netdev - Re: [PATCH v6 09/10] vduse: Introduce VDUSE

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Message-ID: <0f386dfe-45c9-5609-55f7-b8ab2a4abf5e@redhat.com>
Date:   Mon, 12 Apr 2021 17:37:26 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Yongji Xie <xieyongji@...edance.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christian Brauner <christian.brauner@...onical.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, viro@...iv.linux.org.uk,
        Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org,
        Jonathan Corbet <corbet@....net>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v6 09/10] vduse: Introduce VDUSE - vDPA Device in
 Userspace


在 2021/4/12 下午4:02, Yongji Xie 写道:
> On Mon, Apr 12, 2021 at 3:16 PM Jason Wang <jasowang@...hat.com> wrote:
>>
>> 在 2021/4/9 下午4:02, Yongji Xie 写道:
>>>>>>> +};
>>>>>>> +
>>>>>>> +struct vduse_dev_config_data {
>>>>>>> +     __u32 offset; /* offset from the beginning of config space */
>>>>>>> +     __u32 len; /* the length to read/write */
>>>>>>> +     __u8 data[VDUSE_CONFIG_DATA_LEN]; /* data buffer used to read/write */
>>>>>> Note that since VDUSE_CONFIG_DATA_LEN is part of uAPI it means we can
>>>>>> not change it in the future.
>>>>>>
>>>>>> So this might suffcient for future features or all type of virtio devices.
>>>>>>
>>>>> Do you mean 256 is no enough here？
>>>> Yes.
>>>>
>>> But this request will be submitted multiple times if config lengh is
>>> larger than 256. So do you think whether we need to extent the size to
>>> 512 or larger?
>>
>> So I think you'd better either:
>>
>> 1) document the limitation (256) in somewhere, (better both uapi and doc)
>>
> But the VDUSE_CONFIG_DATA_LEN doesn't mean the limitation of
> configuration space. It only means the maximum size of one data
> transfer for configuration space. Do you mean document this?


Yes, and another thing is that since you're using 
data[VDUSE_CONFIG_DATA_LEN] in the uapi, it implies the length is always 
256 which seems not good and not what the code is wrote.

Thanks


>
> Thanks,
> Yongji
>