Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754039AbbFVQ52 (ORCPT ); Mon, 22 Jun 2015 12:57:28 -0400 Received: from verein.lst.de ([213.95.11.211]:43086 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752191AbbFVQ5T (ORCPT ); Mon, 22 Jun 2015 12:57:19 -0400 Date: Mon, 22 Jun 2015 18:57:17 +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: <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> 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: 1366 Lines: 28 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/