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/* save-cwd.c -- Save and restore current working directory.
Copyright (C) 1995, 1997-1998, 2003-2006, 2009-2020 Free Software
Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Gnulib needs to save and restore the current working directory to
fully emulate functions like fstatat. But Emacs doesn't care what
the current working directory is; it always uses absolute file
names. This module replaces the Gnulib module by omitting the code
that Emacs does not need. */
#include <config.h>
#include "save-cwd.h"
#include <fcntl.h>
#include <unistd.h>
/* Record the location of the current working directory in CWD so that
the program may change to other directories and later use restore_cwd
to return to the recorded location. This function may allocate
space using malloc (via getcwd) or leave a file descriptor open;
use free_cwd to perform the necessary free or close. Upon failure,
no memory is allocated, any locally opened file descriptors are
closed; return non-zero -- in that case, free_cwd need not be
called, but doing so is ok. Otherwise, return zero.
The _raison d'etre_ for this interface is that the working directory
is sometimes inaccessible, and getcwd is not robust or as efficient.
So, we prefer to use the open/fchdir approach, but fall back on
getcwd if necessary. This module works for most cases with just
the getcwd-lgpl module, but to be truly robust, use the getcwd module.
Some systems lack fchdir altogether: e.g., OS/2, pre-2001 Cygwin,
SCO Xenix. Also, SunOS 4 and Irix 5.3 provide the function, yet it
doesn't work for partitions on which auditing is enabled. If
you're still using an obsolete system with these problems, please
send email to the maintainer of this code. */
#if !defined HAVE_FCHDIR && !defined fchdir
# define fchdir(fd) (-1)
#endif
int
save_cwd (struct saved_cwd *cwd)
{
cwd->desc = open (".", O_SEARCH | O_CLOEXEC);
/* The 'name' member is present only to minimize differences from
gnulib. Initialize it to zero, if only to simplify debugging. */
cwd->name = 0;
return 0;
}
/* Change to recorded location, CWD, in directory hierarchy.
Upon failure, return -1 (errno is set by chdir or fchdir).
Upon success, return zero. */
int
restore_cwd (const struct saved_cwd *cwd)
{
/* Restore the previous directory if possible, to avoid tying down
the file system of the new directory (Bug#18232).
Don't worry if fchdir fails, as Emacs doesn't care what the
working directory is. The fchdir call is inside an 'if' merely to
pacify compilers that complain if fchdir's return value is ignored. */
if (fchdir (cwd->desc) == 0)
return 0;
return 0;
}
void
free_cwd (struct saved_cwd *cwd)
{
close (cwd->desc);
}
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