Post Migration Announce #66
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…ncements Some devices can do announcements after a live migration, e.g. a network device announces its new location in a network. With this change a device can return an announcer to do that. On-behalf-of: SAP [email protected] Signed-off-by: Sebastian Eydam <[email protected]>
To announce the new location in a network, virtio-net devices can send reverse ARP packets. On-behalf-of: SAP [email protected] Signed-off-by: Sebastian Eydam <[email protected]>
After this change switches in a network should find the new location of a VM quicker. On-behalf-of: SAP [email protected] Signed-off-by: Sebastian Eydam <[email protected]>
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Could you please rephrase your PR title, the commits, and the corresponding internals to something more descriptive than "post migration announce"? Something like "Post-migration ARP Advertisment Packets"? |
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Nice work! Before reviewing this further, we should discuss if the proposed design is something we want to go with. I prefer to use the existing resume() path. Bonus point: it would also work after a cold migration.
Are there any implications I'm missing here by chance?
PS: You also need to do the same for the Neighbor Discovery Protocol (ARP equivalent in IPv6).
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| /// Some devices can announce their location after a live migration to | ||
| /// speed up normal execution. | ||
| fn post_migration_announcer(&mut self) -> std::option::Option<Box<dyn PostMigrationAnnouncer>> { |
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Please use Option and not the fully qualified path
| fn build_rarp_announce(&self) -> [u8; 60] { | ||
| const ETH_P_RARP: u16 = 0x8035; // Ethertype RARP | ||
| const ARP_HTYPE_ETH: u16 = 0x1; // Hardware type Ethernet | ||
| const ARP_PTYPE_IP: u16 = 0x0800; // Protocol type IPv4 |
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do we need to do the same for the ARP equivalent of IPv6?
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As far as I know this works for IPv4 and IPv6. We never put any IP addresses into the packet, only MAC addresses.
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But IPv6 doesn't use ARP AFAICT. ipv6 uses the Neighbor Discovery Protocol (NDP).
I am not 100% with that, but we should clarify and make sure your PR reaches your desired network discovery speedup if guest VMs only uses IPv6!
| // The unwrap is safe, because the state machine makes sure we called | ||
| // vm_receive_state before, which creates the VM. | ||
| let vm = self.vm.vm_mut().unwrap(); | ||
| vm.announce(); |
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I am very surprised about this fully-blown internal abstraction. I think this can be build on the existing resume() mechanism that Cloud Hypervisor already has?
Before I review this further, we should discuss this fundamental design discussion.
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This PR adds a post migration announce to Cloud Hypervisor. After a successful live migration, Cloud Hypervisor now sends reverse ARP packets on all virtio-net devices. That way switches should learn the new location of the VM faster.