runtime: add a new API for Network interface

Add GetEndpointsNum API for Network Interface to get the number of
network endpoints. This is used for caculate the number of pcie root
port for QemuVirt.

Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>

src/runtime/virtcontainers/network.go

@@ -226,6 +226,9 @@ type Network interface {
 
 	// SetEndpoints sets a sandbox's network endpoints.
 	SetEndpoints([]Endpoint)
+
+	// GetEndpoints number of sandbox's network endpoints.
+	GetEndpointsNum() (int, error)
 }
 
 func generateVCNetworkStructures(ctx context.Context, network Network) ([]*pbTypes.Interface, []*pbTypes.Route, []*pbTypes.ARPNeighbor, error) {

src/runtime/virtcontainers/network_darwin.go

@@ -92,6 +92,10 @@ func (n *DarwinNetwork) SetEndpoints(endpoints []Endpoint) {
 	n.eps = endpoints
 }
 
+func (n *DarwinNetwork) GetEndpointsNum() (int, error) {
+	return 0, nil
+}
+
 func validGuestRoute(route netlink.Route) bool {
 	return true
 }

src/runtime/virtcontainers/network_linux.go

@@ -291,6 +291,27 @@ func (n *LinuxNetwork) endpointAlreadyAdded(netInfo *NetworkInfo) bool {
 	return false
 }
 
+func (n *LinuxNetwork) GetEndpointsNum() (int, error) {
+	netnsHandle, err := netns.GetFromPath(n.netNSPath)
+	if err != nil {
+		return 0, err
+	}
+	defer netnsHandle.Close()
+
+	netlinkHandle, err := netlink.NewHandleAt(netnsHandle)
+	if err != nil {
+		return 0, err
+	}
+	defer netlinkHandle.Close()
+
+	linkList, err := netlinkHandle.LinkList()
+	if err != nil {
+		return 0, err
+	}
+
+	return len(linkList), nil
+}
+
 // Scan the networking namespace through netlink and then:
 // 1. Create the endpoints for the relevant interfaces found there.
 // 2. Attach them to the VM.