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Date: Thu, 11 Aug 2016 15:18:11 +0200
From: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20160811131811.GF5035@noname.redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 08/29] qcow2-bitmap: delete bitmap from
 qcow2 after load
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To: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, mreitz@redhat.com, armbru@redhat.com, eblake@redhat.com, jsnow@redhat.com, famz@redhat.com, den@openvz.org, stefanha@redhat.com, pbonzini@redhat.com

Am 08.08.2016 um 17:04 hat Vladimir Sementsov-Ogievskiy geschrieben:
> If we load bitmap for r/w bds, it's data in the image should be
> considered inconsistent from this point. Therefore it is safe to remove
> it from the image.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

The approach that you're taking (keeping the complete bitmap directory
in memory in its on-disk format) means that we can't keep pointers to a
QCow2BitmapHeader anywhere because modifying the directory would move it
around.

Did you consider using a different in-memory representation like a
normal list of structs? This would also allow you to use the normal list
iteration mechanisms (i.e. the existing *_FOREACH macros) instead of the
rather complex ones you need now.

For example, qcow2 snapshots use a different on-disk and in-memory
format and the on-disk format is only implemented in the actual
read/write functions, and anything else can deal with the simpler
in-memory structures.

Kevin