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Re: [Qemu-devel] [PATCH 2/6] qmp: add query-block-dirty-bitmap-ranges
From: |
Fam Zheng |
Subject: |
Re: [Qemu-devel] [PATCH 2/6] qmp: add query-block-dirty-bitmap-ranges |
Date: |
Sun, 14 Feb 2016 13:05:20 +0800 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, 02/10 16:57, 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?
Since Stefan has mentioned "the format" I'm working on, yes, I think it will be
possible to expose the persistent bitmap through NBD if the driver assigns
node-names to the bitmap BDS.
Let me prototype this on top of my branch.
Fam