From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id B17176B0069 for ; Fri, 21 Oct 2016 05:57:22 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id t25so48652817pfg.3 for ; Fri, 21 Oct 2016 02:57:22 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2001:1868:205::9]) by mx.google.com with ESMTPS id he1si1675359pac.124.2016.10.21.02.57.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 21 Oct 2016 02:57:21 -0700 (PDT) Date: Fri, 21 Oct 2016 02:57:14 -0700 From: Christoph Hellwig 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> Sender: owner-linux-mm@kvack.org List-ID: 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" 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. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org