On Tue, May 16, 2017 at 09:11:42AM -0400, J. Bruce Fields wrote: > I think you explained this before, perhaps you could just offer a > pointer: remind us what your requirements or use cases are especially > for VM migration? The NFS over AF_VSOCK configuration is: A guest running on host mounts an NFS export from the host. The NFS server may be kernel nfsd or an NFS frontend to a distributed storage system like Ceph. A little more about these cases below. Kernel nfsd is useful for sharing files. For example, the guest may read some files from the host when it launches and/or it may write out result files to the host when it shuts down. The user may also wish to share their home directory between the guest and the host. NFS frontends are a different use case. They hide distributed storage systems from guests in cloud environments. This way guests don't see the details of the Ceph, Gluster, etc nodes. Besides benefiting security it also allows NFS-capable guests to run without installing specific drivers for the distributed storage system. This use case is "filesystem as a service". The reason for using AF_VSOCK instead of TCP/IP is that traditional networking configuration is fragile. Automatically adding a dedicated NIC to the guest and choosing an IP subnet has a high chance of conflicts (subnet collisions, network interface naming, firewall rules, network management tools). AF_VSOCK is a zero-configuration communications channel so it avoids these problems. On to migration. For the most part, guests can be live migrated between hosts without significant downtime or manual steps. PCI passthrough is an example of a feature that makes it very hard to live migrate. I hope we can allow migration with NFS, although some limitations may be necessary to make it feasible. There are two NFS over AF_VSOCK migration scenarios: 1. The files live on host H1 and host H2 cannot access the files directly. There is no way for an NFS server on H2 to access those same files unless the directory is copied along with the guest or H2 proxies to the NFS server on H1. 2. The files are accessible from both host H1 and host H2 because they are on shared storage or distributed storage system. Here the problem is "just" migrating the state from H1's NFS server to H2 so that file handles remain valid. Stefan
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