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Date: Mon, 3 Nov 2014 11:04:27 -0800
Message-ID: <CA+55aFw29MUj+w46yneut2yxXOH1RQmDud5KL8V-SPyPWm1WqA@mail.gmail.com>
Subject: Re: [RFC PATCH] fs: allow open(dir, O_TMPFILE|..., 0) with mode 0
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Eric Rannaud <e@nanocritical.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
        Christoph Hellwig <hch@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org

On Mon, Nov 3, 2014 at 10:49 AM, Eric Rannaud <e@nanocritical.com> wrote:
>
> Isn't it because they are essentially emulating an atomic open()
> capable of creating a file with inherited ACLs, according to
> relatively complex rules? open *can* be used with O_CREAT|O_RDONLY
> (touch(1) might do that), which would naively translate into:

Oh, so you don't actually need any file contents at all?

If that is actually a real usage, then maybe we should just say that
"O_TMPFILE|O_RDONLY" is fine, and remove the check that it has to be
writable.

That check was always a sanity-check, because people felt that a
temp-file you can't write to is an insane concept. But if there is a
real use case for it, then clearly it's not completely insane. Just
odd.

It's just that single

                if (!(acc_mode & MAY_WRITE))
                        return -EINVAL;

test in build_open_flags(), right?

I'd take a tested patch to remove that (where "tested" means: "yes, I
actually did that unwritable file descriptor thing, and it actually
solved the problem and worked for samba or whatever")

                     Linus
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