chore(logs): Improve network error logging and propagation

There are cases where the environment that we run urunc is not
properly setup. Thus, have more intuitive error messages can help
us identify what the actual error is. In this case, these error
messages helped us identify which kernel config options were missing
from the host system to add TUN/TAP devices properly and to install
the TC filters.

PR: #265
Signed-off-by: Anastassios Nanos <ananos@nubificus.co.uk>
Reviewed-by: Charalampos Mainas <cmainas@nubificus.co.uk>
Approved-by: Charalampos Mainas <cmainas@nubificus.co.uk>

Author: ananos

pkg/network/network.go

@@ -217,49 +217,72 @@ func addRedirectFilter(source netlink.Link, target netlink.Link) error {
 }
 
 func networkSetup(tapName string, ipAddress string, redirectLink netlink.Link, addTCRules bool, uid uint32, gid uint32) (netlink.Link, error) {
+	netlog.Debugf("starting for tapName=%s ipAddress=%s redirectLink=%s addTCRules=%v",
+		tapName, ipAddress, redirectLink.Attrs().Name, addTCRules)
+
+	// Sanity check: ensure eth0 exists in this namespace
 	err := ensureEth0Exists()
-	// if eth0 does not exist in the namespace, the unikernel was spawned using ctr, so we skip the network setup
 	if err != nil {
-		netlog.Warn("eth0 interface not found, assuming unikernel was spawned using ctr")
+		netlog.Warnf("eth0 interface not found in namespace (unikernel may have been spawned using ctr): %v", err)
 		return nil, nil
 	}
+
+	// Create TAP
+	netlog.Debugf("creating tap device %s (mtu=%d)", tapName, redirectLink.Attrs().MTU)
 	newTapDevice, err := createTapDevice(tapName, redirectLink.Attrs().MTU, uid, gid)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("createTapDevice(%s) failed: %w", tapName, err)
+	}
+	netlog.Debugf("created tap device %s (index=%d)", newTapDevice.Attrs().Name, newTapDevice.Attrs().Index)
+
+	// Bring TAP up before qdisc
+	if err = netlink.LinkSetUp(newTapDevice); err != nil {
+		return nil, fmt.Errorf("LinkSetUp(%s) failed: %w", newTapDevice.Attrs().Name, err)
 	}
+	netlog.Debugf("TAP %s is UP", newTapDevice.Attrs().Name)
+
+	// Bring redirectLink (eth0) up before using it in filters
+	if err = netlink.LinkSetUp(redirectLink); err != nil {
+		return nil, fmt.Errorf("LinkSetUp(%s) failed: %w", redirectLink.Attrs().Name, err)
+	}
+	netlog.Debugf("redirectLink %s is UP", redirectLink.Attrs().Name)
+
+	// Add qdisc + redirect filters
 	if addTCRules {
-		err = addIngressQdisc(newTapDevice)
-		if err != nil {
-			return nil, err
+		netlog.Debug("adding tc ingress qdisc + redirect filters")
+
+		if err = addIngressQdisc(newTapDevice); err != nil {
+			return nil, fmt.Errorf("addIngressQdisc(tap=%s) failed: %w",
+				newTapDevice.Attrs().Name, err)
 		}
-		err = addIngressQdisc(redirectLink)
-		if err != nil {
-			return nil, err
+		if err = addIngressQdisc(redirectLink); err != nil {
+			return nil, fmt.Errorf("addIngressQdisc(redirect=%s) failed: %w",
+				redirectLink.Attrs().Name, err)
 		}
-		err = addRedirectFilter(newTapDevice, redirectLink)
-		if err != nil {
-			return nil, err
+		if err = addRedirectFilter(newTapDevice, redirectLink); err != nil {
+			return nil, fmt.Errorf("addRedirectFilter(%s->%s) failed: %w",
+				newTapDevice.Attrs().Name, redirectLink.Attrs().Name, err)
 		}
-		err = addRedirectFilter(redirectLink, newTapDevice)
-		if err != nil {
-			return nil, err
+		if err = addRedirectFilter(redirectLink, newTapDevice); err != nil {
+			return nil, fmt.Errorf("addRedirectFilter(%s->%s) failed: %w",
+				redirectLink.Attrs().Name, newTapDevice.Attrs().Name, err)
 		}
 	}
+
+	// Optionally assign IP to TAP
 	if ipAddress != "" {
+		netlog.Debugf("assigning IP %s to %s", ipAddress, newTapDevice.Attrs().Name)
 		ipn, err := netlink.ParseAddr(ipAddress)
 		if err != nil {
-			return nil, err
+			return nil, fmt.Errorf("ParseAddr(%s) failed: %w", ipAddress, err)
 		}
-		err = netlink.AddrReplace(newTapDevice, ipn)
-		if err != nil {
-			return nil, err
+		if err = netlink.AddrReplace(newTapDevice, ipn); err != nil {
+			return nil, fmt.Errorf("AddrReplace(%s, %s) failed: %w",
+				newTapDevice.Attrs().Name, ipAddress, err)
 		}
 	}
 
-	err = netlink.LinkSetUp(newTapDevice)
-	if err != nil {
-		return nil, err
-	}
+	netlog.Debugf("completed successfully (tap=%s, index=%d)", newTapDevice.Attrs().Name, newTapDevice.Attrs().Index)
 	return newTapDevice, nil
 }
 

pkg/network/network_dynamic.go

@@ -37,25 +37,34 @@ type DynamicNetwork struct {
 func (n DynamicNetwork) NetworkSetup(uid uint32, gid uint32) (*UnikernelNetworkInfo, error) {
 	tapIndex, err := getTapIndex()
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("getTapIndex failed: %w", err)
 	}
 	if tapIndex > 0 {
 		return nil, fmt.Errorf("unsupported operation: can't spawn multiple unikernels in the same network namespace")
 	}
+
+	netlog.Debugf("trying LinkByName(%s)", DefaultInterface)
 	redirectLink, err := netlink.LinkByName(DefaultInterface)
 	if err != nil {
-		netlog.Errorf("failed to find %s interface", DefaultInterface)
-		return nil, err
+		return nil, fmt.Errorf("failed to find interface %s: %w", DefaultInterface, err)
 	}
+	netlog.Debugf("found interface %s (index=%d)", redirectLink.Attrs().Name, redirectLink.Attrs().Index)
+
 	newTapName := strings.ReplaceAll(DefaultTap, "X", strconv.Itoa(tapIndex))
+	netlog.Debugf("creating tap device %s", newTapName)
+
 	newTapDevice, err := networkSetup(newTapName, "", redirectLink, true, uid, gid)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("networkSetup(%s) failed: %w", newTapName, err)
 	}
+	netlog.Debugf("tap device created: %s", newTapDevice.Attrs().Name)
+
+	netlog.Debugf("fetching info for %s", DefaultInterface)
 	ifInfo, err := getInterfaceInfo(DefaultInterface)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("getInterfaceInfo(%s) failed: %w", DefaultInterface, err)
 	}
+
 	return &UnikernelNetworkInfo{
 		TapDevice: newTapDevice.Attrs().Name,
 		EthDevice: ifInfo,