Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755902AbbFUNyM (ORCPT ); Sun, 21 Jun 2015 09:54:12 -0400 Received: from verein.lst.de ([213.95.11.211]:38940 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753433AbbFUNyJ (ORCPT ); Sun, 21 Jun 2015 09:54:09 -0400 Date: Sun, 21 Jun 2015 15:54:06 +0200 From: Christoph Hellwig To: Dan Williams Cc: Christoph Hellwig , Jens Axboe , "linux-nvdimm@lists.01.org" , Boaz Harrosh , "Kani, Toshimitsu" , "linux-kernel@vger.kernel.org" , Linux ACPI , linux-fsdevel , Ingo Molnar Subject: Re: [PATCH 14/15] libnvdimm: support read-only btt backing devices Message-ID: <20150621135406.GA9572@lst.de> References: <20150617235209.12943.24419.stgit@dwillia2-desk3.amr.corp.intel.com> <20150617235602.12943.24958.stgit@dwillia2-desk3.amr.corp.intel.com> <20150621101346.GF5915@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1581 Lines: 33 On Sun, Jun 21, 2015 at 06:21:50AM -0700, Dan Williams wrote: > This question has come up before. Making btt an internal property of > a device makes some things cleaner and others more messy. We lose the > ability to place a btt instance on top of a partition, rather than a > whole disk. I thought the addition of nfit labels avoids the need for a partition table now? > If we ever need to access the raw device we no longer > have a direct block device to reference. Linux has been doing stacked > configurations to change the personality of block devices since > forever (md, dm, bcache...), why invent something new to handle the > btt-personality of ->rw_bytes() devices? Because the underlying abstraction really isn't a block device anymore, it's a byte addressable device. This is more similar to for example how the mtd subsystem is structured. > BTT precludes DAX, if you want both modes on one pmem disk placing BTT > on a partition of the disk for fs metadata and DAX-capable data on the > rest is our proposed solution. We chose this architecture after a > conversation with Dave Chinner about XFS's need to have atomic sector > guarantees for its metadata and wanting to simultaneously enable > XFS-DAX. I can't see why a v5 XFS filesystem with CRCs on all metadata would need sector atomic updates any more. But even in a case where it would it seem like whatever label you use for partioning should sit above the block layer. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/