Merge release-20200219.0-69-g463f421 (automated)

6 files changed, 848 insertions, 0 deletions

diff --git a/pkg/buffer/buffer.go b/pkg/buffer/buffer.go
new file mode 100755
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/buffer_list.go b/pkg/buffer/buffer_list.go
new file mode 100755
index 000000000..f3c27c42c
--- /dev/null
+++ b/pkg/buffer/buffer_list.go
@@ -0,0 +1,173 @@
+package buffer
+
+// ElementMapper provides an identity mapping by default.
+//
+// This can be replaced to provide a struct that maps elements to linker
+// objects, if they are not the same. An ElementMapper is not typically
+// required if: Linker is left as is, Element is left as is, or Linker and
+// Element are the same type.
+type bufferElementMapper struct{}
+
+// linkerFor maps an Element to a Linker.
+//
+// This default implementation should be inlined.
+//
+//go:nosplit
+func (bufferElementMapper) linkerFor(elem *Buffer) *Buffer { return elem }
+
+// List is an intrusive list. Entries can be added to or removed from the list
+// in O(1) time and with no additional memory allocations.
+//
+// The zero value for List is an empty list ready to use.
+//
+// To iterate over a list (where l is a List):
+//      for e := l.Front(); e != nil; e = e.Next() {
+// 		// do something with e.
+//      }
+//
+// +stateify savable
+type bufferList struct {
+	head *Buffer
+	tail *Buffer
+}
+
+// Reset resets list l to the empty state.
+func (l *bufferList) Reset() {
+	l.head = nil
+	l.tail = nil
+}
+
+// Empty returns true iff the list is empty.
+func (l *bufferList) Empty() bool {
+	return l.head == nil
+}
+
+// Front returns the first element of list l or nil.
+func (l *bufferList) Front() *Buffer {
+	return l.head
+}
+
+// Back returns the last element of list l or nil.
+func (l *bufferList) Back() *Buffer {
+	return l.tail
+}
+
+// PushFront inserts the element e at the front of list l.
+func (l *bufferList) PushFront(e *Buffer) {
+	bufferElementMapper{}.linkerFor(e).SetNext(l.head)
+	bufferElementMapper{}.linkerFor(e).SetPrev(nil)
+
+	if l.head != nil {
+		bufferElementMapper{}.linkerFor(l.head).SetPrev(e)
+	} else {
+		l.tail = e
+	}
+
+	l.head = e
+}
+
+// PushBack inserts the element e at the back of list l.
+func (l *bufferList) PushBack(e *Buffer) {
+	bufferElementMapper{}.linkerFor(e).SetNext(nil)
+	bufferElementMapper{}.linkerFor(e).SetPrev(l.tail)
+
+	if l.tail != nil {
+		bufferElementMapper{}.linkerFor(l.tail).SetNext(e)
+	} else {
+		l.head = e
+	}
+
+	l.tail = e
+}
+
+// PushBackList inserts list m at the end of list l, emptying m.
+func (l *bufferList) PushBackList(m *bufferList) {
+	if l.head == nil {
+		l.head = m.head
+		l.tail = m.tail
+	} else if m.head != nil {
+		bufferElementMapper{}.linkerFor(l.tail).SetNext(m.head)
+		bufferElementMapper{}.linkerFor(m.head).SetPrev(l.tail)
+
+		l.tail = m.tail
+	}
+
+	m.head = nil
+	m.tail = nil
+}
+
+// InsertAfter inserts e after b.
+func (l *bufferList) InsertAfter(b, e *Buffer) {
+	a := bufferElementMapper{}.linkerFor(b).Next()
+	bufferElementMapper{}.linkerFor(e).SetNext(a)
+	bufferElementMapper{}.linkerFor(e).SetPrev(b)
+	bufferElementMapper{}.linkerFor(b).SetNext(e)
+
+	if a != nil {
+		bufferElementMapper{}.linkerFor(a).SetPrev(e)
+	} else {
+		l.tail = e
+	}
+}
+
+// InsertBefore inserts e before a.
+func (l *bufferList) InsertBefore(a, e *Buffer) {
+	b := bufferElementMapper{}.linkerFor(a).Prev()
+	bufferElementMapper{}.linkerFor(e).SetNext(a)
+	bufferElementMapper{}.linkerFor(e).SetPrev(b)
+	bufferElementMapper{}.linkerFor(a).SetPrev(e)
+
+	if b != nil {
+		bufferElementMapper{}.linkerFor(b).SetNext(e)
+	} else {
+		l.head = e
+	}
+}
+
+// Remove removes e from l.
+func (l *bufferList) Remove(e *Buffer) {
+	prev := bufferElementMapper{}.linkerFor(e).Prev()
+	next := bufferElementMapper{}.linkerFor(e).Next()
+
+	if prev != nil {
+		bufferElementMapper{}.linkerFor(prev).SetNext(next)
+	} else {
+		l.head = next
+	}
+
+	if next != nil {
+		bufferElementMapper{}.linkerFor(next).SetPrev(prev)
+	} else {
+		l.tail = prev
+	}
+}
+
+// Entry is a default implementation of Linker. Users can add anonymous fields
+// of this type to their structs to make them automatically implement the
+// methods needed by List.
+//
+// +stateify savable
+type bufferEntry struct {
+	next *Buffer
+	prev *Buffer
+}
+
+// Next returns the entry that follows e in the list.
+func (e *bufferEntry) Next() *Buffer {
+	return e.next
+}
+
+// Prev returns the entry that precedes e in the list.
+func (e *bufferEntry) Prev() *Buffer {
+	return e.prev
+}
+
+// SetNext assigns 'entry' as the entry that follows e in the list.
+func (e *bufferEntry) SetNext(elem *Buffer) {
+	e.next = elem
+}
+
+// SetPrev assigns 'entry' as the entry that precedes e in the list.
+func (e *bufferEntry) SetPrev(elem *Buffer) {
+	e.prev = elem
+}
diff --git a/pkg/buffer/buffer_state_autogen.go b/pkg/buffer/buffer_state_autogen.go
new file mode 100755
index 000000000..9565eb6fa
--- /dev/null
+++ b/pkg/buffer/buffer_state_autogen.go
@@ -0,0 +1,70 @@
+// automatically generated by stateify.
+
+package buffer
+
+import (
+	"gvisor.dev/gvisor/pkg/state"
+)
+
+func (x *Buffer) beforeSave() {}
+func (x *Buffer) save(m state.Map) {
+	x.beforeSave()
+	m.Save("data", &x.data)
+	m.Save("read", &x.read)
+	m.Save("write", &x.write)
+	m.Save("bufferEntry", &x.bufferEntry)
+}
+
+func (x *Buffer) afterLoad() {}
+func (x *Buffer) load(m state.Map) {
+	m.Load("data", &x.data)
+	m.Load("read", &x.read)
+	m.Load("write", &x.write)
+	m.Load("bufferEntry", &x.bufferEntry)
+}
+
+func (x *bufferList) beforeSave() {}
+func (x *bufferList) save(m state.Map) {
+	x.beforeSave()
+	m.Save("head", &x.head)
+	m.Save("tail", &x.tail)
+}
+
+func (x *bufferList) afterLoad() {}
+func (x *bufferList) load(m state.Map) {
+	m.Load("head", &x.head)
+	m.Load("tail", &x.tail)
+}
+
+func (x *bufferEntry) beforeSave() {}
+func (x *bufferEntry) save(m state.Map) {
+	x.beforeSave()
+	m.Save("next", &x.next)
+	m.Save("prev", &x.prev)
+}
+
+func (x *bufferEntry) afterLoad() {}
+func (x *bufferEntry) load(m state.Map) {
+	m.Load("next", &x.next)
+	m.Load("prev", &x.prev)
+}
+
+func (x *View) beforeSave() {}
+func (x *View) save(m state.Map) {
+	x.beforeSave()
+	m.Save("data", &x.data)
+	m.Save("size", &x.size)
+}
+
+func (x *View) afterLoad() {}
+func (x *View) load(m state.Map) {
+	m.Load("data", &x.data)
+	m.Load("size", &x.size)
+}
+
+func init() {
+	state.Register("pkg/buffer.Buffer", (*Buffer)(nil), state.Fns{Save: (*Buffer).save, Load: (*Buffer).load})
+	state.Register("pkg/buffer.bufferList", (*bufferList)(nil), state.Fns{Save: (*bufferList).save, Load: (*bufferList).load})
+	state.Register("pkg/buffer.bufferEntry", (*bufferEntry)(nil), state.Fns{Save: (*bufferEntry).save, Load: (*bufferEntry).load})
+	state.Register("pkg/buffer.View", (*View)(nil), state.Fns{Save: (*View).save, Load: (*View).load})
+}
diff --git a/pkg/buffer/safemem.go b/pkg/buffer/safemem.go
new file mode 100755
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 100755
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_unsafe.go b/pkg/buffer/view_unsafe.go
new file mode 100755
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)))