkt;
+	const char *s;
+	const char *name;
+	enum dns_query_type qtype = DNS_A_RECORD;
+
+	name = NetDNSResolve;
+	pkt = p = (uchar *)(NetTxPacket + NetEthHdrSize() + IP_HDR_SIZE);
+
+	/* Prepare DNS packet header */
+	header           = (struct header *) pkt;
+	header->tid      = 1;
+	header->flags    = htons(0x100);	/* standard query */
+	header->nqueries = htons(1);		/* Just one query */
+	header->nanswers = 0;
+	header->nauth    = 0;
+	header->nother   = 0;
+
+	/* Encode DNS name */
+	name_len = strlen(name);
+	p = (uchar *) &header->data;	/* For encoding host name into packet */
+
+	do {
+		s = strchr(name, '.');
+		if (!s)
+			s = name + name_len;
+
+		n = s - name;			/* Chunk length */
+		*p++ = n;			/* Copy length  */
+		memcpy(p, name, n);		/* Copy chunk   */
+		p += n;
+
+		if (*s == '.')
+			n++;
+
+		name += n;
+		name_len -= n;
+	} while (*s != '\0');
+
+	*p++ = 0;			/* Mark end of host name */
+	*p++ = 0;			/* Some servers require double null */
+	*p++ = (unsigned char) qtype;	/* Query Type */
+
+	*p++ = 0;
+	*p++ = 1;				/* Class: inet, 0x0001 */
+
+	n = p - pkt;				/* Total packet length */
+	debug("Packet size %d\n", n);
+
+	DnsOurPort = random_port();
+
+	NetSendUDPPacket(NetServerEther, NetOurDNSIP, DNS_SERVICE_PORT,
+		DnsOurPort, n);
+	debug("DNS packet sent\n");
+}
+
+static void
+DnsTimeout(void)
+{
+	puts("Timeout\n");
+	NetState = NETLOOP_FAIL;
+}
+
+static void
+DnsHandler(uchar *pkt, unsigned dest, unsigned src, unsigned len)
+{
+	struct header *header;
+	const unsigned char *p, *e, *s;
+	u16 type, i;
+	int found, stop, dlen;
+	char IPStr[22];
+	IPaddr_t IPAddress;
+	short tmp;
+
+
+	debug("%s\n", __func__);
+	if (dest != DnsOurPort)
+		return;
+
+	for (i = 0; i < len; i += 4)
+		debug("0x%p - 0x%.2x  0x%.2x  0x%.2x  0x%.2x\n",
+			pkt+i, pkt[i], pkt[i+1], pkt[i+2], pkt[i+3]);
+
+	/* We sent 1 query. We want to see more that 1 answer. */
+	header = (struct header *) pkt;
+	if (ntohs(header->nqueries) != 1)
+		return;
+
+	/* Received 0 answers */
+	if (header->nanswers == 0) {
+		puts("DNS server returned no answers\n");
+		NetState = NETLOOP_SUCCESS;
+		return;
+	}
+
+	/* Skip host name */
+	s = &header->data[0];
+	e = pkt + len;
+	for (p = s; p < e && *p != '\0'; p++)
+		continue;
+
+	/* We sent query class 1, query type 1 */
+	tmp = p[1] | (p[2] << 8);
+	if (&p[5] > e || ntohs(tmp) != DNS_A_RECORD) {
+		puts("DNS response was not A record\n");
+		NetState = NETLOOP_SUCCESS;
+		return;
+	}
+
+	/* Go to the first answer section */
+	p += 5;
+
+	/* Loop through the answers, we want A type answer */
+	for (found = stop = 0; !stop && &p[12] < e; ) {
+
+		/* Skip possible name in CNAME answer */
+		if (*p != 0xc0) {
+			while (*p && &p[12] < e)
+				p++;
+			p--;
+		}
+		debug("Name (Offset in header): %d\n", p[1]);
+
+		tmp = p[2] | (p[3] << 8);
+		type = ntohs(tmp);
+		debug("type = %d\n", type);
+		if (type == DNS_CNAME_RECORD) {
+			/* CNAME answer. shift to the next section */
+			debug("Found canonical name\n");
+			tmp = p[10] | (p[11] << 8);
+			dlen = ntohs(tmp);
+			debug("dlen = %d\n", dlen);
+			p += 12 + dlen;
+		} else if (type == DNS_A_RECORD) {
+			debug("Found A-record\n");
+			found = stop = 1;
+		} else {
+			debug("Unknown type\n");
+			stop = 1;
+		}
+	}
+
+	if (found && &p[12] < e) {
+
+		tmp = p[10] | (p[11] << 8);
+		dlen = ntohs(tmp);
+		p += 12;
+		memcpy(&IPAddress, p, 4);
+
+		if (p + dlen <= e) {
+			ip_to_string(IPAddress, IPStr);
+			printf("%s\n", IPStr);
+			if (NetDNSenvvar)
+				setenv(NetDNSenvvar, IPStr);
+		} else
+			puts("server responded with invalid IP number\n");
+	}
+
+	NetState = NETLOOP_SUCCESS;
+}
+
+void
+DnsStart(void)
+{
+	debug("%s\n", __func__);
+
+	NetSetTimeout(DNS_TIMEOUT, DnsTimeout);
+	NetSetHandler(DnsHandler);
+
+	DnsSend();
+}
+

net/dns.h

@@ -0,0 +1,39 @@
+/*
+ * (C) Masami Komiya <mkomiya@sonare.it> 2005
+ *  Copyright 2009, Robin Getz <rgetz@blackfin.uclinux.org>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2, or (at
+ * your option) any later version.
+ */
+
+#ifndef __DNS_H__
+#define __DNS_H__
+
+#define DNS_SERVICE_PORT 53
+#define DNS_TIMEOUT      10000UL
+
+/* http://en.wikipedia.org/wiki/List_of_DNS_record_types */
+enum dns_query_type {
+	DNS_A_RECORD = 0x01,
+	DNS_CNAME_RECORD = 0x05,
+	DNS_MX_RECORD = 0x0f,
+};
+
+/*
+ * DNS network packet
+ */
+struct header {
+	uint16_t	tid;		/* Transaction ID */
+	uint16_t	flags;		/* Flags */
+	uint16_t	nqueries;	/* Questions */
+	uint16_t	nanswers;	/* Answers */
+	uint16_t	nauth;		/* Authority PRs */
+	uint16_t	nother;		/* Other PRs */
+	unsigned char	data[1];	/* Data, variable length */
+};
+
+extern void DnsStart(void);		/* Begin DNS */
+
+#endif

net/net.c

@@ -92,6 +92,9 @@
 #if defined(CONFIG_CDP_VERSION)
 #include <timestamp.h>
 #endif
+#if defined(CONFIG_CMD_DNS)
+#include "dns.h"
+#endif
 
 #if defined(CONFIG_CMD_NET)
 
@@ -291,6 +294,9 @@ NetInitLoop(proto_t protocol)
 		NetServerIP = getenv_IPaddr ("serverip");
 		NetOurNativeVLAN = getenv_VLAN("nvlan");
 		NetOurVLAN = getenv_VLAN("vlan");
+#if defined(CONFIG_CMD_DNS)
+		NetOurDNSIP = getenv_IPaddr("dnsip");
+#endif
 		env_changed_id = env_id;
 	}
 
@@ -425,6 +431,11 @@ restart:
 		case SNTP:
 			SntpStart();
 			break;
+#endif
+#if defined(CONFIG_CMD_DNS)
+		case DNS:
+			DnsStart();
+			break;
 #endif
 		default:
 			break;
@@ -1518,6 +1529,14 @@ static int net_check_prereq (proto_t protocol)
 		}
 		goto common;
 #endif
+#if defined(CONFIG_CMD_DNS)
+	case DNS:
+		if (NetOurDNSIP == 0) {
+			puts("*** ERROR: DNS server address not given\n");
+			return 1;
+		}
+		goto common;
+#endif
 #if defined(CONFIG_CMD_NFS)
 	case NFS:
 #endif
@@ -1681,6 +1700,16 @@ void copy_filename (char *dst, char *src, int size)
 
 #endif
 
+#if defined(CONFIG_CMD_NFS) || defined(CONFIG_CMD_SNTP) || defined(CONFIG_CMD_DNS)
+/*
+ * make port a little random, but use something trivial to compute
+ */
+unsigned int random_port(void)
+{
+	return 1024 + (get_timer(0) % 0x8000);;
+}
+#endif
+
 void ip_to_string (IPaddr_t x, char *s)
 {
 	x = ntohl (x);