Introduce VectoredReadOp

Read requests can now take vectored responses from the filesystem
implementation and send them to FUSE device via the writev() system call.

This allows file systems to send data without copying it into the
library-provided buffer if the data is already in memory.

The change also speeds up normal ReadFileOps as a side effect because
it removes extra memory allocations.
zerocopy-examples
Vitaliy Filippov 2021-08-25 11:05:53 +03:00
parent b5cbfcd8b6
commit 694c1bf9db
11 changed files with 209 additions and 118 deletions

View File

@ -338,7 +338,7 @@ 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:
@ -405,7 +405,7 @@ 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)
@ -510,10 +510,16 @@ 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())
if err != nil && c.errorLogger != nil {
c.errorLogger.Printf("writeMessage: %v %v", err, outMsg.Bytes())
var err error
if outMsg.Sglist != nil {
_, err = writev(int(c.dev.Fd()), outMsg.Sglist)
} else {
err = c.writeMessage(outMsg.OutHeaderBytes())
}
if err != nil && c.errorLogger != nil {
c.errorLogger.Printf("writeMessage: %v %v", err, outMsg.OutHeaderBytes())
}
outMsg.Sglist = nil
}
}

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@ -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) {
@ -284,24 +285,28 @@ 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 the 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)))
@ -318,7 +323,7 @@ func convertInMessage(
o = to
readSize := int(in.Size)
p := outMsg.GrowNoZero(readSize)
p := outMsg.Grow(readSize)
if p == nil {
return nil, fmt.Errorf("Can't grow for %d-byte read", readSize)
}
@ -489,15 +494,19 @@ 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.Grow(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
@ -514,7 +523,7 @@ func convertInMessage(
readSize := int(in.Size)
if readSize != 0 {
p := outMsg.GrowNoZero(readSize)
p := outMsg.Grow(readSize)
if p == nil {
return nil, fmt.Errorf("Can't grow for %d-byte read", readSize)
}
@ -718,9 +727,11 @@ 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:

View File

@ -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)

View File

@ -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

View File

@ -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)

View File

@ -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 {

View File

@ -42,6 +42,7 @@ func init() {
type InMessage struct {
remaining []byte
storage []byte
size int
}
// NewInMessage creates a new InMessage with its storage initialized.
@ -66,6 +67,7 @@ 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.
@ -114,3 +116,11 @@ 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]
}

View File

@ -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)
}
header fusekernel.OutHeader
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.
@ -64,30 +48,12 @@ func (m *OutMessage) OutHeader() *fusekernel.OutHeader {
return &m.header
}
// Grow grows m's buffer by the given number of bytes, returning a pointer to
// the start of the new segment, which is guaranteed to be zeroed. If there is
// insufficient space, it returns nil.
// Grow adds a new buffer of <n> bytes to the message, returning a pointer to
// the start of the new segment, which is guaranteed to be zeroed.
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 +66,62 @@ 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 {
// First element of Sglist is pre-filled with a pointer to the header
// to allow sending it with a single writev() call without copying the
// slice again
m.Sglist = append(m.Sglist, m.OutHeaderBytes())
}
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
}
// First element of Sglist is the header, so we don't need to count it here
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.
func (m *OutMessage) Bytes() []byte {
l := m.Len()
// OutHeaderBytes returns a byte slice containing the current header.
func (m *OutMessage) OutHeaderBytes() []byte {
l := OutMessageHeaderSize
sh := reflect.SliceHeader{
Data: uintptr(unsafe.Pointer(&m.header)),
Len: l,
Cap: l,
}
return *(*[]byte)(unsafe.Pointer(&sh))
}

View File

@ -107,9 +107,12 @@ 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)
t.Fatalf("len(om.OutHeaderBytes()) = %d, want %d", got, want)
}
want := append(
@ -137,9 +140,12 @@ 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)
t.Fatalf("len(om.OutHeaderBytes()) = %d, want %d", got, want)
}
want := append(
@ -168,9 +174,12 @@ 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)
t.Fatalf("len(om.OutHeaderBytes()) = %d, want %d", got, want)
}
want := append(
@ -201,7 +210,7 @@ func TestOutMessageHeader(t *testing.T) {
*h = want
// Check that the result is as expected.
b := om.Bytes()
b := om.OutHeaderBytes()
if len(b) != int(unsafe.Sizeof(want)) {
t.Fatalf("unexpected length %d; want %d", len(b), unsafe.Sizeof(want))
}
@ -225,9 +234,7 @@ func TestOutMessageReset(t *testing.T) {
}
// Ensure a non-zero payload length.
if p := om.GrowNoZero(128); p == nil {
t.Fatal("GrowNoZero failed")
}
p := om.Grow(128)
// Reset.
om.Reset()
@ -259,10 +266,7 @@ func TestOutMessageGrow(t *testing.T) {
// Set up garbage where the payload will soon be.
const payloadSize = 1234
{
p := om.GrowNoZero(payloadSize)
if p == nil {
t.Fatal("GrowNoZero failed")
}
p := om.Grow(payloadSize)
err := fillWithGarbage(p, payloadSize)
if err != nil {
@ -283,7 +287,10 @@ 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 +311,7 @@ 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 +328,7 @@ func BenchmarkOutMessageReset(b *testing.B) {
oms[i%numMessages].Reset()
}
b.SetBytes(int64(unsafe.Offsetof(oms[0].payload)))
b.SetBytes(int64(oms[0].Len()))
})
}

View File

@ -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

29
writev.go Normal file
View File

@ -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
}