splice: use syscall directly for splice I/O

This avoids involving the go 1.9 poller in I/O, which causes hangs, as
the poller does not understand the fcntl(O_NONBLOCK) tweak that we
executed on the pipe's file descriptors.

Fixes #164

splice/pair.go

@@ -6,11 +6,11 @@ package splice
 
 import (
 	"fmt"
-	"os"
+	"syscall"
 )
 
 type Pair struct {
-	r, w *os.File
+	r, w int
 	size int
 }
 
@@ -30,7 +30,7 @@ func (p *Pair) Grow(n int) error {
 		return fmt.Errorf("splice: want %d bytes, max pipe size %d", n, maxPipeSize)
 	}
 
-	newsize, errNo := fcntl(p.r.Fd(), F_SETPIPE_SZ, n)
+	newsize, errNo := fcntl(uintptr(p.r), F_SETPIPE_SZ, n)
 	if errNo != 0 {
 		return fmt.Errorf("splice: fcntl returned %v", errNo)
 	}
@@ -43,8 +43,8 @@ func (p *Pair) Cap() int {
 }
 
 func (p *Pair) Close() error {
-	err1 := p.r.Close()
-	err2 := p.w.Close()
+	err1 := syscall.Close(p.r)
+	err2 := syscall.Close(p.w)
 	if err1 != nil {
 		return err1
 	}
@@ -52,17 +52,17 @@ func (p *Pair) Close() error {
 }
 
 func (p *Pair) Read(d []byte) (n int, err error) {
-	return p.r.Read(d)
+	return syscall.Read(p.r, d)
 }
 
-func (p *Pair) ReadFd() uintptr {
-	return p.r.Fd()
+func (p *Pair) Write(d []byte) (n int, err error) {
+	return syscall.Write(p.w, d)
 }
 
-func (p *Pair) WriteFd() uintptr {
-	return p.w.Fd()
+func (p *Pair) ReadFd() uintptr {
+	return uintptr(p.r)
 }
 
-func (p *Pair) Write(d []byte) (n int, err error) {
-	return p.w.Write(d)
+func (p *Pair) WriteFd() uintptr {
+	return uintptr(p.w)
 }

splice/pair_linux.go

@@ -11,7 +11,7 @@ import (
 )
 
 func (p *Pair) LoadFromAt(fd uintptr, sz int, off int64) (int, error) {
-	n, err := syscall.Splice(int(fd), &off, int(p.w.Fd()), nil, sz, 0)
+	n, err := syscall.Splice(int(fd), &off, p.w, nil, sz, 0)
 	return int(n), err
 }
 
@@ -21,7 +21,7 @@ func (p *Pair) LoadFrom(fd uintptr, sz int) (int, error) {
 			sz, p.size)
 	}
 
-	n, err := syscall.Splice(int(fd), nil, int(p.w.Fd()), nil, sz, 0)
+	n, err := syscall.Splice(int(fd), nil, p.w, nil, sz, 0)
 	if err != nil {
 		err = os.NewSyscallError("Splice load from", err)
 	}
@@ -29,7 +29,7 @@ func (p *Pair) LoadFrom(fd uintptr, sz int) (int, error) {
 }
 
 func (p *Pair) WriteTo(fd uintptr, n int) (int, error) {
-	m, err := syscall.Splice(int(p.r.Fd()), nil, int(fd), nil, int(n), 0)
+	m, err := syscall.Splice(p.r, nil, int(fd), nil, int(n), 0)
 	if err != nil {
 		err = os.NewSyscallError("Splice write", err)
 	}

splice/pool.go

@@ -5,8 +5,8 @@
 package splice
 
 import (
-	"io"
 	"sync"
+	"syscall"
 )
 
 var splicePool *pairPool
@@ -95,10 +95,15 @@ func (me *pairPool) get() (p *Pair, err error) {
 
 var discardBuffer [32 * 1024]byte
 
-func DiscardAll(r io.Reader) {
+func discardAll(fd int) {
 	buf := discardBuffer[:]
+	r := 0
 	for {
-		n, _ := r.Read(buf)
+		n, _ := syscall.Read(fd, buf)
+		if n > 0 {
+			r += n
+		}
+
 		if n < len(buf) {
 			break
 		}
@@ -106,7 +111,7 @@ func DiscardAll(r io.Reader) {
 }
 
 func (me *pairPool) done(p *Pair) {
-	DiscardAll(p.r)
+	discardAll(p.r)
 
 	me.Lock()
 	me.usedCount--

splice/splice.go

@@ -61,30 +61,27 @@ func fcntl(fd uintptr, cmd int, arg int) (val int, errno syscall.Errno) {
 const F_SETPIPE_SZ = 1031
 const F_GETPIPE_SZ = 1032
 
+func osPipe() (int, int, error) {
+	var fds [2]int
+	err := syscall.Pipe2(fds[:], syscall.O_NONBLOCK)
+	return fds[0], fds[1], err
+}
+
 func newSplicePair() (p *Pair, err error) {
 	p = &Pair{}
-	p.r, p.w, err = os.Pipe()
+	p.r, p.w, err = osPipe()
 	if err != nil {
 		return nil, err
 	}
-
-	errNo := syscall.Errno(0)
-	for _, f := range []*os.File{p.r, p.w} {
-		_, errNo = fcntl(f.Fd(), syscall.F_SETFL, syscall.O_NONBLOCK)
-		if errNo != 0 {
-			p.Close()
-			return nil, os.NewSyscallError("fcntl setfl", errNo)
-		}
-	}
-
-	p.size, errNo = fcntl(p.r.Fd(), F_GETPIPE_SZ, 0)
-	if errNo == syscall.EINVAL {
+	var errNo syscall.Errno
+	p.size, errNo = fcntl(uintptr(p.r), F_GETPIPE_SZ, 0)
+	if err == syscall.EINVAL {
 		p.size = DefaultPipeSize
 		return p, nil
 	}
 	if errNo != 0 {
 		p.Close()
-		return nil, os.NewSyscallError("fcntl getsize", errNo)
+		return nil, fmt.Errorf("fcntl getsize: %v", errNo)
 	}
 	return p, nil
 }