On Wed, May 24, 2023 at 07:48:46AM +0000, Tian, Kevin wrote: > > > > > > * after use. Return the data buffer if success, or ERR_PTR on > > > > > > * failure. > > > > > > * @domain_alloc: allocate iommu domain > > > > > > + * @domain_alloc_user: allocate user iommu domain > > > > > > + * @domain_alloc_user_data_len: return the required length of the > > user > > > > > > data > > > > > > + * to allocate a specific type user iommu domain. > > > > > > + * @hwpt_type is defined as enum > > iommu_hwpt_type > > > > > > + * in include/uapi/linux/iommufd.h. The returned > > > > > > + * length is the corresponding sizeof driver data > > > > > > + * structures in include/uapi/linux/iommufd.h. > > > > > > + * -EOPNOTSUPP would be returned if the input > > > > > > + * @hwpt_type is not supported by the driver. > > > > > > > > > > Can this be merged with earlier @hw_info callback? That will already > > > > > report a list of supported hwpt types. is there a problem to further > > > > > describe the data length for each type in that interface? > > > > > > > > Yi and I had a last minute talk before he sent this version > > > > actually... This version of hw_info no longer reports a list > > > > of supported hwpt types. We previously did that in a bitmap, > > > > but we found that a bitmap will not be sufficient eventually > > > > if there are more than 64 hwpt_types. > > > > > > > > And this domain_alloc_user_data_len might not be necessary, > > > > because in this version the IOMMUFD core doesn't really care > > > > about the actual data_len since it copies the data into the > > > > ucmd_buffer, i.e. we would probably only need a bool op like > > > > "hwpt_type_is_supported". > > > > > > > > > > Or just pass to the @domain_alloc_user ops which should fail > > > if the type is not supported? > > > > The domain_alloc_user returns NULL, which then would be turned > > into an ENOMEM error code. It might be confusing from the user > > space perspective. Having an op at least allows the user space > > to realize that something is wrong with the input structure? > > > > this is a new callback. any reason why it cannot be defined to > allow returning ERR_PTR? Upon a quick check, I think we could. Though it'd be slightly mismatched with the domain_alloc op, it should be fine since iommufd is likely to be the only caller. So, I think we can just take the approach letting user space try a hwpt_type and see if the ioctl would fail with -EINVAL. Thanks Nic
