github.com/stolowski/snapd@v0.0.0-20210407085831-115137ce5a22/osutil/cp_linux.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2014-2015 Canonical Ltd
     5   *
     6   * This program is free software: you can redistribute it and/or modify
     7   * it under the terms of the GNU General Public License version 3 as
     8   * published by the Free Software Foundation.
     9   *
    10   * This program is distributed in the hope that it will be useful,
    11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13   * GNU General Public License for more details.
    14   *
    15   * You should have received a copy of the GNU General Public License
    16   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17   *
    18   */
    19  
    20  package osutil
    21  
    22  import (
    23  	"os"
    24  	"syscall"
    25  )
    26  
    27  const maxint = int64(^uint(0) >> 1)
    28  
    29  var maxcp = maxint // overridden in testing
    30  
    31  func doCopyFile(fin, fout fileish, fi os.FileInfo) error {
    32  	size := fi.Size()
    33  	var offset int64
    34  	for offset < size {
    35  		// sendfile is funny; it only copies up to maxint
    36  		// bytes at a time, but takes an int64 offset.
    37  		count := size - offset
    38  		if count > maxcp {
    39  			count = maxcp
    40  		}
    41  
    42  		if _, err := syscall.Sendfile(int(fout.Fd()), int(fin.Fd()), &offset, int(count)); err != nil {
    43  			return err
    44  		}
    45  	}
    46  
    47  	return nil
    48  }