libgo/go/os/readfrom_linux.go

   1 // Copyright 2020 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 os
   6
   7 import (
   8         "internal/poll"
   9         "io"
  10 )
  11
  12 var pollCopyFileRange = poll.CopyFileRange
  13
  14 func (f *File) readFrom(r io.Reader) (written int64, handled bool, err error) {
  15         // copy_file_range(2) does not support destinations opened with
  16         // O_APPEND, so don't even try.
  17         if f.appendMode {
  18                 return 0, false, nil
  19         }
  20
  21         remain := int64(1 << 62)
  22
  23         lr, ok := r.(*io.LimitedReader)
  24         if ok {
  25                 remain, r = lr.N, lr.R
  26                 if remain <= 0 {
  27                         return 0, true, nil
  28                 }
  29         }
  30
  31         src, ok := r.(*File)
  32         if !ok {
  33                 return 0, false, nil
  34         }
  35         if src.checkValid("ReadFrom") != nil {
  36                 // Avoid returning the error as we report handled as false,
  37                 // leave further error handling as the responsibility of the caller.
  38                 return 0, false, nil
  39         }
  40
  41         written, handled, err = pollCopyFileRange(&f.pfd, &src.pfd, remain)
  42         if lr != nil {
  43                 lr.N -= written
  44         }
  45         return written, handled, NewSyscallError("copy_file_range", err)
  46 }