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  	if err := dstFD.pd.prepareWrite(dstFD.isFile); err != nil {
    20  		return 0, err
    21  	}
    22  
    23  	dst := dstFD.Sysfd
    24  	var written int64
    25  	var err error
    26  	for remain > 0 {
    27  		n := maxSendfileSize
    28  		if int64(n) > remain {
    29  			n = int(remain)
    30  		}
    31  		n, err1 := syscall.Sendfile(dst, src, nil, n)
    32  		if n > 0 {
    33  			written += int64(n)
    34  			remain -= int64(n)
    35  		} else if n == 0 && err1 == nil {
    36  			break
    37  		}
    38  		if err1 == syscall.EINTR {
    39  			continue
    40  		}
    41  		if err1 == syscall.EAGAIN {
    42  			if err1 = dstFD.pd.waitWrite(dstFD.isFile); err1 == nil {
    43  				continue
    44  			}
    45  		}
    46  		if err1 != nil {
    47  			// This includes syscall.ENOSYS (no kernel
    48  			// support) and syscall.EINVAL (fd types which
    49  			// don't implement sendfile)
    50  			err = err1
    51  			break
    52  		}
    53  	}
    54  	return written, err
    55  }
    56
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