linux-kernel - Re: RFC: reject unknown open flags

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Date:   Thu, 30 Mar 2017 20:26:20 +0200
From:   Christoph Hellwig <hch@....de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Christoph Hellwig <hch@....de>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        libc-alpha <libc-alpha@...rceware.org>
Subject: Re: RFC: reject unknown open flags

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.