98 lines
2 KiB
Go
98 lines
2 KiB
Go
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// Copyright 2016 the Go-FUSE Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package splice
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// Routines for efficient file to file copying.
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import (
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"fmt"
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"io/ioutil"
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"log"
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"os"
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"syscall"
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)
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var maxPipeSize int
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var resizable bool
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func Resizable() bool {
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return resizable
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}
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func MaxPipeSize() int {
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return maxPipeSize
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}
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// From manpage on ubuntu Lucid:
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//
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// Since Linux 2.6.11, the pipe capacity is 65536 bytes.
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const DefaultPipeSize = 16 * 4096
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// We empty pipes by splicing to /dev/null.
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var devNullFD uintptr
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func init() {
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content, err := ioutil.ReadFile("/proc/sys/fs/pipe-max-size")
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if err != nil {
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maxPipeSize = DefaultPipeSize
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} else {
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fmt.Sscan(string(content), &maxPipeSize)
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}
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r, w, err := os.Pipe()
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if err != nil {
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log.Panicf("cannot create pipe: %v", err)
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}
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sz, errNo := fcntl(r.Fd(), F_GETPIPE_SZ, 0)
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resizable = (errNo == 0)
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_, errNo = fcntl(r.Fd(), F_SETPIPE_SZ, 2*sz)
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resizable = resizable && (errNo == 0)
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r.Close()
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w.Close()
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fd, err := syscall.Open("/dev/null", os.O_WRONLY, 0)
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if err != nil {
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log.Panicf("splice: %v", err)
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}
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devNullFD = uintptr(fd)
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}
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// copy & paste from syscall.
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func fcntl(fd uintptr, cmd int, arg int) (val int, errno syscall.Errno) {
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r0, _, e1 := syscall.Syscall(syscall.SYS_FCNTL, fd, uintptr(cmd), uintptr(arg))
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val = int(r0)
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errno = syscall.Errno(e1)
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return
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}
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const F_SETPIPE_SZ = 1031
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const F_GETPIPE_SZ = 1032
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func osPipe() (int, int, error) {
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var fds [2]int
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err := syscall.Pipe2(fds[:], syscall.O_NONBLOCK)
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return fds[0], fds[1], err
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}
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func newSplicePair() (p *Pair, err error) {
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p = &Pair{}
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p.r, p.w, err = osPipe()
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if err != nil {
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return nil, err
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}
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var errNo syscall.Errno
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p.size, errNo = fcntl(uintptr(p.r), F_GETPIPE_SZ, 0)
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if err == syscall.EINVAL {
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p.size = DefaultPipeSize
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return p, nil
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}
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if errNo != 0 {
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p.Close()
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return nil, fmt.Errorf("fcntl getsize: %v", errNo)
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}
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return p, nil
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}
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