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Date: Fri, 12 Jul 2013 13:21:07 -0700
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Subject: Re: [git pull] vfs.git part 2
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
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On Fri, Jul 12, 2013 at 12:39 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> I mean something like this:
>
> Safer ABI for O_TMPFILE
>
> [suggested by Rasmus Villemoes] make O_DIRECTORY | O_RDWR part of O_TMPFILE;
> that will fail on old kernels in a lot more cases than what I came up with.

So see earlier about why I'm not convinced about O_RDWR. But even if
we really want that (and it might be better to start off too narrow
than accept anything else) your patch tests those bits the wrong way
(any O_RDWR test should be done using the O_ACCMODE mask, not using
the O_RDWR value itself as a mask)

Also, to make sure that the "no preexisting file" case fails, I still
think you should also verify that O_CREAT is not set. Otherwise
Rasmus' case

    open("/tmp/test/link_to_nowhere", O_DIRECTORY | O_RDWR, 0666) ->
-1; No such file or directory

can work, and the case that rasmus didn't have at all (non-existent
pathname) also just silently succeeds by creating a file instead of
the expected directory..

So you could have something like

  #define O_TMPFILE (__O_TMPFILE | O_DIRECTORY | O_RDWR)
  #define O_TMPFILE_MASK (__O_TMPFILE | O_DIRECTORY | O_CREAT | O_ACCMODE)

and then use

   if ((flags & O_TMPFILE_MASK) != O_TMPFILE)
       return -ENOTSUPP;

or whatever.

Hmm?

              Linus