On Fri, Oct 21, 2016 at 02:57:14AM -0700, Christoph Hellwig wrote: > 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. Oh, that's good to know - pNFS over XFS was exactly what I was thinking of when I wrote my earlier reply. A few months ago someone else was trying to use file mappings in userspace for direct remote client access on fabric connected devices. I told them "pNFS on XFS and write an efficient transport for you hardware".... Now that I know we've got RDMA support for pNFS on XFS in the pipeline, I can just tell them "just write an rdma driver for your hardware" instead. :P Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>