fopen_s returned ENOENT for every failed open, including an invalid mode, a directory opened for writing and the loop and long-name cases. C11 K.3.5.2.1 only asks for a nonzero value; Microsoft's CRT, which shares Dinkumware's library, returns errno. fopen_s now returns the errno fopen set.
freopen closed the stream and returned the host's errno from the failed reopen as is, with the same Linux numbers for a symlink loop or an over-long name as fopen had. It now passes it through GuestErrnoFromHost_nid_no_patch.
fopen left the host's errno in place when the host open failed, so on Linux a symlink loop reached the title as 40 and an over-long name as 36, which are EMSGSIZE and EINPROGRESS on FreeBSD. GuestErrnoFromHost_nid_no_patch maps the host value to FreeBSD 11.4's: 1 to 34 are shared except EAGAIN (35), and ELOOP, ENAMETOOLONG, ENOTEMPTY, EDQUOT, EOVERFLOW and EDEADLK get their FreeBSD numbers; anything else is EIO.
Alexej Szpevák