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Re: [Qemu-block] [PATCH 0/5] block/qcow2-bitmap: Enable resize with pers

From: Kevin Wolf
Subject: Re: [Qemu-block] [PATCH 0/5] block/qcow2-bitmap: Enable resize with persistent bitmaps
Date: Tue, 12 Mar 2019 11:20:40 +0100
User-agent: Mutt/1.11.3 (2019-02-01)

Am 11.03.2019 um 19:35 hat John Snow geschrieben:
> On 3/11/19 2:26 PM, Vladimir Sementsov-Ogievskiy wrote:
> > Also, we have no comments from Max and Kevin who are maintainers of the 
> > only file,
> > changed in the series. And why this don't go through their trees?
> I've discussed it with Kevin in the IRC channel; I don't think he has
> strong feelings on flushing bitmap metadata versus not as much as he
> cares that we make sure we leave openable images on crash. In general I
> think bitmaps are "our problem".

This, pretty much. I haven't been involved much in the bitmap code
before, and today I have other series to deal with for soft freeze. So
I'll trust you to do the right thing.

And the right thing means at least that after the resize operation has
returned (either success or failure), a crash doesn't lead to an image
file that can't be opened again.

Ideally, the same would be true for a crash in the middle the resize
operation, but as John explained to me that we require an exact match of
the size, this doesn't seem to completely work out without more changes:
Either a way to update both atomically (journal?) or at least accept
oversized bitmaps so we can just choose the right order. The latter
sounds tempting to me, though I haven't put much thought in the
consequences this would have.


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