From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH v4 12/16] libnvdimm, nfit: enable support for volatile ranges To: Dan Williams References: <149875877608.10031.17813337234536358002.stgit@dwillia2-desk3.amr.corp.intel.com> <149875884190.10031.6179599135820559644.stgit@dwillia2-desk3.amr.corp.intel.com> <595552F5.5040008@hpe.com> <59556E37.80808@hpe.com> CC: "linux-nvdimm@lists.01.org" , Jan Kara , Matthew Wilcox , X86 ML , "linux-kernel@vger.kernel.org" , Al Viro , linux-fsdevel , Christoph Hellwig From: Linda Knippers Message-ID: <595580A6.9000004@hpe.com> Date: Thu, 29 Jun 2017 18:35:18 -0400 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: On 06/29/2017 06:28 PM, Dan Williams wrote: > On Thu, Jun 29, 2017 at 3:12 PM, Linda Knippers wrote: > [..] >>> The /dev/pmem >>> device name just tells you that your block device is hosted by a >>> driver that knows how to handle persistent memory constraints, but any >>> other details about the nature of the address range need to come from >>> other sources of information, and potentially information sources that >>> the kernel does not know about. >> >> >> I'm asking about the other source of information in this specific case >> where we're exposing pmem devices that will never ever be persistent. >> Before we add these devices, I think we should be able to tell the user >> how they can know the properties of the underlying device. > > The only way I can think to indicate this is with a platform + device > whitelist in a tool like ndctl. Where the tool says "yes, these > xyz-vendor DIMMs on this abc-vendor platform with this 123-version > BIOS" is a known good persistent configuration. Doesn't the kernel know that something will never ever be persistent because the NFIT type says NFIT_SPA_VDISK, NFIT_SPA_VCD, or NFIT_SPA_VOLATILE? That's the case I'm asking about here. In this patch, you're adding support for creating /dev/pmem devices for those address ranges. My question is how the admin/user knows that those devices will never ever be persistent. I don't think we need ndctl to know which vendors' hardware/firmware actually works as advertised. -- ljk