This code is in vicecb.cc. Callback management handles a hash table for FileEntry's and for CallBackEntry's. A CallBackEntry is attached/removed to each FileEntry as needed. A CallBackEntry contains a pointer to the host HostTable (the host (vicedep/srv.h) so that the host to notify can be found back. All structures are managed in VM. For locality of referenence, CallBacks and FileEntry are allocated in blocks. Routines are present to delete the callbacks for a Fid, or to remove all backbacks for a Venus which has failed.