Re: [PATCH v3 0/7] File Sealing & memfd_create()

[David Herrmann <dh.herrmann@gmail.com>]

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