Re: [PATCH v2] iommu: Honor iommufd uapi for zero entry_num args

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Nov 12, 2026 at 03:10:39PM +0000, Pranjal Shrivastava wrote:
> @@ -556,7 +556,8 @@ static inline int __iommu_copy_struct_from_user_array(
>   * @data_type: The data type of the @kdst. Must match with @user_array->type
>   *
>   * Copy the entire user array. kdst must have room for kdst_entry_size *
> - * user_array->entry_num bytes. Return 0 for success, otherwise -error.
> + * user_array->entry_num bytes. An empty array copies nothing, though its
> + * @data_type is still validated. Return 0 for success, otherwise -error.
>   */
>  static inline int
>  iommu_copy_struct_from_full_user_array(void *kdst, size_t kdst_entry_size,
> @@ -569,7 +570,7 @@ iommu_copy_struct_from_full_user_array(void *kdst, size_t kdst_entry_size,
>  	if (user_array->type != data_type)
>  		return -EINVAL;
>  	if (!user_array->entry_num)
> -		return -EINVAL;
> +		return 0;

TBH, this doesn't seem very necessary..

Though I don't have a problem so long as Jason is okay with it..

Yet, this alone would make things inconsistent:
 * The other caller in iommufd selftest isn't updated.
 * __iommu_copy_struct_from_user_array still rejects !entry_num,
   and its callers (intel and selftest) aren't updated either.

Also, please don't omit "linux-kernel@vger.kernel.org" when sending
a patch, as linux-iommu doesn't trigger Sashiko scan.

Nicolin