linux-kernel - Re: [PATCH v4 01/17] iommu: Add hwpt_type with user_data for domain_alloc

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Date:   Mon, 25 Sep 2023 14:22:00 +0800
From:   Yi Liu <yi.l.liu@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>, <joro@...tes.org>,
        <alex.williamson@...hat.com>, <jgg@...dia.com>,
        <kevin.tian@...el.com>, <robin.murphy@....com>
CC:     <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>,
        <joao.m.martins@...cle.com>
Subject: Re: [PATCH v4 01/17] iommu: Add hwpt_type with user_data for
 domain_alloc_user op

On 2023/9/21 20:10, Baolu Lu wrote:
> On 2023/9/21 15:51, Yi Liu wrote:
>> +/**
>> + * iommu_copy_user_data - Copy iommu driver specific user space data
>> + * @dst_data: Pointer to an iommu driver specific user data that is 
>> defined in
>> + *            include/uapi/linux/iommufd.h
>> + * @src_data: Pointer to a struct iommu_user_data for user space data info
>> + * @data_len: Length of current user data structure, i.e. sizeof(struct 
>> _dst)
>> + * @min_len: Initial length of user data structure for backward 
>> compatibility.
>> + *           This should be offsetofend using the last member in the 
>> user data
>> + *           struct that was initially added to 
>> include/uapi/linux/iommufd.h
>> + */
>> +static inline int iommu_copy_user_data(void *dst_data,
>> +                       const struct iommu_user_data *src_data,
>> +                       size_t data_len, size_t min_len)
>> +{
>> +    if (WARN_ON(!dst_data || !src_data))
>> +        return -EINVAL;
>> +    if (src_data->len < min_len || data_len < src_data->len)
>> +        return -EINVAL;
>> +    return copy_struct_from_user(dst_data, data_len,
>> +                     src_data->uptr, src_data->len);
>> +}
> 
> I am not sure that I understand the purpose of "min_len" correctly. It
> seems like it would always be equal to data_len?

no, it will not be equal to data_len once there is extension in the
uAPI structure.

> Or, it means the minimal data length that the iommu driver requires?

it is the minimal data length the uAPI requires. min_len is finalized
per the upstream of the first version of the uAPI.

-- 
Regards,
Yi Liu