Maximilian Bosch
1987c483d8
`vhost-device-vsock`[1] is a custom implementation of AF_VSOCK, but the application on the host-side uses a UNIX domain-socket. This gives us the following nice properties: * We don't need to do `--arg sandbox-paths /dev/vhost-vsock` anymore for debugging builds within the sandbox. That means, untrusted users can also debug these kinds of tests now. * This prevents CID conflicts on the host-side, i.e. there's no need for using `sshBackdoor.vsockOffset` for tests anymore. A big shout-out goes to Allison Karlitskaya, the developer of test.thing[2] who talked about this approach to do AF_VSOCK on All Systems Go 2025. This patch requires systemd 258[3] because this contains `vhost-mux` in its SSH config which is needed to connect to the VMs from now on. To not blow up the patches even more, this only uses AF_VSOCK for the debugger. A potential follow-up for the future would be a removal of the current `backdoor.service` and replace it entirely by this functionality. The internal implementation tries to be consistent with how VLANs and machines are handled, i.e. the processes are started when the Driver's context is entered and cleaned up in __exit__(). I decided to push the process management and creation of sockets for vhost-device-vsock into its own class, that's an implementation detail and not a concern for the test-driver. In fact, `vhost-device-vsock` is something we can drop once QEMU implements native support for using AF_UNIX on the host-side[4]. `VsockPair` is its own class since returning e.g. a triple of `(Path, Path, Int)` would be ambiguous in what is the guest and what the host path (and frankly, I found it hard to distinguish the two when reading the docs of `vhost-device-vsock` initially). Finally, now that we can do the SSH backdoor without adding additional devices to the sandbox, I figured, it's time to write a test-case for it. [1] https://github.com/rust-vmm/vhost-device/blob/main/vhost-device-vsock/README.md [2] https://codeberg.org/lis/test.thing [3] https://github.com/NixOS/nixpkgs/pull/427968 [4] https://gitlab.com/qemu-project/qemu/-/issues/2095
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