src/connectivity/network/netstack/link/eth/client_test.go - fuchsia - Git at Google

 // Copyright 2018 The Fuchsia Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 //go:build !build_with_native_toolchain
 // +build !build_with_native_toolchain

 package eth_test

 import (
 	"context"
 	"errors"
 	"fmt"
 	"math/bits"
 	"runtime"
 	"syscall/zx"
 	"syscall/zx/zxwait"
 	"testing"
 	"time"
 	"unsafe"

 	eth_gen "gen/netstack/link/eth"

 	"go.fuchsia.dev/fuchsia/src/connectivity/network/netstack/link/eth"
 	fifotestutil "go.fuchsia.dev/fuchsia/src/connectivity/network/netstack/link/eth/testutil"
 	"go.fuchsia.dev/fuchsia/src/connectivity/network/netstack/link/fifo"
 	"go.fuchsia.dev/fuchsia/src/connectivity/network/netstack/testutil"

 	fidlethernet "fidl/fuchsia/hardware/ethernet"
 	"fidl/fuchsia/hardware/network"

 	"github.com/google/go-cmp/cmp"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 )

 type DeliverNetworkPacketArgs struct {
 	SrcLinkAddr, DstLinkAddr tcpip.LinkAddress
 	Protocol                 tcpip.NetworkProtocolNumber
 	Pkt                      *stack.PacketBuffer
 }

 type dispatcherChan chan DeliverNetworkPacketArgs

 var _ stack.NetworkDispatcher = (*dispatcherChan)(nil)

 func (ch *dispatcherChan) DeliverNetworkPacket(srcLinkAddr, dstLinkAddr tcpip.LinkAddress, protocol tcpip.NetworkProtocolNumber, pkt *stack.PacketBuffer) {
 	*ch <- DeliverNetworkPacketArgs{
 		SrcLinkAddr: srcLinkAddr,
 		DstLinkAddr: dstLinkAddr,
 		Protocol:    protocol,
 		Pkt:         pkt,
 	}
 }

 func fifoReadsTransformer(in *fifo.FifoStats) []uint64 {
 	reads := make([]uint64, in.Size())
 	for i := in.Size(); i > 0; i-- {
 		reads[i-1] = in.Reads(i).Value()
 	}
 	return reads
 }

 func fifoWritesTransformer(in *fifo.FifoStats) []uint64 {
 	writes := make([]uint64, in.Size())
 	for i := in.Size(); i > 0; i-- {
 		writes[i-1] = in.Writes(i).Value()
 	}
 	return writes
 }

 func uint64Sum(stats []uint64) uint64 {
 	var t uint64
 	for _, v := range stats {
 		t += v
 	}
 	return t
 }

 func cycleTX(txFifo zx.Handle, size uint32, iob eth.IOBuffer, fn func([]byte)) error {
 	b := make([]eth_gen.FifoEntry, size)
 	for toRead := size; toRead != 0; {
 		if _, err := zxwait.WaitContext(context.Background(), txFifo, zx.SignalFIFOReadable); err != nil {
 			return err
 		}
 		status, read := eth_gen.FifoRead(txFifo, b)
 		if status != zx.ErrOk {
 			return &zx.Error{Status: status, Text: "FifoRead"}
 		}
 		for _, entry := range b[:read] {
 			if fn != nil {
 				fn(iob.BufferFromEntry(entry))
 			}
 		}
 		toRead -= read
 		status, wrote := eth_gen.FifoWrite(txFifo, b[:read])
 		if status != zx.ErrOk {
 			return &zx.Error{Status: status, Text: "FifoWrite"}
 		}
 		if wrote != read {
 			return fmt.Errorf("got zx_fifo_write(...) = %d want = %d", wrote, size)
 		}
 	}
 	return nil
 }

 func checkTXDone(txFifo zx.Handle) error {
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
 	defer cancel()
 	if _, err := zxwait.WaitContext(ctx, txFifo, zx.SignalFIFOReadable); !errors.Is(err, context.DeadlineExceeded) {
 		return fmt.Errorf("got zxwait.WaitContext(txFifo, ...) = %v, want %s", err, zx.ErrTimedOut)
 	}
 	return nil
 }

 func TestClient(t *testing.T) {
 	const maxDepth = eth_gen.FifoMaxSize / uint(unsafe.Sizeof(eth_gen.FifoEntry{}))

 	for i := 0; i < bits.Len(maxDepth); i++ {
 		depth := uint32(1 << i)
 		t.Run(fmt.Sprintf("depth=%d", depth), func(t *testing.T) {
 			deviceImpl, deviceFifos := fifotestutil.MakeEthernetDevice(t, fidlethernet.Info{}, depth)

 			var device struct {
 				iob       eth.IOBuffer
 				rxEntries []eth_gen.FifoEntry
 			}
 			defer func() {
 				_ = device.iob.Close()
 			}()

 			deviceImpl.SetIoBufferImpl = func(vmo zx.VMO) (int32, error) {
 				mappedVmo, err := fifo.MapVMO(vmo)
 				if err != nil {
 					t.Fatal(err)
 				}
 				if err := vmo.Close(); err != nil {
 					t.Fatal(err)
 				}
 				device.iob = eth.IOBuffer{MappedVMO: mappedVmo}
 				return int32(zx.ErrOk), nil
 			}

 			client, err := eth.NewClient(t.Name(), "topo", "file", &deviceImpl)
 			if err != nil {
 				t.Fatal(err)
 			}
 			client.SetOnLinkClosed(func() {})
 			defer func() {
 				_ = client.Close()
 				client.Wait()
 			}()

 			if device.iob == (eth.IOBuffer{}) {
 				t.Fatal("eth.NewClient didn't call device.SetIoBuffer")
 			}

 			ch := make(dispatcherChan, 1)
 			client.Attach(&ch)

 			// Attaching a dispatcher to the client should cause it to fill the device's RX buffer pool.
 			{
 				b := make([]eth_gen.FifoEntry, depth+1)
 				if _, err := zxwait.WaitContext(context.Background(), deviceFifos.Rx, zx.SignalFIFOReadable); err != nil {
 					t.Fatal(err)
 				}
 				status, count := eth_gen.FifoRead(deviceFifos.Rx, b)
 				if status != zx.ErrOk {
 					t.Fatal(status)
 				}
 				if count != depth {
 					t.Fatalf("got zx_fifo_read(...) = %d want = %d", count, depth)
 				}
 				device.rxEntries = append(device.rxEntries, b[:count]...)
 			}

 			// Wait until the initial batch of Rx writes is accounted for.
 			for uint64Sum(fifoWritesTransformer(&client.RxStats().FifoStats)) == 0 {
 				runtime.Gosched()
 			}

 			t.Run("Stats", func(t *testing.T) {
 				for excess := depth; ; excess >>= 1 {
 					t.Run(fmt.Sprintf("excess=%d", excess), func(t *testing.T) {
 						// Grab baseline stats to avoid assumptions about ops done to this point.
 						wantRxReads := fifoReadsTransformer(&client.RxStats().FifoStats)
 						wantRxWrites := fifoWritesTransformer(&client.RxStats().FifoStats)
 						wantTxReads := fifoReadsTransformer(&client.TxStats().FifoStats)
 						wantTxWrites := fifoWritesTransformer(&client.TxStats().FifoStats)

 						// Compute expectations.
 						for _, want := range [][]uint64{wantRxReads, wantRxWrites, wantTxReads, wantTxWrites} {
 							for _, write := range []uint32{depth, excess} {
 								if write == 0 {
 									continue
 								}
 								want[write-1]++
 							}
 						}

 						writeSize := depth + excess
 						var pkts stack.PacketBufferList
 						for i := uint32(0); i < writeSize; i++ {
 							pkts.PushBack(stack.NewPacketBuffer(stack.PacketBufferOptions{
 								ReserveHeaderBytes: int(client.MaxHeaderLength()),
 							}))
 						}

 						// Simulate zero-sized incoming packets.
 						for toWrite := writeSize; toWrite != 0; {
 							b := device.rxEntries
 							if toWrite < uint32(len(b)) {
 								b = b[:toWrite]
 							}
 							for i := range b {
 								b[i].SetLength(0)
 							}
 							if _, err := zxwait.WaitContext(context.Background(), deviceFifos.Rx, zx.SignalFIFOWritable); err != nil {
 								t.Fatal(err)
 							}
 							status, count := eth_gen.FifoWrite(deviceFifos.Rx, b)
 							if status != zx.ErrOk {
 								t.Fatal(status)
 							}
 							// The maximum number of RX entries we might be holding is equal to the FIFO depth;
 							// we should always be able to write all of them.
 							if l := uint32(len(b)); count != l {
 								t.Fatalf("got eth_gen.FifoWrite(...) = %d, want = %d", count, l)
 							}
 							toWrite -= count

 							timeout := make(chan struct{})
 							time.AfterFunc(5*time.Second, func() { close(timeout) })
 							for i := uint32(0); i < count; i++ {
 								select {
 								case <-timeout:
 									t.Fatal("timeout waiting for ethernet packet")
 								case args := <-ch:
 									if diff := cmp.Diff(DeliverNetworkPacketArgs{
 										Pkt: stack.NewPacketBuffer(stack.PacketBufferOptions{}),
 									}, args, testutil.PacketBufferCmpTransformer); diff != "" {
 										t.Fatalf("delivered network packet mismatch (-want +got):\n%s", diff)
 									}
 								}
 							}
 							for len(b) != 0 {
 								if _, err := zxwait.WaitContext(context.Background(), deviceFifos.Rx, zx.SignalFIFOReadable); err != nil {
 									t.Fatal(err)
 								}
 								status, count := eth_gen.FifoRead(deviceFifos.Rx, b)
 								if status != zx.ErrOk {
 									t.Fatal(status)
 								}
 								b = b[count:]
 							}
 						}

 						if diff := cmp.Diff(wantRxReads, fifoReadsTransformer(&client.RxStats().FifoStats)); diff != "" {
 							t.Errorf("Stats.Rx.Reads mismatch (-want +got):\n%s", diff)
 						}
 						// RX write stats must be polled since we're unsynchronized on RX
 						// reads; the client will only update the stats after returning the
 						// buffers on the FIFO. We poll based on total counts and later
 						// assert on the correct per-batch values.
 						wantRxWritesTotal := uint64Sum(wantRxWrites)
 						for {
 							gotRxWrites := fifoWritesTransformer(&client.RxStats().FifoStats)
 							if uint64Sum(gotRxWrites) < wantRxWritesTotal {
 								runtime.Gosched()
 								continue
 							}
 							if diff := cmp.Diff(wantRxWrites, gotRxWrites); diff != "" {
 								t.Errorf("Stats.Rx.Writes mismatch (-want +got):\n%s", diff)
 							}
 							break
 						}

 						// Use WritePackets to get deterministic batch sizes.
 						count, err := client.WritePackets(
 							stack.RouteInfo{},
 							pkts,
 							1337,
 						)
 						if err != nil {
 							t.Fatal(err)
 						}
 						if got := uint32(count); got != writeSize {
 							t.Fatalf("got WritePackets(_) = %d, nil, want %d, nil", got, writeSize)
 						}

 						dropsBefore := client.TxStats().Drops.Value()

 						if err := cycleTX(deviceFifos.Tx, writeSize, device.iob, nil); err != nil {
 							t.Fatal(err)
 						}
 						if err := checkTXDone(deviceFifos.Tx); err != nil {
 							t.Fatal(err)
 						}

 						if diff := cmp.Diff(wantTxWrites, fifoWritesTransformer(&client.TxStats().FifoStats)); diff != "" {
 							t.Errorf("Stats.Tx.Writes mismatch (-want +got):\n%s", diff)
 						}
 						// TX read stats must be polled since we're unsynchronized on TX
 						// reads, which is when the stats are updated. We poll based on
 						// total counts and later assert on the correct per-batch values.
 						wantTxReadsTotal := uint64Sum(wantTxReads)
 						for {
 							gotTxReads := fifoReadsTransformer(&client.TxStats().FifoStats)
 							if uint64Sum(gotTxReads) < wantTxReadsTotal {
 								runtime.Gosched()
 								continue
 							}
 							if diff := cmp.Diff(wantTxReads, gotTxReads); diff != "" {
 								t.Errorf("Stats.Tx.Reads mismatch (-want +got):\n%s", diff)
 							}
 							break
 						}

 						// Since we're not setting the TX_OK flag in this test, all these
 						// packets will be considered to have dropped. We similarly need to
 						// poll the dropped stats since they're unsynchronized.
 						for {
 							dropsAfter := client.TxStats().Drops.Value() - dropsBefore
 							if dropsAfter < uint64(writeSize) {
 								runtime.Gosched()
 								continue
 							}
 							if dropsAfter != uint64(writeSize) {
 								t.Errorf("got client.TxStats.Drops.Value() = %d, want %d", dropsAfter, writeSize)
 							}
 							break
 						}
 					})
 					if excess == 0 {
 						break
 					}
 				}
 			})

 			// Test that we build the ethernet frame correctly.
 			// Test that we don't accidentally put unused bytes on the wire.
 			const packetHeader = "foo"
 			const body = "bar"

 			want := []byte(packetHeader + body)

 			t.Run("WritePacket", func(t *testing.T) {
 				for i := 0; i < int(depth)*10; i++ {
 					pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
 						ReserveHeaderBytes: int(client.MaxHeaderLength()) + len(packetHeader) + 5,
 						Data:               buffer.View(body).ToVectorisedView(),
 					})
 					hdr := pkt.NetworkHeader().Push(len(packetHeader))
 					if n := copy(hdr, packetHeader); n != len(packetHeader) {
 						t.Fatalf("copied %d bytes, expected %d bytes", n, len(packetHeader))
 					}
 					if err := client.WritePacket(stack.RouteInfo{}, 1337, pkt); err != nil {
 						t.Fatal(err)
 					}

 					if err := cycleTX(deviceFifos.Tx, 1, device.iob, func(b []byte) {
 						if diff := cmp.Diff(want, b); diff != "" {
 							t.Fatalf("delivered network packet mismatch (-want +got):\n%s", diff)
 						}
 					}); err != nil {
 						t.Fatal(err)
 					}
 				}
 				if err := checkTXDone(deviceFifos.Tx); err != nil {
 					t.Fatal(err)
 				}
 			})

 			// ReceivePacket tests that receiving ethernet frames of size
 			// less than the minimum size does not panic or cause any issues for future
 			// (valid) frames.
 			t.Run("ReceivePacket", func(t *testing.T) {
 				const payload = "foobarbaz"

 				// Send the first sendSize bytes of a frame.
 				send := func(sendSize uint16) {
 					entry := &device.rxEntries[0]
 					buf := device.iob.BufferFromEntry(*entry)
 					if got, want := copy(buf, payload), len(payload); got != want {
 						t.Fatalf("got copy() = %d, want %d", got, want)
 					}
 					entry.SetLength(sendSize)

 					{
 						status, count := eth_gen.FifoWrite(deviceFifos.Rx, device.rxEntries[:1])
 						if status != zx.ErrOk {
 							t.Fatal(status)
 						}
 						if count != 1 {
 							t.Fatalf("got zx_fifo_write(...) = %d want = %d", count, 1)
 						}
 					}
 					if _, err := zxwait.WaitContext(context.Background(), deviceFifos.Rx, zx.SignalFIFOReadable); err != nil {
 						t.Fatal(err)
 					}
 					// Assert that we read back only one entry (when depth is greater than 1).
 					status, count := eth_gen.FifoRead(deviceFifos.Rx, device.rxEntries)
 					if status != zx.ErrOk {
 						t.Fatal(status)
 					}
 					if count != 1 {
 						t.Fatalf("got zx_fifo_write(...) = %d want = %d", count, 1)
 					}
 				}

 				for _, size := range []uint16{
 					// Test receiving a frame that is equal to the minimum frame size.
 					0,
 					// Test receiving a frame that is just greater than the minimum frame size.
 					1,
 					// Test receiving the full frame.
 					uint16(len(payload)),
 				} {
 					send(size)

 					// Wait for a packet to be delivered on ch and validate the delivered
 					// network packet parameters. The packet should be delivered within 5s.
 					select {
 					case <-time.After(5 * time.Second):
 						t.Fatal("timeout waiting for ethernet packet")
 					case args := <-ch:
 						if diff := cmp.Diff(DeliverNetworkPacketArgs{
 							Pkt: stack.NewPacketBuffer(stack.PacketBufferOptions{
 								Data: buffer.View(payload[:size]).ToVectorisedView(),
 							}),
 						}, args, testutil.PacketBufferCmpTransformer); diff != "" {
 							t.Fatalf("delivered network packet mismatch (-want +got):\n%s", diff)
 						}
 					}
 				}
 			})
 		})
 	}
 }

 func TestDeviceClass(t *testing.T) {
 	tests := []struct {
 		features    fidlethernet.Features
 		expectClass network.DeviceClass
 	}{
 		{
 			features:    0,
 			expectClass: network.DeviceClassEthernet,
 		},
 		{
 			features:    fidlethernet.FeaturesWlan,
 			expectClass: network.DeviceClassWlan,
 		},
 	}
 	for _, test := range tests {
 		c := eth.Client{
 			Info: fidlethernet.Info{
 				Features: test.features,
 			},
 		}
 		if got := c.DeviceClass(); got != test.expectClass {
 			t.Errorf("got c.DeviceClass() = %s, want = %s", got, test.expectClass)
 		}
 	}
 }
	// Copyright 2018 The Fuchsia Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	//go:build !build_with_native_toolchain
	// +build !build_with_native_toolchain

	package eth_test

	import (
	"context"
	"errors"
	"fmt"
	"math/bits"
	"runtime"
	"syscall/zx"
	"syscall/zx/zxwait"
	"testing"
	"time"
	"unsafe"

	eth_gen "gen/netstack/link/eth"

	"go.fuchsia.dev/fuchsia/src/connectivity/network/netstack/link/eth"
	fifotestutil "go.fuchsia.dev/fuchsia/src/connectivity/network/netstack/link/eth/testutil"
	"go.fuchsia.dev/fuchsia/src/connectivity/network/netstack/link/fifo"
	"go.fuchsia.dev/fuchsia/src/connectivity/network/netstack/testutil"

	fidlethernet "fidl/fuchsia/hardware/ethernet"
	"fidl/fuchsia/hardware/network"

	"github.com/google/go-cmp/cmp"
	"gvisor.dev/gvisor/pkg/tcpip"
	"gvisor.dev/gvisor/pkg/tcpip/buffer"
	"gvisor.dev/gvisor/pkg/tcpip/stack"
	)

	type DeliverNetworkPacketArgs struct {
	SrcLinkAddr, DstLinkAddr tcpip.LinkAddress
	Protocol tcpip.NetworkProtocolNumber
	Pkt *stack.PacketBuffer
	}

	type dispatcherChan chan DeliverNetworkPacketArgs

	var _ stack.NetworkDispatcher = (*dispatcherChan)(nil)

	func (ch dispatcherChan) DeliverNetworkPacket(srcLinkAddr, dstLinkAddr tcpip.LinkAddress, protocol tcpip.NetworkProtocolNumber, pkt stack.PacketBuffer) {
	*ch <- DeliverNetworkPacketArgs{
	SrcLinkAddr: srcLinkAddr,
	DstLinkAddr: dstLinkAddr,
	Protocol: protocol,
	Pkt: pkt,
	}
	}

	func fifoReadsTransformer(in *fifo.FifoStats) []uint64 {
	reads := make([]uint64, in.Size())
	for i := in.Size(); i > 0; i-- {
	reads[i-1] = in.Reads(i).Value()
	}
	return reads
	}

	func fifoWritesTransformer(in *fifo.FifoStats) []uint64 {
	writes := make([]uint64, in.Size())
	for i := in.Size(); i > 0; i-- {
	writes[i-1] = in.Writes(i).Value()
	}
	return writes
	}

	func uint64Sum(stats []uint64) uint64 {
	var t uint64
	for _, v := range stats {
	t += v
	}
	return t
	}

	func cycleTX(txFifo zx.Handle, size uint32, iob eth.IOBuffer, fn func([]byte)) error {
	b := make([]eth_gen.FifoEntry, size)
	for toRead := size; toRead != 0; {
	if _, err := zxwait.WaitContext(context.Background(), txFifo, zx.SignalFIFOReadable); err != nil {
	return err
	}
	status, read := eth_gen.FifoRead(txFifo, b)
	if status != zx.ErrOk {
	return &zx.Error{Status: status, Text: "FifoRead"}
	}
	for _, entry := range b[:read] {
	if fn != nil {
	fn(iob.BufferFromEntry(entry))
	}
	}
	toRead -= read
	status, wrote := eth_gen.FifoWrite(txFifo, b[:read])
	if status != zx.ErrOk {
	return &zx.Error{Status: status, Text: "FifoWrite"}
	}
	if wrote != read {
	return fmt.Errorf("got zx_fifo_write(...) = %d want = %d", wrote, size)
	}
	}
	return nil
	}

	func checkTXDone(txFifo zx.Handle) error {
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Millisecond)
	defer cancel()
	if _, err := zxwait.WaitContext(ctx, txFifo, zx.SignalFIFOReadable); !errors.Is(err, context.DeadlineExceeded) {
	return fmt.Errorf("got zxwait.WaitContext(txFifo, ...) = %v, want %s", err, zx.ErrTimedOut)
	}
	return nil
	}

	func TestClient(t *testing.T) {
	const maxDepth = eth_gen.FifoMaxSize / uint(unsafe.Sizeof(eth_gen.FifoEntry{}))

	for i := 0; i < bits.Len(maxDepth); i++ {
	depth := uint32(1 << i)
	t.Run(fmt.Sprintf("depth=%d", depth), func(t *testing.T) {
	deviceImpl, deviceFifos := fifotestutil.MakeEthernetDevice(t, fidlethernet.Info{}, depth)

	var device struct {
	iob eth.IOBuffer
	rxEntries []eth_gen.FifoEntry
	}
	defer func() {
	_ = device.iob.Close()
	}()

	deviceImpl.SetIoBufferImpl = func(vmo zx.VMO) (int32, error) {
	mappedVmo, err := fifo.MapVMO(vmo)
	if err != nil {
	t.Fatal(err)
	}
	if err := vmo.Close(); err != nil {
	t.Fatal(err)
	}
	device.iob = eth.IOBuffer{MappedVMO: mappedVmo}
	return int32(zx.ErrOk), nil
	}

	client, err := eth.NewClient(t.Name(), "topo", "file", &deviceImpl)
	if err != nil {
	t.Fatal(err)
	}
	client.SetOnLinkClosed(func() {})
	defer func() {
	_ = client.Close()
	client.Wait()
	}()

	if device.iob == (eth.IOBuffer{}) {
	t.Fatal("eth.NewClient didn't call device.SetIoBuffer")
	}

	ch := make(dispatcherChan, 1)
	client.Attach(&ch)

	// Attaching a dispatcher to the client should cause it to fill the device's RX buffer pool.
	{
	b := make([]eth_gen.FifoEntry, depth+1)
	if _, err := zxwait.WaitContext(context.Background(), deviceFifos.Rx, zx.SignalFIFOReadable); err != nil {
	t.Fatal(err)
	}
	status, count := eth_gen.FifoRead(deviceFifos.Rx, b)
	if status != zx.ErrOk {
	t.Fatal(status)
	}
	if count != depth {
	t.Fatalf("got zx_fifo_read(...) = %d want = %d", count, depth)
	}
	device.rxEntries = append(device.rxEntries, b[:count]...)
	}

	// Wait until the initial batch of Rx writes is accounted for.
	for uint64Sum(fifoWritesTransformer(&client.RxStats().FifoStats)) == 0 {
	runtime.Gosched()
	}

	t.Run("Stats", func(t *testing.T) {
	for excess := depth; ; excess >>= 1 {
	t.Run(fmt.Sprintf("excess=%d", excess), func(t *testing.T) {
	// Grab baseline stats to avoid assumptions about ops done to this point.
	wantRxReads := fifoReadsTransformer(&client.RxStats().FifoStats)
	wantRxWrites := fifoWritesTransformer(&client.RxStats().FifoStats)
	wantTxReads := fifoReadsTransformer(&client.TxStats().FifoStats)
	wantTxWrites := fifoWritesTransformer(&client.TxStats().FifoStats)

	// Compute expectations.
	for _, want := range [][]uint64{wantRxReads, wantRxWrites, wantTxReads, wantTxWrites} {
	for _, write := range []uint32{depth, excess} {
	if write == 0 {
	continue
	}
	want[write-1]++
	}
	}

	writeSize := depth + excess
	var pkts stack.PacketBufferList
	for i := uint32(0); i < writeSize; i++ {
	pkts.PushBack(stack.NewPacketBuffer(stack.PacketBufferOptions{
	ReserveHeaderBytes: int(client.MaxHeaderLength()),
	}))
	}

	// Simulate zero-sized incoming packets.
	for toWrite := writeSize; toWrite != 0; {
	b := device.rxEntries
	if toWrite < uint32(len(b)) {
	b = b[:toWrite]
	}
	for i := range b {
	b[i].SetLength(0)
	}
	if _, err := zxwait.WaitContext(context.Background(), deviceFifos.Rx, zx.SignalFIFOWritable); err != nil {
	t.Fatal(err)
	}
	status, count := eth_gen.FifoWrite(deviceFifos.Rx, b)
	if status != zx.ErrOk {
	t.Fatal(status)
	}
	// The maximum number of RX entries we might be holding is equal to the FIFO depth;
	// we should always be able to write all of them.
	if l := uint32(len(b)); count != l {
	t.Fatalf("got eth_gen.FifoWrite(...) = %d, want = %d", count, l)
	}
	toWrite -= count

	timeout := make(chan struct{})
	time.AfterFunc(5*time.Second, func() { close(timeout) })
	for i := uint32(0); i < count; i++ {
	select {
	case <-timeout:
	t.Fatal("timeout waiting for ethernet packet")
	case args := <-ch:
	if diff := cmp.Diff(DeliverNetworkPacketArgs{
	Pkt: stack.NewPacketBuffer(stack.PacketBufferOptions{}),
	}, args, testutil.PacketBufferCmpTransformer); diff != "" {
	t.Fatalf("delivered network packet mismatch (-want +got):\n%s", diff)
	}
	}
	}
	for len(b) != 0 {
	if _, err := zxwait.WaitContext(context.Background(), deviceFifos.Rx, zx.SignalFIFOReadable); err != nil {
	t.Fatal(err)
	}
	status, count := eth_gen.FifoRead(deviceFifos.Rx, b)
	if status != zx.ErrOk {
	t.Fatal(status)
	}
	b = b[count:]
	}
	}

	if diff := cmp.Diff(wantRxReads, fifoReadsTransformer(&client.RxStats().FifoStats)); diff != "" {
	t.Errorf("Stats.Rx.Reads mismatch (-want +got):\n%s", diff)
	}
	// RX write stats must be polled since we're unsynchronized on RX
	// reads; the client will only update the stats after returning the
	// buffers on the FIFO. We poll based on total counts and later
	// assert on the correct per-batch values.
	wantRxWritesTotal := uint64Sum(wantRxWrites)
	for {
	gotRxWrites := fifoWritesTransformer(&client.RxStats().FifoStats)
	if uint64Sum(gotRxWrites) < wantRxWritesTotal {
	runtime.Gosched()
	continue
	}
	if diff := cmp.Diff(wantRxWrites, gotRxWrites); diff != "" {
	t.Errorf("Stats.Rx.Writes mismatch (-want +got):\n%s", diff)
	}
	break
	}

	// Use WritePackets to get deterministic batch sizes.
	count, err := client.WritePackets(
	stack.RouteInfo{},
	pkts,
	1337,
	)
	if err != nil {
	t.Fatal(err)
	}
	if got := uint32(count); got != writeSize {
	t.Fatalf("got WritePackets(_) = %d, nil, want %d, nil", got, writeSize)
	}

	dropsBefore := client.TxStats().Drops.Value()

	if err := cycleTX(deviceFifos.Tx, writeSize, device.iob, nil); err != nil {
	t.Fatal(err)
	}
	if err := checkTXDone(deviceFifos.Tx); err != nil {
	t.Fatal(err)
	}

	if diff := cmp.Diff(wantTxWrites, fifoWritesTransformer(&client.TxStats().FifoStats)); diff != "" {
	t.Errorf("Stats.Tx.Writes mismatch (-want +got):\n%s", diff)
	}
	// TX read stats must be polled since we're unsynchronized on TX
	// reads, which is when the stats are updated. We poll based on
	// total counts and later assert on the correct per-batch values.
	wantTxReadsTotal := uint64Sum(wantTxReads)
	for {
	gotTxReads := fifoReadsTransformer(&client.TxStats().FifoStats)
	if uint64Sum(gotTxReads) < wantTxReadsTotal {
	runtime.Gosched()
	continue
	}
	if diff := cmp.Diff(wantTxReads, gotTxReads); diff != "" {
	t.Errorf("Stats.Tx.Reads mismatch (-want +got):\n%s", diff)
	}
	break
	}

	// Since we're not setting the TX_OK flag in this test, all these
	// packets will be considered to have dropped. We similarly need to
	// poll the dropped stats since they're unsynchronized.
	for {
	dropsAfter := client.TxStats().Drops.Value() - dropsBefore
	if dropsAfter < uint64(writeSize) {
	runtime.Gosched()
	continue
	}
	if dropsAfter != uint64(writeSize) {
	t.Errorf("got client.TxStats.Drops.Value() = %d, want %d", dropsAfter, writeSize)
	}
	break
	}
	})
	if excess == 0 {
	break
	}
	}
	})

	// Test that we build the ethernet frame correctly.
	// Test that we don't accidentally put unused bytes on the wire.
	const packetHeader = "foo"
	const body = "bar"

	want := []byte(packetHeader + body)

	t.Run("WritePacket", func(t *testing.T) {
	for i := 0; i < int(depth)*10; i++ {
	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
	ReserveHeaderBytes: int(client.MaxHeaderLength()) + len(packetHeader) + 5,
	Data: buffer.View(body).ToVectorisedView(),
	})
	hdr := pkt.NetworkHeader().Push(len(packetHeader))
	if n := copy(hdr, packetHeader); n != len(packetHeader) {
	t.Fatalf("copied %d bytes, expected %d bytes", n, len(packetHeader))
	}
	if err := client.WritePacket(stack.RouteInfo{}, 1337, pkt); err != nil {
	t.Fatal(err)
	}

	if err := cycleTX(deviceFifos.Tx, 1, device.iob, func(b []byte) {
	if diff := cmp.Diff(want, b); diff != "" {
	t.Fatalf("delivered network packet mismatch (-want +got):\n%s", diff)
	}
	}); err != nil {
	t.Fatal(err)
	}
	}
	if err := checkTXDone(deviceFifos.Tx); err != nil {
	t.Fatal(err)
	}
	})

	// ReceivePacket tests that receiving ethernet frames of size
	// less than the minimum size does not panic or cause any issues for future
	// (valid) frames.
	t.Run("ReceivePacket", func(t *testing.T) {
	const payload = "foobarbaz"

	// Send the first sendSize bytes of a frame.
	send := func(sendSize uint16) {
	entry := &device.rxEntries[0]
	buf := device.iob.BufferFromEntry(*entry)
	if got, want := copy(buf, payload), len(payload); got != want {
	t.Fatalf("got copy() = %d, want %d", got, want)
	}
	entry.SetLength(sendSize)

	{
	status, count := eth_gen.FifoWrite(deviceFifos.Rx, device.rxEntries[:1])
	if status != zx.ErrOk {
	t.Fatal(status)
	}
	if count != 1 {
	t.Fatalf("got zx_fifo_write(...) = %d want = %d", count, 1)
	}
	}
	if _, err := zxwait.WaitContext(context.Background(), deviceFifos.Rx, zx.SignalFIFOReadable); err != nil {
	t.Fatal(err)
	}
	// Assert that we read back only one entry (when depth is greater than 1).
	status, count := eth_gen.FifoRead(deviceFifos.Rx, device.rxEntries)
	if status != zx.ErrOk {
	t.Fatal(status)
	}
	if count != 1 {
	t.Fatalf("got zx_fifo_write(...) = %d want = %d", count, 1)
	}
	}

	for _, size := range []uint16{
	// Test receiving a frame that is equal to the minimum frame size.
	0,
	// Test receiving a frame that is just greater than the minimum frame size.
	1,
	// Test receiving the full frame.
	uint16(len(payload)),
	} {
	send(size)

	// Wait for a packet to be delivered on ch and validate the delivered
	// network packet parameters. The packet should be delivered within 5s.
	select {
	case <-time.After(5 * time.Second):
	t.Fatal("timeout waiting for ethernet packet")
	case args := <-ch:
	if diff := cmp.Diff(DeliverNetworkPacketArgs{
	Pkt: stack.NewPacketBuffer(stack.PacketBufferOptions{
	Data: buffer.View(payload[:size]).ToVectorisedView(),
	}),
	}, args, testutil.PacketBufferCmpTransformer); diff != "" {
	t.Fatalf("delivered network packet mismatch (-want +got):\n%s", diff)
	}
	}
	}
	})
	})
	}
	}

	func TestDeviceClass(t *testing.T) {
	tests := []struct {
	features fidlethernet.Features
	expectClass network.DeviceClass
	}{
	{
	features: 0,
	expectClass: network.DeviceClassEthernet,
	},
	{
	features: fidlethernet.FeaturesWlan,
	expectClass: network.DeviceClassWlan,
	},
	}
	for _, test := range tests {
	c := eth.Client{
	Info: fidlethernet.Info{
	Features: test.features,
	},
	}
	if got := c.DeviceClass(); got != test.expectClass {
	t.Errorf("got c.DeviceClass() = %s, want = %s", got, test.expectClass)
	}
	}
	}