Add VSockPath to GetVmInfoResponse

Firecracker's virtio-vsock implementation bypasses the the host kernel
by mediating between AF_UNIX on the host and AF_VSOCK in the guest.
Firecracker-containerd places the host AF_UNIX socket path in the
internal shim storage directory when launching a VM. Vsock is currently
only used for communication between the shim and the in-VM agent.

For some use-cases (e.g. remote snapshotters) it would be useful to
have additional services listening on vsock inside the VM with corresponding
host services to communicate with them. This change adds VSockPath to
GetVmInfoResponse to allow a host service to get the host AF_UNIX socket path
to open additional connections to vsock services in the guest.

Signed-off-by: Kern Walster <walster@amazon.com>

Author: Kern--

proto/firecracker.pb.go

@@ -74,6 +74,7 @@ message GetVMInfoResponse {
     string LogFifoPath = 3;
     string MetricsFifoPath = 4;
     string CgroupPath = 5;
+    string VSockPath = 6;
 }
 
 message SetVMMetadataRequest {

proto/firecracker.proto

@@ -711,6 +711,7 @@ func (s *service) GetVMInfo(requestCtx context.Context, request *proto.GetVMInfo
 		LogFifoPath:     s.machineConfig.LogPath,
 		MetricsFifoPath: s.machineConfig.MetricsPath,
 		CgroupPath:      cgroupPath,
+		VSockPath:       s.shimDir.FirecrackerVSockPath(),
 	}, nil
 }
 

runtime/service.go

@@ -409,6 +409,7 @@ func TestMultipleVMs_Isolated(t *testing.T) {
 				return err
 			}
 			if vmInfoResp.SocketPath != filepath.Join(cfg.ShimBaseDir, nspVMid, "firecracker.sock") ||
+				vmInfoResp.VSockPath != filepath.Join(cfg.ShimBaseDir, nspVMid, "firecracker.vsock") ||
 				vmInfoResp.LogFifoPath != filepath.Join(cfg.ShimBaseDir, nspVMid, "fc-logs.fifo") ||
 				vmInfoResp.MetricsFifoPath != filepath.Join(cfg.ShimBaseDir, nspVMid, "fc-metrics.fifo") ||
 				resp.CgroupPath != vmInfoResp.CgroupPath {