Date: Wed, 16 May 2012 12:02:36 -0400
From: Matthew Wilcox <willy@linux.intel.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: NVM Mapping API
Message-ID: <20120516160236.GI22985@linux.intel.com>
References: <20120515133450.GD22985@linux.intel.com>
 <4FB2E069.7060703@amacapital.net>
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On Tue, May 15, 2012 at 04:02:01PM -0700, Andy Lutomirski wrote:
> I would love to use this from userspace.  If I could carve out a little
> piece of NVM as a file (or whatever) and mmap it, I could do all kinds
> of fun things with that.  It would be nice if it had well-defined, or at
> least configurable or discoverable, caching properties (e.g. WB, WT, WC,
> UC, etc.).

Yes, usage from userspace is definitely planned; again through a
filesystem interface.  Treating it like a regular file will work as
expected; the question is how to expose the interesting properties
(eg is there a lighter weight mechanism than calling msync()).

My hope was that by having a discussion of how to use this stuff within
the kernel, we might come up with some usage models that would inform
how we design a user space library.

> (Even better would be a way to make a clone of an fd that only allows
> mmap, but that's a mostly unrelated issue.)

O_MMAP_ONLY?  And I'm not sure why you'd want to forbid reads and writes.
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