github.com/JimmyHuang454/JLS-go@v0.0.0-20230831150107-90d536585ba0/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, bool) {
    15  	if err := dstFD.writeLock(); err != nil {
    16  		return 0, err, false
    17  	}
    18  	defer dstFD.writeUnlock()
    19  	if err := dstFD.pd.prepareWrite(dstFD.isFile); err != nil {
    20  		return 0, err, false
    21  	}
    22  
    23  	dst := dstFD.Sysfd
    24  	var (
    25  		written int64
    26  		err     error
    27  		handled = true
    28  	)
    29  	for remain > 0 {
    30  		n := maxSendfileSize
    31  		if int64(n) > remain {
    32  			n = int(remain)
    33  		}
    34  		n, err1 := syscall.Sendfile(dst, src, nil, n)
    35  		if n > 0 {
    36  			written += int64(n)
    37  			remain -= int64(n)
    38  		} else if n == 0 && err1 == nil {
    39  			break
    40  		}
    41  		if err1 == syscall.EINTR {
    42  			continue
    43  		}
    44  		if err1 == syscall.EAGAIN {
    45  			if err1 = dstFD.pd.waitWrite(dstFD.isFile); err1 == nil {
    46  				continue
    47  			}
    48  		}
    49  		if err1 != nil {
    50  			// This includes syscall.ENOSYS (no kernel
    51  			// support) and syscall.EINVAL (fd types which
    52  			// don't implement sendfile)
    53  			err = err1
    54  			handled = false
    55  			break
    56  		}
    57  	}
    58  	return written, err, handled
    59  }