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

[Denis V. Lunev]

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 <address@hidden>
> > > > ---
> > > >    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