[dpdk-dev] [PATCH 2/3] net/virtio_user: fix wrong sequence of messages

Tan, Jianfeng jianfeng.tan at intel.com
Fri Sep 9 07:50:16 CEST 2016


On 9/9/2016 12:19 PM, Yuanhan Liu wrote:

>>
>>
>>          Never mind, above fix on the vhost side will not take effect on existing
>>          vpp-vhost implementations.
>>
>>      Actually, I was talking about the DPDK vhost implementation :)
>>
>>
>> This patch is talking about vpp's native vhost implementation, not dpdk-vhost,
>> and not the way vpp uses dpdk-vhost.
> Yes, I know. What I meant is there was a "workaround" in DPDK vhost
> implementation, and since you bring this issue on the table again,
> it's a chance to think about how can we fix it.
>
> A rough idea come to my mind is we could check all the per-vring message
> at the begining of vhost_user_msg_handler() and allocate related vq when
> necessary (when it's the first vring message we got).
>
> Yeah, I know it's a bit ugly, but it at least gets rid of that "not-that-true"
> assumption.

Sounds workable. So we'd define those vq-specific msgs, like:
VHOST_USER_SET_VRING_NUM,
VHOST_USER_SET_VRING_ADDR,
VHOST_USER_SET_VRING_BASE,
VHOST_USER_GET_VRING_BASE(?),
VHOST_USER_SET_VRING_KICK,
VHOST_USER_SET_VRING_CALL,
VHOST_USER_SET_VRING_ENABLE,


>
>>          Still not working. VPP needs SET_VRING_CALL to create vq firstly.
>>
>>      Didn't get it. In the proposal, SET_FEATURES is sent before every other
>>      messages, thus it should not cause the issue you described in this patch.
>>
>>
>> OK. Let me try to explain. We take three vhost implementations into
>> consideration: dpdk-2.2-vhost, dpdk-master-vhost, vpp-native-vhost.
>>
>> If set_feature before set_vring_call, dpdk-2.2-vhost will fail: inside
>> set_feature handler, assigning header length to VQs which will be created in
>> set_vring_call handler.
> Oh, right. That was an in-correct implementation.
>
>> So we need to keep set_vring_call firstly.
>> Then set_feature needs to be sent
>> before any other msgs, this is what vpp-native-vhost requires. In all, the
>> sequence is like this:
>> 1. set_vring_call,
>> 2. set_feature,
>> 3. other msgs
>>
>>
>>      Besides, haven't we already sent SET_VRING_CALL before other messages
>>      (well, execept the SET_FEATURES and SET_MEM_TABLE message)?
>>
>>
>> Yes, set_vring_call is already in the first place, but we need to plugin
>> set_feature between set_vring_call and other msgs. Previously, set_vring_call
>> and other msgs are together.
> Okay. Another thing I noticed is that virtio-user lacks some feature
> negotiations, like GET_FEATURES and GET_PROTOCOL_FEATURES. I think you
> might need add them back somewhen?

GET_FEATURES has been done in virtio_user_dev_init(). 
GET_PROTOCOL_FEATURES is not supported yet. I see those features in 
PROTOCOL_FEATURES is for live migration (right?). Assuming that, anyone 
using container/process now enables live migration so far? I don't think so.

Thanks,
Jianfeng


>
> 	--yliu



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