Re: RFC: reject unknown open flags

[Christoph Hellwig]

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.