actually, there is one thing that probably should be added here. A check if the volume uses rbd-nbd is crucial. If it isn't the case, setting QoS parameters will not have any effect.

A gRPC INVALID_ARGUMENT error should be returned for non rbd-nbd volumes

Originally posted by @nixpanic in #6160

This isn't trivial. There is rbdVol.Mounter that would be set to rbd-nbd, but genVolFromVolIDWithMigration returns an empty rbdVol.Mounter. The logic within genVolFromVolIDWithMigration does not assign a value to rbdVol.Mounter.