diff -r acbdec33f666 xen/common/trace.c
--- a/xen/common/trace.c	Thu Jun 01 16:08:36 2006 -0400
+++ b/xen/common/trace.c	Thu Jun 01 16:13:11 2006 -0400
@@ -178,21 +178,18 @@ int tb_control(dom0_tbufcontrol_t *tbc)
 
     spin_lock(&lock);
 
-    if ( !tb_init_done &&
-         (tbc->op != DOM0_TBUF_SET_SIZE) &&
-         (tbc->op != DOM0_TBUF_ENABLE) )
-    {
-        spin_unlock(&lock);
-        return -EINVAL;
-    }
-
     switch ( tbc->op )
     {
     case DOM0_TBUF_GET_INFO:
         tbc->cpu_mask   = tb_cpu_mask;
         tbc->evt_mask   = tb_event_mask;
-        tbc->buffer_mfn = __pa(t_bufs[0]) >> PAGE_SHIFT;
-        tbc->size       = opt_tbuf_size * PAGE_SIZE;
+        if( opt_tbuf_size ) {
+            tbc->buffer_mfn = __pa(t_bufs[0]) >> PAGE_SHIFT;
+            tbc->size       = opt_tbuf_size * PAGE_SIZE;
+        } else {
+            tbc->buffer_mfn = (unsigned long)-1;
+            tbc->size       = 0;
+        }
         break;
     case DOM0_TBUF_SET_CPU_MASK:
         tb_cpu_mask = tbc->cpu_mask;