Re: [Qemu-devel] [PATCH 2/6] qmp: add query-block-dirty-bitmap-ranges

["Denis V. Lunev" <den@virtuozzo.com>]

On 02/10/2016 06:37 PM, John Snow wrote:
>
> On 02/10/2016 10:36 AM, Denis V. Lunev wrote:
>> On 02/10/2016 06:26 PM, John Snow wrote:
>>> On 02/10/2016 08:57 AM, Denis V. Lunev wrote:
>>>> On 02/10/2016 01:08 PM, Stefan Hajnoczi wrote:
>>>>> On Sat, Jan 30, 2016 at 01:56:30PM +0300, Vladimir Sementsov-Ogievskiy
>>>>> wrote:
>>>>>> Add qmp command to query dirty bitmap contents. This is needed for
>>>>>> external backup.
>>>>>>
>>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>>>>>> ---
>>>>>>     block/dirty-bitmap.c         | 55
>>>>>> +++++++++++++++++++++++++++++++++++++++
>>>>>>     blockdev.c                   | 62
>>>>>> ++++++++++++++++++++++++++++++++++++++++++++
>>>>>>     include/block/dirty-bitmap.h |  7 +++++
>>>>>>     qapi/block-core.json         | 54
>>>>>> ++++++++++++++++++++++++++++++++++++++
>>>>>>     qmp-commands.hx              | 33 +++++++++++++++++++++++
>>>>>>     5 files changed, 211 insertions(+)
>>>>> This API produces large replies and/or requires many calls to fetch all
>>>>> bitmap data.  The worst case is a 101010... bitmap.
>>>>>
>>>>> I consider the dirty bitmap to be data (vs control) and not something
>>>>> that should be sent over a control channel like the QMP monitor.
>>>>>
>>>>> How about writing the dirty bitmap to a file?  The new bitmap file
>>>>> format that Fam is working on could be used.  That way the dirty bitmap
>>>>> can be saved asynchronously without hogging the QMP monitor.
>>>> Reasonable point.
>>>>
>>>> May be it would be better to setup "special" NBD server inside
>>>> QEMU which will allow to directly "read" bitmap data.
>>>>
>>>> Any opinion?
>>>>
>>>> Den
>>> Or perhaps something like migration, where the client receiving the data
>>> opens a socket of some sort, and QEMU connects to that socket to send
>>> the data.
>> no. The point is that QEMU should be queried for data.
>> May be even via several sockets to provide it in
>> parallel.
>>
>> Den
> I don't follow.
>
> You'd use a QMP command to tell QEMU where to connect to send the data.
> You're still "querying" QEMU, it's just not acting as the server for the
> data channel.
ok, I have understood you wrong. This looks working
at the first glance.