+2013-03-02 Paul Eggert <eggert@cs.ucla.edu>
+
+ The lock for FILE is now .#FILE or .#-FILE (Bug#13807).
+ The old approach, which fell back on DIR/.#FILE.0 through
+ DIR/.#FILE.9, had race conditions that could not be easily fixed.
+ If DIR/.#FILE is a non-symlink file, Emacs now does not create a
+ lock file for DIR/FILE; that is, DIR/FILE is no longer partly
+ protected by a lock if DIR/.#FILE is a non-symlink file ("partly"
+ because the locking mechanism was never reliable in that case).
+ This patch fixes this and other bugs discovered by a code
+ inspection that was prompted by
+ <http://lists.gnu.org/archive/html/emacs-devel/2013-02/msg00531.html>.
+ Also, this patch switches to .#-FILE (not .#FILE) on MS-Windows,
+ to avoid interoperability problems between the MS-Windows and
+ non-MS-Windows implementations. MS-Windows and non-MS-Windows
+ instances of Emacs now ignore each others' locks.
+ * filelock.c (defined_WINDOWSNT): New constant.
+ (MAKE_LOCK_NAME, fill_in_lock_file_name):
+ Don't create DIR/.#FILE.0 through DIR/.#FILE.9. Instead, create
+ DIR/.#FILE symlinks on non-MS-Windows hosts, and DIR/.#-FILE
+ regular files on MS-Windows hosts.
+ (MAKE_LOCK_NAME, unlock_file, Ffile_locked_p):
+ Use SAFE_ALLOCA to avoid problems with long file names.
+ (MAX_LFINFO): Now a local constant, not a global macro.
+ (IS_LOCK_FILE): Remove.
+ (lock_file_1): Don't inspect errno if symlink call succeeds;
+ that's not portable.
+ (lock_file): Document that this function can return if lock
+ creation fails.
+
2013-03-02 Andreas Schwab <schwab@linux-m68k.org>
* lisp.h (XPNTR) [!USE_LSB_TAG]: Remove extra paren. (Bug#13734)
#define WTMP_FILE "/var/log/wtmp"
#endif
-/* The strategy: to lock a file FN, create a symlink .#FN in FN's
+/* On non-MS-Windows systems, use a symbolic link to represent a lock.
+ The strategy: to lock a file FN, create a symlink .#FN in FN's
directory, with link data `user@host.pid'. This avoids a single
mount (== failure) point for lock files.
has contributed this implementation for Emacs), and was designed by
Ethan Jacobson, Kimbo Mundy, and others.
- --karl@cs.umb.edu/karl@hq.ileaf.com. */
+ --karl@cs.umb.edu/karl@hq.ileaf.com.
+
+ On MS-Windows, symbolic links do not work well, so instead of a
+ symlink .#FN -> 'user@host.pid', the lock is a regular file .#-FN
+ with contents 'user@host.pid'. MS-Windows and non-MS-Windows
+ versions of Emacs ignore each other's locks. */
\f
/* Return the time of the last system boot. */
/* Free the two dynamically-allocated pieces in PTR. */
#define FREE_LOCK_INFO(i) do { xfree ((i).user); xfree ((i).host); } while (0)
-
-/* Write the name of the lock file for FNAME into LOCKNAME. Length
- will be that of FN plus two more for the leading `.#' plus 1 for
- the trailing period plus one for the digit after it plus one for
- the null. */
-#define MAKE_LOCK_NAME(LOCKNAME, FNAME) \
- (LOCKNAME = alloca (SBYTES (FNAME) + 2 + 1 + 1 + 1), \
- fill_in_lock_file_name (LOCKNAME, (FNAME)))
-
#ifdef WINDOWSNT
-/* 256 chars for user, 1024 chars for host, 10 digits for each of 2 int's. */
-#define MAX_LFINFO (256 + 1024 + 10 + 10 + 2)
- /* min size: .@PID */
-#define IS_LOCK_FILE(ST) (MAX_LFINFO >= (ST).st_size && (ST).st_size >= 3)
+enum { defined_WINDOWSNT = 1 };
#else
-#define IS_LOCK_FILE(ST) S_ISLNK ((ST).st_mode)
+enum { defined_WINDOWSNT = 0 };
#endif
+/* Write the name of the lock file for FNAME into LOCKNAME. Length
+ will be that of FNAME plus two more for the leading ".#",
+ plus one for "-" if MS-Windows, plus one for the null. */
+#define MAKE_LOCK_NAME(lockname, fname) \
+ (lockname = SAFE_ALLOCA (SBYTES (fname) + 2 + defined_WINDOWSNT + 1), \
+ fill_in_lock_file_name (lockname, fname))
+
static void
-fill_in_lock_file_name (register char *lockfile, register Lisp_Object fn)
+fill_in_lock_file_name (char *lockfile, Lisp_Object fn)
{
- ptrdiff_t length = SBYTES (fn);
- register char *p;
- struct stat st;
- int count = 0;
-
- strcpy (lockfile, SSDATA (fn));
-
- /* Shift the nondirectory part of the file name (including the null)
- right two characters. Here is one of the places where we'd have to
- do something to support 14-character-max file names. */
- for (p = lockfile + length; p != lockfile && *p != '/'; p--)
- p[2] = *p;
-
- /* Insert the `.#'. */
- p[1] = '.';
- p[2] = '#';
-
- p = lockfile + length + 2;
-
- while (lstat (lockfile, &st) == 0 && !IS_LOCK_FILE (st))
- {
- if (count > 9)
- {
- *p = '\0';
- return;
- }
- sprintf (p, ".%d", count++);
- }
+ char *last_slash = memrchr (SSDATA (fn), '/', SBYTES (fn));
+ char *base = last_slash + 1;
+ ptrdiff_t dirlen = base - SSDATA (fn);
+ memcpy (lockfile, SSDATA (fn), dirlen);
+ lockfile[dirlen] = '.';
+ lockfile[dirlen + 1] = '#';
+ if (defined_WINDOWSNT)
+ lockfile[dirlen + 2] = '-';
+ strcpy (lockfile + dirlen + 2 + defined_WINDOWSNT, base);
}
static int
{
/* Deny everybody else any kind of access to the file until we are
done writing it and close the handle. This makes the entire
- open/write/close operation atomic, as far as other processes
- are concerned. */
+ open/write/close operation atomic, as far as other WINDOWSNT
+ processes are concerned. */
int fd = _sopen (lfname,
_O_WRONLY | _O_BINARY | _O_CREAT | _O_EXCL | _O_NOINHERIT,
_SH_DENYRW, S_IREAD | S_IWRITE);
}
#else
err = symlink (lock_info_str, lfname);
- if (errno == EEXIST && force)
+ if (err != 0 && errno == EEXIST && force)
{
unlink (lfname);
err = symlink (lock_info_str, lfname);
#else
int fd = emacs_open (lfname, O_RDONLY | O_BINARY, S_IREAD);
ssize_t nbytes;
+ /* 256 chars for user, 1024 chars for host, 10 digits for each of 2 int's. */
+ enum { MAX_LFINFO = 256 + 1024 + 10 + 10 + 2 };
char lfinfo[MAX_LFINFO + 1];
if (fd < 0)
decided to go ahead without locking.
When this returns, either the lock is locked for us,
+ or lock creation failed,
or the user has said to go ahead without locking.
If the file is locked by someone else, this calls
}
void
-unlock_file (register Lisp_Object fn)
+unlock_file (Lisp_Object fn)
{
- register char *lfname;
+ char *lfname;
+ USE_SAFE_ALLOCA;
fn = Fexpand_file_name (fn, Qnil);
fn = ENCODE_FILE (fn);
if (current_lock_owner (0, lfname) == 2)
unlink (lfname);
+
+ SAFE_FREE ();
}
void
(Lisp_Object filename)
{
Lisp_Object ret;
- register char *lfname;
+ char *lfname;
int owner;
lock_info_type locker;
+ USE_SAFE_ALLOCA;
filename = Fexpand_file_name (filename, Qnil);
if (owner > 0)
FREE_LOCK_INFO (locker);
+ SAFE_FREE ();
return ret;
}
projects / emacs.git / commitdiff