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Date: Fri, 21 Oct 2016 02:57:14 -0700 From: Christoph Hellwig <hch@...radead.org> To: Dave Chinner <david@...morbit.com> Cc: Stephen Bates <sbates@...thlin.com>, Dan Williams <dan.j.williams@...el.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-nvdimm@...ts.01.org" <linux-nvdimm@...1.01.org>, linux-rdma@...r.kernel.org, linux-block@...r.kernel.org, Linux MM <linux-mm@...ck.org>, Ross Zwisler <ross.zwisler@...ux.intel.com>, Matthew Wilcox <willy@...ux.intel.com>, jgunthorpe@...idianresearch.com, haggaie@...lanox.com, Christoph Hellwig <hch@...radead.org>, Jens Axboe <axboe@...com>, Jonathan Corbet <corbet@....net>, jim.macdonald@...rspin.com, sbates@...thin.com, Logan Gunthorpe <logang@...tatee.com>, David Woodhouse <dwmw2@...radead.org>, "Raj, Ashok" <ashok.raj@...el.com> Subject: Re: [PATCH 0/3] iopmem : A block device for PCIe memory 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.
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