pkg/ip: add GetVethPeerIfindex()

pkg/ip/link_linux.go

@@ -23,6 +23,7 @@ import (
 
 	"github.com/containernetworking/plugins/pkg/ns"
 	"github.com/containernetworking/plugins/pkg/utils/hwaddr"
+	"github.com/safchain/ethtool"
 	"github.com/vishvananda/netlink"
 )
 
@@ -226,3 +227,43 @@ func SetHWAddrByIP(ifName string, ip4 net.IP, ip6 net.IP) error {
 
 	return nil
 }
+
+// GetVethPeerIfindex returns the veth link object, the peer ifindex of the
+// veth, or an error. This peer ifindex will only be valid in the peer's
+// network namespace.
+func GetVethPeerIfindex(ifName string) (netlink.Link, int, error) {
+	link, err := netlink.LinkByName(ifName)
+	if err != nil {
+		return nil, -1, fmt.Errorf("could not look up %q: %v", ifName, err)
+	}
+	if _, ok := link.(*netlink.Veth); !ok {
+		return nil, -1, fmt.Errorf("interface %q was not a veth interface", ifName)
+	}
+
+	// veth supports IFLA_LINK (what vishvananda/netlink calls ParentIndex)
+	// on 4.1 and higher kernels
+	peerIndex := link.Attrs().ParentIndex
+	if peerIndex <= 0 {
+		// Fall back to ethtool for 4.0 and earlier kernels
+		e, err := ethtool.NewEthtool()
+		if err != nil {
+			return nil, -1, fmt.Errorf("failed to initialize ethtool: %v", err)
+		}
+		defer e.Close()
+
+		stats, err := e.Stats(link.Attrs().Name)
+		if err != nil {
+			return nil, -1, fmt.Errorf("failed to request ethtool stats: %v", err)
+		}
+		n, ok := stats["peer_ifindex"]
+		if !ok {
+			return nil, -1, fmt.Errorf("failed to find 'peer_ifindex' in ethtool stats")
+		}
+		if n > 32767 || n == 0 {
+			return nil, -1, fmt.Errorf("invalid 'peer_ifindex' %d", n)
+		}
+		peerIndex = int(n)
+	}
+
+	return link, peerIndex, nil
+}