Make safeguard against incorrect flags for fsync more portable.
The existing code assumed that O_RDONLY is defined as 0, but this is
not required by POSIX and is not true on GNU Hurd. We can avoid
the assumption by relying on O_ACCMODE to mask the fcntl() result.
(Hopefully, all supported platforms define that.)
Author: Michael Banck <mbanck@gmx.net>
Co-authored-by: Samuel Thibault
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/
6862e8d1.
050a0220.194b8d.76fa@mx.google.com
Discussion: https://postgr.es/m/
68480868.
5d0a0220.1e214d.68a6@mx.google.com
Backpatch-through: 13