Initial commit

Proof-of-concept implementation. Bugs will occur.

vendor/github.com/hanwen/go-fuse/v2/splice/splice.go

@@ -0,0 +1,106 @@
+//go:build linux
+
+// 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"
+	"log"
+	"os"
+	"sync"
+	"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
+
+var (
+	devNullFDOnce  sync.Once
+	devNullFDValue int
+)
+
+func init() {
+	content, err := os.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()
+}
+
+// We empty pipes by splicing to /dev/null.
+func devNullFD() int {
+	devNullFDOnce.Do(func() {
+		fd, err := syscall.Open("/dev/null", os.O_WRONLY, 0)
+		if err != nil {
+			panic(fmt.Sprintf("failed to open /dev/null: %s", err))
+		}
+		devNullFDValue = fd
+	})
+	return devNullFDValue
+}
+
+// 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
+}