Re: [Qemu-devel] [RFC PATCH v2 00/10] Add colo-proxy based on netfilter

[Jason Wang]

On 01/22/2016 02:47 PM, Wen Congyang wrote:
> On 01/22/2016 02:21 PM, Jason Wang wrote:
>>
>> On 01/22/2016 01:56 PM, Wen Congyang wrote:
>>> On 01/22/2016 01:41 PM, Jason Wang wrote:
>>>>>
>>>>> On 01/22/2016 11:28 AM, Wen Congyang wrote:
>>>>>>> On 01/22/2016 11:15 AM, Jason Wang wrote:
>>>>>>>>> On 01/20/2016 06:30 PM, Wen Congyang wrote:
>>>>>>>>>>> On 01/20/2016 06:19 PM, Jason Wang wrote:
>>>>>>>>>>>>>>> On 01/20/2016 06:01 PM, Wen Congyang wrote:
>>>>>>>>>>>>>>>>>>> On 01/20/2016 02:54 PM, Jason Wang wrote:
>>>>>>>>>>>>>>>>>>>>>>> On 01/20/2016 11:29 AM, Zhang Chen wrote:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Sure.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Two main comments/suggestions:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> - TCP analysis is missed in current version, 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> maybe you point a git tree
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> (or another version of RFC) to me for a better 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> understanding of the
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> design. (Just a skeleton for TCP should be 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> sufficient to discuss).
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> - I prefer to make the code as reusable as 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> possible. So it's better to
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> split/decouple the reusable parts from the 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> codes. So a vague idea is:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 1) Decouple the packet comparing from the 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> netfilter. You've achieved
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> this 99% since the work has been done in a 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> thread. Just let the thread
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> poll sockets directly, then the comparing have 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> the possibility to be
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> reused by other kinds of dataplane.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 2) Implement traffic mirror/redirector as 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> filter.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> 3) Implement TCP seq rewriting as a filter.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Then, in primary node, you need just a traffic 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> mirror, which did:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> - mirror ingress traffic to secondary node
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> - mirror outgress traffic to packet comparing 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> thread
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> And in secondadry node, you need two filters:
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> - A TCP seq rewriter which adjust tcp sequence 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> number.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> - A traffic redirector which redirect packet 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> from a socket as ingress
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> traffic, and redirect outgress traffic to the 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> socket which could be
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> polled by remote packet comparing thread.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>   Thoughts?
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Thanks
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> Thanks
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> zhangchen
>>>>>>>>>>>>>>>>>>>>>>>>>>> Hi, Jason.
>>>>>>>>>>>>>>>>>>>>>>>>>>> We consider your suggestion to split/decouple
>>>>>>>>>>>>>>>>>>>>>>>>>>> the reusable parts from the codes.
>>>>>>>>>>>>>>>>>>>>>>>>>>> Due to filter plugin are traversed one by one in 
>>>>>>>>>>>>>>>>>>>>>>>>>>> order
>>>>>>>>>>>>>>>>>>>>>>>>>>> we will split colo-proxy to three filters in each 
>>>>>>>>>>>>>>>>>>>>>>>>>>> side.
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>> But in this plan,primary and secondary both have 
>>>>>>>>>>>>>>>>>>>>>>>>>>> socket
>>>>>>>>>>>>>>>>>>>>>>>>>>> server,startup is a problem.
>>>>>>>>>>>>>>>>>>>>>>> I believe this issue could be solved by reusing socket 
>>>>>>>>>>>>>>>>>>>>>>> chardev.
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>  Primary qemu                                       
>>>>>>>>>>>>>>>>>>>>>>>>>>>                
>>>>>>>>>>>>>>>>>>>>>>>>>>> Secondary qemu
>>>>>>>>>>>>>>>>>>>>>>>>>>> +----------------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>       
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-----------------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>> | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-----------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>   |       | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> +------------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>  |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | |                                                 
>>>>>>>>>>>>>>>>>>>>>>>>>>>     |  |       | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                                                   
>>>>>>>>>>>>>>>>>>>>>>>>>>>    | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | |                        guest                    
>>>>>>>>>>>>>>>>>>>>>>>>>>>     |  |       | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                        guest                      
>>>>>>>>>>>>>>>>>>>>>>>>>>>    | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | |                                                 
>>>>>>>>>>>>>>>>>>>>>>>>>>>     |  |       | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                                                   
>>>>>>>>>>>>>>>>>>>>>>>>>>>    | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-----------^--------------+--------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>   |       | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> +---------------------+--------+-----------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>  |
>>>>>>>>>>>>>>>>>>>>>>>>>>> |             |              |                      
>>>>>>>>>>>>>>>>>>>>>>>>>>>        |      
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                        ^        |                 
>>>>>>>>>>>>>>>>>>>>>>>>>>>         |
>>>>>>>>>>>>>>>>>>>>>>>>>>> |             |              |                      
>>>>>>>>>>>>>>>>>>>>>>>>>>>        |      
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                        |        |                 
>>>>>>>>>>>>>>>>>>>>>>>>>>>         |
>>>>>>>>>>>>>>>>>>>>>>>>>>> |             
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-------------------------------------------------+ 
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                        |        |                 
>>>>>>>>>>>>>>>>>>>>>>>>>>>         |
>>>>>>>>>>>>>>>>>>>>>>>>>>> |  netfilter  |              |                      
>>>>>>>>>>>>>>>>>>>>>>>>>>>        |    |  |  
>>>>>>>>>>>>>>>>>>>>>>>>>>> netfilter            |        |                     
>>>>>>>>>>>>>>>>>>>>>>>>>>>     |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-----------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>   |    |  | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> +------------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>  |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | |           |              |     filter excute 
>>>>>>>>>>>>>>>>>>>>>>>>>>> order  |  |    |  | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                     |        |  filter excute 
>>>>>>>>>>>>>>>>>>>>>>>>>>> order  | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | |           |              |    
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-------------------> |  |    |  | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                     |        | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-------------------> | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | |           |              |                      
>>>>>>>>>>>>>>>>>>>>>>>>>>>     |  |    |  | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                     |        |   TCP              
>>>>>>>>>>>>>>>>>>>>>>>>>>>    | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | | +---------+-+     +------v-----+    +----+ 
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-----+  |  |    |  | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> | +-----------+   +---+----+---v+rewriter+  
>>>>>>>>>>>>>>>>>>>>>>>>>>> +--------+ | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | | |           |     |            |    |           
>>>>>>>>>>>>>>>>>>>>>>>>>>>  |  |  |    |  | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> | |           |   |        |             |  |       
>>>>>>>>>>>>>>>>>>>>>>>>>>>  | | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | | |  mirror   |     |  redirect  +---->  compare  
>>>>>>>>>>>>>>>>>>>>>>>>>>>  |  |  |   
>>>>>>>>>>>>>>>>>>>>>>>>>>> +--------> mirror   +---> adjust |   adjust    
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-->redirect| | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | | |  client   |     |  server    |    |           
>>>>>>>>>>>>>>>>>>>>>>>>>>>  |  |  |       | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> | |  server   |   | ack    |   seq       |  |client 
>>>>>>>>>>>>>>>>>>>>>>>>>>>  | | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | | |           |     |            |    |           
>>>>>>>>>>>>>>>>>>>>>>>>>>>  |  |  |       | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> | |           |   |        |             |  |       
>>>>>>>>>>>>>>>>>>>>>>>>>>>  | | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | | +----^------+     +----^-------+    
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-----+------+  |  |       | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> | +-----------+   +--------+-------------+  
>>>>>>>>>>>>>>>>>>>>>>>>>>> +----+---+ | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | |      |     tx          |      rx          |     
>>>>>>>>>>>>>>>>>>>>>>>>>>> rx  |  |       | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> |            tx                        all       |  
>>>>>>>>>>>>>>>>>>>>>>>>>>> rx | |
>>>>>>>>>>>>>>>>>>>>>>>>>>> | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-----------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>   |       | 
>>>>>>>>>>>>>>>>>>>>>>>>>>> +------------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>  |
>>>>>>>>>>>>>>>>>>>>>>>>>>> |        |                
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-------------------------------------------------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>       
>>>>>>>>>>>>>>>>>>>>>>>>>>> |
>>>>>>>>>>>>>>>>>>>>>>>>>>> |        |                                    |     
>>>>>>>>>>>>>>>>>>>>>>>>>>>        |      
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                                                   
>>>>>>>>>>>>>>>>>>>>>>>>>>>         |
>>>>>>>>>>>>>>>>>>>>>>>>>>> +----------------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>       
>>>>>>>>>>>>>>>>>>>>>>>>>>> +-----------------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>          |                                    |
>>>>>>>>>>>>>>>>>>>>>>>>>>>          |guest receive                       
>>>>>>>>>>>>>>>>>>>>>>>>>>> |guest send
>>>>>>>>>>>>>>>>>>>>>>>>>>>          |                                    |
>>>>>>>>>>>>>>>>>>>>>>>>>>> +--------+------------------------------------v------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                                                   
>>>>>>>>>>>>>>>>>>>>>>>>>>>        |
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                                                   
>>>>>>>>>>>>>>>>>>>>>>>>>>>        |
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                         tap                       
>>>>>>>>>>>>>>>>>>>>>>>>>>>       
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                              NOTE: filter 
>>>>>>>>>>>>>>>>>>>>>>>>>>> direction is rx/tx/all
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                                                   
>>>>>>>>>>>>>>>>>>>>>>>>>>>       
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                              rx:receive packets 
>>>>>>>>>>>>>>>>>>>>>>>>>>> sent to the netdev
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                                                   
>>>>>>>>>>>>>>>>>>>>>>>>>>>       
>>>>>>>>>>>>>>>>>>>>>>>>>>> |                              tx:receive packets 
>>>>>>>>>>>>>>>>>>>>>>>>>>> sent by the netdev
>>>>>>>>>>>>>>>>>>>>>>>>>>> +----------------------------------------------------------+
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> I still like to decouple comparer from netfilter. It 
>>>>>>>>>>>>>>>>>>>>>>> have two obvious
>>>>>>>>>>>>>>>>>>>>>>> advantages:
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> - make it can be reused by other dataplane (e.g vhost)
>>>>>>>>>>>>>>>>>>>>>>> - secondary redirector could redirect rx to comparer on 
>>>>>>>>>>>>>>>>>>>>>>> primary node
>>>>>>>>>>>>>>>>>>>>>>> directly which simplify the design.
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>> guest recv packet route
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>> primary
>>>>>>>>>>>>>>>>>>>>>>>>>>> tap --> mirror client filter
>>>>>>>>>>>>>>>>>>>>>>>>>>> mirror client will send packet to guest,at the
>>>>>>>>>>>>>>>>>>>>>>>>>>> same time, copy and forward packet to secondary
>>>>>>>>>>>>>>>>>>>>>>>>>>> mirror server.
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>> secondary
>>>>>>>>>>>>>>>>>>>>>>>>>>> mirror server filter --> TCP rewriter
>>>>>>>>>>>>>>>>>>>>>>>>>>> if recv packet is TCP packet,we will adjust ack
>>>>>>>>>>>>>>>>>>>>>>>>>>> and update TCP checksum, then send to secondary
>>>>>>>>>>>>>>>>>>>>>>>>>>> guest. else directly send to guest.
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>> guest send packet route
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>> primary
>>>>>>>>>>>>>>>>>>>>>>>>>>> guest --> redirect server filter
>>>>>>>>>>>>>>>>>>>>>>>>>>> redirect server filter recv primary guest packet
>>>>>>>>>>>>>>>>>>>>>>>>>>> but do nothing, just pass to next filter.
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>> redirect server filter --> compare filter
>>>>>>>>>>>>>>>>>>>>>>>>>>> compare filter recv primary guest packet then
>>>>>>>>>>>>>>>>>>>>>>>>>>> waiting scondary redirect packet to compare it.
>>>>>>>>>>>>>>>>>>>>>>>>>>> if packet same,send primary packet and clear 
>>>>>>>>>>>>>>>>>>>>>>>>>>> secondary
>>>>>>>>>>>>>>>>>>>>>>>>>>> packet, else send primary packet and do
>>>>>>>>>>>>>>>>>>>>>>>>>>> checkpoint.
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>> secondary
>>>>>>>>>>>>>>>>>>>>>>>>>>> guest --> TCP rewriter filter
>>>>>>>>>>>>>>>>>>>>>>>>>>> if the packet is TCP packet,we will adjust seq
>>>>>>>>>>>>>>>>>>>>>>>>>>> and update TCP checksum. then send it to
>>>>>>>>>>>>>>>>>>>>>>>>>>> redirect client filter. else directly send to
>>>>>>>>>>>>>>>>>>>>>>>>>>> redirect client filter.
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>> redirect client filter --> redirect server filter
>>>>>>>>>>>>>>>>>>>>>>>>>>> forward packet to primary
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>> In failover scene（primary is down）, the TCP 
>>>>>>>>>>>>>>>>>>>>>>>>>>> rewriter will keep
>>>>>>>>>>>>>>>>>>>>>>>>>>> servicing
>>>>>>>>>>>>>>>>>>>>>>>>>>> for the TCP connection which is established after 
>>>>>>>>>>>>>>>>>>>>>>>>>>> the last checkpoint。
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>> How about this plan?
>>>>>>>>>>>>>>>>>>>>>>> Sounds good.
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> And there's indeed no need to differ client/server by 
>>>>>>>>>>>>>>>>>>>>>>> reusing the socket
>>>>>>>>>>>>>>>>>>>>>>> chardev. E.g:
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> In primary node:
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> ...
>>>>>>>>>>>>>>>>>>>>>>> -chardev 
>>>>>>>>>>>>>>>>>>>>>>> socket,id=comparer0,host=ip_primary,port=X,server,nowait
>>>>>>>>>>>>>>>>>>>>>>> -chardev 
>>>>>>>>>>>>>>>>>>>>>>> socket,id=comparer1,host=ip_primary,port=Y,server,nowait
>>>>>>>>>>>>>>>>>>>>>>> -chardev 
>>>>>>>>>>>>>>>>>>>>>>> socket,id=mirrorer0,host=ip_primary,port=Z,server,nowait
>>>>>>>>>>>>>>>>>>>>>>> -netdev tap,id=hn0
>>>>>>>>>>>>>>>>>>>>>>> -traffic-mirrorer 
>>>>>>>>>>>>>>>>>>>>>>> netdev=hn0,id=t0,indev=comparer0,outdev=mirrorer0
>>>>>>>>>>>>>>>>>>>>>>> -colo-comparer 
>>>>>>>>>>>>>>>>>>>>>>> primary_traffic=comparer0,secondary_traffic=comparer1
>>>>>>>>>>>>>>>>>>> Why mirrorer has indev? 
>>>>>>>>>>>>>>> As I said in the previous mails. I would like to decouple packet
>>>>>>>>>>>>>>> comparing from netfilter. You've already done most of this 
>>>>>>>>>>>>>>> since the
>>>>>>>>>>>>>>> comparing is done in an independent thread. So the indev here 
>>>>>>>>>>>>>>> is to
>>>>>>>>>>>>>>> mirror the packet sent by guest to the packet comparing thread.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> I think we can use traffic-redirector to do it.
>>>>>>>>>>>>>>>>>>> The command line is:
>>>>>>>>>>>>>>>>>>> -netdev tap,id=hn0
>>>>>>>>>>>>>>>>>>> -object 
>>>>>>>>>>>>>>>>>>> traffic-mirrorer,id=f0,netdev=hn0,queue=tx,outdev=mirrorer0
>>>>>>>>>>>>>>>>>>> -object 
>>>>>>>>>>>>>>>>>>> traffic-redirector,id=f1,netdev=hn0,queue=rx,outdev=comparer0
>>>>>>>>>>>>>>>>>>> -colo-comparer 
>>>>>>>>>>>>>>>>>>> primary_traffic=comparer0,secondary_traffic=comparer1,netdev=hn0
>>>>>>>>>>>>>>>>>>> In the comparer thread, we can use 
>>>>>>>>>>>>>>>>>>> qemu_net_queue_send_iov() to send
>>>>>>>>>>>>>>>>>>> out the packet.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> Also, we can merge the socketdev comparer1 and mirrorer0.
>>>>>>>>>>>>>>> It depends on whether or not packet comparing was done in a net 
>>>>>>>>>>>>>>> filter
>>>>>>>>>>>>>>> (which I prefer not).
>>>>>>>>>>> I mean that: packet comapring is done in a thread, not a net filter.
>>>>>>>>>>> The flow of the packet sent from guest:
>>>>>>>>>>> 1. traffice-redirecotr, we will redirector the packet to comparer0, 
>>>>>>>>>>> the next
>>>>>>>>>>>    filter will never see it.
>>>>>>>>>>> 2. comparing thread: read it from socket chardev comparer0
>>>>>>>>>>> 3. call qemu_net_queue_send_iov() to send it back to the netdev.
>>>>>>>>> Ok, looks like I miss something.
>>>>>>>>>
>>>>>>>>> My suggestion tries best to let the packet comparing not tie to filter
>>>>>>>>> or netdev. But your suggestion still need it to be coupled with a
>>>>>>>>> netdev. Any advantages of doing this (or is there a reason that packet
>>>>>>>>> must be sent to netdev after doing comparing?). If not, why not just
>>>>>>> Yes, the packet must be sent to netdev after doing comparing. If both
>>>>>>> the primary packet and secondary packet are the same(contains the same
>>>>>>> application level data), we will drop the secondary packet, and send the
>>>>>>> primary packet to the netdev. Otherwise, we will sync the state.
>>>>> And drop primary packet also here?
>>> No, the primary packet must be sent back to the netdev, so the client can 
>>> receive
>>> the response.
>>>
>>> For example:
>>> 1. guest has a ftp server
>>> 2. we connect to the ftp server via the network
>>> 3. both primary guest and secondary guest receive this request
>>> 4. both primary guest and secondary guest ack it
>>> 5. we compare these two ack packets in the comparing thread
>>> 6. it is the same(the seqno is different, but it is not important, we can 
>>> modify it in
>>>    colo-rewriter). So we drop the secondary packets, and sent back the 
>>> primary packet
>>>    to netdev
>>> 7. The primary ack packet is sent to the ftp client via netdev.
>>>
>>> The ftp client only cares of the received packet. So if the packets from 
>>> primay
>>> and secondary guest contain the same data, we can say they are in the 
>>> "same" state.
>>>
>>> Thanks
>>> Wen Congyang
>>>
>> Thanks for the example. But still don't get why it must be done before
>> comparing consider it will always be sent regardless the result of
>> comparing?
> Our goal is that: the connection is OK after failover, and the user doesn't 
> know one of
> the hosts crashed.
>
> If it sent out regardless the result of comparing, and primary host crashes. 
> The connection
> may be corrupted after failover. For example: the packet from primary and 
> secondary host
> contains different host, and we send the primary packet before comparing. The 
> primary host
> crashes before comparing these two packets. After failover, the connection 
> may be reset or
> the client doesn't receive the correct data, or some unexpected problems 
> occurs.
>
> Another example(tcp):
> 1. primary guest acks 100, and secondary guest only ack 95(some packet is 
> lost in the guest)
> 2. client doesn't resend the lost packet
> 3. the connection will be recovered after the next checkpoint
> If we do failover before the next checkpoint, there is no way to recover this 
> connection.
>
> If we send out the packet after comparing, we can assume that the client 
> always receives the
> same data.

Thanks. I think I get the point. So if there's a difference, primary
packet will only be sent after checkpoint and we could not assume the
checkpoint itself is reliable.

Back to the filters design. We'd better still decouple packet comparing
out of netdev. Maybe a little bit more tweak on what you've suggested:

-netdev tap,id=hn0
-object traffic-mirrorer,id=f0,netdev=hn0,queue=tx,outdev=mirrorer0
-object
traffic-redirector,id=f1,netdev=hn0,queue=rx,outdev=comparer0,indev=comparer2
-colo-comparer
primary_traffic=comparer0,secondary_traffic=comparer1,outdev=comparer2

Just add one more socket for comparer for sending primary packet, and
let f1 redirector its output to netdev?

>
> Thanks
> Wen Congyang
>
>>
>>
>> .
>>
>
>