From: Paul Eggert Date: Sun, 10 Aug 2014 20:40:57 +0000 (-0700) Subject: Don't prevent random file systems from being unmounted. X-Git-Tag: emacs-24.3.93~8 X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=f22bc725a1c8294fc042f6a9541be01a177755f6;p=emacs.git 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 --- diff --git a/ChangeLog b/ChangeLog index cdf4152bc0a..6864b7043e1 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,16 @@ +2014-08-10 Paul Eggert + + Don't prevent random file systems from being unmounted (Bug#18232). + 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. + 2014-07-11 Paul Eggert * Makefile.in (install-arch-indep): Avoid readdir race (Bug#17971). diff --git a/configure.ac b/configure.ac index 8e74f799ec9..04925d59d22 100644 --- a/configure.ac +++ b/configure.ac @@ -3508,7 +3508,7 @@ esac AC_SUBST(BLESSMAIL_TARGET) -AC_CHECK_FUNCS(accept4 gethostname \ +AC_CHECK_FUNCS(accept4 fchdir gethostname \ getrusage get_current_dir_name \ lrand48 \ select getpagesize setlocale \ diff --git a/lib/save-cwd.c b/lib/save-cwd.c index b8dae34ca02..fd746584fa8 100644 --- a/lib/save-cwd.c +++ b/lib/save-cwd.c @@ -1,3 +1,91 @@ +/* save-cwd.c -- Save and restore current working directory. + + Copyright (C) 1995, 1997-1998, 2003-2006, 2009-2014 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 . */ + +/* 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 -#define SAVE_CWD_INLINE _GL_EXTERN_INLINE + #include "save-cwd.h" + +#include +#include + +/* 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. */ + +int +save_cwd (struct saved_cwd *cwd) +{ +#ifdef HAVE_FCHDIR + cwd->desc = open (".", O_SEARCH | O_CLOEXEC); +#else + cwd->desc = -1; +#endif + /* 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) +{ +#ifdef HAVE_FCHDIR + /* Restore the previous directory if possible, to avoid tying down + the file system of the new directory (Bug#18232). */ + if (fchdir (cwd->desc) == 0) + return 0; + + /* 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. */ +#endif + return 0; +} + +void +free_cwd (struct saved_cwd *cwd) +{ + close (cwd->desc); +} diff --git a/lib/save-cwd.h b/lib/save-cwd.h index 9a1eb3519c8..6b84e4601d3 100644 --- a/lib/save-cwd.h +++ b/lib/save-cwd.h @@ -1,6 +1,7 @@ -/* Do not save and restore the current working directory. +/* Save and restore current working directory. - Copyright 2013-2014 Free Software Foundation, Inc. + Copyright (C) 1995, 1997-1998, 2003, 2009-2014 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 @@ -15,32 +16,19 @@ You should have received a copy of the GNU General Public License along with this program. If not, see . */ -/* 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. */ +/* Written by Jim Meyering. */ #ifndef SAVE_CWD_H -#define SAVE_CWD_H 1 +# define SAVE_CWD_H 1 -_GL_INLINE_HEADER_BEGIN -#ifndef SAVE_CWD_INLINE -# define SAVE_CWD_INLINE _GL_INLINE -#endif +struct saved_cwd + { + int desc; + char *name; + }; -struct saved_cwd { int desc; }; +int save_cwd (struct saved_cwd *cwd); +int restore_cwd (const struct saved_cwd *cwd); +void free_cwd (struct saved_cwd *cwd); -SAVE_CWD_INLINE int -save_cwd (struct saved_cwd *cwd) -{ - cwd->desc = -1; - return 0; -} - -SAVE_CWD_INLINE int restore_cwd (struct saved_cwd const *cwd) { return 0; } -SAVE_CWD_INLINE void free_cwd (struct saved_cwd *cwd) { } - -_GL_INLINE_HEADER_END - -#endif +#endif /* SAVE_CWD_H */