libgo/go/net/sendfile_linux.go

   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
   5 package net
   6
   7 import (
   8         "io"
   9         "os"
  10         "syscall"
  11 )
  12
  13 // maxSendfileSize is the largest chunk size we ask the kernel to copy
  14 // at a time.
  15 const maxSendfileSize int = 4 << 20
  16
  17 // sendFile copies the contents of r to c using the sendfile
  18 // system call to minimize copies.
  19 //
  20 // if handled == true, sendFile returns the number of bytes copied and any
  21 // non-EOF error.
  22 //
  23 // if handled == false, sendFile performed no work.
  24 func sendFile(c *netFD, r io.Reader) (written int64, err error, handled bool) {
  25         var remain int64 = 1 << 62 // by default, copy until EOF
  26
  27         lr, ok := r.(*io.LimitedReader)
  28         if ok {
  29                 remain, r = lr.N, lr.R
  30                 if remain <= 0 {
  31                         return 0, nil, true
  32                 }
  33         }
  34         f, ok := r.(*os.File)
  35         if !ok {
  36                 return 0, nil, false
  37         }
  38
  39         if err := c.writeLock(); err != nil {
  40                 return 0, err, true
  41         }
  42         defer c.writeUnlock()
  43
  44         dst := c.sysfd
  45         src := int(f.Fd())
  46         for remain > 0 {
  47                 n := maxSendfileSize
  48                 if int64(n) > remain {
  49                         n = int(remain)
  50                 }
  51                 n, err1 := syscall.Sendfile(dst, src, nil, n)
  52                 if n > 0 {
  53                         written += int64(n)
  54                         remain -= int64(n)
  55                 }
  56                 if n == 0 && err1 == nil {
  57                         break
  58                 }
  59                 if err1 == syscall.EAGAIN {
  60                         if err1 = c.pd.waitWrite(); err1 == nil {
  61                                 continue
  62                         }
  63                 }
  64                 if err1 != nil {
  65                         // This includes syscall.ENOSYS (no kernel
  66                         // support) and syscall.EINVAL (fd types which
  67                         // don't implement sendfile)
  68                         err = err1
  69                         break
  70                 }
  71         }
  72         if lr != nil {
  73                 lr.N = remain
  74         }
  75         if err != nil {
  76                 err = os.NewSyscallError("sendfile", err)
  77         }
  78         return written, err, written > 0
  79 }