Track handed out buffers explicitly.

This makes sure we never take ownership of read only data from a file
system.

examplelib/passthrough.go

@@ -159,7 +159,7 @@ type PassThroughFile struct {
 }
 
 func (self *PassThroughFile) Read(input *fuse.ReadIn, buffers *fuse.BufferPool) ([]byte, fuse.Status) {
-	slice := buffers.GetBuffer(input.Size)
+	slice := buffers.AllocBuffer(input.Size)
 
 	n, err := self.file.ReadAt(slice, int64(input.Offset))
 	if err == os.EOF {

examplelib/zipfs.go

@@ -73,7 +73,7 @@ func (me *ZipDirTree) FindDir(name string) *ZipDirTree {
 type ZipFileFuse struct {
 	zipReader *zip.Reader
 	tree      *ZipDirTree
-	
+
 	fuse.DefaultPathFilesystem
 }
 
@@ -204,7 +204,6 @@ func (self *ZipFile) Read(input *fuse.ReadIn, bp *fuse.BufferPool) ([]byte, fuse
 		end = len(self.data)
 	}
 
-	// TODO - robustify bufferpool
 	return self.data[input.Offset:end], fuse.OK
 }
 

fuse/bufferpool.go

@@ -3,6 +3,7 @@ package fuse
 import (
 	"sync"
 	"fmt"
+	"unsafe"
 )
 
 // This implements a pool of buffers that returns slices with capacity
@@ -13,6 +14,9 @@ type BufferPool struct {
 
 	// For each exponent a list of slice pointers.
 	buffersByExponent [][][]byte
+
+	// start of slice -> exponent.
+	outstandingBuffers map[uintptr]uint
 }
 
 // Returns the smallest E such that 2^E >= Z.
@@ -33,6 +37,7 @@ func IntToExponent(z int) uint {
 func NewBufferPool() *BufferPool {
 	bp := new(BufferPool)
 	bp.buffersByExponent = make([][][]byte, 0, 8)
+	bp.outstandingBuffers = make(map[uintptr]uint)
 	return bp
 }
 
@@ -44,12 +49,7 @@ func (self *BufferPool) String() string {
 	return s
 }
 
-
-func (self *BufferPool) getBuffer(sz int) []byte {
-	exponent := int(IntToExponent(sz) - IntToExponent(PAGESIZE))
-	self.lock.Lock()
-	defer self.lock.Unlock()
-
+func (self *BufferPool) getBuffer(exponent uint) []byte {
 	if len(self.buffersByExponent) <= int(exponent) {
 		return nil
 	}
@@ -60,30 +60,10 @@ func (self *BufferPool) getBuffer(sz int) []byte {
 
 	result := bufferList[len(bufferList)-1]
 	self.buffersByExponent[exponent] = self.buffersByExponent[exponent][:len(bufferList)-1]
-
-	if cap(result) < sz {
-		panic("returning incorrect buffer.")
-	}
-
 	return result
 }
 
-func (self *BufferPool) addBuffer(slice []byte) {
-	if cap(slice)&(PAGESIZE-1) != 0 {
-		return
-	}
-
-	pages := cap(slice) / PAGESIZE
-	if pages == 0 {
-		return
-	}
-	exp := IntToExponent(pages)
-	if (1 << exp) != pages {
-		return
-	}
-
-	self.lock.Lock()
-	defer self.lock.Unlock()
+func (self *BufferPool) addBuffer(slice []byte, exp uint) {
 	for len(self.buffersByExponent) <= int(exp) {
 		self.buffersByExponent = append(self.buffersByExponent, make([][]byte, 0))
 	}
@@ -91,18 +71,46 @@ func (self *BufferPool) addBuffer(slice []byte) {
 }
 
 
-func (self *BufferPool) GetBuffer(size uint32) []byte {
+func (self *BufferPool) AllocBuffer(size uint32) []byte {
 	sz := int(size)
 	if sz < PAGESIZE {
 		sz = PAGESIZE
 	}
-	rounded := 1 << IntToExponent(sz)
-	b := self.getBuffer(rounded)
+
+	exp := IntToExponent(sz)
+	rounded := 1 << exp
+
+	exp -= IntToExponent(PAGESIZE)
+
+	self.lock.Lock()
+	defer self.lock.Unlock()
+
+	b := self.getBuffer(exp)
 
 	if b != nil {
 		b = b[:size]
 		return b
 	}
 
-	return make([]byte, size, rounded)
+	b = make([]byte, size, rounded)
+	self.outstandingBuffers[uintptr(unsafe.Pointer(&b[0]))] = exp
+	return b
+}
+
+// Takes back a buffer if it was allocated through AllocBuffer.  It is
+// not an error to call FreeBuffer() on a slice obtained elsewhere.
+func (self *BufferPool) FreeBuffer(slice []byte) {
+	self.lock.Lock()
+	defer self.lock.Unlock()
+
+	if cap(slice) < PAGESIZE {
+		return
+	}
+
+	key := uintptr(unsafe.Pointer(&slice[0]))
+	exp, ok := self.outstandingBuffers[key]
+	if ok {
+		self.addBuffer(slice, exp)
+		self.outstandingBuffers[key] = 0, false
+	}
 }

fuse/bufferpool_test.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 	"fmt"
 )
+var _ = fmt.Println
 
 func TestIntToExponent(t *testing.T) {
 	e := IntToExponent(1)
@@ -27,53 +28,13 @@ func TestIntToExponent(t *testing.T) {
 func TestBufferPool(t *testing.T) {
 	bp := NewBufferPool()
 
-	b := bp.getBuffer(PAGESIZE - 1)
-	if b != nil {
-		t.Error("bp 0")
-	}
-	b = bp.getBuffer(PAGESIZE)
-	if b != nil {
-		t.Error("bp 1")
-	}
-
-	s := make([]byte, PAGESIZE-1)
-
-	bp.addBuffer(s)
-	b = bp.getBuffer(PAGESIZE - 1)
-	if b != nil {
-		t.Error("bp 3")
-	}
-
-	s = make([]byte, PAGESIZE)
-	bp.addBuffer(s)
-	b = bp.getBuffer(PAGESIZE)
-	if b == nil {
-		t.Error("not found.")
-	}
-
-	b = bp.getBuffer(PAGESIZE)
-	if b != nil {
-		t.Error("should fail.")
-	}
+	b1 := bp.AllocBuffer(PAGESIZE)
+	_ = bp.AllocBuffer(2*PAGESIZE)
+	bp.FreeBuffer(b1)
 
-	bp.addBuffer(make([]byte, 3*PAGESIZE))
-	b = bp.getBuffer(2 * PAGESIZE)
-	if b != nil {
-		t.Error("should fail.")
-	}
-	b = bp.getBuffer(4 * PAGESIZE)
-	if b != nil {
-		t.Error("should fail.")
-	}
-	bp.addBuffer(make([]byte, 4*PAGESIZE))
-	fmt.Println(bp)
-	b = bp.getBuffer(2 * PAGESIZE)
-	if b != nil {
-		t.Error("should fail.")
-	}
-	b = bp.getBuffer(4 * PAGESIZE)
-	if b == nil {
-		t.Error("4*ps should succeed.")
+	b1_2 := bp.AllocBuffer(PAGESIZE)
+	if &b1[0] != &b1_2[0] {
+		t.Error("bp 0")
 	}
 
 }

fuse/direntry.go

@@ -110,6 +110,6 @@ func (me *FuseDir) ReadDir(input *ReadIn) (*DirEntryList, Status) {
 }
 
 func (me *FuseDir) ReleaseDir() {
-	close(me.stream)
+	// TODO - should close ?
 }
 

fuse/fuse.go

@@ -222,7 +222,7 @@ func (self *MountState) syncWrite(packet [][]byte) {
 		self.Error(os.NewError(fmt.Sprintf("writer: Writev %v failed, err: %v", packet, err)))
 	}
 	for _, v := range packet {
-		self.buffers.addBuffer(v)
+		self.buffers.FreeBuffer(v)
 	}
 }
 
@@ -233,7 +233,7 @@ func (self *MountState) syncWrite(packet [][]byte) {
 func (self *MountState) loop() {
 	// See fuse_kern_chan_receive()
 	for {
-		buf := self.buffers.GetBuffer(bufSize)
+		buf := self.buffers.AllocBuffer(bufSize)
 		n, err := self.mountFile.Read(buf)
 		if err != nil {
 			errNo := OsErrorToFuseError(err)
@@ -280,7 +280,7 @@ func (self *MountState) handle(in_data []byte) {
 		return
 	}
 	self.Write(dispatch(self, header, r))
-	self.buffers.addBuffer(in_data)
+	self.buffers.FreeBuffer(in_data)
 }