Re: [RESEND PATCH v7 4/5] ndctl/papr_scm,uapi: Add support for PAPR nvdimm specific methods

On Wed, May 20, 2020 at 12:30:57AM +0530, Vaibhav Jain wrote: > Introduce support for Papr nvDimm Specific Methods (PDSM) in papr_scm > modules and add the command family to the white list of NVDIMM command > sets. Also advertise support for ND_CMD_CALL for the dimm > command mask and implement necessary scaffolding in the module to > handle ND_CMD_CALL ioctl and PDSM requests that we receive.

> + * > + * Payload Version: > + * > + * A 'payload_version' field is present in PDSM header that indicates a specific > + * version of the structure present in PDSM Payload for a given PDSM command. > + * This provides backward compatibility in case the PDSM Payload structure > + * evolves and different structures are supported by 'papr_scm' and 'libndctl'. > + * > + * When sending a PDSM Payload to 'papr_scm', 'libndctl' should send the version > + * of the payload struct it supports via 'payload_version' field. The 'papr_scm' > + * module when servicing the PDSM envelope checks the 'payload_version' and then > + * uses 'payload struct version' == MIN('payload_version field', > + * 'max payload-struct-version supported by papr_scm') to service the PDSM. > + * After servicing the PDSM, 'papr_scm' put the negotiated version of payload > + * struct in returned 'payload_version' field. FWIW many people believe using a size rather than version is more sustainable. It is expected that new payload structures are larger (more features) than the previous payload structure. I can't find references at the moment through.