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  }
    47
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