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Re: [Qemu-block] [PATCH 08/29] qcow2-bitmap: delete bitmap from qcow2 af


From: Vladimir Sementsov-Ogievskiy
Subject: Re: [Qemu-block] [PATCH 08/29] qcow2-bitmap: delete bitmap from qcow2 after load
Date: Tue, 30 Aug 2016 18:03:40 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0

On 11.08.2016 16:18, Kevin Wolf wrote:
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 <address@hidden>
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

Hmm. It was some kind of optimization (not to rewrite the whole directory when rewriting one entry).. But for now, after deciding to clear bitmap directory after reading bitmaps, it(my approach) obviously becomes unnecessary complication.. So, I will change this.

--
Best regards,
Vladimir




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