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Re: [libvirt] [PATCH 2/2] qemu: Update next usable PCI slot on domain reconnect



> Why do we need it to be exactly the same value ?  nextslot is just an
> efficiency optimization isn't it. ie, so instead of starting from
> slot 0 and iterating over 'N' already used slots till we find a free
> slot, we can get the next free slot in 1 step. As such do we really
> need to worry about restoring it to the same value after restarting
> libvirtd.

That was my understanding too. But Eric was concerned (in an older thread)
about hotplugging PCI devices in a nonmonotonic way. He thinks it could upset
Windows guests. Of course, if nextslot ever wraps from
QEMU_PCI_ADDRESS_LAST_SLOT back to zero, such guests would be doomed anyway so
we are only a bit nicer to them. I don't know if this is a real issue or not
since I haven't met a Windows guest which I'd like to hotplug a PCI device in.

Jirka


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