linux-kernel - Re: [PATCH v4 12/16] libnvdimm, nfit: enable support for volatile ranges

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Message-ID: <CAPcyv4huf0ENTz=LEVC6xC7xKRPc-GAZJsZMTSYpy+UoaduTMg@mail.gmail.com>
Date:   Thu, 29 Jun 2017 15:28:55 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Linda Knippers <linda.knippers@....com>
Cc:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Jan Kara <jack@...e.cz>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v4 12/16] libnvdimm, nfit: enable support for volatile ranges

On Thu, Jun 29, 2017 at 3:12 PM, Linda Knippers <linda.knippers@....com> 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.