+@item
+@samp{O_CLOEXEC} is not defined on some platforms. The gnulib
+replacement is not atomic on these platforms.
+
+@item
+@samp{O_SEARCH} and @samp{O_EXEC} are not defined
+on some platforms.
+
+@item
+@samp{F_DUPFD}, @samp{F_DUPFD_CLOEXEC}, @samp{F_GETFD}, and
+@samp{F_SETFD} are not defined on some platforms:
+mingw
+
+@item
+@samp{F_GETFL}, @samp{F_SETFL}, @samp{F_GETLK}, @samp{F_SETLK},
+@samp{F_SETLOKW}, @samp{F_GETOWN}, and @samp{F_SETOWN} are not defined
+on some platforms.
+
+@item
+@samp{POSIX_FADV_DONTNEED}, @samp{POSIX_FADV_NOREUSE},
+@samp{POSIX_FADV_NORMAL}, @samp{POSIX_FADV_RANDOM},
+@samp{POSIX_FADV_SEQUENTIAL}, and @samp{POSIX_FADV_WILLNEED} are not
+defined on some platforms.