Share server migration fails to reuse network allocations and use wrong vserver_name

[Sylvan Le Deunff]

ISSUE 1
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When performing a share server migration, if no new network is specified same allocations should be reused on destination share server.

But the code responsible to update existing allocations with new share_server_id seems to be missing here:
https://opendev.org/openstack/manila/src/tag/18.1.0/manila/share/manager.py#L6099

ISSUE 2
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The way share server name is retrieved in NetApp driver prevents doing another migration after the first one.

- NetApp driver determines the name of the source share server for a migration using templating (something like "os_{server_id}" by default).
- Migration of NetApp vserver with manila creates a new share_server entry in manila DB with a different server_id, but vserver still has the same name on NetApp cluster.
- Now the name "os_{server_id}" does not match "vserver_name" anymore.
- This breaks ability to migrate vserver a second time.

The problem occurs in those functions related to migration:
- _check_for_migration_support: https://opendev.org/openstack/manila/src/tag/18.1.0/manila/share/drivers/netapp/dataontap/cluster_mode/lib_multi_svm.py#L1286
- _migration_start_using_svm_migrate: https://opendev.org/openstack/manila/src/tag/18.1.0/manila/share/drivers/netapp/dataontap/cluster_mode/lib_multi_svm.py#L1525

And can be fixed by replacing templating by using backend_details stored in manila
- source_share_server["backend_details"]["vserver_name"]

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/manila/+/918297

[Sylvan Le Deunff (sylvanld)]

Hello! It there a status for this bug ? It seems to have been discussed in triage meeting but importance is not set and no milestone is defined :)