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

[Maxime Coquelin <maxime.coquelin@redhat.com>]

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.

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.

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