xdp: clean up the XDP flag situation

A single flag now controls XDP. More modes will be added as we test XDP, and we
don't want to proliferate confusing flags.

PiperOrigin-RevId: 595502921

runsc/config/config.go

@@ -282,17 +282,8 @@ type Config struct {
 	// Use pools to manage buffer memory instead of heap.
 	BufferPooling bool `flag:"buffer-pooling"`
 
-	// AFXDP defines whether to use an AF_XDP socket to receive packets
-	// (rather than AF_PACKET). Enabling it disables RX checksum offload.
-	AFXDP bool `flag:"EXPERIMENTAL-afxdp"`
-
-	// AFXDPRedirectHost is the name of a network interface. runsc will
-	// scrape the address, routes, and neighbors of that interface, and
-	// send packets via an AF_XDP socket on that interface.
-	//
-	// Requires use of `xdp_loader redirect` to setup the XDP program and
-	// eBPF map that runsc hooks into.
-	AFXDPRedirectHost string `flag:"EXPERIMENTAL-xdp-redirect-host"`
+	// XDP controls Whether and how to use XDP.
+	XDP XDP `flag:"EXPERIMENTAL-xdp"`
 
 	// AFXDPUseNeedWakeup determines whether XDP_USE_NEED_WAKEUP is set
 	// when using AF_XDP sockets.
@@ -924,3 +915,75 @@ func (o *Overlay2) SubMountOverlayMedium() OverlayMedium {
 	}
 	return o.medium
 }
+
+// XDP holds configuration for whether and how to use XDP.
+type XDP struct {
+	Mode      XDPMode
+	IfaceName string
+}
+
+// XDPMode specifies a particular use of XDP.
+type XDPMode int
+
+const (
+	// XDPModeOff doesn't use XDP.
+	XDPModeOff XDPMode = iota
+
+	// XDPModeNS uses an AF_XDP socket to read from the VETH device inside
+	// the container's network namespace.
+	XDPModeNS
+
+	// XDPModeRedirect uses an AF_XDP socket on the host NIC to bypass the
+	// Linux network stack.
+	XDPModeRedirect
+)
+
+const (
+	xdpModeStrOff      = "off"
+	xdpModeStrNS       = "ns"
+	xdpModeStrRedirect = "redirect"
+)
+
+var xdpConfig XDP
+
+// Get implements flag.Getter.
+func (xd *XDP) Get() any {
+	return *xd
+}
+
+// String implements flag.Getter.
+func (xd *XDP) String() string {
+	switch xd.Mode {
+	case XDPModeOff:
+		return xdpModeStrOff
+	case XDPModeNS:
+		return xdpModeStrNS
+	case XDPModeRedirect:
+		return fmt.Sprintf("%s:%s", xdpModeStrRedirect, xd.IfaceName)
+	default:
+		panic(fmt.Sprintf("unknown mode %d", xd.Mode))
+	}
+}
+
+// Set implements flag.Getter.
+func (xd *XDP) Set(input string) error {
+	parts := strings.Split(input, ":")
+	if len(parts) > 2 {
+		return fmt.Errorf("invalid --xdp value: %q", input)
+	}
+
+	switch {
+	case input == xdpModeStrOff:
+		xd.Mode = XDPModeOff
+		xd.IfaceName = ""
+	case input == xdpModeStrNS:
+		xd.Mode = XDPModeNS
+		xd.IfaceName = ""
+	case len(parts) == 2 && parts[0] == xdpModeStrRedirect && parts[1] != "":
+		xd.Mode = XDPModeRedirect
+		xd.IfaceName = parts[1]
+	default:
+		return fmt.Errorf("invalid --xdp value: %q", input)
+	}
+	return nil
+}

runsc/config/flags.go

@@ -120,9 +120,8 @@ func RegisterFlags(flagSet *flag.FlagSet) {
 	flagSet.Var(queueingDisciplinePtr(QDiscFIFO), "qdisc", "specifies which queueing discipline to apply by default to the non loopback nics used by the sandbox.")
 	flagSet.Int("num-network-channels", 1, "number of underlying channels(FDs) to use for network link endpoints.")
 	flagSet.Bool("buffer-pooling", true, "enable allocation of buffers from a shared pool instead of the heap.")
-	flagSet.Bool("EXPERIMENTAL-afxdp", false, "EXPERIMENTAL. Use an AF_XDP socket to receive packets.")
-	flagSet.String("EXPERIMENTAL-xdp-redirect-host", "", "EXPERIMENTAL. Use an AF_XDP socket attached to <interface name>. Use the IP of that interface.")
-	flagSet.Bool("EXPERIMENTAL-xdp-need-wakeup", true, "EXPERIMENTAL. Use XDP_USE_NEED_WAKEUP with XDP sockets.")
+	flagSet.Var(&xdpConfig, "EXPERIMENTAL-xdp", `whether and how to use XDP. Can be one of: "off" (default), "ns", or "redirect:<device name>"`)
+	flagSet.Bool("EXPERIMENTAL-xdp-need-wakeup", true, "EXPERIMENTAL. Use XDP_USE_NEED_WAKEUP with XDP sockets.") // TODO(b/240191988): Figure out whether this helps and remove it as a flag.
 	flagSet.Bool("reproduce-nat", false, "Scrape the host netns NAT table and reproduce it in the sandbox.")
 	flagSet.Bool("reproduce-nftables", false, "Attempt to scrape and reproduce nftable rules inside the sandbox. Overrides reproduce-nat when true.")
 

runsc/sandbox/network.go

@@ -120,11 +120,16 @@ func isRootNS() (bool, error) {
 // net namespace with the given path, creates them in the sandbox, and removes
 // them from the host.
 func createInterfacesAndRoutesFromNS(conn *urpc.Client, nsPath string, conf *config.Config) error {
-	if conf.AFXDPRedirectHost != "" {
+	switch conf.XDP.Mode {
+	case config.XDPModeOff:
+	case config.XDPModeNS:
+	case config.XDPModeRedirect:
 		if err := createRedirectInterfacesAndRoutes(conn, conf); err != nil {
 			return fmt.Errorf("failed to create XDP redirect interface: %w", err)
 		}
 		return nil
+	default:
+		return fmt.Errorf("unknown XDP mode: %v", conf.XDP.Mode)
 	}
 
 	// Join the network namespace that we will be copying.
@@ -250,7 +255,7 @@ func createInterfacesAndRoutesFromNS(conn *urpc.Client, nsPath string, conf *con
 			}
 		}
 
-		if conf.AFXDP {
+		if conf.XDP.Mode == config.XDPModeNS {
 			xdpSockFDs, err := createSocketXDP(iface)
 			if err != nil {
 				return fmt.Errorf("failed to create XDP socket: %v", err)

runsc/sandbox/xdp.go

@@ -157,7 +157,7 @@ func prepareRedirectInterfaceArgs(conf *config.Config) (boot.CreateLinksAndRoute
 			continue
 		}
 
-		if iface.Name != conf.AFXDPRedirectHost {
+		if iface.Name != conf.XDP.IfaceName {
 			log.Infof("Skipping interface %q", iface.Name)
 			continue
 		}