writev.go

     1  // Copyright 2016 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  //go:build unix
     6  
     7  package poll
     8  
     9  import (
    10  	"io"
    11  	"runtime"
    12  	"syscall"
    13  )
    14  
    15  // Writev wraps the writev system call.
    16  func (fd *FD) Writev(v *[][]byte) (int64, error) {
    17  	if err := fd.writeLock(); err != nil {
    18  		return 0, err
    19  	}
    20  	defer fd.writeUnlock()
    21  	if err := fd.pd.prepareWrite(fd.isFile); err != nil {
    22  		return 0, err
    23  	}
    24  
    25  	var iovecs []syscall.Iovec
    26  	if fd.iovecs != nil {
    27  		iovecs = *fd.iovecs
    28  	}
    29  	// TODO: read from sysconf(_SC_IOV_MAX)? The Linux default is
    30  	// 1024 and this seems conservative enough for now. Darwin's
    31  	// UIO_MAXIOV also seems to be 1024.
    32  	maxVec := 1024
    33  	if runtime.GOOS == "aix" || runtime.GOOS == "solaris" {
    34  		// IOV_MAX is set to XOPEN_IOV_MAX on AIX and Solaris.
    35  		maxVec = 16
    36  	}
    37  
    38  	var n int64
    39  	var err error
    40  	for len(*v) > 0 {
    41  		iovecs = iovecs[:0]
    42  		for _, chunk := range *v {
    43  			if len(chunk) == 0 {
    44  				continue
    45  			}
    46  			iovecs = append(iovecs, newIovecWithBase(&chunk[0]))
    47  			if fd.IsStream && len(chunk) > 1<<30 {
    48  				iovecs[len(iovecs)-1].SetLen(1 << 30)
    49  				break // continue chunk on next writev
    50  			}
    51  			iovecs[len(iovecs)-1].SetLen(len(chunk))
    52  			if len(iovecs) == maxVec {
    53  				break
    54  			}
    55  		}
    56  		if len(iovecs) == 0 {
    57  			break
    58  		}
    59  		if fd.iovecs == nil {
    60  			fd.iovecs = new([]syscall.Iovec)
    61  		}
    62  		*fd.iovecs = iovecs // cache
    63  
    64  		var wrote uintptr
    65  		wrote, err = writev(fd.Sysfd, iovecs)
    66  		if wrote == ^uintptr(0) {
    67  			wrote = 0
    68  		}
    69  		TestHookDidWritev(int(wrote))
    70  		n += int64(wrote)
    71  		consume(v, int64(wrote))
    72  		clear(iovecs)
    73  		if err != nil {
    74  			if err == syscall.EINTR {
    75  				continue
    76  			}
    77  			if err == syscall.EAGAIN {
    78  				if err = fd.pd.waitWrite(fd.isFile); err == nil {
    79  					continue
    80  				}
    81  			}
    82  			break
    83  		}
    84  		if n == 0 {
    85  			err = io.ErrUnexpectedEOF
    86  			break
    87  		}
    88  	}
    89  	return n, err
    90  }
    91
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