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

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Message-ID: <CACycT3vbDhUKM0OX-zo02go09gh2+EEdyZ_YQuz8PXzo3EngXw@mail.gmail.com>
Date:   Mon, 12 Apr 2021 17:59:56 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Jason Wang <jasowang@...hat.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: Re: [PATCH v6 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace

On Mon, Apr 12, 2021 at 5:37 PM Jason Wang <jasowang@...hat.com> wrote:
>
>
> 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.
>

How about renaming VDUSE_CONFIG_DATA_LEN to VDUSE_MAX_TRANSFER_LEN?

Thanks,
Yongji