Make pipe buffer implementation standard.

A follow-up change will convert the networking code to use this standard
pipe implementation.

PiperOrigin-RevId: 297903206

6 files changed, 877 insertions, 0 deletions

diff --git a/pkg/buffer/BUILD b/pkg/buffer/BUILD
new file mode 100644
index 000000000..a77a3beea
--- /dev/null
+++ b/pkg/buffer/BUILD
@@ -0,0 +1,39 @@
+load("//tools:defs.bzl", "go_library", "go_test")
+load("//tools/go_generics:defs.bzl", "go_template_instance")
+
+package(licenses = ["notice"])
+
+go_template_instance(
+    name = "buffer_list",
+    out = "buffer_list.go",
+    package = "buffer",
+    prefix = "buffer",
+    template = "//pkg/ilist:generic_list",
+    types = {
+        "Element": "*Buffer",
+        "Linker": "*Buffer",
+    },
+)
+
+go_library(
+    name = "buffer",
+    srcs = [
+        "buffer.go",
+        "buffer_list.go",
+        "safemem.go",
+        "view.go",
+        "view_unsafe.go",
+    ],
+    visibility = ["//visibility:public"],
+    deps = [
+        "//pkg/log",
+        "//pkg/safemem",
+    ],
+)
+
+go_test(
+    name = "buffer_test",
+    size = "small",
+    srcs = ["view_test.go"],
+    library = ":buffer",
+)
diff --git a/pkg/buffer/buffer.go b/pkg/buffer/buffer.go
new file mode 100644
index 000000000..d5f64609b
--- /dev/null
+++ b/pkg/buffer/buffer.go
@@ -0,0 +1,67 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package buffer provides the implementation of a buffer view.
+package buffer
+
+import (
+	"sync"
+)
+
+const bufferSize = 8144 // See below.
+
+// Buffer encapsulates a queueable byte buffer.
+//
+// Note that the total size is slightly less than two pages. This is done
+// intentionally to ensure that the buffer object aligns with runtime
+// internals. We have no hard size or alignment requirements. This two page
+// size will effectively minimize internal fragmentation, but still have a
+// large enough chunk to limit excessive segmentation.
+//
+// +stateify savable
+type Buffer struct {
+	data  [bufferSize]byte
+	read  int
+	write int
+	bufferEntry
+}
+
+// Reset resets internal data.
+//
+// This must be called before use.
+func (b *Buffer) Reset() {
+	b.read = 0
+	b.write = 0
+}
+
+// Empty indicates the buffer is empty.
+//
+// This indicates there is no data left to read.
+func (b *Buffer) Empty() bool {
+	return b.read == b.write
+}
+
+// Full indicates the buffer is full.
+//
+// This indicates there is no capacity left to write.
+func (b *Buffer) Full() bool {
+	return b.write == len(b.data)
+}
+
+// bufferPool is a pool for buffers.
+var bufferPool = sync.Pool{
+	New: func() interface{} {
+		return new(Buffer)
+	},
+}
diff --git a/pkg/buffer/safemem.go b/pkg/buffer/safemem.go
new file mode 100644
index 000000000..071aaa488
--- /dev/null
+++ b/pkg/buffer/safemem.go
@@ -0,0 +1,131 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package buffer
+
+import (
+	"io"
+
+	"gvisor.dev/gvisor/pkg/safemem"
+)
+
+// WriteBlock returns this buffer as a write Block.
+func (b *Buffer) WriteBlock() safemem.Block {
+	return safemem.BlockFromSafeSlice(b.data[b.write:])
+}
+
+// ReadBlock returns this buffer as a read Block.
+func (b *Buffer) ReadBlock() safemem.Block {
+	return safemem.BlockFromSafeSlice(b.data[b.read:b.write])
+}
+
+// WriteFromBlocks implements safemem.Writer.WriteFromBlocks.
+//
+// This will advance the write index.
+func (v *View) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
+	need := int(srcs.NumBytes())
+	if need == 0 {
+		return 0, nil
+	}
+
+	var (
+		dst    safemem.BlockSeq
+		blocks []safemem.Block
+	)
+
+	// Need at least one buffer.
+	firstBuf := v.data.Back()
+	if firstBuf == nil {
+		firstBuf = bufferPool.Get().(*Buffer)
+		v.data.PushBack(firstBuf)
+	}
+
+	// Does the last block have sufficient capacity alone?
+	if l := len(firstBuf.data) - firstBuf.write; l >= need {
+		dst = safemem.BlockSeqOf(firstBuf.WriteBlock())
+	} else {
+		// Append blocks until sufficient.
+		need -= l
+		blocks = append(blocks, firstBuf.WriteBlock())
+		for need > 0 {
+			emptyBuf := bufferPool.Get().(*Buffer)
+			v.data.PushBack(emptyBuf)
+			need -= len(emptyBuf.data) // Full block.
+			blocks = append(blocks, emptyBuf.WriteBlock())
+		}
+		dst = safemem.BlockSeqFromSlice(blocks)
+	}
+
+	// Perform the copy.
+	n, err := safemem.CopySeq(dst, srcs)
+	v.size += int64(n)
+
+	// Update all indices.
+	for left := int(n); left > 0; firstBuf = firstBuf.Next() {
+		if l := len(firstBuf.data) - firstBuf.write; left >= l {
+			firstBuf.write += l // Whole block.
+			left -= l
+		} else {
+			firstBuf.write += left // Partial block.
+			left = 0
+		}
+	}
+
+	return n, err
+}
+
+// ReadToBlocks implements safemem.Reader.ReadToBlocks.
+//
+// This will not advance the read index; the caller should follow
+// this call with a call to TrimFront in order to remove the read
+// data from the buffer. This is done to support pipe sematics.
+func (v *View) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
+	need := int(dsts.NumBytes())
+	if need == 0 {
+		return 0, nil
+	}
+
+	var (
+		src    safemem.BlockSeq
+		blocks []safemem.Block
+	)
+
+	firstBuf := v.data.Front()
+	if firstBuf == nil {
+		return 0, io.EOF
+	}
+
+	// Is all the data in a single block?
+	if l := firstBuf.write - firstBuf.read; l >= need {
+		src = safemem.BlockSeqOf(firstBuf.ReadBlock())
+	} else {
+		// Build a list of all the buffers.
+		need -= l
+		blocks = append(blocks, firstBuf.ReadBlock())
+		for buf := firstBuf.Next(); buf != nil && need > 0; buf = buf.Next() {
+			need -= buf.write - buf.read
+			blocks = append(blocks, buf.ReadBlock())
+		}
+		src = safemem.BlockSeqFromSlice(blocks)
+	}
+
+	// Perform the copy.
+	n, err := safemem.CopySeq(dsts, src)
+
+	// See above: we would normally advance the read index here, but we
+	// don't do that in order to support pipe semantics. We rely on a
+	// separate call to TrimFront() in this case.
+
+	return n, err
+}
diff --git a/pkg/buffer/view.go b/pkg/buffer/view.go
new file mode 100644
index 000000000..00fc11e9c
--- /dev/null
+++ b/pkg/buffer/view.go
@@ -0,0 +1,382 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package buffer
+
+import (
+	"fmt"
+	"io"
+)
+
+// View is a non-linear buffer.
+//
+// All methods are thread compatible.
+//
+// +stateify savable
+type View struct {
+	data bufferList
+	size int64
+}
+
+// TrimFront removes the first count bytes from the buffer.
+func (v *View) TrimFront(count int64) {
+	if count >= v.size {
+		v.advanceRead(v.size)
+	} else {
+		v.advanceRead(count)
+	}
+}
+
+// Read implements io.Reader.Read.
+//
+// Note that reading does not advance the read index. This must be done
+// manually using TrimFront or other methods.
+func (v *View) Read(p []byte) (int, error) {
+	return v.ReadAt(p, 0)
+}
+
+// ReadAt implements io.ReaderAt.ReadAt.
+func (v *View) ReadAt(p []byte, offset int64) (int, error) {
+	var (
+		skipped int64
+		done    int64
+	)
+	for buf := v.data.Front(); buf != nil && done < int64(len(p)); buf = buf.Next() {
+		needToSkip := int(offset - skipped)
+		if l := buf.write - buf.read; l <= needToSkip {
+			skipped += int64(l)
+			continue
+		}
+
+		// Actually read data.
+		n := copy(p[done:], buf.data[buf.read+needToSkip:buf.write])
+		skipped += int64(needToSkip)
+		done += int64(n)
+	}
+	if int(done) < len(p) {
+		return int(done), io.EOF
+	}
+	return int(done), nil
+}
+
+// Write implements io.Writer.Write.
+func (v *View) Write(p []byte) (int, error) {
+	v.Append(p) // Does not fail.
+	return len(p), nil
+}
+
+// advanceRead advances the view's read index.
+//
+// Precondition: there must be sufficient bytes in the buffer.
+func (v *View) advanceRead(count int64) {
+	for buf := v.data.Front(); buf != nil && count > 0; {
+		l := int64(buf.write - buf.read)
+		if l > count {
+			// There is still data for reading.
+			buf.read += int(count)
+			v.size -= count
+			count = 0
+			break
+		}
+
+		// Read from this buffer.
+		buf.read += int(l)
+		count -= l
+		v.size -= l
+
+		// When all data has been read from a buffer, we push
+		// it into the empty buffer pool for reuse.
+		oldBuf := buf
+		buf = buf.Next() // Iterate.
+		v.data.Remove(oldBuf)
+		oldBuf.Reset()
+		bufferPool.Put(oldBuf)
+	}
+	if count > 0 {
+		panic(fmt.Sprintf("advanceRead still has %d bytes remaining", count))
+	}
+}
+
+// Truncate truncates the view to the given bytes.
+func (v *View) Truncate(length int64) {
+	if length < 0 || length >= v.size {
+		return // Nothing to do.
+	}
+	for buf := v.data.Back(); buf != nil && v.size > length; buf = v.data.Back() {
+		l := int64(buf.write - buf.read) // Local bytes.
+		switch {
+		case v.size-l >= length:
+			// Drop the buffer completely; see above.
+			v.data.Remove(buf)
+			v.size -= l
+			buf.Reset()
+			bufferPool.Put(buf)
+
+		case v.size > length && v.size-l < length:
+			// Just truncate the buffer locally.
+			delta := (length - (v.size - l))
+			buf.write = buf.read + int(delta)
+			v.size = length
+
+		default:
+			// Should never happen.
+			panic("invalid buffer during truncation")
+		}
+	}
+	v.size = length // Save the new size.
+}
+
+// Grow grows the given view to the number of bytes. If zero
+// is true, all these bytes will be zero. If zero is false,
+// then this is the caller's responsibility.
+//
+// Precondition: length must be >= 0.
+func (v *View) Grow(length int64, zero bool) {
+	if length < 0 {
+		panic("negative length provided")
+	}
+	for v.size < length {
+		buf := v.data.Back()
+
+		// Is there at least one buffer?
+		if buf == nil || buf.Full() {
+			buf = bufferPool.Get().(*Buffer)
+			v.data.PushBack(buf)
+		}
+
+		// Write up to length bytes.
+		l := len(buf.data) - buf.write
+		if int64(l) > length-v.size {
+			l = int(length - v.size)
+		}
+
+		// Zero the written section; note that this pattern is
+		// specifically recognized and optimized by the compiler.
+		if zero {
+			for i := buf.write; i < buf.write+l; i++ {
+				buf.data[i] = 0
+			}
+		}
+
+		// Advance the index.
+		buf.write += l
+		v.size += int64(l)
+	}
+}
+
+// Prepend prepends the given data.
+func (v *View) Prepend(data []byte) {
+	// Is there any space in the first buffer?
+	if buf := v.data.Front(); buf != nil && buf.read > 0 {
+		// Fill up before the first write.
+		avail := buf.read
+		copy(buf.data[0:], data[len(data)-avail:])
+		data = data[:len(data)-avail]
+		v.size += int64(avail)
+	}
+
+	for len(data) > 0 {
+		// Do we need an empty buffer?
+		buf := bufferPool.Get().(*Buffer)
+		v.data.PushFront(buf)
+
+		// The buffer is empty; copy last chunk.
+		start := len(data) - len(buf.data)
+		if start < 0 {
+			start = 0 // Everything.
+		}
+
+		// We have to put the data at the end of the current
+		// buffer in order to ensure that the next prepend will
+		// correctly fill up the beginning of this buffer.
+		bStart := len(buf.data) - len(data[start:])
+		n := copy(buf.data[bStart:], data[start:])
+		buf.read = bStart
+		buf.write = len(buf.data)
+		data = data[:start]
+		v.size += int64(n)
+	}
+}
+
+// Append appends the given data.
+func (v *View) Append(data []byte) {
+	for done := 0; done < len(data); {
+		buf := v.data.Back()
+
+		// Find the first empty buffer.
+		if buf == nil || buf.Full() {
+			buf = bufferPool.Get().(*Buffer)
+			v.data.PushBack(buf)
+		}
+
+		// Copy in to the given buffer.
+		n := copy(buf.data[buf.write:], data[done:])
+		done += n
+		buf.write += n
+		v.size += int64(n)
+	}
+}
+
+// Flatten returns a flattened copy of this data.
+//
+// This method should not be used in any performance-sensitive paths. It may
+// allocate a fresh byte slice sufficiently large to contain all the data in
+// the buffer.
+//
+// N.B. Tee data still belongs to this view, as if there is a single buffer
+// present, then it will be returned directly. This should be used for
+// temporary use only, and a reference to the given slice should not be held.
+func (v *View) Flatten() []byte {
+	if buf := v.data.Front(); buf.Next() == nil {
+		return buf.data[buf.read:buf.write] // Only one buffer.
+	}
+	data := make([]byte, 0, v.size) // Need to flatten.
+	for buf := v.data.Front(); buf != nil; buf = buf.Next() {
+		// Copy to the allocated slice.
+		data = append(data, buf.data[buf.read:buf.write]...)
+	}
+	return data
+}
+
+// Size indicates the total amount of data available in this view.
+func (v *View) Size() (sz int64) {
+	sz = v.size // Pre-calculated.
+	return sz
+}
+
+// Copy makes a strict copy of this view.
+func (v *View) Copy() (other View) {
+	for buf := v.data.Front(); buf != nil; buf = buf.Next() {
+		other.Append(buf.data[buf.read:buf.write])
+	}
+	return other
+}
+
+// Apply applies the given function across all valid data.
+func (v *View) Apply(fn func([]byte)) {
+	for buf := v.data.Front(); buf != nil; buf = buf.Next() {
+		if l := int64(buf.write - buf.read); l > 0 {
+			fn(buf.data[buf.read:buf.write])
+		}
+	}
+}
+
+// Merge merges the provided View with this one.
+//
+// The other view will be empty after this operation.
+func (v *View) Merge(other *View) {
+	// Copy over all buffers.
+	for buf := other.data.Front(); buf != nil && !buf.Empty(); buf = other.data.Front() {
+		other.data.Remove(buf)
+		v.data.PushBack(buf)
+	}
+
+	// Adjust sizes.
+	v.size += other.size
+	other.size = 0
+}
+
+// WriteFromReader writes to the buffer from an io.Reader.
+func (v *View) WriteFromReader(r io.Reader, count int64) (int64, error) {
+	var (
+		done int64
+		n    int
+		err  error
+	)
+	for done < count {
+		buf := v.data.Back()
+
+		// Find the first empty buffer.
+		if buf == nil || buf.Full() {
+			buf = bufferPool.Get().(*Buffer)
+			v.data.PushBack(buf)
+		}
+
+		// Is this less than the minimum batch?
+		if len(buf.data[buf.write:]) < minBatch && (count-done) >= int64(minBatch) {
+			tmp := make([]byte, minBatch)
+			n, err = r.Read(tmp)
+			v.Write(tmp[:n])
+			done += int64(n)
+			if err != nil {
+				break
+			}
+			continue
+		}
+
+		// Limit the read, if necessary.
+		end := len(buf.data)
+		if int64(end-buf.write) > (count - done) {
+			end = buf.write + int(count-done)
+		}
+
+		// Pass the relevant portion of the buffer.
+		n, err = r.Read(buf.data[buf.write:end])
+		buf.write += n
+		done += int64(n)
+		v.size += int64(n)
+		if err == io.EOF {
+			err = nil // Short write allowed.
+			break
+		} else if err != nil {
+			break
+		}
+	}
+	return done, err
+}
+
+// ReadToWriter reads from the buffer into an io.Writer.
+//
+// N.B. This does not consume the bytes read. TrimFront should
+// be called appropriately after this call in order to do so.
+func (v *View) ReadToWriter(w io.Writer, count int64) (int64, error) {
+	var (
+		done int64
+		n    int
+		err  error
+	)
+	offset := 0 // Spill-over for batching.
+	for buf := v.data.Front(); buf != nil && done < count; buf = buf.Next() {
+		l := buf.write - buf.read - offset
+
+		// Is this less than the minimum batch?
+		if l < minBatch && (count-done) >= int64(minBatch) && (v.size-done) >= int64(minBatch) {
+			tmp := make([]byte, minBatch)
+			n, err = v.ReadAt(tmp, done)
+			w.Write(tmp[:n])
+			done += int64(n)
+			offset = n - l // Reset below.
+			if err != nil {
+				break
+			}
+			continue
+		}
+
+		// Limit the write if necessary.
+		if int64(l) >= (count - done) {
+			l = int(count - done)
+		}
+
+		// Perform the actual write.
+		n, err = w.Write(buf.data[buf.read+offset : buf.read+offset+l])
+		done += int64(n)
+		if err != nil {
+			break
+		}
+
+		// Reset spill-over.
+		offset = 0
+	}
+	return done, err
+}
diff --git a/pkg/buffer/view_test.go b/pkg/buffer/view_test.go
new file mode 100644
index 000000000..37e652f16
--- /dev/null
+++ b/pkg/buffer/view_test.go
@@ -0,0 +1,233 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package buffer
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+func TestView(t *testing.T) {
+	testCases := []struct {
+		name   string
+		input  string
+		output string
+		ops    []func(*View)
+	}{
+		// Prepend.
+		{
+			name:  "prepend",
+			input: "world",
+			ops: []func(*View){
+				func(v *View) {
+					v.Prepend([]byte("hello "))
+				},
+			},
+			output: "hello world",
+		},
+		{
+			name:  "prepend fill",
+			input: strings.Repeat("1", bufferSize-1),
+			ops: []func(*View){
+				func(v *View) {
+					v.Prepend([]byte("0"))
+				},
+			},
+			output: "0" + strings.Repeat("1", bufferSize-1),
+		},
+		{
+			name:  "prepend overflow",
+			input: strings.Repeat("1", bufferSize),
+			ops: []func(*View){
+				func(v *View) {
+					v.Prepend([]byte("0"))
+				},
+			},
+			output: "0" + strings.Repeat("1", bufferSize),
+		},
+		{
+			name:  "prepend multiple buffers",
+			input: strings.Repeat("1", bufferSize-1),
+			ops: []func(*View){
+				func(v *View) {
+					v.Prepend([]byte(strings.Repeat("0", bufferSize*3)))
+				},
+			},
+			output: strings.Repeat("0", bufferSize*3) + strings.Repeat("1", bufferSize-1),
+		},
+
+		// Append.
+		{
+			name:  "append",
+			input: "hello",
+			ops: []func(*View){
+				func(v *View) {
+					v.Append([]byte(" world"))
+				},
+			},
+			output: "hello world",
+		},
+		{
+			name:  "append fill",
+			input: strings.Repeat("1", bufferSize-1),
+			ops: []func(*View){
+				func(v *View) {
+					v.Append([]byte("0"))
+				},
+			},
+			output: strings.Repeat("1", bufferSize-1) + "0",
+		},
+		{
+			name:  "append overflow",
+			input: strings.Repeat("1", bufferSize),
+			ops: []func(*View){
+				func(v *View) {
+					v.Append([]byte("0"))
+				},
+			},
+			output: strings.Repeat("1", bufferSize) + "0",
+		},
+		{
+			name:  "append multiple buffers",
+			input: strings.Repeat("1", bufferSize-1),
+			ops: []func(*View){
+				func(v *View) {
+					v.Append([]byte(strings.Repeat("0", bufferSize*3)))
+				},
+			},
+			output: strings.Repeat("1", bufferSize-1) + strings.Repeat("0", bufferSize*3),
+		},
+
+		// Truncate.
+		{
+			name:  "truncate",
+			input: "hello world",
+			ops: []func(*View){
+				func(v *View) {
+					v.Truncate(5)
+				},
+			},
+			output: "hello",
+		},
+		{
+			name:  "truncate multiple buffers",
+			input: strings.Repeat("1", bufferSize*2),
+			ops: []func(*View){
+				func(v *View) {
+					v.Truncate(bufferSize*2 - 1)
+				},
+			},
+			output: strings.Repeat("1", bufferSize*2-1),
+		},
+		{
+			name:  "truncate multiple buffers to one buffer",
+			input: strings.Repeat("1", bufferSize*2),
+			ops: []func(*View){
+				func(v *View) {
+					v.Truncate(5)
+				},
+			},
+			output: "11111",
+		},
+
+		// TrimFront.
+		{
+			name:  "trim",
+			input: "hello world",
+			ops: []func(*View){
+				func(v *View) {
+					v.TrimFront(6)
+				},
+			},
+			output: "world",
+		},
+		{
+			name:  "trim multiple buffers",
+			input: strings.Repeat("1", bufferSize*2),
+			ops: []func(*View){
+				func(v *View) {
+					v.TrimFront(1)
+				},
+			},
+			output: strings.Repeat("1", bufferSize*2-1),
+		},
+		{
+			name:  "trim multiple buffers to one buffer",
+			input: strings.Repeat("1", bufferSize*2),
+			ops: []func(*View){
+				func(v *View) {
+					v.TrimFront(bufferSize*2 - 1)
+				},
+			},
+			output: "1",
+		},
+
+		// Grow.
+		{
+			name:  "grow",
+			input: "hello world",
+			ops: []func(*View){
+				func(v *View) {
+					v.Grow(1, true)
+				},
+			},
+			output: "hello world",
+		},
+		{
+			name: "grow from zero",
+			ops: []func(*View){
+				func(v *View) {
+					v.Grow(1024, true)
+				},
+			},
+			output: strings.Repeat("\x00", 1024),
+		},
+		{
+			name:  "grow from non-zero",
+			input: strings.Repeat("1", bufferSize),
+			ops: []func(*View){
+				func(v *View) {
+					v.Grow(bufferSize*2, true)
+				},
+			},
+			output: strings.Repeat("1", bufferSize) + strings.Repeat("\x00", bufferSize),
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			// Construct the new view.
+			var view View
+			view.Append([]byte(tc.input))
+
+			// Run all operations.
+			for _, op := range tc.ops {
+				op(&view)
+			}
+
+			// Flatten and validate.
+			out := view.Flatten()
+			if !bytes.Equal([]byte(tc.output), out) {
+				t.Errorf("expected %q, got %q", tc.output, string(out))
+			}
+
+			// Ensure the size is correct.
+			if len(out) != int(view.Size()) {
+				t.Errorf("size is wrong: expected %d, got %d", len(out), view.Size())
+			}
+		})
+	}
+}
diff --git a/pkg/buffer/view_unsafe.go b/pkg/buffer/view_unsafe.go
new file mode 100644
index 000000000..d1ef39b26
--- /dev/null
+++ b/pkg/buffer/view_unsafe.go
@@ -0,0 +1,25 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package buffer
+
+import (
+	"unsafe"
+)
+
+// minBatch is the smallest Read or Write operation that the
+// WriteFromReader and ReadToWriter functions will use.
+//
+// This is defined as the size of a native pointer.
+const minBatch = int(unsafe.Sizeof(uintptr(0)))