Add TRANS(Listen) function to re-enable specific listen sockets

This will allow a server to disable listeners by default and then
let later configuration re-enable them. In particular, this lets the X
server disable inet and unix listen sockets by default while still
providing a '-listen' command line option to re-enable them later on.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>

Xtrans.c

@@ -803,6 +803,31 @@ TRANS(NoListen) (const char * protocol)
    return ret;
 }
 
+int
+TRANS(Listen) (const char * protocol)
+{
+   Xtransport *trans;
+   int i = 0, ret = 0;
+
+   if ((trans = TRANS(SelectTransport)(protocol)) == NULL)
+   {
+	prmsg (1,"TransListen: unable to find transport: %s\n",
+	       protocol);
+
+	return -1;
+   }
+   if (trans->flags & TRANS_ALIAS) {
+       if (trans->nolisten)
+	   while (trans->nolisten[i]) {
+	       ret |= TRANS(Listen)(trans->nolisten[i]);
+	       i++;
+       }
+   }
+
+   trans->flags &= ~TRANS_NOLISTEN;
+   return ret;
+}
+
 int
 TRANS(IsListening) (const char * protocol)
 {

Xtrans.h

@@ -311,6 +311,10 @@ int TRANS(NoListen) (
     const char*         /* protocol*/
 );
 
+int TRANS(Listen) (
+    const char*         /* protocol*/
+);
+
 int TRANS(IsListening) (
     const char*         /* protocol*/
 );