On 06/29/2017 06:28 PM, Dan Williams wrote: > On Thu, Jun 29, 2017 at 3:12 PM, Linda Knippers <linda.knippers@xxxxxxx> 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
