From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v6 4/5] fs, xfs: introduce MAP_DIRECT for creating
	block-map-atomic file ranges
Date: Thu, 24 Aug 2017 18:39:25 +0200
Message-ID: <20170824163925.GA28503@lst.de>
References: <150353211413.5039.5228914877418362329.stgit@dwillia2-desk3.amr.corp.intel.com> <150353213655.5039.7662200155640827407.stgit@dwillia2-desk3.amr.corp.intel.com> <20170824161152.GB27591@lst.de> <CAPcyv4jjNi_+c5DW9nsBLEnYMBtsR_v67+bF6bC4Cb9mY7T+Ww@mail.gmail.com>
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To: Dan Williams <dan.j.williams@intel.com>
Cc: Christoph Hellwig <hch@lst.de>, Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>, "Darrick J. Wong" <darrick.wong@oracle.com>, Linux API <linux-api@vger.kernel.org>, "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>, Dave Chinner <david@fromorbit.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, linux-xfs@vger.kernel.org, Linux MM <linux-mm@kvack.org>, Jeff Moyer <jmoyer@redhat.com>, Alexander Viro <viro@zeniv.linux.org.uk>, Andy Lutomirski <luto@kernel.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, Ross Zwisler <ross.zwisler@linux.intel.com>, xen-devel@lists.xen.org
List-Id: linux-api@vger.kernel.org

On Thu, Aug 24, 2017 at 09:31:17AM -0700, Dan Williams wrote:
> External agent is a DMA device, or a hypervisor like Xen. In the DMA
> case perhaps we can use the fcntl lease mechanism, I'll investigate.
> In the Xen case it actually would need to use fiemap() to discover the
> physical addresses that back the file to setup their M2P tables.
> Here's the discussion where we discovered that physical address
> dependency:
> 
>     https://lists.xen.org/archives/html/xen-devel/2017-04/msg00419.html

fiemap does not work to discover physical addresses.  If they want
to do anything involving physical address they will need a kernel
driver.

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