linux-kernel - Re: [PATCH v6 3/4] iommufd: Add IOMMU_GET_HW

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Date:   Thu, 10 Aug 2023 10:05:55 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Yi Liu <yi.l.liu@...el.com>,
        joro@...tes.org, alex.williamson@...hat.com, kevin.tian@...el.com,
        robin.murphy@....com, cohuck@...hat.com, eric.auger@...hat.com,
        nicolinc@...dia.com, kvm@...r.kernel.org, mjrosato@...ux.ibm.com,
        chao.p.peng@...ux.intel.com, yi.y.sun@...ux.intel.com,
        peterx@...hat.com, jasowang@...hat.com,
        shameerali.kolothum.thodi@...wei.com, lulu@...hat.com,
        suravee.suthikulpanit@....com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        zhenzhong.duan@...el.com
Subject: Re: [PATCH v6 3/4] iommufd: Add IOMMU_GET_HW_INFO

On 2023/8/10 0:16, Jason Gunthorpe wrote:
> On Wed, Aug 09, 2023 at 06:16:19PM +0800, Baolu Lu wrote:
>> On 2023/8/8 23:35, Yi Liu wrote:
>>> +static int iommufd_fill_hw_info(struct device *dev, void __user *user_ptr,
>>> +				unsigned int *length, u32 *type)
>>> +{
>>> +	const struct iommu_ops *ops;
>>> +	unsigned int data_len;
>>> +	void *data;
>>> +	int rc = 0;
>>> +
>>> +	ops = dev_iommu_ops(dev);
>>> +	if (!ops->hw_info) {
>>> +		*length = 0;
>>> +		*type = IOMMU_HW_INFO_TYPE_NONE;
>>> +		return 0;
>>> +	}
>>> +
>>> +	data = ops->hw_info(dev, &data_len, type);
>>> +	if (IS_ERR(data))
>>> +		return PTR_ERR(data);
>>> +
>>> +	/*
>>> +	 * drivers that have hw_info callback should have a unique
>>> +	 * iommu_hw_info_type.
>>> +	 */
>>> +	if (WARN_ON_ONCE(*type == IOMMU_HW_INFO_TYPE_NONE)) {
>>> +		rc = -ENODEV;
>>> +		goto err_free;
>>> +	}
>>> +
>>> +	*length = min(*length, data_len);
>>> +	if (copy_to_user(user_ptr, data, *length)) {
>> copy_to_user() returns the number of bytes that were successfully
>> copied, right?
> It returns length on failure and 0 on success

Then it's fine. Thanks for the explanation.

Best regards,
baolu