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) (written int64, err error, handled bool) {
    15  	defer func() {
    16  		TestHookDidSendFile(dstFD, src, written, err, handled)
    17  	}()
    18  	if err := dstFD.writeLock(); err != nil {
    19  		return 0, err, false
    20  	}
    21  	defer dstFD.writeUnlock()
    22  
    23  	if err := dstFD.pd.prepareWrite(dstFD.isFile); err != nil {
    24  		return 0, err, false
    25  	}
    26  
    27  	dst := dstFD.Sysfd
    28  	for remain > 0 {
    29  		n := maxSendfileSize
    30  		if int64(n) > remain {
    31  			n = int(remain)
    32  		}
    33  		n, err = syscall.Sendfile(dst, src, nil, n)
    34  		if n > 0 {
    35  			written += int64(n)
    36  			remain -= int64(n)
    37  			continue
    38  		} else if err != syscall.EAGAIN && err != syscall.EINTR {
    39  			// This includes syscall.ENOSYS (no kernel
    40  			// support) and syscall.EINVAL (fd types which
    41  			// don't implement sendfile), and other errors.
    42  			// We should end the loop when there is no error
    43  			// returned from sendfile(2) or it is not a retryable error.
    44  			break
    45  		}
    46  		if err == syscall.EINTR {
    47  			continue
    48  		}
    49  		if err = dstFD.pd.waitWrite(dstFD.isFile); err != nil {
    50  			break
    51  		}
    52  	}
    53  	if err == syscall.EAGAIN {
    54  		err = nil
    55  	}
    56  	handled = written != 0 || (err != syscall.ENOSYS && err != syscall.EINVAL)
    57  	return
    58  }
    59
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