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90 lines
3.3 KiB
C
90 lines
3.3 KiB
C
/* save-cwd.c -- Save and restore current working directory.
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Copyright (C) 1995, 1997-1998, 2003-2006, 2009-2018 Free Software
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Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* Gnulib needs to save and restore the current working directory to
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fully emulate functions like fstatat. But Emacs doesn't care what
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the current working directory is; it always uses absolute file
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names. This module replaces the Gnulib module by omitting the code
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that Emacs does not need. */
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#include <config.h>
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#include "save-cwd.h"
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#include <fcntl.h>
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#include <unistd.h>
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/* Record the location of the current working directory in CWD so that
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the program may change to other directories and later use restore_cwd
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to return to the recorded location. This function may allocate
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space using malloc (via getcwd) or leave a file descriptor open;
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use free_cwd to perform the necessary free or close. Upon failure,
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no memory is allocated, any locally opened file descriptors are
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closed; return non-zero -- in that case, free_cwd need not be
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called, but doing so is ok. Otherwise, return zero.
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The _raison d'etre_ for this interface is that the working directory
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is sometimes inaccessible, and getcwd is not robust or as efficient.
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So, we prefer to use the open/fchdir approach, but fall back on
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getcwd if necessary. This module works for most cases with just
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the getcwd-lgpl module, but to be truly robust, use the getcwd module.
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Some systems lack fchdir altogether: e.g., OS/2, pre-2001 Cygwin,
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SCO Xenix. Also, SunOS 4 and Irix 5.3 provide the function, yet it
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doesn't work for partitions on which auditing is enabled. If
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you're still using an obsolete system with these problems, please
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send email to the maintainer of this code. */
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#if !defined HAVE_FCHDIR && !defined fchdir
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# define fchdir(fd) (-1)
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#endif
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int
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save_cwd (struct saved_cwd *cwd)
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{
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cwd->desc = open (".", O_SEARCH | O_CLOEXEC);
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/* The 'name' member is present only to minimize differences from
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gnulib. Initialize it to zero, if only to simplify debugging. */
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cwd->name = 0;
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return 0;
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}
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/* Change to recorded location, CWD, in directory hierarchy.
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Upon failure, return -1 (errno is set by chdir or fchdir).
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Upon success, return zero. */
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int
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restore_cwd (const struct saved_cwd *cwd)
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{
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/* Restore the previous directory if possible, to avoid tying down
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the file system of the new directory (Bug#18232).
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Don't worry if fchdir fails, as Emacs doesn't care what the
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working directory is. The fchdir call is inside an 'if' merely to
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pacify compilers that complain if fchdir's return value is ignored. */
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if (fchdir (cwd->desc) == 0)
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return 0;
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return 0;
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}
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void
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free_cwd (struct saved_cwd *cwd)
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{
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close (cwd->desc);
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}
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