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Re: [Xen-devel] [RFC] Auto rebind PCI devices

* If the device specificed in the config is bound *and* pci-force-rebind is set, then unbind it from the existing driver and rebind it to pciback, then start the domain.

That sounds awkward. What's the use case you see in mind from stealing
devices from a domain while it's running?

If a driver in domain 0 has grabbed a device but isn't actually doing anything useful with it I can't start a domU without explicitly unbinding. Rather than having to do the unbind (or add it to rc.local, or whatever) it's somewhat convenient to have Xend trust my domU device allocations as being correct and override this binding. It won't steal from another domU, however.

I see switching force-rebind off by default as being a "safety catch": it'll stop new users for PCI passthrough from shooting themselves in the foot.

When force-rebind is on, the behaviour is suitable either for an experienced administrator with a known working config (I'd think they're not going to change PCI device allocations often) or for config files generated by some other management tool (which can do safety checks when allocating the device). In either of these cases, the user is confident that rebinding is the correct thing to do, and can let Xend do it automatically.

For what it's worth, we'll be looking soon at creating IOMMU IO spaces
for devices automatically when they're granted to domains.

That would be way cool. :-)


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