Re: [Qemu-devel] [PATCH v2 11/18] block/backup: upgrade copy_bitmap to BdrvDirtyBitmap

[Max Reitz]

On 05.07.19 18:52, John Snow wrote:
> 
> 
> On 7/4/19 1:29 PM, Max Reitz wrote:

[...]

>> Which brings me to a question: Why is the copy bitmap assigned to the
>> target in the first place?  Wouldn’t it make more sense on the source?
>>
> 
> *cough*;
> 
> the idea was that the target is *most likely* to be the temporary node
> created for the purpose of this backup, even though backup does not
> explicitly create the node.
> 
> So ... by creating it on the target, we avoid cluttering up the results
> in block query; and otherwise it doesn't actually matter what node we
> created it on, really.
> 
> I can move it over to the source, but the testing code has to get a
> little smarter in order to find the "right" anonymous bitmap, which is
> not impossible; but I thought this would actually be a convenience for
> people.

You didn’t really say whether you think it makes more sense on the
source or on the target.

This is an internal bitmap, so from my understanding, the user better
not sees it at all.  It should be easy for them to ignore it, regardless
of which node it is on.  (I don’t consider “clutter” a strong point,
because, well, most of our current query interfaces are nothing but
clutter.)  Sure, that makes it a bit difficult for testing, but testing
shouldn’t really be the focus.

So for me, it comes down to where it makes more sense.  And I think it
makes more sense on the source, because it flags source clusters to copy.

Max

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