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AshleyYakeley / NixVirt

LibVirt domain management for Nix
MIT License
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Domains without MAC address specified always restart #9

Closed AshleyYakeley closed 9 months ago

AshleyYakeley commented 9 months ago

Given a domain definition with an interface with no MAC address specified, libvirt will assign a MAC address, apparently non-reproducibly. This makes Nix module activation non-idempotent, causing domain restarts.

Possible solution: if a MAC address is missing, invent one by hashing the domain UUID together with the index (since there may be more than one interface).

cannedmoose commented 9 months ago

Hashing could work though note all kvm MAC addresses must start with 52:54:00:. Unfortunately I cant find any official documentation why just random notes and I get an error when changing that prefix.

AshleyYakeley commented 9 months ago

OK, the size of each network is small, so even with only 24 bits, collisions are unlikely (and in any case, this is no worse than what libvirt does).

Is this just a QEMU/KVM thing, or are there restrictions for other connection types?

AshleyYakeley commented 9 months ago

Second MAC digit probably needs to be 2 for unicast / locally administered / administratively assigned.

cannedmoose commented 9 months ago

Yeah still should be plenty of room and from what I can see it's a QEMU/KVM thing - I'm not aware of any restrictions for other connection types.

AshleyYakeley commented 9 months ago

Done.