Date: Thu, 14 Dec 2017 14:54:43 +0000
From: Edward Napierala <trasz@freebsd.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-api@vger.kernel.org,
        Khalid Aziz <khalid.aziz@oracle.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        Andrea Arcangeli <aarcange@redhat.com>, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>, linux-arch@vger.kernel.org,
        Florian Weimer <fweimer@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Matthew Wilcox <willy@infradead.org>,
        Abdul Haleem <abdhalee@linux.vnet.ibm.com>,
        Joel Stanley <joel@jms.id.au>, Kees Cook <keescook@chromium.org>,
        jasone@google.com, davidtgoldblatt@gmail.com
Subject: Re: [PATCH v2 0/2] mm: introduce MAP_FIXED_SAFE
Message-ID: <20171214145443.GA2202@brick>
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 <20171214131526.GM16951@dhcp22.suse.cz>
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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.