Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754530AbbFVRAH (ORCPT ); Mon, 22 Jun 2015 13:00:07 -0400 Received: from mail-wi0-f182.google.com ([209.85.212.182]:34721 "EHLO mail-wi0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754210AbbFVQ77 (ORCPT ); Mon, 22 Jun 2015 12:59:59 -0400 MIME-Version: 1.0 In-Reply-To: <20150622165717.GA9803@lst.de> References: <20150621135406.GA9572@lst.de> <20150622063028.GA30434@lst.de> <20150622072844.GA31263@lst.de> <20150622154056.GB7952@lst.de> <20150622164515.GA9281@lst.de> <20150622165717.GA9803@lst.de> Date: Mon, 22 Jun 2015 09:59:58 -0700 Message-ID: Subject: Re: [PATCH 14/15] libnvdimm: support read-only btt backing devices From: Dan Williams To: Christoph Hellwig Cc: Jens Axboe , "linux-nvdimm@lists.01.org" , Boaz Harrosh , "Kani, Toshimitsu" , "linux-kernel@vger.kernel.org" , Linux ACPI , linux-fsdevel , Ingo Molnar Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1624 Lines: 33 On Mon, Jun 22, 2015 at 9:57 AM, Christoph Hellwig wrote: > On Mon, Jun 22, 2015 at 09:54:51AM -0700, Dan Williams wrote: >> > I don't see why you're comparing with MD and DM here. MD and DM >> > sit cleanly ontop of any block device. If btt was independent of >> > libnvdimm and just used ->rw_bytes we could see it as this. >> > >> > But it's all a giant entangled mess, where btt for example is probed >> > by libnvdimm. At the same time pmem.c isn't really a true block >> > driver, it's really just a trivial shim between the block API >> > and pmem-style memcpy. Especially with the proper pmem API btt >> > would become cleaner just calling that directly. >> >> The pmem api does nothing to fix torn sectors, there's no extra >> atomicity guarantees that come from those instructions. > > Of course not. And neither does pmem.c help with you in any way. > > That's the point: btt should be a peer to pmem.c, not on top of it > as there's no value add in pmem.c for it, and they are logically peers. > >> Well, let's start with per-disk btt and see where that gets us, we can >> always ramp up complexity later. I'd just as soon make the default >> opt-in/out a Kconfig toggle with a sysfs override. > > Kconfig or sysfs are both utterly horrible choices. It's a disk format > choice so it needs to be persisted. Of course it will be persisted with an on disk BTT superblock. Establishing that superblock by default and deleting at on-demand are via Kconfig and sysfs. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/