On Wed, May 24, 2023 at 07:48:46AM +0000, Tian, Kevin wrote:
after use. Return the data buffer if success, or ERR_PTR onfailure.- @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 enumiommu_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