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

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Message-ID: <473d4050-2f2a-f9a2-6c40-3efd5b582b4e@linux.intel.com>
Date:   Mon, 25 Sep 2023 16:01:55 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Yi Liu <yi.l.liu@...el.com>, joro@...tes.org,
        alex.williamson@...hat.com, jgg@...dia.com, kevin.tian@...el.com,
        robin.murphy@....com
Cc:     baolu.lu@...ux.intel.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, joao.m.martins@...cle.com
Subject: Re: [PATCH v4 01/17] iommu: Add hwpt_type with user_data for
 domain_alloc_user op

On 2023/9/25 14:22, Yi Liu wrote:
> 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.

So, it looks like a constant. Perhaps we should document it in the
uapi/iommuf.h and avoid using it as a parameter of a helper function?

Best regards,
baolu