1  /* save-cwd.c -- Save and restore current working directory.
       2  
       3     Copyright (C) 1995, 1997-1998, 2003-2006, 2009-2022 Free Software
       4     Foundation, Inc.
       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 as published by
       8     the Free Software Foundation, either version 3 of the License, or
       9     (at your option) any later version.
      10  
      11     This program is distributed in the hope that it will be useful,
      12     but WITHOUT ANY WARRANTY; without even the implied warranty of
      13     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      14     GNU General Public License for more details.
      15  
      16     You should have received a copy of the GNU General Public License
      17     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
      18  
      19  /* Written by Jim Meyering.  */
      20  
      21  #include <config.h>
      22  
      23  #include "save-cwd.h"
      24  
      25  #include <errno.h>
      26  #include <fcntl.h>
      27  #include <stdbool.h>
      28  #include <stdio.h>
      29  #include <stdlib.h>
      30  
      31  #include "chdir-long.h"
      32  #include "unistd--.h"
      33  
      34  #if GNULIB_FCNTL_SAFER
      35  # include "fcntl--.h"
      36  #else
      37  # define GNULIB_FCNTL_SAFER 0
      38  #endif
      39  
      40  /* Record the location of the current working directory in CWD so that
      41     the program may change to other directories and later use restore_cwd
      42     to return to the recorded location.  This function may allocate
      43     space using malloc (via getcwd) or leave a file descriptor open;
      44     use free_cwd to perform the necessary free or close.  Upon failure,
      45     no memory is allocated, any locally opened file descriptors are
      46     closed;  return non-zero -- in that case, free_cwd need not be
      47     called, but doing so is ok.  Otherwise, return zero.
      48  
      49     The _raison d'etre_ for this interface is that the working directory
      50     is sometimes inaccessible, and getcwd is not robust or as efficient.
      51     So, we prefer to use the open/fchdir approach, but fall back on
      52     getcwd if necessary.  This module works for most cases with just
      53     the getcwd-lgpl module, but to be truly robust, use the getcwd module.
      54  
      55     Some systems lack fchdir altogether: e.g., OS/2, pre-2001 Cygwin,
      56     SCO Xenix.  Also, SunOS 4 and Irix 5.3 provide the function, yet it
      57     doesn't work for partitions on which auditing is enabled.  If
      58     you're still using an obsolete system with these problems, please
      59     send email to the maintainer of this code.  */
      60  
      61  int
      62  save_cwd (struct saved_cwd *cwd)
      63  {
      64    cwd->name = NULL;
      65  
      66    cwd->desc = open (".", O_SEARCH | O_CLOEXEC);
      67    if (!GNULIB_FCNTL_SAFER)
      68      cwd->desc = fd_safer_flag (cwd->desc, O_CLOEXEC);
      69    if (cwd->desc < 0)
      70      {
      71        cwd->name = getcwd (NULL, 0);
      72        return cwd->name ? 0 : -1;
      73      }
      74  
      75    return 0;
      76  }
      77  
      78  /* Change to recorded location, CWD, in directory hierarchy.
      79     Upon failure, return -1 (errno is set by chdir or fchdir).
      80     Upon success, return zero.  */
      81  
      82  int
      83  restore_cwd (const struct saved_cwd *cwd)
      84  {
      85    if (0 <= cwd->desc)
      86      return fchdir (cwd->desc);
      87    else
      88      return chdir_long (cwd->name);
      89  }
      90  
      91  void
      92  free_cwd (struct saved_cwd *cwd)
      93  {
      94    if (cwd->desc >= 0)
      95      close (cwd->desc);
      96    free (cwd->name);
      97  }