Re: [PATCH v4 01/17] iommu: Add hwpt_type with user_data for domain_alloc_user op

[Baolu Lu]

On 2023/9/25 14:22, Yi Liu wrote:
> On 2023/9/21 20:10, Baolu Lu wrote:
> > On 2023/9/21 15:51, Yi Liu wrote:
> > > +/**
> > > + * iommu_copy_user_data - Copy iommu driver specific user space data
> > > + * @dst_data: Pointer to an iommu driver specific user data that is 
> > > defined in
> > > + *            include/uapi/linux/iommufd.h
> > > + * @src_data: Pointer to a struct iommu_user_data for user space 
> > > data info
> > > + * @data_len: Length of current user data structure, i.e. 
> > > sizeof(struct _dst)
> > > + * @min_len: Initial length of user data structure for backward 
> > > compatibility.
> > > + *           This should be offsetofend using the last member in the 
> > > user data
> > > + *           struct that was initially added to 
> > > include/uapi/linux/iommufd.h
> > > + */
> > > +static inline int iommu_copy_user_data(void *dst_data,
> > > +                       const struct iommu_user_data *src_data,
> > > +                       size_t data_len, size_t min_len)
> > > +{
> > > +    if (WARN_ON(!dst_data || !src_data))
> > > +        return -EINVAL;
> > > +    if (src_data->len < min_len || data_len < src_data->len)
> > > +        return -EINVAL;
> > > +    return copy_struct_from_user(dst_data, data_len,
> > > +                     src_data->uptr, src_data->len);
> > > +}
> >
> > I am not sure that I understand the purpose of "min_len" correctly. It
> > seems like it would always be equal to data_len?
>
> no, it will not be equal to data_len once there is extension in the
> uAPI structure.
>
> > Or, it means the minimal data length that the iommu driver requires?
>
> it is the minimal data length the uAPI requires. min_len is finalized
> per the upstream of the first version of the uAPI.

So, it looks like a constant. Perhaps we should document it in the
uapi/iommuf.h and avoid using it as a parameter of a helper function?

Best regards,
baolu