libgo/go/net/sendfile_dragonfly.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         // DragonFly uses 0 as the "until EOF" value. If you pass in more bytes than the
  26         // file contains, it will loop back to the beginning ad nauseam until it's sent
  27         // exactly the number of bytes told to. As such, we need to know exactly how many
  28         // bytes to send.
  29         var remain int64 = 0
  30
  31         lr, ok := r.(*io.LimitedReader)
  32         if ok {
  33                 remain, r = lr.N, lr.R
  34                 if remain <= 0 {
  35                         return 0, nil, true
  36                 }
  37         }
  38         f, ok := r.(*os.File)
  39         if !ok {
  40                 return 0, nil, false
  41         }
  42
  43         if remain == 0 {
  44                 fi, err := f.Stat()
  45                 if err != nil {
  46                         return 0, err, false
  47                 }
  48
  49                 remain = fi.Size()
  50         }
  51
  52         // The other quirk with DragonFly's sendfile implementation is that it doesn't
  53         // use the current position of the file -- if you pass it offset 0, it starts
  54         // from offset 0. There's no way to tell it "start from current position", so
  55         // we have to manage that explicitly.
  56         pos, err := f.Seek(0, os.SEEK_CUR)
  57         if err != nil {
  58                 return 0, err, false
  59         }
  60
  61         if err := c.writeLock(); err != nil {
  62                 return 0, err, true
  63         }
  64         defer c.writeUnlock()
  65
  66         dst := c.sysfd
  67         src := int(f.Fd())
  68         for remain > 0 {
  69                 n := maxSendfileSize
  70                 if int64(n) > remain {
  71                         n = int(remain)
  72                 }
  73                 pos1 := pos
  74                 n, err1 := syscall.Sendfile(dst, src, &pos1, n)
  75                 if n > 0 {
  76                         pos += int64(n)
  77                         written += int64(n)
  78                         remain -= int64(n)
  79                 }
  80                 if n == 0 && err1 == nil {
  81                         break
  82                 }
  83                 if err1 == syscall.EAGAIN {
  84                         if err1 = c.pd.WaitWrite(); err1 == nil {
  85                                 continue
  86                         }
  87                 }
  88                 if err1 == syscall.EINTR {
  89                         continue
  90                 }
  91                 if err1 != nil {
  92                         // This includes syscall.ENOSYS (no kernel
  93                         // support) and syscall.EINVAL (fd types which
  94                         // don't implement sendfile together)
  95                         err = &OpError{"sendfile", c.net, c.raddr, err1}
  96                         break
  97                 }
  98         }
  99         if lr != nil {
 100                 lr.N = remain
 101         }
 102         return written, err, written > 0
 103 }