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save-cwd.c revision 1.1.1.1.2.1 
      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 }
     98