Support reopen tap FD if something wrong to VM

pkg/nettools/nettools.go

@@ -705,6 +705,10 @@ func RecoverContainerSideNetwork(csn *network.ContainerSideNetwork, nsPath strin
 			bindDeviceToVFIO(devIdentifier)
 		} else {
 			ifaceType = network.InterfaceTypeTap
+			// It's OK if OpenTAP failed as the device is busy and used by running VM
+			if fo, err := OpenTAP(link.Attrs().Name); err == nil {
+				desc.Fo = fo
+			}
 		}
 		if desc.Type != ifaceType {
 			return fmt.Errorf("bad interface type for %q", desc.Name)

pkg/tapmanager/fdserver.go

@@ -106,6 +106,8 @@ type FDSource interface {
 	// specified key. It's intended to be called after
 	// Virtlet restart.
 	Recover(key string, data []byte) error
+	// RetrieveFDs retrieves FDs in case the FD is null
+	RetrieveFDs(key string) ([]int, error)
 	// Stop stops any goroutines associated with FDSource
 	// but doesn't release the namespaces
 	Stop() error
@@ -162,6 +164,19 @@ func (s *FDServer) getFDs(key string) ([]int, error) {
 	if !found {
 		return nil, fmt.Errorf("bad fd key: %q", key)
 	}
+
+	var err error
+	if fds == nil {
+		// Run here means:
+		// first: the virtlet gets restarted and recoverNetworkNamespaces is called
+		//        but tap fd is missing
+		// then: VM gets restarted for some reasons
+		fds, err = s.source.RetrieveFDs(key)
+		if err != nil {
+			return nil, err
+		}
+		s.fds[key] = fds
+	}
 	return fds, nil
 }
 

pkg/tapmanager/tapfdsource.go

@@ -341,6 +341,45 @@ func (s *TapFDSource) Recover(key string, data []byte) error {
 	})
 }
 
+// RetrieveFDs retrieve the FDs
+// It is only the case if VM exited but recover didn't populate the FDs
+func (s *TapFDSource) RetrieveFDs(key string) ([]int, error) {
+	var podNet *podNetwork
+	var fds []int
+	func() {
+		s.Lock()
+		defer s.Unlock()
+		podNet = s.fdMap[key]
+	}()
+	if podNet == nil {
+		return nil, fmt.Errorf("bad key (%s) to retrieve FDs", key)
+	}
+
+	netNSPath := cni.PodNetNSPath(podNet.pnd.PodID)
+	vmNS, err := ns.GetNS(netNSPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open network namespace at %q: %v", netNSPath, err)
+	}
+
+	if err := utils.CallInNetNSWithSysfsRemounted(vmNS, func(hostNS ns.NetNS) error {
+		allLinks, err := netlink.LinkList()
+		if err != nil {
+			return fmt.Errorf("error listing the links: %v", err)
+		}
+
+		return nettools.RecoverContainerSideNetwork(podNet.csn, netNSPath, allLinks, hostNS)
+	}); err != nil {
+		return nil, err
+	}
+
+	for _, ifDesc := range podNet.csn.Interfaces {
+		if ifDesc.Fo != nil {
+			fds = append(fds, int(ifDesc.Fo.Fd()))
+		}
+	}
+	return fds, nil
+}
+
 func (s *TapFDSource) setupNetNS(key string, pnd *PodNetworkDesc, initNet func(netNSPath string, allLinks []netlink.Link, hostNS ns.NetNS) (*network.ContainerSideNetwork, error)) error {
 	netNSPath := cni.PodNetNSPath(pnd.PodID)
 	vmNS, err := ns.GetNS(netNSPath)