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