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Re: [Qemu-devel] [PATCH] block/snapshot: dirty all dirty bitmaps on snap

From: Max Reitz
Subject: Re: [Qemu-devel] [PATCH] block/snapshot: dirty all dirty bitmaps on snapshot-switch
Date: Fri, 17 Nov 2017 16:01:56 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

On 2017-11-17 13:30, Kevin Wolf wrote:
> Am 23.10.2017 um 11:29 hat Vladimir Sementsov-Ogievskiy geschrieben:
>> Snapshot-switch actually changes active state of disk so it should
>> reflect on dirty bitmaps. Otherwise next incremental backup using
>> these bitmaps will be invalid.
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> We discussed this quite a while ago, and I'm still not convinced that
> this approach makes sense.

I think it at least makes more sense than not handling this case at all.

> Can you give just one example of a use case where dirtying the whole
> bitmap while loading a snapshot is the desired behaviour?
> I think the most useful behaviour would be something where the bitmaps
> themselves are snapshotted, too.


>                                  But for the time being, the easiest and
> safest solution might just be to error out in any snapshot operations
> if any bitmaps are in use.

Sounds OK, too.  I personally don't have an opinion either way.

But in any case, what we did before this patch was definitely wrong so I
consider it an improvement.


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