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) (written int64, err error, handled bool) {
15	defer func() {
16		TestHookDidSendFile(dstFD, src, written, err, handled)
17	}()
18	if err := dstFD.writeLock(); err != nil {
19		return 0, err, false
20	}
21	defer dstFD.writeUnlock()
22
23	if err := dstFD.pd.prepareWrite(dstFD.isFile); err != nil {
24		return 0, err, false
25	}
26
27	dst := dstFD.Sysfd
28	for remain > 0 {
29		n := maxSendfileSize
30		if int64(n) > remain {
31			n = int(remain)
32		}
33		n, err = syscall.Sendfile(dst, src, nil, n)
34		if n > 0 {
35			written += int64(n)
36			remain -= int64(n)
37			continue
38		} else if err != syscall.EAGAIN && err != syscall.EINTR {
39			// This includes syscall.ENOSYS (no kernel
40			// support) and syscall.EINVAL (fd types which
41			// don't implement sendfile), and other errors.
42			// We should end the loop when there is no error
43			// returned from sendfile(2) or it is not a retryable error.
44			break
45		}
46		if err == syscall.EINTR {
47			continue
48		}
49		if err = dstFD.pd.waitWrite(dstFD.isFile); err != nil {
50			break
51		}
52	}
53	handled = written != 0 || (err != syscall.ENOSYS && err != syscall.EINVAL)
54	return
55}
56