Add extensions/drain

This takes the simplest possible approach: load the module and you're in
drain mode.

extensions/Makefile.am

@@ -75,4 +75,5 @@ extension_LTLIBRARIES =		\
   spy_stats_notice.la		\
   spy_stats_p_notice.la		\
   spy_trace_notice.la		\
+  drain.la			\
   example_module.la

extensions/drain.c

@@ -0,0 +1,38 @@
+#include "stdinc.h"
+#include "modules.h"
+#include "hook.h"
+#include "client.h"
+#include "ircd.h"
+#include "send.h"
+#include "hash.h"
+#include "s_conf.h"
+#include "s_user.h"
+#include "s_serv.h"
+#include "numeric.h"
+
+static void check_new_user(void *data);
+mapi_hfn_list_av1 drain_hfnlist[] = {
+	{ "new_local_user", (hookfn) check_new_user },
+	{ NULL, NULL }
+};
+
+static const char drain_desc[] = "Prevents new, non-exempt users from connecting to this server.";
+
+DECLARE_MODULE_AV2(drain, NULL, NULL, NULL, NULL,
+			drain_hfnlist, NULL, NULL, drain_desc);
+
+
+static void
+check_new_user(void *vdata)
+{
+	struct Client *source_p = vdata;
+	const char *drain_reason = ConfigFileEntry.drain_reason;
+
+	if (drain_reason == NULL)
+		drain_reason = "This server is not accepting connections.";
+
+	if(IsExemptKline(source_p))
+		return;
+
+	exit_client(source_p, source_p, &me, drain_reason);
+}

include/s_conf.h

@@ -240,6 +240,8 @@ struct config_file_entry
 
 	int hide_opers_in_whois;
 	int hide_opers;
+
+	char *drain_reason;
 };
 
 struct config_channel_entry

ircd/newconf.c

@@ -2799,6 +2799,7 @@ static struct ConfEntry conf_general_table[] =
 	{ "hide_opers_in_whois",	CF_YESNO, NULL, 0, &ConfigFileEntry.hide_opers_in_whois		},
 	{ "hide_opers",		CF_YESNO, NULL, 0, &ConfigFileEntry.hide_opers		},
 	{ "certfp_method",	CF_STRING, conf_set_general_certfp_method, 0, NULL },
+	{ "drain_reason",	CF_QSTRING, NULL, BUFSIZE, &ConfigFileEntry.drain_reason	},
 	{ "\0", 		0, 	  NULL, 0, NULL }
 };