Directory creation
val v_op : id:id -> mark:mark -> mode:int -> created:B00_std.Time.span -> ?post_exec:(op -> unit) -> ?k:(op -> unit) -> B00_std.Fpath.t -> opv_op declares a directory creation operation, see the corresponding accessors for the semantics of the various arguments.
val v : dir:B00_std.Fpath.t -> mode:int -> tv constructs a bare mkdir operation.
val dir : t -> B00_std.Fpath.tdir mk is the directory created by mk.
val mode : t -> intmode mk are the permissions of the directory created by mk.