Vaibhav Jain <vaib...@linux.ibm.com> writes: ....
+ > +/* Papr-scm-header + payload expected with ND_CMD_CALL ioctl from libnvdimm > */ > +struct nd_pdsm_cmd_pkg { > + struct nd_cmd_pkg hdr; /* Package header containing sub-cmd */ > + __s32 cmd_status; /* Out: Sub-cmd status returned back */ > + __u16 payload_offset; /* In: offset from start of struct */ > + __u16 payload_version; /* In/Out: version of the payload */ > + __u8 payload[]; /* In/Out: Sub-cmd data buffer */ > +} __packed; that payload_offset can be avoided if we prevent userspace to user a different variant of nd_pdsm_cmd_pkg which different header. We can keep things simpler if we can always find payload at nd_pdsm_cmd_pkg->payload. > + > +/* > + * Methods to be embedded in ND_CMD_CALL request. These are sent to the > kernel > + * via 'nd_pdsm_cmd_pkg.hdr.nd_command' member of the ioctl struct > + */ > +enum papr_scm_pdsm { > + PAPR_SCM_PDSM_MIN = 0x0, > + PAPR_SCM_PDSM_MAX, > +}; > + > +/* Convert a libnvdimm nd_cmd_pkg to pdsm specific pkg */ > +static inline struct nd_pdsm_cmd_pkg *nd_to_pdsm_cmd_pkg(struct nd_cmd_pkg > *cmd) > +{ > + return (struct nd_pdsm_cmd_pkg *) cmd; > +} > + > +/* Return the payload pointer for a given pcmd */ > +static inline void *pdsm_cmd_to_payload(struct nd_pdsm_cmd_pkg *pcmd) > +{ > + if (pcmd->hdr.nd_size_in == 0 && pcmd->hdr.nd_size_out == 0) > + return NULL; > + else > + return (void *)((__u8 *) pcmd + pcmd->payload_offset); > +} > + we need to make sure userspace is not passing a wrong payload_offset. and in the next patch you do + /* Copy the health struct to the payload */ + memcpy(pdsm_cmd_to_payload(pkg), &p->health, copysize); + pkg->hdr.nd_fw_size = copysize; + All this can be simplified if you can keep payload at nd_pdsm_cmd_pkg->payload. If you still want to have the ability to extend the header, then added a reserved field similar to nd_cmd_pkg. -aneesh