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code.delx.au - gnu-emacs/blob - src/filelock.c
1 /* Copyright (C) 1985, 86, 87, 93, 94, 96 Free Software Foundation, Inc.
3 This file is part of GNU Emacs.
5 GNU Emacs is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 2, or (at your option)
10 GNU Emacs is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with GNU Emacs; see the file COPYING. If not, write to
17 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
18 Boston, MA 02111-1307, USA. */
21 #include <sys/types.h>
45 #ifdef CLASH_DETECTION
47 /* The strategy: to lock a file FN, create a symlink .#FN in FN's
48 directory, with link data `user@host.pid'. This avoids a single
49 mount (== failure) point for lock files.
51 When the host in the lock data is the current host, we can check if
52 the pid is valid with kill.
54 Otherwise, we could look at a separate file that maps hostnames to
55 reboot times to see if the remote pid can possibly be valid, since we
56 don't want Emacs to have to communicate via pipes or sockets or
57 whatever to other processes, either locally or remotely; rms says
58 that's too unreliable. Hence the separate file, which could
59 theoretically be updated by daemons running separately -- but this
60 whole idea is unimplemented; in practice, at least in our
61 environment, it seems such stale locks arise fiarly infrequently, and
62 Emacs' standard methods of dealing with clashes suffice.
64 We use symlinks instead of normal files because (1) they can be
65 stored more efficiently on the filesystem, since the kernel knows
66 they will be small, and (2) all the info about the lock can be read
67 in a single system call (readlink). Although we could use regular
68 files to be useful on old systems lacking symlinks, noawdays
69 virtually all such systems are probably single-user anyway, so it
70 didn't seem worth the complication.
72 Similarly, we don't worry about a possible 14-character limit on
73 file names, because those are all the same systems that don't have
76 This is compatible with the locking scheme used by Interleaf (which
77 has contributed this implementation for Emacs), and was designed by
78 Ethan Jacobson, Kimbo Mundy, and others.
80 --karl@cs.umb.edu/karl@hq.ileaf.com. */
83 /* Here is the structure that stores information about a lock. */
92 /* When we read the info back, we might need this much more. */
93 #define LOCK_PID_MAX 21 /* enough for signed 64 bits plus null */
95 /* Free the two dynamically-allocated pieces in PTR. */
96 #define FREE_LOCK_INFO(i) do { xfree ((i).user); xfree ((i).host); } while (0)
99 /* Write the name of the lock file for FN into LFNAME. Length will be
100 that of FN plus two more for the leading `.#' plus one for the null. */
101 #define MAKE_LOCK_NAME(lock, file) \
102 (lock = (char *) alloca (XSTRING (file)->size + 2 + 1), \
103 fill_in_lock_file_name (lock, (file)))
106 fill_in_lock_file_name (lockfile
, fn
)
107 register char *lockfile
;
108 register Lisp_Object fn
;
112 strcpy (lockfile
, XSTRING (fn
)->data
);
114 /* Shift the nondirectory part of the file name (including the null)
115 right two characters. Here is one of the places where we'd have to
116 do something to support 14-character-max file names. */
117 for (p
= lockfile
+ strlen (lockfile
); p
!= lockfile
&& *p
!= '/'; p
--)
120 /* Insert the `.#'. */
125 /* Lock the lock file named LFNAME.
126 If FORCE is nonzero, we do so even if it is already locked.
127 Return 1 if successful, 0 if not. */
130 lock_file_1 (lfname
, force
)
135 char *user_name
= XSTRING (Fuser_login_name (Qnil
))->data
;
136 char *host_name
= XSTRING (Fsystem_name ())->data
;
137 char *lock_info_str
= alloca (strlen (user_name
) + strlen (host_name
) + 21);
139 sprintf (lock_info_str
, "%s@%s.%d", user_name
, host_name
, getpid ());
141 err
= symlink (lock_info_str
, lfname
);
142 if (errno
== EEXIST
&& force
)
145 err
= symlink (lock_info_str
, lfname
);
153 /* Return 0 if nobody owns the lock file LFNAME or the lock is obsolete,
154 1 if another process owns it (and set OWNER (if non-null) to info),
155 2 if the current process owns it,
156 or -1 if something is wrong with the locking mechanism. */
159 current_lock_owner (owner
, lfname
)
160 lock_info_type
*owner
;
164 extern char *rindex (), *index ();
171 /* Read arbitrarily-long contents of symlink. Similar code in
172 file-symlink-p in fileio.c. */
176 lfinfo
= (char *) xrealloc (lfinfo
, bufsize
);
177 len
= readlink (lfname
, lfinfo
, bufsize
);
179 while (len
>= bufsize
);
181 /* If nonexistent lock file, all is well; otherwise, got strange error. */
185 return errno
== ENOENT
? 0 : -1;
188 /* Link info exists, so `len' is its length. Null terminate. */
191 /* Even if the caller doesn't want the owner info, we still have to
192 read it to determine return value, so allocate it. */
195 owner
= alloca (sizeof (lock_info_type
));
199 /* Parse USER@HOST.PID. If can't parse, return -1. */
200 /* The USER is everything before the first @. */
201 at
= index (lfinfo
, '@');
202 dot
= rindex (lfinfo
, '.');
208 owner
->user
= (char *) xmalloc (len
+ 1);
209 strncpy (owner
->user
, lfinfo
, len
);
210 owner
->user
[len
] = 0;
212 /* The PID is everything after the last `.'. */
213 owner
->pid
= atoi (dot
+ 1);
215 /* The host is everything in between. */
217 owner
->host
= (char *) xmalloc (len
+ 1);
218 strncpy (owner
->host
, at
+ 1, len
);
219 owner
->host
[len
] = 0;
221 /* We're done looking at the link info. */
224 /* On current host? */
225 if (strcmp (owner
->host
, XSTRING (Fsystem_name ())->data
) == 0)
227 if (owner
->pid
== getpid ())
228 ret
= 2; /* We own it. */
231 && (kill (owner
->pid
, 0) >= 0 || errno
== EPERM
))
232 ret
= 1; /* An existing process on this machine owns it. */
234 /* The owner process is dead or has a strange pid (<=0), so try to
236 if (unlink (lfname
) < 0)
242 { /* If we wanted to support the check for stale locks on remote machines,
243 here's where we'd do it. */
248 if (local_owner
|| ret
<= 0)
250 FREE_LOCK_INFO (*owner
);
256 /* Lock the lock named LFNAME if possible.
257 Return 0 in that case.
258 Return positive if some other process owns the lock, and info about
259 that process in CLASHER.
260 Return -1 if cannot lock for any other reason. */
263 lock_if_free (clasher
, lfname
)
264 lock_info_type
*clasher
;
265 register char *lfname
;
267 while (lock_file_1 (lfname
, 0) == 0)
274 locker
= current_lock_owner (clasher
, lfname
);
277 FREE_LOCK_INFO (*clasher
);
278 return 0; /* We ourselves locked it. */
280 else if (locker
== 1)
281 return 1; /* Someone else has it. */
282 else if (locker
== -1)
283 return -1; /* Something's wrong. */
285 /* If some other error, or no such lock, try to lock again. */
286 /* Is there a case where we loop forever? */
291 /* lock_file locks file FN,
292 meaning it serves notice on the world that you intend to edit that file.
293 This should be done only when about to modify a file-visiting
294 buffer previously unmodified.
295 Do not (normally) call this for a buffer already modified,
296 as either the file is already locked, or the user has already
297 decided to go ahead without locking.
299 When this returns, either the lock is locked for us,
300 or the user has said to go ahead without locking.
302 If the file is locked by someone else, this calls
303 ask-user-about-lock (a Lisp function) with two arguments,
304 the file name and info about the user who did the locking.
305 This function can signal an error, or return t meaning
306 take away the lock, or return nil meaning ignore the lock. */
310 register Lisp_Object fn
;
312 register Lisp_Object attack
, orig_fn
;
313 register char *lfname
, *locker
;
314 lock_info_type lock_info
;
317 fn
= Fexpand_file_name (fn
, Qnil
);
319 /* Create the name of the lock-file for file fn */
320 MAKE_LOCK_NAME (lfname
, fn
);
322 /* See if this file is visited and has changed on disk since it was
325 register Lisp_Object subject_buf
;
326 subject_buf
= get_truename_buffer (orig_fn
);
327 if (!NILP (subject_buf
)
328 && NILP (Fverify_visited_file_modtime (subject_buf
))
329 && !NILP (Ffile_exists_p (fn
)))
330 call1 (intern ("ask-user-about-supersession-threat"), fn
);
333 /* Try to lock the lock. */
334 if (lock_if_free (&lock_info
, lfname
) <= 0)
335 /* Return now if we have locked it, or if lock creation failed */
338 /* Else consider breaking the lock */
339 locker
= alloca (strlen (lock_info
.user
) + strlen (lock_info
.host
)
341 sprintf (locker
, "%s@%s (pid %d)", lock_info
.user
, lock_info
.host
,
343 FREE_LOCK_INFO (lock_info
);
345 attack
= call2 (intern ("ask-user-about-lock"), fn
, build_string (locker
));
347 /* User says take the lock */
349 lock_file_1 (lfname
, 1);
352 /* User says ignore the lock */
357 register Lisp_Object fn
;
359 register char *lfname
;
361 fn
= Fexpand_file_name (fn
, Qnil
);
363 MAKE_LOCK_NAME (lfname
, fn
);
365 if (current_lock_owner (0, lfname
) == 2)
372 register Lisp_Object tail
;
373 register struct buffer
*b
;
375 for (tail
= Vbuffer_alist
; GC_CONSP (tail
); tail
= XCONS (tail
)->cdr
)
377 b
= XBUFFER (XCONS (XCONS (tail
)->car
)->cdr
);
378 if (STRINGP (b
->file_truename
) && BUF_SAVE_MODIFF (b
) < BUF_MODIFF (b
))
379 unlock_file (b
->file_truename
);
383 DEFUN ("lock-buffer", Flock_buffer
, Slock_buffer
,
385 "Lock FILE, if current buffer is modified.\n\
386 FILE defaults to current buffer's visited file,\n\
387 or else nothing is done if current buffer isn't visiting a file.")
392 file
= current_buffer
->file_truename
;
394 CHECK_STRING (file
, 0);
395 if (SAVE_MODIFF
< MODIFF
401 DEFUN ("unlock-buffer", Funlock_buffer
, Sunlock_buffer
,
403 "Unlock the file visited in the current buffer,\n\
404 if it should normally be locked.")
407 if (SAVE_MODIFF
< MODIFF
408 && STRINGP (current_buffer
->file_truename
))
409 unlock_file (current_buffer
->file_truename
);
413 /* Unlock the file visited in buffer BUFFER. */
415 unlock_buffer (buffer
)
416 struct buffer
*buffer
;
418 if (BUF_SAVE_MODIFF (buffer
) < BUF_MODIFF (buffer
)
419 && STRINGP (buffer
->file_truename
))
420 unlock_file (buffer
->file_truename
);
423 DEFUN ("file-locked-p", Ffile_locked_p
, Sfile_locked_p
, 0, 1, 0,
424 "Return nil if the FILENAME is not locked,\n\
425 t if it is locked by you, else a string of the name of the locker.")
427 Lisp_Object filename
;
430 register char *lfname
;
432 lock_info_type locker
;
434 filename
= Fexpand_file_name (filename
, Qnil
);
436 MAKE_LOCK_NAME (lfname
, filename
);
438 owner
= current_lock_owner (&locker
, lfname
);
444 ret
= build_string (locker
.user
);
447 FREE_LOCK_INFO (locker
);
453 /* Initialization functions. */
460 lock_dir
= egetenv ("EMACSLOCKDIR");
462 lock_dir
= PATH_LOCK
;
464 /* Copy the name in case egetenv got it from a Lisp string. */
465 new_name
= (char *) xmalloc (strlen (lock_dir
) + 2);
466 strcpy (new_name
, lock_dir
);
469 /* Make sure it ends with a slash. */
470 if (lock_dir
[strlen (lock_dir
) - 1] != '/')
471 strcat (lock_dir
, "/");
473 superlock_file
= (char *) xmalloc ((strlen (lock_dir
)
474 + sizeof (SUPERLOCK_NAME
)));
475 strcpy (superlock_file
, lock_dir
);
476 strcat (superlock_file
, SUPERLOCK_NAME
);
482 defsubr (&Sunlock_buffer
);
483 defsubr (&Slock_buffer
);
484 defsubr (&Sfile_locked_p
);
487 #endif /* CLASH_DETECTION */