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Message-ID: <52E84941.4080704@zytor.com>
Date: Tue, 28 Jan 2014 16:20:17 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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Subject: Re: [RFC] shmgetfd idea
References: <52E709C0.1050006@linaro.org> <52E7298D.5020001@zytor.com> <52E80B85.8020302@linaro.org> <52E814FF.6060403@zytor.com> <52E819F0.6040806@linaro.org> <CAPXgP11Fv6TU+o2Eui5rVW0A37U7KjwC0DZYbQOJJ8rEAYOiJg@mail.gmail.com> <52E81BB3.6060306@linaro.org> <52E81CE2.3030304@zytor.com> <52E8271B.4030201@linaro.org> <CAPXgP13G14B3YFpaE+m_AtFfFR6NRVSi1JYAvLZSsfftSkgwBQ@mail.gmail.com> <52E83719.9060709@zytor.com> <CAPXgP116TBZx82=J_pKxgSqJsy4HY1nofMOkUtZELBYvcFhDcw@mail.gmail.com> <52E83AEB.4020809@zytor.com> <CAPXgP13u+0PCFsRDRFqSdopDuXyAvZCS2crOCDrPoT6m8Nq2Og@mail.gmail.com>
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To: Kay Sievers <kay@vrfy.org>
Cc: John Stultz <john.stultz@linaro.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Greg KH <gregkh@linuxfoundation.org>, Android Kernel Team <kernel-team@android.com>, Andrew Morton <akpm@linux-foundation.org>, Mel Gorman <mgorman@suse.de>, Hugh Dickins <hughd@google.com>, Dave Hansen <dave.hansen@intel.com>, Rik van Riel <riel@redhat.com>, Michel Lespinasse <walken@google.com>, Johannes Weiner <hannes@cmpxchg.org>, Neil Brown <neilb@suse.de>, Andrea Arcangeli <aarcange@redhat.com>, Takahiro Akashi <takahiro.akashi@linaro.org>, Minchan Kim <minchan@kernel.org>, Lennart Poettering <mzxreary@0pointer.de>

On 01/28/2014 04:14 PM, Kay Sievers wrote:
>>
>> If the "single owner" is determined by the file structure (e.g. via a
>> fcntl as opposed to a ioctl), then presumably we would simply deny an
>> attempt to open the inode and create a new file structure for it.
>>
>> On Linux, /proc/$PID/fd is an open as opposed to a dup (as much as I
>> personally don't like those semantics, they are well set in stone at
>> this point) so it satisfies your requirements.
> 
> If that all could be made working, for the kdbus case we would be fine
> with requiring *any* tmpfs mount, create a new memfd from there with
> O_TMPFILE, and use new fcntl() definitios to protect/seal/unseal and
> identify that fd.
> 
> For the more restricted cases like Android that tmpfs mount could get
> a mount option to not allow the creation of any non-unlinked file, I
> guess.
> 

Right, that would be the idea.

	-hpa


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