network: fix DHCPv6 on networks with prefix != 64

According to the dnsmasq manpage, the netmask for IPv4 address ranges
will be auto-deteremined from the interface dnsmasq is listening on,
but it can't do this for IPv6 for some reason - it instead assumes a
network prefix of 64 for all IPv6 address ranges. If this is
incorrect, dnsmasq will refuse to give out an address to clients,
instead logging this message:

 dnsmasq-dhcp[2380]: no address range available for DHCPv6 request via virbr0

The solution is for libvirt to add ",$prefix" to all IPv6 dhcp-range
arguments when building the dnsmasq.conf file.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1033739
(cherry picked from commit bf3d9f30)

src/network/bridge_driver.c

@@ -1180,6 +1180,15 @@ networkDnsmasqConfContents(virNetworkObjPtr network,
     ipdef = ipv4def ? ipv4def : ipv6def;
 
     while (ipdef) {
+        int prefix;
+
+        prefix = virNetworkIpDefPrefix(ipdef);
+        if (prefix < 0) {
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                           _("bridge '%s' has an invalid prefix"),
+                           network->def->bridge);
+            goto cleanup;
+        }
         for (r = 0; r < ipdef->nranges; r++) {
             int thisRange;
 
@@ -1187,8 +1196,12 @@ networkDnsmasqConfContents(virNetworkObjPtr network,
                 !(eaddr = virSocketAddrFormat(&ipdef->ranges[r].end)))
                 goto cleanup;
 
-            virBufferAsprintf(&configbuf, "dhcp-range=%s,%s\n",
+            virBufferAsprintf(&configbuf, "dhcp-range=%s,%s",
                               saddr, eaddr);
+            if (VIR_SOCKET_ADDR_IS_FAMILY(&ipdef->address, AF_INET6))
+               virBufferAsprintf(&configbuf, ",%d", prefix);
+            virBufferAddLit(&configbuf, "\n");
+
             VIR_FREE(saddr);
             VIR_FREE(eaddr);
             thisRange = virSocketAddrGetRange(&ipdef->ranges[r].start,
@@ -1210,7 +1223,11 @@ networkDnsmasqConfContents(virNetworkObjPtr network,
             char *bridgeaddr = virSocketAddrFormat(&ipdef->address);
             if (!bridgeaddr)
                 goto cleanup;
-            virBufferAsprintf(&configbuf, "dhcp-range=%s,static\n", bridgeaddr);
+            virBufferAsprintf(&configbuf, "dhcp-range=%s,static",
+                              bridgeaddr);
+            if (VIR_SOCKET_ADDR_IS_FAMILY(&ipdef->address, AF_INET6))
+               virBufferAsprintf(&configbuf, ",%d", prefix);
+            virBufferAddLit(&configbuf, "\n");
             VIR_FREE(bridgeaddr);
         }
 

tests/networkxml2confdata/dhcp6-nat-network.conf

@@ -10,7 +10,7 @@ bind-dynamic
 interface=virbr0
 dhcp-range=192.168.122.2,192.168.122.254
 dhcp-no-override
-dhcp-range=2001:db8:ac10:fd01::1:10,2001:db8:ac10:fd01::1:ff
+dhcp-range=2001:db8:ac10:fd01::1:10,2001:db8:ac10:fd01::1:ff,64
 dhcp-lease-max=493
 dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile
 addn-hosts=/var/lib/libvirt/dnsmasq/default.addnhosts

tests/networkxml2confdata/dhcp6-network.conf

@@ -10,7 +10,7 @@ expand-hosts
 except-interface=lo
 bind-dynamic
 interface=virbr0
-dhcp-range=2001:db8:ac10:fd01::1:10,2001:db8:ac10:fd01::1:ff
+dhcp-range=2001:db8:ac10:fd01::1:10,2001:db8:ac10:fd01::1:ff,64
 dhcp-lease-max=240
 dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile
 addn-hosts=/var/lib/libvirt/dnsmasq/default.addnhosts

tests/networkxml2confdata/dhcp6host-routed-network.conf

@@ -10,7 +10,7 @@ bind-dynamic
 interface=virbr1
 dhcp-range=192.168.122.1,static
 dhcp-no-override
-dhcp-range=2001:db8:ac10:fd01::1,static
+dhcp-range=2001:db8:ac10:fd01::1,static,64
 dhcp-hostsfile=/var/lib/libvirt/dnsmasq/local.hostsfile
 addn-hosts=/var/lib/libvirt/dnsmasq/local.addnhosts
 enable-ra