loopback support CNI CHECK

Signed-off-by: Bruce Ma <[email protected]>

plugins/main/loopback/loopback.go

@@ -15,6 +15,9 @@
 package main
 
 import (
+ "errors"
+ "net"
+
  "github.com/vishvananda/netlink"
 
  "github.com/containernetworking/cni/pkg/skel"
@@ -78,6 +81,18 @@ func main() {
 }
 
 func cmdCheck(args *skel.CmdArgs) error {
- // TODO: implement
- return nil
+ args.IfName = "lo" // ignore config, this only works for loopback
+
+ return ns.WithNetNSPath(args.Netns, func(_ ns.NetNS) error {
+ link, err := netlink.LinkByName(args.IfName)
+ if err != nil {
+ return err
+ }
+
+ if link.Attrs().Flags&net.FlagUp != net.FlagUp {
+ return errors.New("loopback interface is down")
+ }
+
+ return nil
+ })
 }