[GXemul-devel] patch for DHCP

[George K. <xke...@ne...>]

GXemul responds to DHCP requests, but the responses are not valid.

Here is a patch so that NetBSD/pmax 5.1.2, running inside the emulator, 
can use dhcpcd to configure the network.

First, this patch fixes the calculation for UDP checksums.  I deleted "- 
8".  This is so dhcpcd no longer complains about "invalid UDP packet".

Second, this patch adds these DHCP options: subnet mask, router, domain 
name server, server identifier.  This is so dhcpcd does not "reject 
DHCP"; it seems that dhcpcd requires the option for server identifier.

Where should I post the patch?  Here to gxemul-devel, or elsewhere?

--George Koehler


Index: src/net/net_ip.cc
===================================================================
--- src/net/net_ip.cc    (revision 5802)
+++ src/net/net_ip.cc    (working copy)
@@ -936,7 +936,7 @@
   *
   *  Handle an IPv4 DHCP broadcast packet, coming from the emulated NIC.
   *
- *  Read http://www.ietf.org/rfc/rfc2131.txt for details on DHCP.
+ *  Read http://tools.ietf.org/html/rfc2131 for details on DHCP.
   *  (And http://users.telenet.be/mydotcom/library/network/dhcp.htm.)
   */
  static void net_ip_broadcast_dhcp(struct net *net, void *extra,
@@ -947,7 +947,7 @@
       */
  #if 1
      struct ethernet_packet_link *lp;
-    int i;
+    int i, reply_len;

      fatal("[ net: IPv4 DHCP: ");
  #if 1
@@ -1007,15 +1007,21 @@
       */
      fatal(" ]\n");

-    lp = net_allocate_ethernet_packet_link(net, extra, len);
+    reply_len = 307;
+    lp = net_allocate_ethernet_packet_link(net, extra, reply_len);

-    /*  Copy the old packet first:  */
-    memcpy(lp->data, packet, len);
+    /*  From old packet, copy everything before options field:  */
+    memcpy(lp->data, packet, 278);

      /*  We are sending to the client, from the gateway:  */
      memcpy(lp->data + 0, packet + 6, 6);
      memcpy(lp->data + 6, net->gateway_ethernet_addr, 6);

+        /*  Set IP length:  */
+    lp->data[16] = (reply_len - 14) >> 8;
+    lp->data[17] = (reply_len - 14) & 0xff;
+
+        /*  Set IP addresses:  */
      memcpy(lp->data + 26, &net->gateway_ipv4_addr[0], 4);
      lp->data[30] = 0xff;
      lp->data[31] = 0xff;
@@ -1026,6 +1032,10 @@
      memcpy(lp->data + 34, packet + 36, 2);
      memcpy(lp->data + 36, packet + 34, 2);

+    /*  Set UDP length:  */
+    lp->data[38] = (reply_len - 34) >> 8;
+    lp->data[39] = (reply_len - 34) & 0xff;
+
      /*  Client's (yiaddr) IPv4 address:  */
      lp->data[58] = 10;
      lp->data[59] = 0;
@@ -1040,11 +1050,35 @@

      snprintf((char *)lp->data + 70+16+64, 8, "gxemul");

+    /*  Options field at offset 278:  */
+    lp->data[278] = 99;
+    lp->data[279] = 130;
+    lp->data[280] = 83;
+    lp->data[281] = 99;
+
+    /*  DHCP options, http://tools.ietf.org/html/rfc1533  */
+    lp->data[282] = 1; /* subnet mask */
+    lp->data[283] = 4;
+    lp->data[284] = 255;
+    lp->data[285] = 0;
+    lp->data[286] = 0;
+    lp->data[287] = 0;
+    lp->data[288] = 3; /* router */
+    lp->data[289] = 4;
+    memcpy(lp->data + 290, &net->gateway_ipv4_addr[0], 4);
+    lp->data[294] = 6; /* domain name server */
+    lp->data[295] = 4;
+    memcpy(lp->data + 296, &net->gateway_ipv4_addr[0], 4);
+    lp->data[300] = 54; /* server identifier */
+    lp->data[301] = 4;
+    memcpy(lp->data + 302, &net->gateway_ipv4_addr[0], 4);
+    lp->data[306] = 255; /* end */
+
      /*  Recalculate IP header checksum:  */
      net_ip_checksum(lp->data + 14, 10, 20);

      /*  ... and the UDP checksum:  */
-    net_ip_tcp_checksum(lp->data + 34, 6, len - 34 - 8,
+    net_ip_tcp_checksum(lp->data + 34, 6, reply_len - 34,
          lp->data + 26, lp->data + 30, 1);