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

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

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.

> 
> 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.

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