Don't prevent random file systems from being unmounted.
This fix relies on having the 'fchdir' function, and on having "." be searchable (or at least readable, on platforms lacking O_SEARCH), but that's good enough to handle the vast majority of cases and the remaining folks can just live with the annoyance of file systems that occasionally can't be unmounted. * configure.ac (fchdir): New function to check for. * lib/save-cwd.c: Copy from gnulib, except omit the part that allocates memory, since that can cause problems in Emacs. * lib/save-cwd.h: Copy from gnulib. Fixes: debbugs:18232
This commit is contained in:
Paul Eggert
parent
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4 changed files with 117 additions and 28 deletions
13
ChangeLog
13
ChangeLog
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@ -1,3 +1,16 @@
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2014-08-10 Paul Eggert <eggert@cs.ucla.edu>
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Don't prevent random file systems from being unmounted (Bug#18232).
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This fix relies on having the 'fchdir' function, and on having
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"." be searchable (or at least readable, on platforms lacking O_SEARCH),
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but that's good enough to handle the vast majority of cases and the
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remaining folks can just live with the annoyance of file systems
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that occasionally can't be unmounted.
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* configure.ac (fchdir): New function to check for.
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* lib/save-cwd.c: Copy from gnulib, except omit the part that
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allocates memory, since that can cause problems in Emacs.
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* lib/save-cwd.h: Copy from gnulib.
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2014-07-11 Paul Eggert <eggert@cs.ucla.edu>
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* Makefile.in (install-arch-indep): Avoid readdir race (Bug#17971).
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@ -3508,7 +3508,7 @@ esac
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AC_SUBST(BLESSMAIL_TARGET)
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AC_CHECK_FUNCS(accept4 gethostname \
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AC_CHECK_FUNCS(accept4 fchdir gethostname \
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getrusage get_current_dir_name \
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lrand48 \
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select getpagesize setlocale \
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@ -1,3 +1,91 @@
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/* save-cwd.c -- Save and restore current working directory.
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Copyright (C) 1995, 1997-1998, 2003-2006, 2009-2014 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 <http://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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#define SAVE_CWD_INLINE _GL_EXTERN_INLINE
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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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int
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save_cwd (struct saved_cwd *cwd)
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{
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#ifdef HAVE_FCHDIR
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cwd->desc = open (".", O_SEARCH | O_CLOEXEC);
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#else
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cwd->desc = -1;
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#endif
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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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#ifdef HAVE_FCHDIR
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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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if (fchdir (cwd->desc) == 0)
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return 0;
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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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#endif
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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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@ -1,6 +1,7 @@
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/* Do not save and restore the current working directory.
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/* Save and restore current working directory.
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Copyright 2013-2014 Free Software Foundation, Inc.
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Copyright (C) 1995, 1997-1998, 2003, 2009-2014 Free Software Foundation,
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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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@ -15,32 +16,19 @@
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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 <http://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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/* Written by Jim Meyering. */
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#ifndef SAVE_CWD_H
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#define SAVE_CWD_H 1
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# define SAVE_CWD_H 1
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_GL_INLINE_HEADER_BEGIN
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#ifndef SAVE_CWD_INLINE
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# define SAVE_CWD_INLINE _GL_INLINE
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#endif
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struct saved_cwd
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{
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int desc;
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char *name;
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};
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struct saved_cwd { int desc; };
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int save_cwd (struct saved_cwd *cwd);
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int restore_cwd (const struct saved_cwd *cwd);
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void free_cwd (struct saved_cwd *cwd);
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SAVE_CWD_INLINE int
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save_cwd (struct saved_cwd *cwd)
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{
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cwd->desc = -1;
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return 0;
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}
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SAVE_CWD_INLINE int restore_cwd (struct saved_cwd const *cwd) { return 0; }
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SAVE_CWD_INLINE void free_cwd (struct saved_cwd *cwd) { }
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_GL_INLINE_HEADER_END
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#endif
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#endif /* SAVE_CWD_H */
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