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// Copyright 2016 the Go-FUSE Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package splice
// Routines for efficient file to file copying.
import (
"fmt"
"io/ioutil"
"log"
"os"
"syscall"
)
var maxPipeSize int
var resizable bool
func Resizable() bool {
return resizable
}
func MaxPipeSize() int {
return maxPipeSize
}
// From manpage on ubuntu Lucid:
//
// Since Linux 2.6.11, the pipe capacity is 65536 bytes.
const DefaultPipeSize = 16 * 4096
// We empty pipes by splicing to /dev/null.
var devNullFD uintptr
func init() {
content, err := ioutil.ReadFile("/proc/sys/fs/pipe-max-size")
if err != nil {
maxPipeSize = DefaultPipeSize
} else {
fmt.Sscan(string(content), &maxPipeSize)
}
r, w, err := os.Pipe()
if err != nil {
log.Panicf("cannot create pipe: %v", err)
}
sz, errNo := fcntl(r.Fd(), F_GETPIPE_SZ, 0)
resizable = (errNo == 0)
_, errNo = fcntl(r.Fd(), F_SETPIPE_SZ, 2*sz)
resizable = resizable && (errNo == 0)
r.Close()
w.Close()
fd, err := syscall.Open("/dev/null", os.O_WRONLY, 0)
if err != nil {
log.Panicf("splice: %v", err)
}
devNullFD = uintptr(fd)
}
// copy & paste from syscall.
func fcntl(fd uintptr, cmd int, arg int) (val int, errno syscall.Errno) {
r0, _, e1 := syscall.Syscall(syscall.SYS_FCNTL, fd, uintptr(cmd), uintptr(arg))
val = int(r0)
errno = syscall.Errno(e1)
return
}
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 = osPipe()
if err != nil {
return nil, err
}
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, fmt.Errorf("fcntl getsize: %v", errNo)
}
return p, nil
}
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