On Thu, Jun 29, 2017 at 3:35 PM, Linda Knippers <linda.knippers@xxxxxxx> wrote: > 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. The parent region of the namespace will have a 'volatile' type: # cat /sys/bus/nd/devices/region0/devtype nd_volatile > I don't think we need ndctl to know which vendors' hardware/firmware > actually works as advertised. Certification stickers is what I was thinking, but I was missing your direction question.
