Re: [PATCH v8 00/10] nvdimm: Add an IOCTL pass thru for DSM calls

The NVDIMM code in the kernel supports an IOCTL interface to user space based upon the Intel Example DSM: http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf This interface cannot be used by other NVDIMM DSMs that support incompatible functions. An alternative DSM specification for Type N DSM being developed by Hewlett Packard Enterprise can be found at: https://github.com/HewlettPackard/hpe-nvm/tree/master/Documentation

To accommodate multiple and conflicting DSM specifications, this patch set adds a generic "pass-thru" IOCTL interface which is not tied to a particular DSM. A new _IOC_NR ND_CMD_CALL == "10" is added for the pass thru call. The new data structure nd_cmd_pkg serves as a wrapper for the pass-thru calls. This wrapper supplies the data that the kernel needs to make the _DSM call. Unlike the definitions of the _DSM functions themselves, the nd_cmd_pkg provides the calling information (input/output sizes) in an uniform manner making the kernel marshaling of the arguments straight forward. This shifts the marshaling burden from the kernel to the user space application while still permitting the kernel to internally call _DSM functions. The kernel functions __nd_ioctl and acpi_nfit_ctl were modified to accommodate ND_CMD_CALL.