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Date: Tue, 17 Jun 2014 12:10:20 +0200
Message-ID: <CANq1E4QinvVA-O=dX4N819jVK3xSihJcpz9juFj+A3qv0MXODg@mail.gmail.com>
Subject: Re: [PATCH v3 0/7] File Sealing & memfd_create()
From: David Herrmann <dh.herrmann@gmail.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Michael Kerrisk <mtk.manpages@gmail.com>, Ryan Lortie <desrt@desrt.ca>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Greg Kroah-Hartman <greg@kroah.com>,
        John Stultz <john.stultz@linaro.org>,
        Lennart Poettering <lennart@poettering.net>,
        Daniel Mack <zonque@gmail.com>, Kay Sievers <kay@vrfy.org>,
        Hugh Dickins <hughd@google.com>,
        Tony Battersby <tonyb@cybernetics.com>
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Hi

On Tue, Jun 17, 2014 at 12:04 PM, Florian Weimer <fweimer@redhat.com> wrote:
> On 06/17/2014 12:01 PM, David Herrmann wrote:
>
>>> I don't think this is what potential users expect because mlock requires
>>> capabilities which are not available to them.
>>>
>>> A couple of weeks ago, sealing was to be applied to anonymous shared
>>> memory.
>>> Has this changed?  Why should *reading* it trigger OOM?
>>
>> The file might have holes, therefore, you'd have to allocate backing
>> pages. This might hit a soft-limit and fail. To avoid this, use
>> fallocate() to allocate pages prior to mmap()
>
> This does not work because the consuming side does not know how the
> descriptor was set up if sealing does not imply that.

The consuming side has to very seals via F_GET_SEALS. After that, it
shall do a simple fallocate() on the whole file if it wants to go sure
that all pages are allocated. Why shouldn't that be possible? Please
elaborate.

Thanks
David