Add knob to limit hostname length

On Linux systems the length limit for hostnames is hardcoded
at 64 in MAXHOSTNAMELEN

Solaris, for example, allows 255 characters, and DNS allows the
total length to be up to 255 (with each label < 64).

Add a knob to allow configuring the maximum hostname length (FQDN)

The same validators are used between hosts and DNS to apply
the knob only when dealing with a FQDN as a hostname.

The maxlen option is included so installers can limit the length
of allowed hostnames when the --hostname option is used.

https://pagure.io/freeipa/issue/2018

Signed-off-by: Rob Crittenden <rcritten@redhat.com>
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>
Reviewed-By: Christian Heimes <cheimes@redhat.com>

ipaserver/plugins/host.py

@@ -653,6 +653,15 @@ class host_add(LDAPCreate):
 
     def pre_callback(self, ldap, dn, entry_attrs, attrs_list, *keys, **options):
         assert isinstance(dn, DN)
+        config = ldap.get_ipa_config()
+        if 'ipamaxhostnamelength' in config:
+            maxlen = int(config.get('ipamaxhostnamelength')[0])
+            if len(keys[-1]) > maxlen:
+                raise errors.ValidationError(
+                    name=self.obj.primary_key.cli_name,
+                    error=_('can be at most %(len)d characters' %
+                            dict(len=maxlen))
+                )
         if options.get('ip_address') and dns_container_exists(ldap):
             parts = keys[-1].split('.')
             host = parts[0]
@@ -762,7 +771,9 @@ class host_del(LDAPDelete):
     def pre_callback(self, ldap, dn, *keys, **options):
         assert isinstance(dn, DN)
         # If we aren't given a fqdn, find it
-        if hostname_validator(None, keys[-1]) is not None:
+        config = ldap.get_ipa_config()
+        maxlen = int(config.get('ipamaxhostnamelength')[0])
+        if hostname_validator(None, keys[-1], maxlen=maxlen) is not None:
             hostentry = api.Command['host_show'](keys[-1])['result']
             fqdn = hostentry['fqdn'][0]
         else: