sendfile_linux.go

Documentation: internal/poll

     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  }
    51
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