pull deps in for optimization, maybe slice back out later

overlay/virtio/doc.go

@@ -0,0 +1,3 @@
+// Package virtio contains some generic types and concepts related to the virtio
+// protocol.
+package virtio

overlay/virtio/features.go

@@ -0,0 +1,136 @@
+package virtio
+
+// Feature contains feature bits that describe a virtio device or driver.
+type Feature uint64
+
+// Device-independent feature bits.
+//
+// Source: https://docs.oasis-open.org/virtio/virtio/v1.2/csd01/virtio-v1.2-csd01.html#x1-6600006
+const (
+	// FeatureIndirectDescriptors indicates that the driver can use descriptors
+	// with an additional layer of indirection.
+	FeatureIndirectDescriptors Feature = 1 << 28
+
+	// FeatureVersion1 indicates compliance with version 1.0 of the virtio
+	// specification.
+	FeatureVersion1 Feature = 1 << 32
+)
+
+// Feature bits for networking devices.
+//
+// Source: https://docs.oasis-open.org/virtio/virtio/v1.2/csd01/virtio-v1.2-csd01.html#x1-2200003
+const (
+	// FeatureNetDeviceCsum indicates that the device can handle packets with
+	// partial checksum (checksum offload).
+	FeatureNetDeviceCsum Feature = 1 << 0
+
+	// FeatureNetDriverCsum indicates that the driver can handle packets with
+	// partial checksum.
+	FeatureNetDriverCsum Feature = 1 << 1
+
+	// FeatureNetCtrlDriverOffloads indicates support for dynamic offload state
+	// reconfiguration.
+	FeatureNetCtrlDriverOffloads Feature = 1 << 2
+
+	// FeatureNetMTU indicates that the device reports a maximum MTU value.
+	FeatureNetMTU Feature = 1 << 3
+
+	// FeatureNetMAC indicates that the device provides a MAC address.
+	FeatureNetMAC Feature = 1 << 5
+
+	// FeatureNetDriverTSO4 indicates that the driver supports the TCP
+	// segmentation offload for received IPv4 packets.
+	FeatureNetDriverTSO4 Feature = 1 << 7
+
+	// FeatureNetDriverTSO6 indicates that the driver supports the TCP
+	// segmentation offload for received IPv6 packets.
+	FeatureNetDriverTSO6 Feature = 1 << 8
+
+	// FeatureNetDriverECN indicates that the driver supports the TCP
+	// segmentation offload with ECN for received packets.
+	FeatureNetDriverECN Feature = 1 << 9
+
+	// FeatureNetDriverUFO indicates that the driver supports the UDP
+	// fragmentation offload for received packets.
+	FeatureNetDriverUFO Feature = 1 << 10
+
+	// FeatureNetDeviceTSO4 indicates that the device supports the TCP
+	// segmentation offload for received IPv4 packets.
+	FeatureNetDeviceTSO4 Feature = 1 << 11
+
+	// FeatureNetDeviceTSO6 indicates that the device supports the TCP
+	// segmentation offload for received IPv6 packets.
+	FeatureNetDeviceTSO6 Feature = 1 << 12
+
+	// FeatureNetDeviceECN indicates that the device supports the TCP
+	// segmentation offload with ECN for received packets.
+	FeatureNetDeviceECN Feature = 1 << 13
+
+	// FeatureNetDeviceUFO indicates that the device supports the UDP
+	// fragmentation offload for received packets.
+	FeatureNetDeviceUFO Feature = 1 << 14
+
+	// FeatureNetMergeRXBuffers indicates that the driver can handle merged
+	// receive buffers.
+	// When this feature is negotiated, devices may merge multiple descriptor
+	// chains together to transport large received packets. [NetHdr.NumBuffers]
+	// will then contain the number of merged descriptor chains.
+	FeatureNetMergeRXBuffers Feature = 1 << 15
+
+	// FeatureNetStatus indicates that the device configuration status field is
+	// available.
+	FeatureNetStatus Feature = 1 << 16
+
+	// FeatureNetCtrlVQ indicates that a control channel virtqueue is
+	// available.
+	FeatureNetCtrlVQ Feature = 1 << 17
+
+	// FeatureNetCtrlRX indicates support for RX mode control (e.g. promiscuous
+	// or all-multicast) for packet receive filtering.
+	FeatureNetCtrlRX Feature = 1 << 18
+
+	// FeatureNetCtrlVLAN indicates support for VLAN filtering through the
+	// control channel.
+	FeatureNetCtrlVLAN Feature = 1 << 19
+
+	// FeatureNetDriverAnnounce indicates that the driver can send gratuitous
+	// packets.
+	FeatureNetDriverAnnounce Feature = 1 << 21
+
+	// FeatureNetMQ indicates that the device supports multiqueue with automatic
+	// receive steering.
+	FeatureNetMQ Feature = 1 << 22
+
+	// FeatureNetCtrlMACAddr indicates that the MAC address can be set through
+	// the control channel.
+	FeatureNetCtrlMACAddr Feature = 1 << 23
+
+	// FeatureNetDeviceUSO indicates that the device supports the UDP
+	// segmentation offload for received packets.
+	FeatureNetDeviceUSO Feature = 1 << 56
+
+	// FeatureNetHashReport indicates that the device can report a per-packet
+	// hash value and type.
+	FeatureNetHashReport Feature = 1 << 57
+
+	// FeatureNetDriverHdrLen indicates that the driver can provide the exact
+	// header length value (see [NetHdr.HdrLen]).
+	// Devices may benefit from knowing the exact header length.
+	FeatureNetDriverHdrLen Feature = 1 << 59
+
+	// FeatureNetRSS indicates that the device supports RSS (receive-side
+	// scaling) with configurable hash parameters.
+	FeatureNetRSS Feature = 1 << 60
+
+	// FeatureNetRSCExt indicates that the device can process duplicated ACKs
+	// and report the number of coalesced segments and duplicated ACKs.
+	FeatureNetRSCExt Feature = 1 << 61
+
+	// FeatureNetStandby indicates that the device may act as a standby for a
+	// primary device with the same MAC address.
+	FeatureNetStandby Feature = 1 << 62
+
+	// FeatureNetSpeedDuplex indicates that the device can report link speed and
+	// duplex mode.
+	FeatureNetSpeedDuplex Feature = 1 << 63
+)

overlay/virtio/net_hdr.go

@@ -0,0 +1,77 @@
+package virtio
+
+import (
+	"errors"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+)
+
+// Workaround to make Go doc links work.
+var _ unix.Errno
+
+// NetHdrSize is the number of bytes needed to store a [NetHdr] in memory.
+const NetHdrSize = 12
+
+// ErrNetHdrBufferTooSmall is returned when a buffer is too small to fit a
+// virtio_net_hdr.
+var ErrNetHdrBufferTooSmall = errors.New("the buffer is too small to fit a virtio_net_hdr")
+
+// NetHdr defines the virtio_net_hdr as described by the virtio specification.
+type NetHdr struct {
+	// Flags that describe the packet.
+	// Possible values are:
+	//   - [unix.VIRTIO_NET_HDR_F_NEEDS_CSUM]
+	//   - [unix.VIRTIO_NET_HDR_F_DATA_VALID]
+	//   - [unix.VIRTIO_NET_HDR_F_RSC_INFO]
+	Flags uint8
+	// GSOType contains the type of segmentation offload that should be used for
+	// the packet.
+	// Possible values are:
+	//   - [unix.VIRTIO_NET_HDR_GSO_NONE]
+	//   - [unix.VIRTIO_NET_HDR_GSO_TCPV4]
+	//   - [unix.VIRTIO_NET_HDR_GSO_UDP]
+	//   - [unix.VIRTIO_NET_HDR_GSO_TCPV6]
+	//   - [unix.VIRTIO_NET_HDR_GSO_UDP_L4]
+	//   - [unix.VIRTIO_NET_HDR_GSO_ECN]
+	GSOType uint8
+	// HdrLen contains the length of the headers that need to be replicated by
+	// segmentation offloads. It's the number of bytes from the beginning of the
+	// packet to the beginning of the transport payload.
+	// Only used when [FeatureNetDriverHdrLen] is negotiated.
+	HdrLen uint16
+	// GSOSize contains the maximum size of each segmented packet beyond the
+	// header (payload size). In case of TCP, this is the MSS.
+	GSOSize uint16
+	// CsumStart contains the offset within the packet from which on the
+	// checksum should be computed.
+	CsumStart uint16
+	// CsumOffset specifies how many bytes after [NetHdr.CsumStart] the computed
+	// 16-bit checksum should be inserted.
+	CsumOffset uint16
+	// NumBuffers contains the number of merged descriptor chains when
+	// [FeatureNetMergeRXBuffers] is negotiated.
+	// This field is only used for packets received by the driver and should be
+	// zero for transmitted packets.
+	NumBuffers uint16
+}
+
+// Decode decodes the [NetHdr] from the given byte slice. The slice must contain
+// at least [NetHdrSize] bytes.
+func (v *NetHdr) Decode(data []byte) error {
+	if len(data) < NetHdrSize {
+		return ErrNetHdrBufferTooSmall
+	}
+	copy(unsafe.Slice((*byte)(unsafe.Pointer(v)), NetHdrSize), data[:NetHdrSize])
+	return nil
+}
+
+// Encode encodes the [NetHdr] into the given byte slice. The slice must have
+// room for at least [NetHdrSize] bytes.
+func (v *NetHdr) Encode(data []byte) error {
+	if len(data) < NetHdrSize {
+		return ErrNetHdrBufferTooSmall
+	}
+	copy(data[:NetHdrSize], unsafe.Slice((*byte)(unsafe.Pointer(v)), NetHdrSize))
+	return nil
+}

overlay/virtio/net_hdr_test.go

@@ -0,0 +1,43 @@
+package virtio
+
+import (
+	"testing"
+	"unsafe"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"golang.org/x/sys/unix"
+)
+
+func TestNetHdr_Size(t *testing.T) {
+	assert.EqualValues(t, NetHdrSize, unsafe.Sizeof(NetHdr{}))
+}
+
+func TestNetHdr_Encoding(t *testing.T) {
+	vnethdr := NetHdr{
+		Flags:      unix.VIRTIO_NET_HDR_F_NEEDS_CSUM,
+		GSOType:    unix.VIRTIO_NET_HDR_GSO_UDP_L4,
+		HdrLen:     42,
+		GSOSize:    1472,
+		CsumStart:  34,
+		CsumOffset: 6,
+		NumBuffers: 16,
+	}
+
+	buf := make([]byte, NetHdrSize)
+	require.NoError(t, vnethdr.Encode(buf))
+
+	assert.Equal(t, []byte{
+		0x01, 0x05,
+		0x2a, 0x00,
+		0xc0, 0x05,
+		0x22, 0x00,
+		0x06, 0x00,
+		0x10, 0x00,
+	}, buf)
+
+	var decoded NetHdr
+	require.NoError(t, decoded.Decode(buf))
+
+	assert.Equal(t, vnethdr, decoded)
+}