Re: [RFC v2] migration: Add migrate-set-bitmap-node-mapping

[Kevin Wolf <kwolf@redhat.com>]

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Am 14.05.2020 um 11:09 hat Max Reitz geschrieben:
> On 13.05.20 22:09, Vladimir Sementsov-Ogievskiy wrote:
> [...]
> > 1. So, you decided to make only node-mapping, not bitmap-mapping, so we
> > can't rename bitmaps in-flight and can't migrate bitmaps from one node
> > to several and visa-versa. I think it's OK, nothing good in such
> > possibilities, and this simplifies things.
> 
> On second thought, I wonder whether it would be useful to migrate
> bitmaps from multiple nodes to a single one.  But probably not, this
> would only make sense for filters, really, and in such a case the
> bitmaps should probably just be moved prior to migration.
> 
> (And I can’t imagine any other case.  When flattening backing chains,
> the bitmaps from the dropped layers basically become useless.)

I agree, you can always move the bitmaps in a separate step, either on
the source before migration or on the destination afterwards. Migration
is already complicated enough, let's not move things into it that don't
necessarily have to be there.

You would get complications like possibly conflicting bitmap names when
you migrate the bitmaps of two nodes into a single one.

Kevin

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