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Stating my restriction in a different way, the attach may start with {ualink, pcie} as options. Then we do the first map and select ualink. Then we get an invalidation and do a second map. Here we need a way to change the mapping type options to {ualink}. The exporter would have to make the memory visible on ualink to succeed the map. > Looking at current GPU drivers, what you describe above is typically > done at pin() time, but if some importers want an early very likely > decision on what mapping_type to use, one could introduce a separate > function that match the mapping_types, but that would be very similar > to the map() function but without returning a sgt/mapping, or a pin() > without actually pinning. One could reuse the invalidate_mappings() > callback to indicate the mapping type is no longer valid? I don't know that anyone needs a very early decision, but mlx5 certainly needs something like the above flow.. Jason