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Date: Sun, 12 Jun 2016 12:23:38 +0800
From: Fam Zheng <famz@redhat.com>
Message-ID: <20160612042338.GI27167@ad.usersys.redhat.com>
References: <20160610185750.30956-1-mreitz@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v3 0/5] block/mirror: Fix (?) target
 backing BDS
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To: Max Reitz <mreitz@redhat.com>
Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Kevin Wolf <kwolf@redhat.com>

On Fri, 06/10 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=3Dfull; existing: because the target
> image does not have a backing file; blockdev-mirror: because of an
> explicit "backing": ""). Then, this is pretty bad behavior.
>=20
> This should generally not change the target's visible data, but it stil=
l
> is ugly.
>=20
> Issue #2: Currently the backing chain of the target is basically opened
> using bdrv_open_backing_file() (except for sometimes=E2=84=A2). This re=
sults in
> multiple BDSs for a single physical file, which is bad. In most use
> cases, this is only temporary, but it still is bad.
>=20
> 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.

Looks good overall. I left a few trivial comments/questions in individual
patches.

Reviewed-by: Fam Zheng <famz@redhat.com>