Re: [dpdk-dev] vhost: add virtio configuration space access socket messages

[Ilya Maximets <i.maximets@samsung.com>]

On 26.02.2019 16:43, Maxime Coquelin wrote:
> 
> 
> On 2/26/19 2:36 PM, Ilya Maximets wrote:
>> On 26.02.2019 15:32, Maxime Coquelin wrote:
>>>
>>>
>>> On 2/26/19 9:42 AM, Ilya Maximets wrote:
>>>> On 26.02.2019 11:13, Liu, Changpeng wrote:
>>>>>
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Ilya Maximets [mailto:i.maximets@samsung.com]
>>>>>> Sent: Tuesday, February 26, 2019 3:39 PM
>>>>>> To: Liu, Changpeng <changpeng.liu@intel.com>; dev@dpdk.org
>>>>>> Cc: Stojaczyk, Dariusz <dariusz.stojaczyk@intel.com>;
>>>>>> maxime.coquelin@redhat.com; Bie, Tiwei <tiwei.bie@intel.com>; Wang,
>>>>>> Zhihong <zhihong.wang@intel.com>; Jason Wang <jasowang@redhat.com>
>>>>>> Subject: Re: vhost: add virtio configuration space access socket messages
>>>>>>
>>>>>> On 26.02.2019 10:01, Liu, Changpeng wrote:
>>>>>>>
>>>>>>>
>>>>>>>> -----Original Message-----
>>>>>>>> From: Ilya Maximets [mailto:i.maximets@samsung.com]
>>>>>>>> Sent: Monday, February 25, 2019 9:20 PM
>>>>>>>> To: Liu, Changpeng <changpeng.liu@intel.com>; dev@dpdk.org
>>>>>>>> Cc: Stojaczyk, Dariusz <dariusz.stojaczyk@intel.com>;
>>>>>>>> maxime.coquelin@redhat.com; Bie, Tiwei <tiwei.bie@intel.com>; Wang,
>>>>>>>> Zhihong <zhihong.wang@intel.com>; Jason Wang <jasowang@redhat.com>
>>>>>>>> Subject: Re: vhost: add virtio configuration space access socket messages
>>>>>>>>
>>>>>>>> On 25.02.2019 10:51, Changpeng Liu wrote:
>>>>>>>>> This patch adds new vhost user messages GET_CONFIG and SET_CONFIG
>>>>>>>>> used to get/set virtio device's PCI configuration space.
>>>>>>>>
>>>>>>>> Beside the fact that some additional description and reasoning required,
>>>>>>>> I do not see the usage of this feature. You're defining the flag
>>>>>>>> VHOST_USER_PROTOCOL_F_CONFIG, but it's never used. So, none of dpdk
>>>>>> vhost
>>>>>>>> backends (vdpa, vhost-user) will use this feature.
>>>>>>>> You, probably, missed adding it to VHOST_USER_PROTOCOL_FEATURES or
>>>>>>>> VDPA_SUPPORTED_PROTOCOL_FEATURES.
>>>>>>>>
>>>>>>>>   From the other side, current implementation forces application to properly
>>>>>>>> implement the get/set_config callbacks. Otherwise, receiving of the messages
>>>>>>>> will result in RTE_VHOST_MSG_RESULT_ERR and subsequent vhost
>>>>>>>> disconnection.
>>>>>>>> This looks strange, because supported protocol features normally enabled by
>>>>>>>> default. Am I misunderstood something ?
>>>>>>> QEMU will not send the messages if VHOST_USER_PROTOCOL_F_CONFIG
>>>>>> wasn't enabled.
>>>>>>
>>>>>> So, you're going to enable it only by explicit call to
>>>>>> 'rte_vhost_driver_set_features' ?
>>>>>>
>>>>>> In this case I'm assuming that you're implementing your own vhost backend.
>>>>>> But why you're not using 'dev->extern_ops' and corresponding 'pre_msg_handle'
>>>>>> or 'post_msg_handle' to handle your GET/SET_CONFIG messages like it does
>>>>>> 'vhost_crypto' backend ?
>>>>> The patch was developed one year ago, while DPDK didn't have external ops.
>>>>
>>>> So, maybe it's time to reconsider the implementation.
>>>
>>> +1
>>>
>>>>> The get_config/set_config was defined for all the virtio devices, so I think it makes
>>>>> more sense adding here.
>>>>
>>>> VHOST_USER_*_CRYPTO_SESSION messages are defined for all the virtio devices
>>>> too, however they makes sense for vhost_crypto backend only. These messages
>>>> (GET/SET_CONFIG) makes sense only when callbacks (get/set_config) are
>>>> implemented, so IMHO it's better to implement their handlers along with the
>>>> callbacks, i.e. inside the implementation of your vhost backend.
>>>>
>>>> Maxime, Tiwei, what do you think ?
>>>
>>> I would prefer it to be implemented in SPDK directly as a pre_handler
>>> callback, as I don't foresee a need for it for other backends, and it
>>> would avoid breaking the API.
>>>
>>> It would imply fixing the beginning of vhost_user_msg_handler() to accept requests > VHOST_USER_MAX and add necessary check before doing
>>> the debug logs.
>>
>> VHOST_USER_MAX is 31 and both new requests are
>> defined in the same enum VhostUserRequest:
>>
>>     VHOST_USER_GET_CONFIG = 24,
>>     VHOST_USER_SET_CONFIG = 25
>>
>> I don't think that any change is needed here.
> 
> I didn't meant GET_SET_CONFIG specifically. I meant that if we want
> something really generic, we would need to do that.

OK. I understand now.

> 
> BTW, it would crash as vhost_message_str[VHOST_USER_GET/SET_CONFIG] would not be defined.
> 
>>
>>>
>>> With above change we would also be able to remove VHOST_CRYPTO requests
>>> from vhost_user.c,
>>
>> Maybe you're looking at the different git HEAD ? I don't see any crypto
>> related code in vhost_user.c. Only name definition in vhost_message_str.
> 
> Yes, I meant removing their definition in vhost_message_str[].
> 
> My point is that if we want to have external backends to handle their
> specific requests, we should not have to modify vhost_user.c as it
> creates a useless dependency.

That's a good point. I agree.

Maybe we'll need some new API to make vhost library more dynamic?
Something like
    rte_vhost_message_register(enum VhostUserRequest request,
                               const char *resuest_str,
                               vhost_message_handler_t handler);
This could be flexible.

> 
>>> and we could then work on moving vhost-net bits
>>> out of this file too.
>>>
>>> Regards,
>>> Maxime
>>>
>>>
>>>
> 
>