linux-kernel - Re: [PATCH 0/2] mm: introduce MAP_FIXED

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Date:   Wed, 6 Dec 2017 08:33:37 +0100
From:   Rasmus Villemoes <rasmus.villemoes@...vas.dk>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...nel.org>,
        Kees Cook <keescook@...omium.org>
CC:     Linux API <linux-api@...r.kernel.org>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Florian Weimer <fweimer@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Abdul Haleem <abdhalee@...ux.vnet.ibm.com>,
        Joel Stanley <joel@....id.au>
Subject: Re: [PATCH 0/2] mm: introduce MAP_FIXED_SAFE

On 2017-12-06 05:50, Michael Ellerman wrote:
> Michal Hocko <mhocko@...nel.org> writes:
> 
>> On Wed 29-11-17 14:25:36, Kees Cook wrote:
>> It is safe in a sense it doesn't perform any address space dangerous
>> operations. mmap is _inherently_ about the address space so the context
>> should be kind of clear.
> 
> So now you have to define what "dangerous" means.
> 
>>> MAP_FIXED_UNIQUE
>>> MAP_FIXED_ONCE
>>> MAP_FIXED_FRESH
>>
>> Well, I can open a poll for the best name, but none of those you are
>> proposing sound much better to me. Yeah, naming sucks...

I also don't like the _SAFE name - MAP_FIXED in itself isn't unsafe [1],
but I do agree that having a way to avoid clobbering (parts of) an
existing mapping is quite useful. Since we're bikeshedding names, how
about MAP_FIXED_EXCL, in analogy with the O_ flag.

[1] I like the analogy between MAP_FIXED and dup2 made in
<stackoverflow.com/questions/28575893>.

Rasmus