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

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Message-ID: <YZJdJH4AS+vm0j06@infradead.org>
Date:   Mon, 15 Nov 2021 05:14:12 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Chaitanya Kulkarni <kch@...dia.com>, kvm@...r.kernel.org,
        rafael@...nel.org, linux-pci@...r.kernel.org,
        Cornelia Huck <cohuck@...hat.com>,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Diana Craciun <diana.craciun@....nxp.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH 01/11] iommu: Add device dma ownership set/release
 interfaces

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.