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Re: [Qemu-block] [PATCH v3 0/5] block/mirror: Fix (?) target backing BDS

From: Max Reitz
Subject: Re: [Qemu-block] [PATCH v3 0/5] block/mirror: Fix (?) target backing BDS
Date: Tue, 14 Jun 2016 17:53:25 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1

On 10.06.2016 20:57, Max Reitz wrote:
> Issue #1: If the target image does not have a backing BDS before mirror
> completion, qemu tries really hard to give it a backing BDS. If the
> source has a backing BDS, it will actually always "succeed".
> In some cases, the target is not supposed to have a backing BDS, though
> (absolute-paths: because of sync=full; existing: because the target
> image does not have a backing file; blockdev-mirror: because of an
> explicit "backing": ""). Then, this is pretty bad behavior.
> This should generally not change the target's visible data, but it still
> is ugly.
> Issue #2: Currently the backing chain of the target is basically opened
> using bdrv_open_backing_file() (except for sometimes™). This results in
> multiple BDSs for a single physical file, which is bad. In most use
> cases, this is only temporary, but it still is bad.
> If we can reuse the existing backing chain of the source (which is with
> drive-mirror in "absolute-paths" mode), we should just do so.

Following encouragement from Kevin on IRC, and apparently his acceptance
of my commit message proposal for patch 3, I have applied the series to
my block branch with said commit message added to patch 3 and the
superfluous imports removed from patch 4 (thanks, Fam!).


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