checkpt

overlay/tuntap/options.go

@@ -0,0 +1,116 @@
+package tuntap
+
+import (
+	"errors"
+
+	"golang.org/x/sys/unix"
+)
+
+// DeviceType is the TUN/TAP device type.
+type DeviceType int
+
+const (
+	// DeviceTypeTUN can be used to create TUN devices that operate on layer 3.
+	// Packets that are transported over TUN devices do not have an Ethernet
+	// header.
+	DeviceTypeTUN DeviceType = unix.IFF_TUN
+	// DeviceTypeTAP can be used to create TAP devices that operate on layer 2.
+	// Packets that are transported over TAP devices do have an Ethernet header.
+	DeviceTypeTAP DeviceType = unix.IFF_TAP
+)
+
+type optionValues struct {
+	name           string
+	deviceType     DeviceType
+	virtioNetHdr   bool
+	offloads       int
+	interfaceFlags uint16
+}
+
+func (o *optionValues) apply(options []Option) {
+	for _, option := range options {
+		option(o)
+	}
+}
+
+func (o *optionValues) validate() error {
+	if len(o.name) >= unix.IFNAMSIZ {
+		return errors.New("name must not be longer that 15 characters")
+	}
+	if o.deviceType != DeviceTypeTUN && o.deviceType != DeviceTypeTAP {
+		return errors.New("device type is required and must be either TUN or TAP")
+	}
+	return nil
+}
+
+func (o *optionValues) ifreqFlags() uint16 {
+	flags := uint16(o.deviceType)
+
+	// Disable the packet information prefix.
+	flags |= unix.IFF_NO_PI
+
+	// Ensure the ioctl fails when a device with the same name already exists.
+	flags |= unix.IFF_TUN_EXCL
+
+	if o.virtioNetHdr {
+		// Also requires the TUNSETVNETHDRSZ ioctl at a later time.
+		flags |= unix.IFF_VNET_HDR
+	}
+
+	return flags
+}
+
+var optionDefaults = optionValues{
+	// Let the kernel auto-select a name.
+	name: "",
+	// Required.
+	deviceType: -1,
+	// Don't enable it by default to avoid surprises.
+	virtioNetHdr: false,
+	// Optional. No offload support advertised by default.
+	offloads: 0,
+	// Optional. IFF_UP will always be set.
+	interfaceFlags: 0,
+}
+
+// Option can be passed to [NewDevice] to influence device creation.
+type Option func(*optionValues)
+
+// WithName returns an [Option] that sets the name of the to be created device.
+// This is optional. When no name is specified, the kernel will auto-select a
+// name using the scheme "tunX" or "tapX".
+func WithName(name string) Option {
+	return func(o *optionValues) { o.name = name }
+}
+
+// WithDeviceType returns an [Option] that sets the type of device that should
+// be created.
+// This is required.
+func WithDeviceType(deviceType DeviceType) Option {
+	return func(o *optionValues) { o.deviceType = deviceType }
+}
+
+// WithVirtioNetHdr returns an [Option] that sets whether packets that are
+// transported over the device are prepended with a [virtio.NetHdr].
+// This is optional and disabled by default.
+func WithVirtioNetHdr(enable bool) Option {
+	return func(o *optionValues) { o.virtioNetHdr = enable }
+}
+
+// WithOffloads returns an [Option] that sets the supported offloads that the
+// device should advertise. This tells the kernel which offloads the owner of
+// the device can deal with ([unix.TUN_F_CSUM] for example).
+// This is optional. By default, no offloads are supported.
+// When configured, then [WithVirtioNetHdr] should also be enabled.
+func WithOffloads(offloads int) Option {
+	return func(o *optionValues) { o.offloads = offloads }
+}
+
+// WithInterfaceFlags returns an [Option] that sets the flags that should be
+// used when taking the created interface up.
+// This is optional. The [unix.IFF_UP] flag will always be set.
+// The [unix.IFF_NOARP] flag may be useful in some scenarios to avoid packets
+// from the Linux networking stack interfering with your application.
+func WithInterfaceFlags(flags uint16) Option {
+	return func(o *optionValues) { o.interfaceFlags = flags }
+}