Op.Mkdirval v_op :
id:id ->
mark:mark ->
mode:int ->
created:B0_std.Mtime.span ->
?post_exec:(op -> unit) ->
?k:(op -> unit) ->
B0_std.Fpath.t ->
opval v : dir:B0_std.Fpath.t -> mode:int -> tval dir : t -> B0_std.Fpath.tval mode : t -> int