Virtualization - Apr 2021 - [PATCH v6 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace

? 2021/4/12 ??5:59, Yongji Xie ??:
> On Mon, Apr 12, 2021 at 5:37 PM Jason Wang <jasowang at redhat.com>
wrote:
>>
>> ? 2021/4/12 ??4:02, Yongji Xie ??:
>>> On Mon, Apr 12, 2021 at 3:16 PM Jason Wang <jasowang at
redhat.com> wrote:
>>>> ? 2021/4/9 ??4:02, Yongji Xie ??:
>>>>>>>>> +};
>>>>>>>>> +
>>>>>>>>> +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

So a question is the reason to have a limitation of this in the uAPI? 
Note that in vhost-vdpa we don't have such:

struct vhost_vdpa_config {
 ??????? __u32 off;
 ??????? __u32 len;
 ??????? __u8 buf[0];
};

Thanks

>