Make pipe buffer implementation standard.

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

PiperOrigin-RevId: 297903206

5 files changed, 35 insertions, 273 deletions

diff --git a/pkg/sentry/kernel/pipe/BUILD b/pkg/sentry/kernel/pipe/BUILD
index 4c049d5b4..f29dc0472 100644
--- a/pkg/sentry/kernel/pipe/BUILD
+++ b/pkg/sentry/kernel/pipe/BUILD
@@ -1,25 +1,10 @@
 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 = "pipe",
-    prefix = "buffer",
-    template = "//pkg/ilist:generic_list",
-    types = {
-        "Element": "*buffer",
-        "Linker": "*buffer",
-    },
-)
-
 go_library(
     name = "pipe",
     srcs = [
-        "buffer.go",
-        "buffer_list.go",
         "device.go",
         "node.go",
         "pipe.go",
@@ -33,8 +18,8 @@ go_library(
     deps = [
         "//pkg/abi/linux",
         "//pkg/amutex",
+        "//pkg/buffer",
         "//pkg/context",
-        "//pkg/safemem",
         "//pkg/sentry/arch",
         "//pkg/sentry/device",
         "//pkg/sentry/fs",
@@ -51,7 +36,6 @@ go_test(
     name = "pipe_test",
     size = "small",
     srcs = [
-        "buffer_test.go",
         "node_test.go",
         "pipe_test.go",
     ],
diff --git a/pkg/sentry/kernel/pipe/buffer.go b/pkg/sentry/kernel/pipe/buffer.go
deleted file mode 100644
index fe3be5dbd..000000000
--- a/pkg/sentry/kernel/pipe/buffer.go
+++ /dev/null
@@ -1,115 +0,0 @@
-// Copyright 2018 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 pipe
-
-import (
-	"io"
-
-	"gvisor.dev/gvisor/pkg/safemem"
-	"gvisor.dev/gvisor/pkg/sync"
-)
-
-// 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  [8144]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)
-}
-
-// WriteFromBlocks implements safemem.Writer.WriteFromBlocks.
-func (b *buffer) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
-	dst := safemem.BlockSeqOf(safemem.BlockFromSafeSlice(b.data[b.write:]))
-	n, err := safemem.CopySeq(dst, srcs)
-	b.write += int(n)
-	return n, err
-}
-
-// WriteFromReader writes to the buffer from an io.Reader.
-func (b *buffer) WriteFromReader(r io.Reader, count int64) (int64, error) {
-	dst := b.data[b.write:]
-	if count < int64(len(dst)) {
-		dst = b.data[b.write:][:count]
-	}
-	n, err := r.Read(dst)
-	b.write += n
-	return int64(n), err
-}
-
-// ReadToBlocks implements safemem.Reader.ReadToBlocks.
-func (b *buffer) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
-	src := safemem.BlockSeqOf(safemem.BlockFromSafeSlice(b.data[b.read:b.write]))
-	n, err := safemem.CopySeq(dsts, src)
-	b.read += int(n)
-	return n, err
-}
-
-// ReadToWriter reads from the buffer into an io.Writer.
-func (b *buffer) ReadToWriter(w io.Writer, count int64, dup bool) (int64, error) {
-	src := b.data[b.read:b.write]
-	if count < int64(len(src)) {
-		src = b.data[b.read:][:count]
-	}
-	n, err := w.Write(src)
-	if !dup {
-		b.read += n
-	}
-	return int64(n), err
-}
-
-// bufferPool is a pool for buffers.
-var bufferPool = sync.Pool{
-	New: func() interface{} {
-		return new(buffer)
-	},
-}
-
-// newBuffer grabs a new buffer from the pool.
-func newBuffer() *buffer {
-	b := bufferPool.Get().(*buffer)
-	b.Reset()
-	return b
-}
diff --git a/pkg/sentry/kernel/pipe/buffer_test.go b/pkg/sentry/kernel/pipe/buffer_test.go
deleted file mode 100644
index 4d54b8b8f..000000000
--- a/pkg/sentry/kernel/pipe/buffer_test.go
+++ /dev/null
@@ -1,32 +0,0 @@
-// Copyright 2019 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 pipe
-
-import (
-	"testing"
-	"unsafe"
-
-	"gvisor.dev/gvisor/pkg/usermem"
-)
-
-func TestBufferSize(t *testing.T) {
-	bufferSize := unsafe.Sizeof(buffer{})
-	if bufferSize < usermem.PageSize {
-		t.Errorf("buffer is less than a page")
-	}
-	if bufferSize > (2 * usermem.PageSize) {
-		t.Errorf("buffer is greater than two pages")
-	}
-}
diff --git a/pkg/sentry/kernel/pipe/pipe.go b/pkg/sentry/kernel/pipe/pipe.go
index 08410283f..725e9db7d 100644
--- a/pkg/sentry/kernel/pipe/pipe.go
+++ b/pkg/sentry/kernel/pipe/pipe.go
@@ -20,6 +20,7 @@ import (
 	"sync/atomic"
 	"syscall"
 
+	"gvisor.dev/gvisor/pkg/buffer"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sync"
@@ -70,10 +71,10 @@ type Pipe struct {
 	// mu protects all pipe internal state below.
 	mu sync.Mutex `state:"nosave"`
 
-	// data is the buffer queue of pipe contents.
+	// view is the underlying set of buffers.
 	//
 	// This is protected by mu.
-	data bufferList
+	view buffer.View
 
 	// max is the maximum size of the pipe in bytes. When this max has been
 	// reached, writers will get EWOULDBLOCK.
@@ -81,11 +82,6 @@ type Pipe struct {
 	// This is protected by mu.
 	max int64
 
-	// size is the current size of the pipe in bytes.
-	//
-	// This is protected by mu.
-	size int64
-
 	// hadWriter indicates if this pipe ever had a writer. Note that this
 	// does not necessarily indicate there is *currently* a writer, just
 	// that there has been a writer at some point since the pipe was
@@ -196,7 +192,7 @@ type readOps struct {
 	limit func(int64)
 
 	// read performs the actual read operation.
-	read func(*buffer) (int64, error)
+	read func(*buffer.View) (int64, error)
 }
 
 // read reads data from the pipe into dst and returns the number of bytes
@@ -213,7 +209,7 @@ func (p *Pipe) read(ctx context.Context, ops readOps) (int64, error) {
 	defer p.mu.Unlock()
 
 	// Is the pipe empty?
-	if p.size == 0 {
+	if p.view.Size() == 0 {
 		if !p.HasWriters() {
 			// There are no writers, return EOF.
 			return 0, nil
@@ -222,71 +218,13 @@ func (p *Pipe) read(ctx context.Context, ops readOps) (int64, error) {
 	}
 
 	// Limit how much we consume.
-	if ops.left() > p.size {
-		ops.limit(p.size)
+	if ops.left() > p.view.Size() {
+		ops.limit(p.view.Size())
 	}
 
-	done := int64(0)
-	for ops.left() > 0 {
-		// Pop the first buffer.
-		first := p.data.Front()
-		if first == nil {
-			break
-		}
-
-		// Copy user data.
-		n, err := ops.read(first)
-		done += int64(n)
-		p.size -= n
-
-		// Empty buffer?
-		if first.Empty() {
-			// Push to the free list.
-			p.data.Remove(first)
-			bufferPool.Put(first)
-		}
-
-		// Handle errors.
-		if err != nil {
-			return done, err
-		}
-	}
-
-	return done, nil
-}
-
-// dup duplicates all data from this pipe into the given writer.
-//
-// There is no blocking behavior implemented here. The writer may propagate
-// some blocking error. All the writes must be complete writes.
-func (p *Pipe) dup(ctx context.Context, ops readOps) (int64, error) {
-	p.mu.Lock()
-	defer p.mu.Unlock()
-
-	// Is the pipe empty?
-	if p.size == 0 {
-		if !p.HasWriters() {
-			// See above.
-			return 0, nil
-		}
-		return 0, syserror.ErrWouldBlock
-	}
-
-	// Limit how much we consume.
-	if ops.left() > p.size {
-		ops.limit(p.size)
-	}
-
-	done := int64(0)
-	for buf := p.data.Front(); buf != nil; buf = buf.Next() {
-		n, err := ops.read(buf)
-		done += n
-		if err != nil {
-			return done, err
-		}
-	}
-
-	return done, nil
+	// Copy user data; the read op is responsible for trimming.
+	done, err := ops.read(&p.view)
+	return done, err
 }
 
 type writeOps struct {
@@ -297,7 +235,7 @@ type writeOps struct {
 	limit func(int64)
 
 	// write should write to the provided buffer.
-	write func(*buffer) (int64, error)
+	write func(*buffer.View) (int64, error)
 }
 
 // write writes data from sv into the pipe and returns the number of bytes
@@ -317,33 +255,19 @@ func (p *Pipe) write(ctx context.Context, ops writeOps) (int64, error) {
 	// POSIX requires that a write smaller than atomicIOBytes (PIPE_BUF) be
 	// atomic, but requires no atomicity for writes larger than this.
 	wanted := ops.left()
-	if avail := p.max - p.size; wanted > avail {
+	if avail := p.max - p.view.Size(); wanted > avail {
 		if wanted <= p.atomicIOBytes {
 			return 0, syserror.ErrWouldBlock
 		}
 		ops.limit(avail)
 	}
 
-	done := int64(0)
-	for ops.left() > 0 {
-		// Need a new buffer?
-		last := p.data.Back()
-		if last == nil || last.Full() {
-			// Add a new buffer to the data list.
-			last = newBuffer()
-			p.data.PushBack(last)
-		}
-
-		// Copy user data.
-		n, err := ops.write(last)
-		done += int64(n)
-		p.size += n
-
-		// Handle errors.
-		if err != nil {
-			return done, err
-		}
+	// Copy user data.
+	done, err := ops.write(&p.view)
+	if err != nil {
+		return done, err
 	}
+
 	if wanted > done {
 		// Partial write due to full pipe.
 		return done, syserror.ErrWouldBlock
@@ -396,7 +320,7 @@ func (p *Pipe) HasWriters() bool {
 // Precondition: mu must be held.
 func (p *Pipe) rReadinessLocked() waiter.EventMask {
 	ready := waiter.EventMask(0)
-	if p.HasReaders() && p.data.Front() != nil {
+	if p.HasReaders() && p.view.Size() != 0 {
 		ready |= waiter.EventIn
 	}
 	if !p.HasWriters() && p.hadWriter {
@@ -422,7 +346,7 @@ func (p *Pipe) rReadiness() waiter.EventMask {
 // Precondition: mu must be held.
 func (p *Pipe) wReadinessLocked() waiter.EventMask {
 	ready := waiter.EventMask(0)
-	if p.HasWriters() && p.size < p.max {
+	if p.HasWriters() && p.view.Size() < p.max {
 		ready |= waiter.EventOut
 	}
 	if !p.HasReaders() {
@@ -451,7 +375,7 @@ func (p *Pipe) rwReadiness() waiter.EventMask {
 func (p *Pipe) queued() int64 {
 	p.mu.Lock()
 	defer p.mu.Unlock()
-	return p.size
+	return p.view.Size()
 }
 
 // FifoSize implements fs.FifoSizer.FifoSize.
@@ -474,7 +398,7 @@ func (p *Pipe) SetFifoSize(size int64) (int64, error) {
 	}
 	p.mu.Lock()
 	defer p.mu.Unlock()
-	if size < p.size {
+	if size < p.view.Size() {
 		return 0, syserror.EBUSY
 	}
 	p.max = size
diff --git a/pkg/sentry/kernel/pipe/pipe_util.go b/pkg/sentry/kernel/pipe/pipe_util.go
index 80158239e..5a1d4fd57 100644
--- a/pkg/sentry/kernel/pipe/pipe_util.go
+++ b/pkg/sentry/kernel/pipe/pipe_util.go
@@ -21,6 +21,7 @@ import (
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/amutex"
+	"gvisor.dev/gvisor/pkg/buffer"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
 	"gvisor.dev/gvisor/pkg/sync"
@@ -49,9 +50,10 @@ func (p *Pipe) Read(ctx context.Context, dst usermem.IOSequence) (int64, error)
 		limit: func(l int64) {
 			dst = dst.TakeFirst64(l)
 		},
-		read: func(buf *buffer) (int64, error) {
-			n, err := dst.CopyOutFrom(ctx, buf)
+		read: func(view *buffer.View) (int64, error) {
+			n, err := dst.CopyOutFrom(ctx, view)
 			dst = dst.DropFirst64(n)
+			view.TrimFront(n)
 			return n, err
 		},
 	})
@@ -70,16 +72,15 @@ func (p *Pipe) WriteTo(ctx context.Context, w io.Writer, count int64, dup bool)
 		limit: func(l int64) {
 			count = l
 		},
-		read: func(buf *buffer) (int64, error) {
-			n, err := buf.ReadToWriter(w, count, dup)
+		read: func(view *buffer.View) (int64, error) {
+			n, err := view.ReadToWriter(w, count)
+			if !dup {
+				view.TrimFront(n)
+			}
 			count -= n
 			return n, err
 		},
 	}
-	if dup {
-		// There is no notification for dup operations.
-		return p.dup(ctx, ops)
-	}
 	n, err := p.read(ctx, ops)
 	if n > 0 {
 		p.Notify(waiter.EventOut)
@@ -96,8 +97,8 @@ func (p *Pipe) Write(ctx context.Context, src usermem.IOSequence) (int64, error)
 		limit: func(l int64) {
 			src = src.TakeFirst64(l)
 		},
-		write: func(buf *buffer) (int64, error) {
-			n, err := src.CopyInTo(ctx, buf)
+		write: func(view *buffer.View) (int64, error) {
+			n, err := src.CopyInTo(ctx, view)
 			src = src.DropFirst64(n)
 			return n, err
 		},
@@ -117,8 +118,8 @@ func (p *Pipe) ReadFrom(ctx context.Context, r io.Reader, count int64) (int64, e
 		limit: func(l int64) {
 			count = l
 		},
-		write: func(buf *buffer) (int64, error) {
-			n, err := buf.WriteFromReader(r, count)
+		write: func(view *buffer.View) (int64, error) {
+			n, err := view.WriteFromReader(r, count)
 			count -= n
 			return n, err
 		},