1// Copyright 2011 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package poll
6
7import "syscall"
8
9// maxSendfileSize is the largest chunk size we ask the kernel to copy
10// at a time.
11const maxSendfileSize int = 4 << 20
12
13// SendFile wraps the sendfile system call.
14func SendFile(dstFD *FD, src int, remain int64) (int64, error) {
15	if err := dstFD.writeLock(); err != nil {
16		return 0, err
17	}
18	defer dstFD.writeUnlock()
19
20	dst := int(dstFD.Sysfd)
21	var written int64
22	var err error
23	for remain > 0 {
24		n := maxSendfileSize
25		if int64(n) > remain {
26			n = int(remain)
27		}
28		n, err1 := syscall.Sendfile(dst, src, nil, n)
29		if n > 0 {
30			written += int64(n)
31			remain -= int64(n)
32		} else if n == 0 && err1 == nil {
33			break
34		}
35		if err1 == syscall.EAGAIN {
36			if err1 = dstFD.pd.waitWrite(dstFD.isFile); err1 == nil {
37				continue
38			}
39		}
40		if err1 != nil {
41			// This includes syscall.ENOSYS (no kernel
42			// support) and syscall.EINVAL (fd types which
43			// don't implement sendfile)
44			err = err1
45			break
46		}
47	}
48	return written, err
49}
50