github.com/geraldss/go/src@v0.0.0-20210511222824-ac7d0ebfc235/internal/poll/sendfile_linux.go (about)

     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  		} else if n == 0 && err1 == nil {
    33  			break
    34  		}
    35  		if err1 == syscall.EINTR {
    36  			continue
    37  		}
    38  		if err1 == syscall.EAGAIN {
    39  			if err1 = dstFD.pd.waitWrite(dstFD.isFile); err1 == nil {
    40  				continue
    41  			}
    42  		}
    43  		if err1 != nil {
    44  			// This includes syscall.ENOSYS (no kernel
    45  			// support) and syscall.EINVAL (fd types which
    46  			// don't implement sendfile)
    47  			err = err1
    48  			break
    49  		}
    50  	}
    51  	return written, err
    52  }