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

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

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