RFE: support AF_UNIX userspace backend for virtio-vsock matching firecracker
Goal
QEMU's current support for AF_VSOCK is done via the vhost-vsock backend which exposes guests via the host kernel AF_VSOCK protocol.
This has some limitations:
- The mgmt application needs to track and assign a unique VSOCK CID for each guest since they're in a global kernel namespace
- This is not portable to non-Linux platforms. eg you can't run a Linux guest using VSOCK from a non-Linux host.
- Only host apps that understand VSOCK can communicate with the guest
A simpler to manage and more portable approach would be to map VSOCK onto UNIX sockets in the host.
Technical details
Firecracker has designed a way to map guest AF_VSOCK onto host AF_UNIX described here:
This is something we should implement natively in QEMU in a manner compatible with firecrackers design.