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. */
20 /* Synced with FSF 20.2 */
31 #include "syssignal.h" /* for kill */
33 Lisp_Object Qask_user_about_supersession_threat;
34 Lisp_Object Qask_user_about_lock;
36 #ifdef CLASH_DETECTION
38 /* The strategy: to lock a file FN, create a symlink .#FN in FN's
39 directory, with link data `user@host.pid'. This avoids a single
40 mount (== failure) point for lock files.
42 When the host in the lock data is the current host, we can check if
43 the pid is valid with kill.
45 Otherwise, we could look at a separate file that maps hostnames to
46 reboot times to see if the remote pid can possibly be valid, since we
47 don't want Emacs to have to communicate via pipes or sockets or
48 whatever to other processes, either locally or remotely; rms says
49 that's too unreliable. Hence the separate file, which could
50 theoretically be updated by daemons running separately -- but this
51 whole idea is unimplemented; in practice, at least in our
52 environment, it seems such stale locks arise fairly infrequently, and
53 Emacs' standard methods of dealing with clashes suffice.
55 We use symlinks instead of normal files because (1) they can be
56 stored more efficiently on the filesystem, since the kernel knows
57 they will be small, and (2) all the info about the lock can be read
58 in a single system call (readlink). Although we could use regular
59 files to be useful on old systems lacking symlinks, nowadays
60 virtually all such systems are probably single-user anyway, so it
61 didn't seem worth the complication.
63 Similarly, we don't worry about a possible 14-character limit on
64 file names, because those are all the same systems that don't have
67 This is compatible with the locking scheme used by Interleaf (which
68 has contributed this implementation for Emacs), and was designed by
69 Ethan Jacobson, Kimbo Mundy, and others.
71 --karl@cs.umb.edu/karl@hq.ileaf.com. */
74 /* Here is the structure that stores information about a lock. */
83 /* When we read the info back, we might need this much more,
84 enough for decimal representation plus null. */
85 #define LOCK_PID_MAX (4 * sizeof (unsigned long))
87 /* Free the two dynamically-allocated pieces in PTR. */
88 #define FREE_LOCK_INFO(i) do { xfree ((i).user); xfree ((i).host); } while (0)
90 /* Write the name of the lock file for FN into LFNAME. Length will be
91 that of FN plus two more for the leading `.#' plus one for the null. */
92 #define MAKE_LOCK_NAME(lock, file) \
93 (lock = (char *) alloca (XSTRING_LENGTH(file) + 2 + 1), \
94 fill_in_lock_file_name (lock, (file)))
97 fill_in_lock_file_name (lockfile, fn)
98 register char *lockfile;
99 register Lisp_Object fn;
103 strcpy (lockfile, XSTRING_DATA(fn));
105 /* Shift the nondirectory part of the file name (including the null)
106 right two characters. Here is one of the places where we'd have to
107 do something to support 14-character-max file names. */
108 for (p = lockfile + strlen (lockfile); p != lockfile && *p != '/'; p--)
111 /* Insert the `.#'. */
116 /* Lock the lock file named LFNAME.
117 If FORCE is nonzero, we do so even if it is already locked.
118 Return 1 if successful, 0 if not. */
121 lock_file_1 (char *lfname,int force)
128 if (STRINGP (Fuser_login_name (Qnil)))
129 user_name = (char *)XSTRING_DATA((Fuser_login_name (Qnil)));
132 if (STRINGP (Fsystem_name ()))
133 host_name = (char *)XSTRING_DATA((Fsystem_name ()));
136 lock_info_str = (char *)alloca (strlen (user_name) + strlen (host_name)
139 sprintf (lock_info_str, "%s@%s.%lu", user_name, host_name,
140 (unsigned long) getpid ());
142 err = symlink (lock_info_str, lfname);
143 if (errno == EEXIST && force)
146 err = symlink (lock_info_str, lfname);
152 /* Return 0 if nobody owns the lock file LFNAME or the lock is obsolete,
153 1 if another process owns it (and set OWNER (if non-null) to info),
154 2 if the current process owns it,
155 or -1 if something is wrong with the locking mechanism. */
158 current_lock_owner (lock_info_type *owner, char *lfname)
165 /* Read arbitrarily-long contents of symlink. Similar code in
166 file-symlink-p in fileio.c. */
170 lfinfo = (char *) xrealloc (lfinfo, bufsize);
171 len = readlink (lfname, lfinfo, bufsize);
173 while (len >= bufsize);
175 /* If nonexistent lock file, all is well; otherwise, got strange error. */
179 return errno == ENOENT ? 0 : -1;
182 /* Link info exists, so `len' is its length. Null terminate. */
185 /* Even if the caller doesn't want the owner info, we still have to
186 read it to determine return value, so allocate it. */
189 owner = (lock_info_type *) alloca (sizeof (lock_info_type));
193 /* Parse USER@HOST.PID. If can't parse, return -1. */
194 /* The USER is everything before the first @. */
195 at = strchr (lfinfo, '@');
196 dot = strrchr (lfinfo, '.');
202 owner->user = (char *) xmalloc (len + 1);
203 strncpy (owner->user, lfinfo, len);
204 owner->user[len] = 0;
206 /* The PID is everything after the last `.'. */
207 owner->pid = atoi (dot + 1);
209 /* The host is everything in between. */
211 owner->host = (char *) xmalloc (len + 1);
212 strncpy (owner->host, at + 1, len);
213 owner->host[len] = 0;
215 /* We're done looking at the link info. */
218 /* On current host? */
219 if (STRINGP (Fsystem_name ())
220 && strcmp (owner->host, XSTRING_DATA(Fsystem_name ())) == 0)
222 if (owner->pid == getpid ())
223 ret = 2; /* We own it. */
224 else if (owner->pid > 0
225 && (kill (owner->pid, 0) >= 0 || errno == EPERM))
226 ret = 1; /* An existing process on this machine owns it. */
227 /* The owner process is dead or has a strange pid (<=0), so try to
229 else if (unlink (lfname) < 0)
235 { /* If we wanted to support the check for stale locks on remote machines,
236 here's where we'd do it. */
241 if (local_owner || ret <= 0)
243 FREE_LOCK_INFO (*owner);
248 /* Lock the lock named LFNAME if possible.
249 Return 0 in that case.
250 Return positive if some other process owns the lock, and info about
251 that process in CLASHER.
252 Return -1 if cannot lock for any other reason. */
255 lock_if_free (lock_info_type *clasher, char *lfname)
257 if (lock_file_1 (lfname, 0) == 0)
264 locker = current_lock_owner (clasher, lfname);
267 FREE_LOCK_INFO (*clasher);
268 return 0; /* We ourselves locked it. */
270 else if (locker == 1)
271 return 1; /* Someone else has it. */
273 return -1; /* Something's wrong. */
278 /* lock_file locks file FN,
279 meaning it serves notice on the world that you intend to edit that file.
280 This should be done only when about to modify a file-visiting
281 buffer previously unmodified.
282 Do not (normally) call this for a buffer already modified,
283 as either the file is already locked, or the user has already
284 decided to go ahead without locking.
286 When this returns, either the lock is locked for us,
287 or the user has said to go ahead without locking.
289 If the file is locked by someone else, this calls
290 ask-user-about-lock (a Lisp function) with two arguments,
291 the file name and info about the user who did the locking.
292 This function can signal an error, or return t meaning
293 take away the lock, or return nil meaning ignore the lock. */
296 lock_file (Lisp_Object fn)
298 /* This function can GC. */
299 /* dmoore - and can destroy current_buffer and all sorts of other
300 mean nasty things with pointy teeth. If you call this make sure
301 you protect things right. */
302 /* Somebody updated the code in this function and removed the previous
305 register Lisp_Object attack, orig_fn;
306 register char *lfname, *locker;
307 lock_info_type lock_info;
308 struct gcpro gcpro1,gcpro2;
309 Lisp_Object subject_buf;
311 GCPRO2 (fn, subject_buf);
313 fn = Fexpand_file_name (fn, Qnil);
315 /* Create the name of the lock-file for file fn */
316 MAKE_LOCK_NAME (lfname, fn);
318 /* See if this file is visited and has changed on disk since it was
321 subject_buf = get_truename_buffer (orig_fn);
322 if (!NILP (subject_buf)
323 && NILP (Fverify_visited_file_modtime (subject_buf))
324 && !NILP (Ffile_exists_p (fn)))
325 call1_in_buffer (XBUFFER(subject_buf),
326 Qask_user_about_supersession_threat, fn);
329 /* Try to lock the lock. */
330 if (lock_if_free (&lock_info, lfname) <= 0)
331 /* Return now if we have locked it, or if lock creation failed */
334 /* Else consider breaking the lock */
335 locker = (char *) alloca (strlen (lock_info.user) + strlen (lock_info.host)
337 sprintf (locker, "%s@%s (pid %lu)", lock_info.user, lock_info.host,
339 FREE_LOCK_INFO (lock_info);
341 attack = call2_in_buffer (BUFFERP (subject_buf) ? XBUFFER (subject_buf) :
342 current_buffer, Qask_user_about_lock , fn,
343 build_string (locker));
345 /* User says take the lock */
347 lock_file_1 (lfname, 1);
350 /* User says ignore the lock */
356 unlock_file (Lisp_Object fn)
358 register char *lfname;
360 fn = Fexpand_file_name (fn, Qnil);
362 MAKE_LOCK_NAME (lfname, fn);
364 if (current_lock_owner (0, lfname) == 2)
371 register Lisp_Object tail;
372 register struct buffer *b;
374 for (tail = Vbuffer_alist; GC_CONSP (tail); tail = XCDR (tail))
376 b = XBUFFER (XCDR (XCAR (tail)));
377 if (STRINGP (b->file_truename) && BUF_SAVE_MODIFF (b) < BUF_MODIFF (b))
378 unlock_file (b->file_truename);
382 DEFUN ("lock-buffer", Flock_buffer, 0, 1, 0, /*
383 Lock FILE, if current buffer is modified.\n\
384 FILE defaults to current buffer's visited file,\n\
385 or else nothing is done if current buffer isn't visiting a file.
390 file = current_buffer->file_truename;
392 if (BUF_SAVE_MODIFF (current_buffer) < BUF_MODIFF (current_buffer)
398 DEFUN ("unlock-buffer", Funlock_buffer, 0, 0, 0, /*
399 Unlock the file visited in the current buffer,
400 if it should normally be locked.
404 /* This function can GC */
405 /* dmoore - and can destroy current_buffer and all sorts of other
406 mean nasty things with pointy teeth. If you call this make sure
407 you protect things right. */
409 if (BUF_SAVE_MODIFF (current_buffer) < BUF_MODIFF (current_buffer)
410 && STRINGP (current_buffer->file_truename))
411 unlock_file (current_buffer->file_truename);
415 /* Unlock the file visited in buffer BUFFER. */
419 unlock_buffer (struct buffer *buffer)
421 /* This function can GC */
422 /* dmoore - and can destroy current_buffer and all sorts of other
423 mean nasty things with pointy teeth. If you call this make sure
424 you protect things right. */
425 if (BUF_SAVE_MODIFF (buffer) < BUF_MODIFF (buffer)
426 && STRINGP (buffer->file_truename))
427 unlock_file (buffer->file_truename);
430 DEFUN ("file-locked-p", Ffile_locked_p, 0, 1, 0, /*
431 Return nil if the FILENAME is not locked,\n\
432 t if it is locked by you, else a string of the name of the locker.
437 register char *lfname;
439 lock_info_type locker;
441 filename = Fexpand_file_name (filename, Qnil);
443 MAKE_LOCK_NAME (lfname, filename);
445 owner = current_lock_owner (&locker, lfname);
451 ret = build_string (locker.user);
454 FREE_LOCK_INFO (locker);
460 /* Initialization functions. */
463 syms_of_filelock (void)
465 /* This function can GC */
466 DEFSUBR (Funlock_buffer);
467 DEFSUBR (Flock_buffer);
468 DEFSUBR (Ffile_locked_p);
470 defsymbol (&Qask_user_about_supersession_threat,
471 "ask-user-about-supersession-threat");
472 defsymbol (&Qask_user_about_lock, "ask-user-about-lock");
476 #endif /* CLASH_DETECTION */