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References: <20170504105444.8940-1-daniel.kucera@gmail.com>
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From: "Denis V. Lunev" <den@openvz.org>
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Date: Mon, 8 May 2017 23:02:19 +0200
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Subject: Re: [Qemu-devel] [PATCH] mirror: add sync mode incremental to
 drive-mirror and blockdev-mirror
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To: Stefan Hajnoczi <stefanha@gmail.com>, Daniel Kucera <daniel.kucera@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, "open list:Block Jobs" <qemu-block@nongnu.org>, Markus Armbruster <armbru@redhat.com>, Jeff Cody <jcody@redhat.com>, qemu-devel@nongnu.org, Max Reitz <mreitz@redhat.com>, "Denis V. Lunev" <den@openvz.org>, jsnow@redhat.com, Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

On 05/08/2017 10:35 PM, Stefan Hajnoczi wrote:
> On Thu, May 04, 2017 at 12:54:40PM +0200, Daniel Kucera wrote:
>
> Seems like a logical extension along the same lines as the backup block
> job's dirty bitmap sync mode.
>
>> parameter bitmap chooses existing dirtymap instead of newly created
>> in mirror_start_job
>>
>> Signed-off-by: Daniel Kucera <daniel.kucera@gmail.com>
Can you pls describe the use case pls in a bit more details.

For now this could be a bit strange:
- dirty bitmap, which can be found via bdrv_create_dirty_bitmap
  could be read-only or read-write, i.e. being modified by writes
  or be read-only, which should not be modified. Thus adding
  r/o bitmap to the mirror could result in interesting things.

Minimally we should prohibit usage of r/o bitmaps this way.

So, why to use mirror, not backup for the case?

Den