linux-kernel - RE: [PATCH v2 0/2] mm: introduce MAP_FIXED

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Date:   Tue, 19 Dec 2017 12:40:16 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Edward Napierala' <trasz@...ebsd.org>,
        Michal Hocko <mhocko@...nel.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Florian Weimer <fweimer@...hat.com>,
        "John Hubbard" <jhubbard@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Abdul Haleem" <abdhalee@...ux.vnet.ibm.com>,
        Joel Stanley <joel@....id.au>,
        "Kees Cook" <keescook@...omium.org>,
        "jasone@...gle.com" <jasone@...gle.com>,
        "davidtgoldblatt@...il.com" <davidtgoldblatt@...il.com>
Subject: RE: [PATCH v2 0/2] mm: introduce MAP_FIXED_SAFE

From: Edward Napierala
> Sent: 14 December 2017 14:55
>
> On 1214T1415, Michal Hocko wrote:
> > On Thu 14-12-17 12:44:17, Edward Napierala wrote:
> > > Regarding the name - how about adopting MAP_EXCL?  It was introduced in
> > > FreeBSD,
> > > and seems to do exactly this; quoting mmap(2):
> > >
> > > MAP_FIXED    Do not permit the system to select a different address
> > >                         than the one specified.  If the specified address
> > >                         cannot be used, mmap() will fail.  If MAP_FIXED is
> > >                         specified, addr must be a multiple of the page size.
> > >                         If MAP_EXCL is not specified, a successful MAP_FIXED
> > >                         request replaces any previous mappings for the
> > >                         process' pages in the range from addr to addr + len.
> > >                         In contrast, if MAP_EXCL is specified, the request
> > >                         will fail if a mapping already exists within the
> > >                         range.
> >
> > I am not familiar with the FreeBSD implementation but from the above it
> > looks like MAP_EXCL is a MAP_FIXED mofifier which is not how we are
> > going to implement it in linux due to reasons mentioned in this cover
> > letter. Using the same name would be more confusing than helpful I am
> > afraid.
> 
> Sorry, missed that.  Indeed, reusing a name with a different semantics
> would be a bad idea.

I don't remember any discussion about using MAP_FIXED | MAP_EXCL ?

Why not match the prior art??

	David