* Arranges that Xen library handles (fds etc.) which are currently held
* by Xen libraries, can no longer be used other than to affect domid.
*
+ * Does not prevent effects that amount only to
+ * - denial of service, possibly host-wide, by resource exhaustion etc.
+ * - leak of not-very-interesting metainformation about other domains
+ * eg, specifically, event channel signals relating to other domains
+ *
* If this cannot be achieved, returns -1 and sets errno.
* If called again with the same domid, it may succeed, or it may
* fail (even though such a call is potentially meaningful).