Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754655AbcJUJ5Y (ORCPT ); Fri, 21 Oct 2016 05:57:24 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:39937 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754398AbcJUJ5T (ORCPT ); Fri, 21 Oct 2016 05:57:19 -0400 Date: Fri, 21 Oct 2016 02:57:14 -0700 From: Christoph Hellwig To: Dave Chinner Cc: Stephen Bates , Dan Williams , "linux-kernel@vger.kernel.org" , "linux-nvdimm@lists.01.org" , linux-rdma@vger.kernel.org, linux-block@vger.kernel.org, Linux MM , Ross Zwisler , Matthew Wilcox , jgunthorpe@obsidianresearch.com, haggaie@mellanox.com, Christoph Hellwig , Jens Axboe , Jonathan Corbet , jim.macdonald@everspin.com, sbates@raithin.com, Logan Gunthorpe , David Woodhouse , "Raj, Ashok" Subject: Re: [PATCH 0/3] iopmem : A block device for PCIe memory Message-ID: <20161021095714.GA12209@infradead.org> References: <1476826937-20665-1-git-send-email-sbates@raithlin.com> <20161019184814.GC16550@cgy1-donard.priv.deltatee.com> <20161020232239.GQ23194@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161020232239.GQ23194@dastard> User-Agent: Mutt/1.6.1 (2016-04-27) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 881 Lines: 17 On Fri, Oct 21, 2016 at 10:22:39AM +1100, Dave Chinner wrote: > You do realise that local filesystems can silently change the > location of file data at any point in time, so there is no such > thing as a "stable mapping" of file data to block device addresses > in userspace? > > If you want remote access to the blocks owned and controlled by a > filesystem, then you need to use a filesystem with a remote locking > mechanism to allow co-ordinated, coherent access to the data in > those blocks. Anything else is just asking for ongoing, unfixable > filesystem corruption or data leakage problems (i.e. security > issues). And at least for XFS we have such a mechanism :) E.g. I have a prototype of a pNFS layout that uses XFS+DAX to allow clients to do RDMA directly to XFS files, with the same locking mechanism we use for the current block and scsi layout in xfs_pnfs.c.