Re: [PATCH 01/11] iommu: Add device dma ownership set/release interfaces

[Christoph Hellwig]

On Mon, Nov 15, 2021 at 10:05:42AM +0800, Lu Baolu wrote:
> +enum iommu_dma_owner {
> +	DMA_OWNER_NONE,
> +	DMA_OWNER_KERNEL,
> +	DMA_OWNER_USER,
> +};
> +

> +	enum iommu_dma_owner dma_owner;
> +	refcount_t owner_cnt;
> +	struct file *owner_user_file;

I'd just overload the ownership into owner_user_file,

 NULL			-> no owner
 (struct file *)1UL)	-> kernel
 real pointer		-> user

Which could simplify a lot of the code dealing with the owner.