1// Copyright 2015 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// Not strictly needed, but very helpful for debugging, see issue #10221.
10//go:cgo_import_dynamic _ _ "libsendfile.so"
11//go:cgo_import_dynamic _ _ "libsocket.so"
12
13// maxSendfileSize is the largest chunk size we ask the kernel to copy
14// at a time.
15const maxSendfileSize int = 4 << 20
16
17// SendFile wraps the sendfile system call.
18func SendFile(dstFD *FD, src int, pos, remain int64) (int64, error) {
19	if err := dstFD.writeLock(); err != nil {
20		return 0, err
21	}
22	defer dstFD.writeUnlock()
23
24	dst := int(dstFD.Sysfd)
25	var written int64
26	var err error
27	for remain > 0 {
28		n := maxSendfileSize
29		if int64(n) > remain {
30			n = int(remain)
31		}
32		pos1 := pos
33		n, err1 := syscall.Sendfile(dst, src, &pos1, n)
34		if err1 == syscall.EAGAIN || err1 == syscall.EINTR {
35			// partial write may have occurred
36			n = int(pos1 - pos)
37		}
38		if n > 0 {
39			pos += int64(n)
40			written += int64(n)
41			remain -= int64(n)
42		} else if n == 0 && err1 == nil {
43			break
44		}
45		if err1 == syscall.EAGAIN {
46			if err1 = dstFD.pd.waitWrite(dstFD.isFile); err1 == nil {
47				continue
48			}
49		}
50		if err1 == syscall.EINTR {
51			continue
52		}
53		if err1 != nil {
54			// This includes syscall.ENOSYS (no kernel
55			// support) and syscall.EINVAL (fd types which
56			// don't implement sendfile)
57			err = err1
58			break
59		}
60	}
61	return written, err
62}
63