Re: [Qemu-devel] [PATCH v5 0/4] qapi: child add/delete support

[Wen Congyang <wency@cn.fujitsu.com>]

On 09/22/2015 07:15 PM, Dr. David Alan Gilbert wrote:
> * Wen Congyang (wency@cn.fujitsu.com) wrote:
>> If quorum's child is broken, we can use mirror job to replace it.
>> But sometimes, the user only need to remove the broken child, and
>> add it later when the problem is fixed.
>>
> 
> Hi,
>   Two questions:
>     1) Do you have an example of a pair of add/remove commands that work
>       together? (I'm not quite sure I understand where the ID for the remove
>       comes from).

The command line:
-drive if=virtio,id=disk1,driver=quorum,read-pattern=fifo,vote-threshold=1,children.0.file.filename=/data/images/kvm/suse/suse11_3.img,children.0.driver=raw

And the QMP monitor command:
{'execute':'blockdev-add', 'arguments':{'options':{'driver': 'raw', 'node-name': 'test1', 'file': {'driver': 'file', 'filename': '/dev/null'}, 'id': 'test11' }  } }
{'execute': 'human-monitor-command', 'arguments': {'command-line': 'drive_add buddy driver=nbd,host=192.168.3.1,port=8889,export=colo-disk1,node-name=test2,if=none'}}
{'execute':'x-blockdev-child-add', 'arguments':{'parent': 'disk1', 'child': 'test1' } }
{'execute':'x-blockdev-child-add', 'arguments':{'parent': 'disk1', 'child': 'test2' } }
{'execute': 'x-blockdev-child-del', 'arguments': {'parent': 'disk1', 'child': 'test1' } }
{'execute': 'x-blockdev-child-del', 'arguments': {'parent': 'disk1', 'child': 'test2' } }

Note: the qmp monitor command doesn't support nbd now, and I use the hmp command to add a BDS.

> 
>     2) If the child has failed and is not responding to block operations
>        at all (e.g a networking failure to an nbd device which may take minutes
>        to time out); how do you recover - flush or drain on the devices
>        hang at that point.

If the network fails, the kernel doesn't notify the application...

> 
> (I was trying to test recovery from a failed secondary using the July COLO
> release; but the primary gets stuck in bdrv_drain or bdrv_flush if I kill
> the secondary in the right way).

IIRC, if the qemu is killed, the connection is closed at the same time. bdrv_drain()
or bdrv_flush() should not get stuck.

Thanks
Wen Congyang

> 
> Dave
> 
> 
>> It is based on the following patch:
>> http://lists.nongnu.org/archive/html/qemu-devel/2015-09/msg04579.html
>>
>> ChangLog:
>> v5:
>> 1. Address Eric Blake's comments
>> v4:
>> 1. drop nbd driver's implementation. We can use human-monitor-command
>>    to do it.
>> 2. Rename the command name.
>> v3:
>> 1. Don't open BDS in bdrv_add_child(). Use the existing BDS which is
>>    created by the QMP command blockdev-add.
>> 2. The driver NBD can support filename, path, host:port now.
>> v2:
>> 1. Use bdrv_get_device_or_node_name() instead of new function
>>    bdrv_get_id_or_node_name()
>> 2. Update the error message
>> 3. Update the documents in block-core.json
>>
>> Wen Congyang (4):
>>   Add new block driver interface to add/delete a BDS's child
>>   quorum: implement bdrv_add_child() and bdrv_del_child()
>>   qmp: add monitor command to add/remove a child
>>   hmp: add monitor command to add/remove a child
>>
>>  block.c                   | 56 ++++++++++++++++++++++++++++++++++--
>>  block/quorum.c            | 72 +++++++++++++++++++++++++++++++++++++++++++++--
>>  blockdev.c                | 48 +++++++++++++++++++++++++++++++
>>  hmp-commands.hx           | 28 ++++++++++++++++++
>>  hmp.c                     | 20 +++++++++++++
>>  hmp.h                     |  2 ++
>>  include/block/block.h     |  8 ++++++
>>  include/block/block_int.h |  5 ++++
>>  qapi/block-core.json      | 34 ++++++++++++++++++++++
>>  qmp-commands.hx           | 61 +++++++++++++++++++++++++++++++++++++++
>>  10 files changed, 329 insertions(+), 5 deletions(-)
>>
>> -- 
>> 2.4.3
>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> .
>