/usr/share/gocode/src/github.com/hanwen/go-fuse/fuse/splice_linux.go is in golang-github-hanwen-go-fuse-dev 0.0~git20171124.0.14c3015-4.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 | // 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 fuse
import (
"fmt"
"os"
"github.com/hanwen/go-fuse/splice"
)
func (s *Server) setSplice() {
s.canSplice = splice.Resizable()
}
// trySplice: Zero-copy read from fdData.Fd into /dev/fuse
//
// This is a four-step process:
//
// 1) Splice data form fdData.Fd into the "pair1" pipe buffer --> pair1: [payload]
// Now we know the actual payload length and can
// construct the reply header
// 2) Write header into the "pair2" pipe buffer --> pair2: [header]
// 4) Splice data from "pair1" into "pair2" --> pair2: [header][payload]
// 3) Splice the data from "pair2" into /dev/fuse
//
// This dance is neccessary because header and payload cannot be split across
// two splices and we cannot seek in a pipe buffer.
func (ms *Server) trySplice(header []byte, req *request, fdData *readResultFd) error {
var err error
// Get a pair of connected pipes
pair1, err := splice.Get()
if err != nil {
return err
}
defer splice.Done(pair1)
// Grow buffer pipe to requested size + one extra page
// Without the extra page the kernel will block once the pipe is almost full
pair1Sz := fdData.Size() + os.Getpagesize()
if err := pair1.Grow(pair1Sz); err != nil {
return err
}
// Read data from file
payloadLen, err := pair1.LoadFromAt(fdData.Fd, fdData.Size(), fdData.Off)
if err != nil {
// TODO - extract the data from splice.
return err
}
// Get another pair of connected pipes
pair2, err := splice.Get()
if err != nil {
return err
}
defer splice.Done(pair2)
// Grow pipe to header + actually read size + one extra page
// Without the extra page the kernel will block once the pipe is almost full
header = req.serializeHeader(payloadLen)
total := len(header) + payloadLen
pair2Sz := total + os.Getpagesize()
if err := pair2.Grow(pair2Sz); err != nil {
return err
}
// Write header into pair2
n, err := pair2.Write(header)
if err != nil {
return err
}
if n != len(header) {
return fmt.Errorf("Short write into splice: wrote %d, want %d", n, len(header))
}
// Write data into pair2
n, err = pair2.LoadFrom(pair1.ReadFd(), payloadLen)
if err != nil {
return err
}
if n != payloadLen {
return fmt.Errorf("Short splice: wrote %d, want %d", n, payloadLen)
}
// Write header + data to /dev/fuse
_, err = pair2.WriteTo(uintptr(ms.mountFd), total)
if err != nil {
return err
}
return nil
}
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