Re: [Qemu-block] [Qemu-devel] [PATCH COLO-BLOCK v7 00/17] Block replication for continuous checkpoints

[Wen Congyang]

On 07/08/2015 11:49 PM, Michael R. Hines wrote:
> On 07/07/2015 08:38 PM, Wen Congyang wrote:
>> On 07/08/2015 12:56 AM, Michael R. Hines wrote:
>>> On 07/07/2015 04:23 AM, Paolo Bonzini wrote:
>>>> On 07/07/2015 11:13, Dr. David Alan Gilbert wrote:
>>>>>>> This log is very stange. The NBD client connects to NBD server, and NBD 
>>>>>>> server wants to read data
>>>>>>> from NBD client, but reading fails. It seems that the connection is 
>>>>>>> closed unexpectedly. Can you
>>>>>>> give me more log and how do you use it?
>>>>> That was the same failure I was getting.   I think it's that the NBD 
>>>>> server and client are in different
>>>>> modes, with one of them expecting the export.
>>>> nbd_server_add always expects the export.
>>>>
>>>> Paolo
>>>>
>>> OK, Wen, so your wiki finally does reflect this, but now we're back to the 
>>> "export not found error".
>>>
>>> Again, here's the exact command line:
>>>
>>> 1. First on the secondary VM:
>>>
>>> qemu-system-x86_64 .........snip...........  -drive 
>>> if=none,driver=qcow2,file=foo.qcow2,id=mc1,cache=none,aio=native -drive 
>>> if=virtio,driver=replication,mode=secondary,throttling.bps-total-max=70000000,file.file.filename=active_disk.qcow2,file.driver=qcow2,file.backing.file.filename=hidden_disk.qcow2,file.backing.driver=qcow2,file.backing.allow-write-backing-file=on,file.backing.backing.backing_reference=mc1
>>>
>>> 2. Then, then HMP commands:
>>>
>>> nbd_server_start 0:6262
>>> nbd_server_add -w mc1
>>>
>>> 3. Then the primary VM:
>>>
>>> qemu-system-x86_64 .........snip...........  -drive 
>>> if=virtio,driver=quorum,read-pattern=fifo,no-connect=on,children.0.file.filename=bar.qcow2,children.0.driver=qcow2,children.1.file.driver=nbd,children.1.file.host=127.0.0.1,children.1.file.port=6262,children.1.driver=replication,children.1.mode=primary,children.1.ignore-errors=on
>>>
>>> With the error: Server requires an export name
>>>
>>> *but*, your wiki has no export name on the primary VM size, so I added the 
>>> export name back which is on your old wiki:
>>>
>>> qemu-system-x86_64 .........snip...........  -drive 
>>> if=virtio,driver=quorum,read-pattern=fifo,no-connect=on,children.0.file.filename=bar.qcow2,children.0.driver=qcow2,children.1.file.driver=nbd,children.1.file.export=mc1,children.1.file.host=127.0.0.1,children.1.file.port=6262,children.1.driver=replication,children.1.mode=primary,children.1.ignore-errors=on:
>>>  Failed to read export length
>>>
>> Hmm, I think you use v7 version. Is it right?
>> In this version, the correct useage for primary qemu is:
>> 1. qemu-system-x86_64 .........snip...........  -drive 
>> if=virtio,driver=quorum,read-pattern=fifo,id=disk1,
>>                        
>> children.0.file.filename=bar.qcow2,children.0.driver=qcow2,
>>
>> Then run hmp monitor command(It should be run after you run nbd_server_add 
>> in the secondary qemu):
>> child_add disk1 
>> child.driver=replication,child.mode=primary,child.file.host=127.0.0.1,child.file.port=6262,child.file.export=mc1,child.file.driver=nbd,child.ignore-errors=on
>>
>> Thanks
>> Wen Congyang
>>
>>> And server now says:
>>>
>>> nbd.c:nbd_handle_export_name():L416: export not found
>>> nbd.c:nbd_send_negotiate():L562: option negotiation failed
>>>
>>> .
>>>
>>
> 
> OK, I'm totally confused at this point. =)
> 
> Maybe it would be easier to just wait for your next clean patchset + 
> documentation which is all consistent with each other.

I have sent the v8. But the usage is not changed. You can setup the environment 
according to the wiki.
When we open nbd client, we need to connect to the nbd server. So I introduce a 
new command child_add to add NBD client
as a quorum child when the nbd server is ready.

The nbd server is ready after you run the following command:
nbd_server_start 0:6262 # the secondary qemu will listen to host:port
nbd_server_add -w mc1   # the NBD server will know this disk is used as NBD 
server. The export name is its id wc1.
                        # -w means we allow to write to this disk.

Then you can run the following command in the primary qemu:
child_add disk1 
child.driver=replication,child.mode=primary,child.file.host=127.0.0.1,child.file.port=6262,child.file.export=mc1,child.file.driver=nbd,child.ignore-errors=on

After this monitor command, nbd client has connected to the nbd server.

Thanks
Wen Congyang

> 
> - Michael
> 
> .
>