libgo/go/internal/poll/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 poll
   6
   7 import "syscall"
   8
   9 // maxSendfileSize is the largest chunk size we ask the kernel to copy
  10 // at a time.
  11 const maxSendfileSize int = 4 << 20
  12
  13 // SendFile wraps the sendfile system call.
  14 func 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                 }
  33                 if n == 0 && err1 == nil {
  34                         break
  35                 }
  36                 if err1 == syscall.EAGAIN {
  37                         if err1 = dstFD.pd.waitWrite(dstFD.isFile); err1 == nil {
  38                                 continue
  39                         }
  40                 }
  41                 if err1 != nil {
  42                         // This includes syscall.ENOSYS (no kernel
  43                         // support) and syscall.EINVAL (fd types which
  44                         // don't implement sendfile)
  45                         err = err1
  46                         break
  47                 }
  48         }
  49         return written, err
  50 }