To optimize directory reading, vn_readdir is designed to return as many entries as possible on each call. The C run-time library deblocks the entries for POSIX programs, to provide the sequencing that they expect.

Like vn_rdwr and vn_readwritev, vn_readdir is a UIO operation, but the interpretation of the cursor is different. Cursor technique is described in the next topic. See also Opening and closing files and first references to files.