network: always create dnsmasq hosts and addnhosts files, even if empty

This fixes the problem reported in:

  https://bugzilla.redhat.com/show_bug.cgi?id=868389

Previously, the dnsmasq hosts file (used for static dhcp entries, and
addnhosts file (used for additional dns host entries) were only
created/referenced on the dnsmasq commandline if there was something
to put in them at the time the network was started. Once we can update
a network definition while it's active (which is now possible with
virNetworkUpdate), this is no longer a valid strategy - if there were
0 dhcp static hosts (resulting in no reference to the hosts file on the
commandline), then one was later added, the commandline wouldn't have
linked dnsmasq up to the file, so even though we create it, dnsmasq
doesn't pay any attention.

The solution is to just always create these files and reference them
on the dnsmasq commandline (almost always, anyway). That way dnsmasq
can notice when a new entry is added at runtime (a SIGHUP is sent to
dnsmasq by virNetworkUdpate whenever a host entry is added or removed)

The exception to this is that the dhcp static hosts file isn't created
if there are no lease ranges *and* no static hosts. This is because in
this case dnsmasq won't be setup to listen for dhcp requests anyway -
in that case, if the count of dhcp hosts goes from 0 to 1, dnsmasq
will need to be restarted anyway (to get it listening on the dhcp
port). Likewise, if the dhcp hosts count goes from 1 to 0 (and there
are no dhcp ranges) we need to restart dnsmasq so that it will stop
listening on port 67. These special situations are handled in the
bridge driver's networkUpdate() by checking for ((bool)
nranges||nhosts) both before and after the update, and triggering a
dnsmasq restart if the before and after don't match.

src/network/bridge_driver.c

@@ -751,12 +751,19 @@ networkBuildDnsmasqArgv(virNetworkObjPtr network,
         if (networkBuildDnsmasqHostsfile(dctx, ipdef, network->def->dns) < 0)
             goto cleanup;
 
-        if (dctx->hostsfile->nhosts)
+        /* Even if there are currently no static hosts, if we're
+         * listening for DHCP, we should write a 0-length hosts
+         * file to allow for runtime additions.
+         */
+        if (ipdef->nranges || ipdef->nhosts)
             virCommandAddArgPair(cmd, "--dhcp-hostsfile",
                                  dctx->hostsfile->path);
-        if (dctx->addnhostsfile->nhosts)
-            virCommandAddArgPair(cmd, "--addn-hosts",
-                                 dctx->addnhostsfile->path);
+
+        /* Likewise, always create this file and put it on the commandline, to allow for
+         * for runtime additions.
+         */
+        virCommandAddArgPair(cmd, "--addn-hosts",
+                             dctx->addnhostsfile->path);
 
         if (ipdef->tftproot) {
             virCommandAddArgList(cmd, "--enable-tftp",
@@ -2882,7 +2889,10 @@ networkUpdate(virNetworkPtr net,
 {
     struct network_driver *driver = net->conn->networkPrivateData;
     virNetworkObjPtr network = NULL;
-    int isActive, ret = -1;
+    int isActive, ret = -1, ii;
+    virNetworkIpDefPtr ipdef;
+    bool oldDhcpActive = false;
+
 
     virCheckFlags(VIR_NETWORK_UPDATE_AFFECT_LIVE |
                   VIR_NETWORK_UPDATE_AFFECT_CONFIG,
@@ -2897,6 +2907,16 @@ networkUpdate(virNetworkPtr net,
         goto cleanup;
     }
 
+    /* see if we are listening for dhcp pre-modification */
+    for (ii = 0;
+         (ipdef = virNetworkDefGetIpByIndex(network->def, AF_INET, ii));
+         ii++) {
+        if (ipdef->nranges || ipdef->nhosts) {
+            oldDhcpActive = true;
+            break;
+        }
+    }
+
     /* VIR_NETWORK_UPDATE_AFFECT_CURRENT means "change LIVE if network
      * is active, else change CONFIG
     */
@@ -2938,8 +2958,30 @@ networkUpdate(virNetworkPtr net,
             if (networkRestartDhcpDaemon(network) < 0)
                 goto cleanup;
 
-        } else if (section == VIR_NETWORK_SECTION_IP_DHCP_HOST ||
-                   section == VIR_NETWORK_SECTION_DNS_HOST ||
+        } else if (section == VIR_NETWORK_SECTION_IP_DHCP_HOST) {
+            /* if we previously weren't listening for dhcp and now we
+             * are (or vice-versa) then we need to do a restart,
+             * otherwise we just need to do a refresh (redo the config
+             * files and send SIGHUP)
+             */
+            bool newDhcpActive = false;
+
+            for (ii = 0;
+                 (ipdef = virNetworkDefGetIpByIndex(network->def, AF_INET, ii));
+                 ii++) {
+                if (ipdef->nranges || ipdef->nhosts) {
+                    newDhcpActive = true;
+                    break;
+                }
+            }
+
+            if ((newDhcpActive != oldDhcpActive &&
+                networkRestartDhcpDaemon(network) < 0) ||
+                networkRefreshDhcpDaemon(network) < 0) {
+                goto cleanup;
+            }
+
+        } else if (section == VIR_NETWORK_SECTION_DNS_HOST ||
                    section == VIR_NETWORK_SECTION_DNS_TXT ||
                    section == VIR_NETWORK_SECTION_DNS_SRV) {
             /* these sections only change things in config files, so we

src/util/dnsmasq.c

 /*
- * Copyright (C) 2007-2011 Red Hat, Inc.
+ * Copyright (C) 2007-2012 Red Hat, Inc.
  * Copyright (C) 2010 Satoru SATOH <satoru.satoh@gmail.com>
  *
  * This library is free software; you can redistribute it and/or
@@ -176,8 +176,9 @@ addnhostsWrite(const char *path,
     unsigned int i, ii;
     int rc = 0;
 
-    if (nhosts == 0)
-        return rc;
+    /* even if there are 0 hosts, create a 0 length file, to allow
+     * for runtime addition.
+     */
 
     if (virAsprintf(&tmp, "%s.new", path) < 0)
         return -ENOMEM;
@@ -364,8 +365,9 @@ hostsfileWrite(const char *path,
     unsigned int i;
     int rc = 0;
 
-    if (nhosts == 0)
-        return rc;
+    /* even if there are 0 hosts, create a 0 length file, to allow
+     * for runtime addition.
+     */
 
     if (virAsprintf(&tmp, "%s.new", path) < 0)
         return -ENOMEM;

tests/networkxml2argvdata/isolated-network.argv

@@ -4,4 +4,6 @@
 --listen-address 192.168.152.1 \
 --dhcp-range 192.168.152.2,192.168.152.254 \
 --dhcp-leasefile=/var/lib/libvirt/dnsmasq/private.leases --dhcp-lease-max=253 \
---dhcp-no-override\
+--dhcp-no-override \
+--dhcp-hostsfile=/var/lib/libvirt/dnsmasq/private.hostsfile \
+--addn-hosts=/var/lib/libvirt/dnsmasq/private.addnhosts\

tests/networkxml2argvdata/nat-network-dns-srv-record-minimal.argv

@@ -13,4 +13,5 @@
 --dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases \
 --dhcp-lease-max=253 \
 --dhcp-no-override \
---dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile\
+--dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile \
+--addn-hosts=/var/lib/libvirt/dnsmasq/default.addnhosts\

tests/networkxml2argvdata/nat-network-dns-srv-record.argv

@@ -13,4 +13,5 @@
 --dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases \
 --dhcp-lease-max=253 \
 --dhcp-no-override \
---dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile\
+--dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile \
+--addn-hosts=/var/lib/libvirt/dnsmasq/default.addnhosts\

tests/networkxml2argvdata/nat-network-dns-txt-record.argv

@@ -7,4 +7,5 @@
 --dhcp-range 192.168.122.2,192.168.122.254 \
 --dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases \
 --dhcp-lease-max=253 --dhcp-no-override \
---dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile\
+--dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile \
+--addn-hosts=/var/lib/libvirt/dnsmasq/default.addnhosts\

tests/networkxml2argvdata/nat-network.argv

@@ -6,4 +6,5 @@
 --dhcp-range 192.168.122.2,192.168.122.254 \
 --dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases \
 --dhcp-lease-max=253 --dhcp-no-override \
---dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile\
+--dhcp-hostsfile=/var/lib/libvirt/dnsmasq/default.hostsfile \
+--addn-hosts=/var/lib/libvirt/dnsmasq/default.addnhosts\

tests/networkxml2argvdata/netboot-network.argv

@@ -3,5 +3,8 @@
 --except-interface lo --listen-address 192.168.122.1 \
 --dhcp-range 192.168.122.2,192.168.122.254 \
 --dhcp-leasefile=/var/lib/libvirt/dnsmasq/netboot.leases \
---dhcp-lease-max=253 --dhcp-no-override --expand-hosts --enable-tftp \
+--dhcp-lease-max=253 --dhcp-no-override --expand-hosts \
+--dhcp-hostsfile=/var/lib/libvirt/dnsmasq/netboot.hostsfile \
+--addn-hosts=/var/lib/libvirt/dnsmasq/netboot.addnhosts \
+--enable-tftp \
 --tftp-root /var/lib/tftproot --dhcp-boot pxeboot.img\

tests/networkxml2argvdata/netboot-proxy-network.argv

@@ -4,4 +4,6 @@
 --dhcp-range 192.168.122.2,192.168.122.254 \
 --dhcp-leasefile=/var/lib/libvirt/dnsmasq/netboot.leases \
 --dhcp-lease-max=253 --dhcp-no-override --expand-hosts \
+--dhcp-hostsfile=/var/lib/libvirt/dnsmasq/netboot.hostsfile \
+--addn-hosts=/var/lib/libvirt/dnsmasq/netboot.addnhosts \
 --dhcp-boot pxeboot.img,,10.20.30.40\

tests/networkxml2argvdata/routed-network.argv

 @DNSMASQ@ --strict-order --bind-interfaces \
 --local=// --domain-needed --conf-file= \
---except-interface lo --listen-address 192.168.122.1\
+--except-interface lo --listen-address 192.168.122.1 \
+--addn-hosts=/var/lib/libvirt/dnsmasq/local.addnhosts\