On Thu, Mar 30, 2017 at 11:19:53AM -0700, Linus Torvalds wrote:

So quite frankly, I'd much rather see that people who really want to
check would instead just

     fd = open(... O_ATOMIC);
     if (fd < 0)
          .. regular error handling ..

     /* Did we actually get O_ATOMIC? */
     if (!(O_ATOMIC & fnctl(fd, F_GETFL, NULL)))
          .. warn about lack of O_ATOMIC ..

because I suspect that you will find users that might *want* atomic
behavior, but in the absence of atomicity guarantees will want to
still be able to do IO.

That would be nice, but still won't work as we blindly copy f_flags
into F_GETFL, not even masking our internal FMODE_ bits.