Fix RenameOp compatibility with macfuse 4.x

Closed-source macfuse 4.x has broken compatibility with osxfuse 3.x:
it passes an additional 64-bit field (flags) after RenameIn regardless
that we don't enable the support for RENAME_SWAP/RENAME_EXCL.

The simplest fix is just to check for the presence of all-zero flags
and strip them when they're present.

connection.go

@@ -333,7 +333,7 @@ func (c *Connection) readMessage() (*buffer.InMessage, error) {
 
 	// Loop past transient errors.
 	for {
-		// Attempt a reaed.
+		// Attempt a read.
 		err := m.Init(c.dev)
 
 		// Special cases:
@@ -400,7 +400,7 @@ func (c *Connection) ReadOp() (_ context.Context, op interface{}, _ error) {
 
 		// Convert the message to an op.
 		outMsg := c.getOutMessage()
-		op, err = convertInMessage(inMsg, outMsg, c.protocol)
+		op, err = convertInMessage(&c.cfg, inMsg, outMsg, c.protocol)
 		if err != nil {
 			c.putOutMessage(outMsg)
 			return nil, nil, fmt.Errorf("convertInMessage: %v", err)
@@ -480,8 +480,15 @@ func (c *Connection) Reply(ctx context.Context, opErr error) {
 	outMsg := state.outMsg
 	fuseID := inMsg.Header().Unique
 
+	suppressReuse := false
+	if wr, ok := op.(*fuseops.WriteFileOp); ok {
+		suppressReuse = wr.SuppressReuse
+	}
+
 	// Make sure we destroy the messages when we're done.
-	defer c.putInMessage(inMsg)
+	if !suppressReuse {
+		defer c.putInMessage(inMsg)
+	}
 	defer c.putOutMessage(outMsg)
 
 	// Clean up state for this op.
@@ -505,10 +512,16 @@ func (c *Connection) Reply(ctx context.Context, opErr error) {
 	noResponse := c.kernelResponse(outMsg, inMsg.Header().Unique, op, opErr)
 
 	if !noResponse {
-		err := c.writeMessage(outMsg.Bytes())
+		var err error
+		if outMsg.Sglist != nil {
+			_, err = writev(int(c.dev.Fd()), outMsg.Sglist)
+		} else {
+			err = c.writeMessage(outMsg.Bytes())
+		}
 		if err != nil && c.errorLogger != nil {
 			c.errorLogger.Printf("writeMessage: %v %v", err, outMsg.Bytes())
 		}
+		outMsg.Sglist = nil
 	}
 }
 

conversions.go

@@ -38,6 +38,7 @@ import (
 //
 // The caller is responsible for arranging for the message to be destroyed.
 func convertInMessage(
+	config *MountConfig,
 	inMsg *buffer.InMessage,
 	outMsg *buffer.OutMessage,
 	protocol fusekernel.Protocol) (o interface{}, err error) {
@@ -206,6 +207,15 @@ func convertInMessage(
 		}
 
 		names := inMsg.ConsumeBytes(inMsg.Len())
+		// closed-source macfuse 4.x has broken compatibility with osxfuse 3.x:
+		// it passes an additional 64-bit field (flags) after RenameIn regardless
+		// that we don't enable the support for RENAME_SWAP/RENAME_EXCL
+		// the simplest fix is just to check for the presence of all-zero flags
+		if len(names) >= 8 &&
+			names[0] == 0 && names[1] == 0 && names[2] == 0 && names[3] == 0 &&
+			names[4] == 0 && names[5] == 0 && names[6] == 0 && names[7] == 0 {
+			names = names[8 : ]
+		}
 		// names should be "old\x00new\x00"
 		if len(names) < 4 {
 			return nil, errors.New("Corrupt OpRename")
@@ -271,24 +281,28 @@ func convertInMessage(
 			return nil, errors.New("Corrupt OpRead")
 		}
 
-		to := &fuseops.ReadFileOp{
-			Inode:     fuseops.InodeID(inMsg.Header().Nodeid),
-			Handle:    fuseops.HandleID(in.Fh),
-			Offset:    int64(in.Offset),
-			OpContext: fuseops.OpContext{Pid: inMsg.Header().Pid},
+		if !config.UseVectoredRead {
+			// Use part of the incoming message storage as a read buffer
+			buf := inMsg.GetFree(int(in.Size))
+			to := &fuseops.ReadFileOp{
+				Inode:     fuseops.InodeID(inMsg.Header().Nodeid),
+				Handle:    fuseops.HandleID(in.Fh),
+				Offset:    int64(in.Offset),
+				Dst:       buf,
+				OpContext: fuseops.OpContext{Pid: inMsg.Header().Pid},
+			}
+			o = to
+		} else {
+			// Don't allocate any buffers when zero-copy is used
+			to := &fuseops.VectoredReadOp{
+				Inode:     fuseops.InodeID(inMsg.Header().Nodeid),
+				Handle:    fuseops.HandleID(in.Fh),
+				Offset:    int64(in.Offset),
+				Size:      int64(in.Size),
+				OpContext: fuseops.OpContext{Pid: inMsg.Header().Pid},
+			}
+			o = to
 		}
-		o = to
-
-		readSize := int(in.Size)
-		p := outMsg.GrowNoZero(readSize)
-		if p == nil {
-			return nil, fmt.Errorf("Can't grow for %d-byte read", readSize)
-		}
-
-		sh := (*reflect.SliceHeader)(unsafe.Pointer(&to.Dst))
-		sh.Data = uintptr(p)
-		sh.Len = readSize
-		sh.Cap = readSize
 
 	case fusekernel.OpReaddir:
 		in := (*fusekernel.ReadIn)(inMsg.Consume(fusekernel.ReadInSize(protocol)))
@@ -476,15 +490,19 @@ func convertInMessage(
 		o = to
 
 		readSize := int(in.Size)
-		p := outMsg.GrowNoZero(readSize)
-		if p == nil {
-			return nil, fmt.Errorf("Can't grow for %d-byte read", readSize)
-		}
+		if readSize > 0 {
+			p := outMsg.GrowNoZero(readSize)
+			if p == nil {
+				return nil, fmt.Errorf("Can't grow for %d-byte read", readSize)
+			}
 
-		sh := (*reflect.SliceHeader)(unsafe.Pointer(&to.Dst))
-		sh.Data = uintptr(p)
-		sh.Len = readSize
-		sh.Cap = readSize
+			sh := (*reflect.SliceHeader)(unsafe.Pointer(&to.Dst))
+			sh.Data = uintptr(p)
+			sh.Len = readSize
+			sh.Cap = readSize
+		} else {
+			to.Dst = nil
+		}
 
 	case fusekernel.OpListxattr:
 		type input fusekernel.ListxattrIn
@@ -705,9 +723,11 @@ func (c *Connection) kernelResponseForOp(
 		}
 
 	case *fuseops.ReadFileOp:
-		// convertInMessage already set up the destination buffer to be at the end
-		// of the out message. We need only shrink to the right size based on how
-		// much the user read.
+		m.Append(o.Dst)
+		m.ShrinkTo(buffer.OutMessageHeaderSize + o.BytesRead)
+
+	case *fuseops.VectoredReadOp:
+		m.Append(o.Data...)
 		m.ShrinkTo(buffer.OutMessageHeaderSize + o.BytesRead)
 
 	case *fuseops.WriteFileOp:

debug.go

@@ -97,6 +97,11 @@ func describeRequest(op interface{}) (s string) {
 		addComponent("offset %d", typed.Offset)
 		addComponent("%d bytes", len(typed.Dst))
 
+	case *fuseops.VectoredReadOp:
+		addComponent("handle %d", typed.Handle)
+		addComponent("offset %d", typed.Offset)
+		addComponent("%d bytes", typed.Size)
+
 	case *fuseops.WriteFileOp:
 		addComponent("handle %d", typed.Handle)
 		addComponent("offset %d", typed.Offset)

fuseops/ops.go

@@ -654,6 +654,37 @@ type ReadFileOp struct {
 	OpContext OpContext
 }
 
+// Vectored read - same as ReadFileOp, but the buffer isn't provided by the library.
+// The file system returns a list of slices instead.
+type VectoredReadOp struct {
+	// The file inode that we are reading, and the handle previously returned by
+	// CreateFile or OpenFile when opening that inode.
+	Inode  InodeID
+	Handle HandleID
+
+	// The offset within the file at which to read.
+	Offset int64
+
+	// The size of the read.
+	Size int64
+
+	// Set by the file system: data to send back to the client.
+	Data [][]byte
+
+	// Set by the file system: the number of bytes read.
+	//
+	// The FUSE documentation requires that exactly the requested number of bytes
+	// be returned, except in the case of EOF or error (http://goo.gl/ZgfBkF).
+	// This appears to be because it uses file mmapping machinery
+	// (http://goo.gl/SGxnaN) to read a page at a time. It appears to understand
+	// where EOF is by checking the inode size (http://goo.gl/0BkqKD), returned
+	// by a previous call to LookUpInode, GetInodeAttributes, etc.
+	//
+	// If direct IO is enabled, semantics should match those of read(2).
+	BytesRead int
+	OpContext OpContext
+}
+
 // Write data to a file previously opened with CreateFile or OpenFile.
 //
 // When the user writes data using write(2), the write goes into the page
@@ -710,7 +741,18 @@ type WriteFileOp struct {
 	// be written, except on error (http://goo.gl/KUpwwn). This appears to be
 	// because it uses file mmapping machinery (http://goo.gl/SGxnaN) to write a
 	// page at a time.
-	Data      []byte
+	Data []byte
+
+	// Set by the file system: "no reuse" flag.
+	//
+	// By default, the Data buffer is reused by the library, so the file system
+	// must copy the data if it wants to use it later.
+	//
+	// However, if the file system sets this flag to true, the library doesn't
+	// reuse this buffer, so the file system can safely store and use Data slice
+	// without copying memory.
+	SuppressReuse bool
+
 	OpContext OpContext
 }
 

fuseutil/file_system.go

@@ -52,6 +52,7 @@ type FileSystem interface {
 	ReleaseDirHandle(context.Context, *fuseops.ReleaseDirHandleOp) error
 	OpenFile(context.Context, *fuseops.OpenFileOp) error
 	ReadFile(context.Context, *fuseops.ReadFileOp) error
+	VectoredRead(context.Context, *fuseops.VectoredReadOp) error
 	WriteFile(context.Context, *fuseops.WriteFileOp) error
 	SyncFile(context.Context, *fuseops.SyncFileOp) error
 	FlushFile(context.Context, *fuseops.FlushFileOp) error
@@ -190,6 +191,9 @@ func (s *fileSystemServer) handleOp(
 	case *fuseops.ReadFileOp:
 		err = s.fs.ReadFile(ctx, typed)
 
+	case *fuseops.VectoredReadOp:
+		err = s.fs.VectoredRead(ctx, typed)
+
 	case *fuseops.WriteFileOp:
 		err = s.fs.WriteFile(ctx, typed)
 

fuseutil/not_implemented_file_system.go

@@ -138,6 +138,12 @@ func (fs *NotImplementedFileSystem) ReadFile(
 	return fuse.ENOSYS
 }
 
+func (fs *NotImplementedFileSystem) VectoredRead(
+	ctx context.Context,
+	op *fuseops.VectoredReadOp) error {
+	return fuse.ENOSYS
+}
+
 func (fs *NotImplementedFileSystem) WriteFile(
 	ctx context.Context,
 	op *fuseops.WriteFileOp) error {

internal/buffer/in_message.go

@@ -42,13 +42,16 @@ func init() {
 type InMessage struct {
 	remaining []byte
 	storage   []byte
+	size      int
 }
 
 // Initialize with the data read by a single call to r.Read. The first call to
 // Consume will consume the bytes directly after the fusekernel.InHeader
 // struct.
 func (m *InMessage) Init(r io.Reader) error {
-	m.storage = make([]byte, bufSize, bufSize)
+	if m.storage == nil {
+		m.storage = make([]byte, bufSize, bufSize)
+	}
 	n, err := r.Read(m.storage[:])
 	if err != nil {
 		return err
@@ -60,6 +63,7 @@ func (m *InMessage) Init(r io.Reader) error {
 		return fmt.Errorf("Unexpectedly read only %d bytes.", n)
 	}
 
+	m.size = n
 	m.remaining = m.storage[headerSize:n]
 
 	// Check the header's length.
@@ -108,3 +112,11 @@ func (m *InMessage) ConsumeBytes(n uintptr) []byte {
 
 	return b
 }
+
+// Get the next n bytes after the message to use them as a temporary buffer
+func (m *InMessage) GetFree(n int) []byte {
+	if n <= 0 || n > len(m.storage)-m.size {
+		return nil
+	}
+	return m.storage[m.size : m.size+n]
+}

internal/buffer/in_message_linux.go

@@ -17,4 +17,4 @@ package buffer
 // The maximum fuse write request size that InMessage can acommodate.
 //
 // As of kernel 4.20 Linux accepts writes up to 256 pages or 1MiB
-const MaxWriteSize = 1 << 20
+const MaxWriteSize = 1 << 17

internal/buffer/out_message.go

@@ -16,7 +16,6 @@ package buffer
 
 import (
 	"fmt"
-	"log"
 	"reflect"
 	"unsafe"
 
@@ -33,30 +32,15 @@ const OutMessageHeaderSize = int(unsafe.Sizeof(fusekernel.OutHeader{}))
 //
 // Must be initialized with Reset.
 type OutMessage struct {
-	// The offset into payload to which we're currently writing.
-	payloadOffset int
-
 	header  fusekernel.OutHeader
-	payload [MaxReadSize]byte
-}
-
-// Make sure that the header and payload are contiguous.
-func init() {
-	a := unsafe.Offsetof(OutMessage{}.header) + uintptr(OutMessageHeaderSize)
-	b := unsafe.Offsetof(OutMessage{}.payload)
-
-	if a != b {
-		log.Panicf(
-			"header ends at offset %d, but payload starts at offset %d",
-			a, b)
-	}
+	Sglist  [][]byte
 }
 
 // Reset resets m so that it's ready to be used again. Afterward, the contents
 // are solely a zeroed fusekernel.OutHeader struct.
 func (m *OutMessage) Reset() {
-	m.payloadOffset = 0
 	m.header = fusekernel.OutHeader{}
+	m.Sglist = nil
 }
 
 // OutHeader returns a pointer to the header at the start of the message.
@@ -69,25 +53,15 @@ func (m *OutMessage) OutHeader() *fusekernel.OutHeader {
 // insufficient space, it returns nil.
 func (m *OutMessage) Grow(n int) unsafe.Pointer {
 	p := m.GrowNoZero(n)
-	if p != nil {
-		jacobsa_fuse_memclr(p, uintptr(n))
-	}
-
 	return p
 }
 
 // GrowNoZero is equivalent to Grow, except the new segment is not zeroed. Use
 // with caution!
 func (m *OutMessage) GrowNoZero(n int) unsafe.Pointer {
-	// Will we overflow the buffer?
-	o := m.payloadOffset
-	if len(m.payload)-o < n {
-		return nil
-	}
-
-	p := unsafe.Pointer(uintptr(unsafe.Pointer(&m.payload)) + uintptr(o))
-	m.payloadOffset = o + n
-
+	b := make([]byte, n)
+	m.Append(b)
+	p := unsafe.Pointer(&b[0])
 	return p
 }
 
@@ -100,51 +74,63 @@ func (m *OutMessage) ShrinkTo(n int) {
 			n,
 			m.Len()))
 	}
-
-	m.payloadOffset = n - OutMessageHeaderSize
+	if n == OutMessageHeaderSize {
+		m.Sglist = nil
+	} else {
+		i := 1
+		n -= OutMessageHeaderSize
+		for len(m.Sglist) > i && n >= len(m.Sglist[i]) {
+			n -= len(m.Sglist[i])
+			i++
+		}
+		if n > 0 {
+			m.Sglist[i] = m.Sglist[i][0 : n]
+			i++
+		}
+		m.Sglist = m.Sglist[0 : i]
+	}
 }
 
 // Append is equivalent to growing by len(src), then copying src over the new
 // segment. Int panics if there is not enough room available.
-func (m *OutMessage) Append(src []byte) {
-	p := m.GrowNoZero(len(src))
-	if p == nil {
-		panic(fmt.Sprintf("Can't grow %d bytes", len(src)))
+func (m *OutMessage) Append(src ...[]byte) {
+	if m.Sglist == nil {
+		m.Sglist = append(m.Sglist, nil)
+		*(*reflect.SliceHeader)(unsafe.Pointer(&m.Sglist[0])) = reflect.SliceHeader{
+			Data: uintptr(unsafe.Pointer(&m.header)),
+			Len:  OutMessageHeaderSize,
+			Cap:  OutMessageHeaderSize,
+		}
 	}
-
-	sh := (*reflect.SliceHeader)(unsafe.Pointer(&src))
-	jacobsa_fuse_memmove(p, unsafe.Pointer(sh.Data), uintptr(sh.Len))
-
+	m.Sglist = append(m.Sglist, src...)
 	return
 }
 
 // AppendString is like Append, but accepts string input.
 func (m *OutMessage) AppendString(src string) {
-	p := m.GrowNoZero(len(src))
-	if p == nil {
-		panic(fmt.Sprintf("Can't grow %d bytes", len(src)))
-	}
-
-	sh := (*reflect.StringHeader)(unsafe.Pointer(&src))
-	jacobsa_fuse_memmove(p, unsafe.Pointer(sh.Data), uintptr(sh.Len))
-
+	m.Append([]byte(src))
 	return
 }
 
 // Len returns the current size of the message, including the leading header.
 func (m *OutMessage) Len() int {
-	return OutMessageHeaderSize + m.payloadOffset
+	if m.Sglist == nil {
+		return OutMessageHeaderSize
+	}
+	r := 0
+	for _, b := range m.Sglist {
+		r += len(b)
+	}
+	return r
 }
 
-// Bytes returns a reference to the current contents of the buffer, including
-// the leading header.
+// Bytes returns a byte slice containing the current header.
 func (m *OutMessage) Bytes() []byte {
-	l := m.Len()
+	l := OutMessageHeaderSize
 	sh := reflect.SliceHeader{
 		Data: uintptr(unsafe.Pointer(&m.header)),
 		Len:  l,
 		Cap:  l,
 	}
-
 	return *(*[]byte)(unsafe.Pointer(&sh))
 }

internal/buffer/out_message_test.go

@@ -107,7 +107,10 @@ func TestOutMessageAppend(t *testing.T) {
 		t.Errorf("om.Len() = %d, want %d", got, want)
 	}
 
-	b := om.Bytes()
+	b := []byte(nil)
+	for i := 0; i < len(om.Sglist); i++ {
+		b = append(b, om.Sglist[i]...)
+	}
 	if got, want := len(b), wantLen; got != want {
 		t.Fatalf("len(om.Bytes()) = %d, want %d", got, want)
 	}
@@ -137,7 +140,10 @@ func TestOutMessageAppendString(t *testing.T) {
 		t.Errorf("om.Len() = %d, want %d", got, want)
 	}
 
-	b := om.Bytes()
+	b := []byte(nil)
+	for i := 0; i < len(om.Sglist); i++ {
+		b = append(b, om.Sglist[i]...)
+	}
 	if got, want := len(b), wantLen; got != want {
 		t.Fatalf("len(om.Bytes()) = %d, want %d", got, want)
 	}
@@ -168,7 +174,10 @@ func TestOutMessageShrinkTo(t *testing.T) {
 		t.Errorf("om.Len() = %d, want %d", got, want)
 	}
 
-	b := om.Bytes()
+	b := []byte(nil)
+	for i := 0; i < len(om.Sglist); i++ {
+		b = append(b, om.Sglist[i]...)
+	}
 	if got, want := len(b), wantLen; got != want {
 		t.Fatalf("len(om.Bytes()) = %d, want %d", got, want)
 	}
@@ -283,7 +292,10 @@ func TestOutMessageGrow(t *testing.T) {
 		t.Errorf("om.Len() = %d, want %d", got, want)
 	}
 
-	b := om.Bytes()
+	b := []byte(nil)
+	for i := 0; i < len(om.Sglist); i++ {
+		b = append(b, om.Sglist[i]...)
+	}
 	if got, want := len(b), wantLen; got != want {
 		t.Fatalf("len(om.Len()) = %d, want %d", got, want)
 	}
@@ -304,7 +316,7 @@ func BenchmarkOutMessageReset(b *testing.B) {
 			om.Reset()
 		}
 
-		b.SetBytes(int64(unsafe.Offsetof(om.payload)))
+		b.SetBytes(int64(om.Len()))
 	})
 
 	// Many megabytes worth of buffers, which should defeat the CPU cache.
@@ -321,7 +333,7 @@ func BenchmarkOutMessageReset(b *testing.B) {
 			oms[i%numMessages].Reset()
 		}
 
-		b.SetBytes(int64(unsafe.Offsetof(oms[0].payload)))
+		b.SetBytes(int64(oms[0].Len()))
 	})
 }
 

mount.go

@@ -17,7 +17,10 @@ package fuse
 import (
 	"context"
 	"fmt"
+	"net"
 	"os"
+	"os/exec"
+	"syscall"
 )
 
 // Server is an interface for any type that knows how to serve ops read from a
@@ -93,3 +96,82 @@ func Mount(
 
 	return mfs, nil
 }
+
+func fusermount(binary string, argv []string, additionalEnv []string, wait bool) (*os.File, error) {
+	// Create a socket pair.
+	fds, err := syscall.Socketpair(syscall.AF_UNIX, syscall.SOCK_STREAM, 0)
+	if err != nil {
+		return nil, fmt.Errorf("Socketpair: %v", err)
+	}
+
+	// Wrap the sockets into os.File objects that we will pass off to fusermount.
+	writeFile := os.NewFile(uintptr(fds[0]), "fusermount-child-writes")
+	defer writeFile.Close()
+
+	readFile := os.NewFile(uintptr(fds[1]), "fusermount-parent-reads")
+	defer readFile.Close()
+
+	// Start fusermount/mount_macfuse/mount_osxfuse.
+	cmd := exec.Command(binary, argv...)
+	cmd.Env = append(os.Environ(), "_FUSE_COMMFD=3")
+	cmd.Env = append(cmd.Env, additionalEnv...)
+	cmd.ExtraFiles = []*os.File{writeFile}
+	cmd.Stderr = os.Stderr
+
+	// Run the command.
+	if wait {
+		err = cmd.Run()
+	} else {
+		err = cmd.Start()
+	}
+	if err != nil {
+		return nil, fmt.Errorf("running %v: %v", binary, err)
+	}
+
+	// Wrap the socket file in a connection.
+	c, err := net.FileConn(readFile)
+	if err != nil {
+		return nil, fmt.Errorf("FileConn: %v", err)
+	}
+	defer c.Close()
+
+	// We expect to have a Unix domain socket.
+	uc, ok := c.(*net.UnixConn)
+	if !ok {
+		return nil, fmt.Errorf("Expected UnixConn, got %T", c)
+	}
+
+	// Read a message.
+	buf := make([]byte, 32) // expect 1 byte
+	oob := make([]byte, 32) // expect 24 bytes
+	_, oobn, _, _, err := uc.ReadMsgUnix(buf, oob)
+	if err != nil {
+		return nil, fmt.Errorf("ReadMsgUnix: %v", err)
+	}
+
+	// Parse the message.
+	scms, err := syscall.ParseSocketControlMessage(oob[:oobn])
+	if err != nil {
+		return nil, fmt.Errorf("ParseSocketControlMessage: %v", err)
+	}
+
+	// We expect one message.
+	if len(scms) != 1 {
+		return nil, fmt.Errorf("expected 1 SocketControlMessage; got scms = %#v", scms)
+	}
+
+	scm := scms[0]
+
+	// Pull out the FD returned by fusermount
+	gotFds, err := syscall.ParseUnixRights(&scm)
+	if err != nil {
+		return nil, fmt.Errorf("syscall.ParseUnixRights: %v", err)
+	}
+
+	if len(gotFds) != 1 {
+		return nil, fmt.Errorf("wanted 1 fd; got %#v", gotFds)
+	}
+
+	// Turn the FD into an os.File.
+	return os.NewFile(uintptr(gotFds[0]), "/dev/fuse"), nil
+}

mount_config.go

@@ -156,6 +156,11 @@ type MountConfig struct {
 	// actually utilise any form of qualifiable UNIX permissions.
 	DisableDefaultPermissions bool
 
+	// Use VectoredReadOp instead of ReadFileOp.
+	// Vectored read allows file systems to reduce memory copying overhead if
+	// the data is already in memory when they return it to FUSE.
+	UseVectoredRead bool
+
 	// OS X only.
 	//
 	// The name of the mounted volume, as displayed in the Finder. If empty, a

mount_darwin.go

@@ -40,6 +40,10 @@ type osxfuseInstallation struct {
 
 	// Environment variable used to pass the "called by library" flag.
 	LibVar string
+
+	// Open device manually (false) or receive the FD through a UNIX socket,
+	// like with fusermount (true)
+	UseCommFD bool
 }
 
 var (
@@ -51,6 +55,7 @@ var (
 			Mount:        "/Library/Filesystems/macfuse.fs/Contents/Resources/mount_macfuse",
 			DaemonVar:    "_FUSE_DAEMON_PATH",
 			LibVar:       "_FUSE_CALL_BY_LIB",
+			UseCommFD:    true,
 		},
 
 		// v3
@@ -106,6 +111,36 @@ func openOSXFUSEDev(devPrefix string) (dev *os.File, err error) {
 	}
 }
 
+func convertMountArgs(daemonVar string, libVar string,
+	cfg *MountConfig) ([]string, []string, error) {
+
+	// The mount helper doesn't understand any escaping.
+	for k, v := range cfg.toMap() {
+		if strings.Contains(k, ",") || strings.Contains(v, ",") {
+			return nil, nil, fmt.Errorf(
+				"mount options cannot contain commas on darwin: %q=%q",
+				k,
+				v)
+		}
+	}
+
+	env := []string{ libVar+"=" }
+	if daemonVar != "" {
+		env = append(env, daemonVar+"="+os.Args[0])
+	}
+	argv := []string{
+		"-o", cfg.toOptionsString(),
+		// Tell osxfuse-kext how large our buffer is. It must split
+		// writes larger than this into multiple writes.
+		//
+		// OSXFUSE seems to ignore InitResponse.MaxWrite, and uses
+		// this instead.
+		"-o", "iosize="+strconv.FormatUint(buffer.MaxWriteSize, 10),
+	}
+
+	return argv, env, nil
+}
+
 func callMount(
 	bin string,
 	daemonVar string,
@@ -115,39 +150,21 @@ func callMount(
 	dev *os.File,
 	ready chan<- error) error {
 
-	// The mount helper doesn't understand any escaping.
-	for k, v := range cfg.toMap() {
-		if strings.Contains(k, ",") || strings.Contains(v, ",") {
-			return fmt.Errorf(
-				"mount options cannot contain commas on darwin: %q=%q",
-				k,
-				v)
-		}
+	argv, env, err := convertMountArgs(daemonVar, libVar, cfg)
+	if err != nil {
+		return err
 	}
 
 	// Call the mount helper, passing in the device file and saving output into a
 	// buffer.
-	cmd := exec.Command(
-		bin,
-		"-o", cfg.toOptionsString(),
-		// Tell osxfuse-kext how large our buffer is. It must split
-		// writes larger than this into multiple writes.
-		//
-		// OSXFUSE seems to ignore InitResponse.MaxWrite, and uses
-		// this instead.
-		"-o", "iosize="+strconv.FormatUint(buffer.MaxWriteSize, 10),
+	argv = append(argv,
 		// refers to fd passed in cmd.ExtraFiles
 		"3",
 		dir,
 	)
+	cmd := exec.Command(bin, argv...)
 	cmd.ExtraFiles = []*os.File{dev}
-	cmd.Env = os.Environ()
-	cmd.Env = append(cmd.Env, libVar+"=")
-
-	daemon := os.Args[0]
-	if daemonVar != "" {
-		cmd.Env = append(cmd.Env, daemonVar+"="+daemon)
-	}
+	cmd.Env = env
 
 	var buf bytes.Buffer
 	cmd.Stdout = &buf
@@ -174,6 +191,23 @@ func callMount(
 	return nil
 }
 
+func callMountCommFD(
+	bin string,
+	daemonVar string,
+	libVar string,
+	dir string,
+	cfg *MountConfig) (*os.File, error) {
+
+	argv, env, err := convertMountArgs(daemonVar, libVar, cfg)
+	if err != nil {
+		return nil, err
+	}
+	env = append(env, "_FUSE_COMMVERS=2")
+	argv = append(argv, dir)
+
+	return fusermount(bin, argv, env, false)
+}
+
 // Begin the process of mounting at the given directory, returning a connection
 // to the kernel. Mounting continues in the background, and is complete when an
 // error is written to the supplied channel. The file system may need to
@@ -189,6 +223,16 @@ func mount(
 			continue
 		}
 
+		if loc.UseCommFD {
+			// Call the mount binary with the device.
+			ready <- nil
+			dev, err = callMountCommFD(loc.Mount, loc.DaemonVar, loc.LibVar, dir, cfg)
+			if err != nil {
+				return nil, fmt.Errorf("callMount: %v", err)
+			}
+			return
+		}
+
 		// Open the device.
 		dev, err = openOSXFUSEDev(loc.DevicePrefix)
 

mount_linux.go

@@ -1,10 +1,8 @@
 package fuse
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
-	"net"
 	"os"
 	"os/exec"
 	"syscall"
@@ -23,92 +21,6 @@ func findFusermount() (string, error) {
 	return path, nil
 }
 
-func fusermount(dir string, cfg *MountConfig) (*os.File, error) {
-	// Create a socket pair.
-	fds, err := syscall.Socketpair(syscall.AF_FILE, syscall.SOCK_STREAM, 0)
-	if err != nil {
-		return nil, fmt.Errorf("Socketpair: %v", err)
-	}
-
-	// Wrap the sockets into os.File objects that we will pass off to fusermount.
-	writeFile := os.NewFile(uintptr(fds[0]), "fusermount-child-writes")
-	defer writeFile.Close()
-
-	readFile := os.NewFile(uintptr(fds[1]), "fusermount-parent-reads")
-	defer readFile.Close()
-
-	// Start fusermount, passing it a buffer in which to write stderr.
-	var stderr bytes.Buffer
-
-	fusermount, err := findFusermount()
-	if err != nil {
-		return nil, err
-	}
-	cmd := exec.Command(
-		fusermount,
-		"-o", cfg.toOptionsString(),
-		"--",
-		dir,
-	)
-
-	cmd.Env = append(os.Environ(), "_FUSE_COMMFD=3")
-	cmd.ExtraFiles = []*os.File{writeFile}
-	cmd.Stderr = &stderr
-
-	// Run the command.
-	err = cmd.Run()
-	if err != nil {
-		return nil, fmt.Errorf("running fusermount: %v\n\nstderr:\n%s", err, stderr.Bytes())
-	}
-
-	// Wrap the socket file in a connection.
-	c, err := net.FileConn(readFile)
-	if err != nil {
-		return nil, fmt.Errorf("FileConn: %v", err)
-	}
-	defer c.Close()
-
-	// We expect to have a Unix domain socket.
-	uc, ok := c.(*net.UnixConn)
-	if !ok {
-		return nil, fmt.Errorf("Expected UnixConn, got %T", c)
-	}
-
-	// Read a message.
-	buf := make([]byte, 32) // expect 1 byte
-	oob := make([]byte, 32) // expect 24 bytes
-	_, oobn, _, _, err := uc.ReadMsgUnix(buf, oob)
-	if err != nil {
-		return nil, fmt.Errorf("ReadMsgUnix: %v", err)
-	}
-
-	// Parse the message.
-	scms, err := syscall.ParseSocketControlMessage(oob[:oobn])
-	if err != nil {
-		return nil, fmt.Errorf("ParseSocketControlMessage: %v", err)
-	}
-
-	// We expect one message.
-	if len(scms) != 1 {
-		return nil, fmt.Errorf("expected 1 SocketControlMessage; got scms = %#v", scms)
-	}
-
-	scm := scms[0]
-
-	// Pull out the FD returned by fusermount
-	gotFds, err := syscall.ParseUnixRights(&scm)
-	if err != nil {
-		return nil, fmt.Errorf("syscall.ParseUnixRights: %v", err)
-	}
-
-	if len(gotFds) != 1 {
-		return nil, fmt.Errorf("wanted 1 fd; got %#v", gotFds)
-	}
-
-	// Turn the FD into an os.File.
-	return os.NewFile(uintptr(gotFds[0]), "/dev/fuse"), nil
-}
-
 func enableFunc(flag uintptr) func(uintptr) uintptr {
 	return func(v uintptr) uintptr {
 		return v | flag
@@ -198,7 +110,16 @@ func mount(dir string, cfg *MountConfig, ready chan<- error) (*os.File, error) {
 	// have the CAP_SYS_ADMIN capability.
 	dev, err := directmount(dir, cfg)
 	if err == errFallback {
-		return fusermount(dir, cfg)
+		fusermountPath, err := findFusermount()
+		if err != nil {
+			return nil, err
+		}
+		argv := []string{
+			"-o", cfg.toOptionsString(),
+			"--",
+			dir,
+		}
+		return fusermount(fusermountPath, argv, []string{}, true)
 	}
 	return dev, err
 }

samples/mount_readbenchfs/mount.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"log"
+	"os"
+	"github.com/jacobsa/fuse"
+	"github.com/jacobsa/fuse/samples/readbenchfs"
+)
+
+var fMountPoint = flag.String("mount_point", "", "Path to mount point.")
+var fReadOnly = flag.Bool("read_only", false, "Mount in read-only mode.")
+var fVectored = flag.Bool("vectored", false, "Use vectored read.")
+var fDebug = flag.Bool("debug", false, "Enable debug logging.")
+
+func main() {
+	flag.Parse()
+
+	server, err := readbenchfs.NewReadBenchServer()
+	if err != nil {
+		log.Fatalf("makeFS: %v", err)
+	}
+
+	// Mount the file system.
+	if *fMountPoint == "" {
+		log.Fatalf("You must set --mount_point.")
+	}
+
+	cfg := &fuse.MountConfig{
+		ReadOnly: *fReadOnly,
+		UseVectoredRead: *fVectored,
+	}
+
+	if *fDebug {
+		cfg.DebugLogger = log.New(os.Stderr, "fuse: ", 0)
+	}
+
+	mfs, err := fuse.Mount(*fMountPoint, server, cfg)
+	if err != nil {
+		log.Fatalf("Mount: %v", err)
+	}
+
+	// Wait for it to be unmounted.
+	if err = mfs.Join(context.Background()); err != nil {
+		log.Fatalf("Join: %v", err)
+	}
+}

samples/readbenchfs/readbenchfs.go

@@ -0,0 +1,213 @@
+// Copyright 2021 Vitaliy Filippov
+//
+// 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 readbenchfs
+
+import (
+	"golang.org/x/net/context"
+	"os"
+	"io"
+	"math/rand"
+
+	"github.com/jacobsa/fuse"
+	"github.com/jacobsa/fuse/fuseops"
+	"github.com/jacobsa/fuse/fuseutil"
+)
+
+type readBenchFS struct {
+	fuseutil.NotImplementedFileSystem
+	buf    []byte
+}
+
+const FILE_SIZE = 1024*1024*1024*1024
+
+var _ fuseutil.FileSystem = &readBenchFS{}
+
+func NewReadBenchServer() (server fuse.Server, err error) {
+	// 1 GB of random data to exceed CPU cache
+	buf := make([]byte, 1024*1024*1024)
+	rand.Read(buf)
+	server = fuseutil.NewFileSystemServer(&readBenchFS{
+		buf: buf,
+	})
+	return
+}
+
+func (fs *readBenchFS) StatFS(
+	ctx context.Context,
+	op *fuseops.StatFSOp) error {
+	return nil
+}
+
+func (fs *readBenchFS) LookUpInode(
+	ctx context.Context,
+	op *fuseops.LookUpInodeOp) error {
+	if op.Name == "test" {
+		op.Entry = fuseops.ChildInodeEntry{
+			Child: 2,
+			Attributes: fuseops.InodeAttributes{
+				Size: FILE_SIZE,
+				Nlink: 1,
+				Mode: 0444,
+			},
+		}
+		return nil
+	}
+	return fuse.ENOENT
+}
+
+func (fs *readBenchFS) GetInodeAttributes(
+	ctx context.Context,
+	op *fuseops.GetInodeAttributesOp) error {
+	if op.Inode == 1 {
+		op.Attributes = fuseops.InodeAttributes{
+			Nlink: 1,
+			Mode: 0755 | os.ModeDir,
+		}
+		return nil
+	} else if op.Inode == 2 {
+		op.Attributes = fuseops.InodeAttributes{
+			Size: FILE_SIZE,
+			Nlink: 1,
+			Mode: 0444,
+		}
+		return nil
+	}
+	return fuse.ENOENT
+}
+
+func (fs *readBenchFS) OpenDir(
+	ctx context.Context,
+	op *fuseops.OpenDirOp) error {
+	// Allow opening any directory.
+	return nil
+}
+
+func (fs *readBenchFS) ReadDir(
+	ctx context.Context,
+	op *fuseops.ReadDirOp) error {
+	if op.Inode != 1 {
+		return fuse.ENOENT
+	}
+	if op.Offset > 0 {
+		return nil
+	}
+	entries := []fuseutil.Dirent{
+		fuseutil.Dirent{
+			Offset: 1,
+			Inode:  2,
+			Name:   "test",
+			Type:   fuseutil.DT_File,
+		},
+	}
+	for _, e := range entries[op.Offset:] {
+		n := fuseutil.WriteDirent(op.Dst[op.BytesRead:], e)
+		if n == 0 {
+			break
+		}
+		op.BytesRead += n
+	}
+	return nil
+}
+
+func (fs *readBenchFS) OpenFile(
+	ctx context.Context,
+	op *fuseops.OpenFileOp) error {
+	// Allow opening any file.
+	return nil
+}
+
+func (fs *readBenchFS) ReadFile(
+	ctx context.Context,
+	op *fuseops.ReadFileOp) error {
+	if op.Offset > FILE_SIZE {
+		return io.EOF
+	}
+	end := op.Offset+int64(len(op.Dst))
+	if end > FILE_SIZE {
+		end = FILE_SIZE
+	}
+	buflen := int64(len(fs.buf))
+	for pos := op.Offset; pos < end; {
+		s := pos % buflen
+		e := buflen
+		if e-s > end-pos {
+			e = s+end-pos
+		}
+		copy(op.Dst[pos-op.Offset : ], fs.buf[s : ])
+		pos = op.Offset+e
+	}
+	op.BytesRead = int(end-op.Offset)
+	return nil
+}
+
+func (fs *readBenchFS) VectoredRead(
+	ctx context.Context,
+	op *fuseops.VectoredReadOp) error {
+	if op.Offset > FILE_SIZE {
+		return io.EOF
+	}
+	end := op.Offset+op.Size
+	if end > FILE_SIZE {
+		end = FILE_SIZE
+	}
+	buflen := int64(len(fs.buf))
+	for pos := op.Offset; pos < end; {
+		s := pos % buflen
+		e := buflen
+		if e-s > end-pos {
+			e = s+end-pos
+		}
+		op.Data = append(op.Data, fs.buf[s : e])
+		pos = op.Offset+e
+	}
+	op.BytesRead = int(end-op.Offset)
+	return nil
+}
+
+func (fs *readBenchFS) ReleaseDirHandle(
+	ctx context.Context,
+	op *fuseops.ReleaseDirHandleOp) error {
+	return nil
+}
+
+func (fs *readBenchFS) GetXattr(
+	ctx context.Context,
+	op *fuseops.GetXattrOp) error {
+	return nil
+}
+
+func (fs *readBenchFS) ListXattr(
+	ctx context.Context,
+	op *fuseops.ListXattrOp) error {
+	return nil
+}
+
+func (fs *readBenchFS) ForgetInode(
+	ctx context.Context,
+	op *fuseops.ForgetInodeOp) error {
+	return nil
+}
+
+func (fs *readBenchFS) ReleaseFileHandle(
+	ctx context.Context,
+	op *fuseops.ReleaseFileHandleOp) error {
+	return nil
+}
+
+func (fs *readBenchFS) FlushFile(
+	ctx context.Context,
+	op *fuseops.FlushFileOp) error {
+	return nil
+}

writev.go

@@ -0,0 +1,29 @@
+package fuse
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+func writev(fd int, packet [][]byte) (n int, err error) {
+	iovecs := make([]syscall.Iovec, 0, len(packet))
+	for _, v := range packet {
+		if len(v) == 0 {
+			continue
+		}
+		vec := syscall.Iovec{
+			Base: &v[0],
+		}
+		vec.SetLen(len(v))
+		iovecs = append(iovecs, vec)
+	}
+	n1, _, e1 := syscall.Syscall(
+		syscall.SYS_WRITEV,
+		uintptr(fd), uintptr(unsafe.Pointer(&iovecs[0])), uintptr(len(iovecs)),
+	)
+	n = int(n1)
+	if e1 != 0 {
+		err = syscall.Errno(e1)
+	}
+	return
+}