Date:   Mon, 15 Nov 2021 05:14:12 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Lu Baolu <baolu.lu@linux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Joerg Roedel <joro@8bytes.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Kevin Tian <kevin.tian@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Chaitanya Kulkarni <kch@nvidia.com>, kvm@vger.kernel.org,
        rafael@kernel.org, linux-pci@vger.kernel.org,
        Cornelia Huck <cohuck@redhat.com>,
        linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
        Jacob jun Pan <jacob.jun.pan@intel.com>,
        Diana Craciun <diana.craciun@oss.nxp.com>,
        Will Deacon <will@kernel.org>
Subject: Re: [PATCH 01/11] iommu: Add device dma ownership set/release
 interfaces
Message-ID: <YZJdJH4AS+vm0j06@infradead.org>
References: <20211115020552.2378167-1-baolu.lu@linux.intel.com>
 <20211115020552.2378167-2-baolu.lu@linux.intel.com>
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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.