From 8f911263e9304740b182ff3781a2a1ace0de5b42 Mon Sep 17 00:00:00 2001
From: Thomas Strobel <ts468@cam.ac.uk>
Date: Tue, 23 Jun 2015 13:36:32 +0200
Subject: [PATCH] Xen Dom0: add dnsmasq to xen-bridge.

---
 nixos/modules/virtualisation/xen-dom0.nix | 101 +++++++++++++++++++---
 1 file changed, 90 insertions(+), 11 deletions(-)

diff --git a/nixos/modules/virtualisation/xen-dom0.nix b/nixos/modules/virtualisation/xen-dom0.nix
index 7b5d714622c8..c750286a3970 100644
--- a/nixos/modules/virtualisation/xen-dom0.nix
+++ b/nixos/modules/virtualisation/xen-dom0.nix
@@ -47,13 +47,32 @@ in
           '';
       };
 
-    virtualisation.xen.bridge =
-      mkOption {
-        default = "xenbr0";
-        description =
-          ''
-            Create a bridge for the Xen domUs to connect to.
+    virtualisation.xen.bridge = {
+        name = mkOption {
+          default = "xenbr0";
+          description = ''
+              Name of bridge the Xen domUs connect to.
+            '';
+        };
+
+        address = mkOption {
+          type = types.str;
+          default = "172.16.0.1";
+          description = ''
+            IPv4 address of the bridge.
           '';
+        };
+
+        prefixLength = mkOption {
+          type = types.addCheck types.int (n: n >= 0 && n <= 32);
+          default = 16;
+          description = ''
+            Subnet mask of the bridge interface, specified as the number of
+            bits in the prefix (<literal>24</literal>).
+            A DHCP server will provide IP addresses for the whole, remaining
+            subnet.
+          '';
+        };
       };
 
     virtualisation.xen.stored =
@@ -261,11 +280,71 @@ in
       description = "Xen bridge";
       wantedBy = [ "multi-user.target" ];
       before = [ "xen-domains.service" ];
-      serviceConfig.RemainAfterExit = "yes";
-      serviceConfig.ExecStart = "${pkgs.bridge-utils}/bin/brctl addbr ${cfg.bridge}";
-      postStart = "${pkgs.inetutils}/bin/ifconfig ${cfg.bridge} up";
-      serviceConfig.ExecStop = "${pkgs.inetutils}/bin/ifconfig ${cfg.bridge} down";
-      postStop = "${pkgs.bridge-utils}/bin/brctl delbr ${cfg.bridge}";
+      preStart = ''
+        mkdir -p /var/run/xen
+        touch /var/run/xen/dnsmasq.pid
+        touch /var/run/xen/dnsmasq.etherfile
+        touch /var/run/xen/dnsmasq.leasefile
+
+        IFS='-' read -a data <<< `${pkgs.sipcalc}/bin/sipcalc ${cfg.bridge.address}/${toString cfg.bridge.prefixLength} | grep Usable\ range`
+        export XEN_BRIDGE_IP_RANGE_START="${"\${data[1]//[[:blank:]]/}"}"
+        export XEN_BRIDGE_IP_RANGE_END="${"\${data[2]//[[:blank:]]/}"}"
+
+        IFS='-' read -a data <<< `${pkgs.sipcalc}/bin/sipcalc ${cfg.bridge.address}/${toString cfg.bridge.prefixLength} | grep Network\ address`
+        export XEN_BRIDGE_NETWORK_ADDRESS="${"\${data[1]//[[:blank:]]/}"}"
+
+        echo "${cfg.bridge.address} host gw dns" > /var/run/xen/dnsmasq.hostsfile
+
+        cat <<EOF > /var/run/xen/dnsmasq.conf
+        no-daemon
+        pid-file=/var/run/xen/dnsmasq.pid
+        interface=${cfg.bridge.name}
+        except-interface=lo
+        bind-interfaces
+        auth-server=dns.xen.local,${cfg.bridge.name}
+        auth-zone=xen.local,$XEN_BRIDGE_NETWORK_ADDRESS/${toString cfg.bridge.prefixLength}
+        domain=xen.local
+        addn-hosts=/var/run/xen/dnsmasq.hostsfile
+        expand-hosts
+        strict-order
+        no-hosts
+        bogus-priv
+        no-resolv
+        no-poll
+        filterwin2k
+        clear-on-reload
+        domain-needed
+        dhcp-hostsfile=/var/run/xen/dnsmasq.etherfile
+        dhcp-authoritative
+        dhcp-range=$XEN_BRIDGE_IP_RANGE_START,$XEN_BRIDGE_IP_RANGE_END,$XEN_BRIDGE_NETWORK_ADDRESS
+        dhcp-no-override
+        no-ping
+        dhcp-leasefile=/var/run/xen/dnsmasq.leasefile
+        EOF
+
+        # DHCP
+        ${pkgs.iptables}/bin/iptables -I INPUT  -i ${cfg.bridge.name} -p tcp -s $XEN_BRIDGE_NETWORK_ADDRESS/${toString cfg.bridge.prefixLength} --sport 68 --dport 67 -j ACCEPT
+        ${pkgs.iptables}/bin/iptables -I INPUT  -i ${cfg.bridge.name} -p udp -s $XEN_BRIDGE_NETWORK_ADDRESS/${toString cfg.bridge.prefixLength} --sport 68 --dport 67 -j ACCEPT
+        # DNS
+        ${pkgs.iptables}/bin/iptables -I INPUT  -i ${cfg.bridge.name} -p tcp -d ${cfg.bridge.address} --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
+        ${pkgs.iptables}/bin/iptables -I INPUT  -i ${cfg.bridge.name} -p udp -d ${cfg.bridge.address} --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
+
+        ${pkgs.bridge-utils}/bin/brctl addbr ${cfg.bridge.name}
+        ${pkgs.inetutils}/bin/ifconfig ${cfg.bridge.name} ${cfg.bridge.address}
+        ${pkgs.inetutils}/bin/ifconfig ${cfg.bridge.name} up
+      '';
+      serviceConfig.ExecStart = "${pkgs.dnsmasq}/bin/dnsmasq --conf-file=/var/run/xen/dnsmasq.conf";
+      postStop = ''
+        ${pkgs.inetutils}/bin/ifconfig ${cfg.bridge.name} down
+        ${pkgs.bridge-utils}/bin/brctl delbr ${cfg.bridge.name}
+
+        # DNS
+        ${pkgs.iptables}/bin/iptables -D INPUT  -i ${cfg.bridge.name} -p udp -d ${cfg.bridge.address} --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
+        ${pkgs.iptables}/bin/iptables -D INPUT  -i ${cfg.bridge.name} -p tcp -d ${cfg.bridge.address} --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
+        # DHCP
+        ${pkgs.iptables}/bin/iptables -D INPUT  -i ${cfg.bridge.name} -p udp --sport 68 --dport 67 -j ACCEPT
+        ${pkgs.iptables}/bin/iptables -D INPUT  -i ${cfg.bridge.name} -p tcp --sport 68 --dport 67 -j ACCEPT
+      '';
     };