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8dbbc384 | 1 | /* Copyright (C) 1985, 86, 87, 93, 94, 96 Free Software Foundation, Inc. |
8489eb67 RS |
2 | |
3 | This file is part of GNU Emacs. | |
4 | ||
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 | |
32676c08 | 7 | the Free Software Foundation; either version 2, or (at your option) |
8489eb67 RS |
8 | any later version. |
9 | ||
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. | |
14 | ||
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 | |
3b7ad313 EN |
17 | the Free Software Foundation, Inc., 59 Temple Place - Suite 330, |
18 | Boston, MA 02111-1307, USA. */ | |
8489eb67 RS |
19 | |
20 | ||
21 | #include <sys/types.h> | |
22 | #include <sys/stat.h> | |
18160b98 | 23 | #include <config.h> |
bfb61299 JB |
24 | |
25 | #ifdef VMS | |
b350a838 | 26 | #include "vms-pwd.h" |
bfb61299 | 27 | #else |
8489eb67 | 28 | #include <pwd.h> |
8dbbc384 | 29 | #endif /* not VMS */ |
bfb61299 | 30 | |
8489eb67 RS |
31 | #include <sys/file.h> |
32 | #ifdef USG | |
33 | #include <fcntl.h> | |
8dbbc384 | 34 | #include <string.h> |
8489eb67 RS |
35 | #endif /* USG */ |
36 | ||
8489eb67 | 37 | #include "lisp.h" |
8489eb67 RS |
38 | #include "buffer.h" |
39 | ||
8dbbc384 RS |
40 | #include <errno.h> |
41 | #ifndef errno | |
8489eb67 | 42 | extern int errno; |
79941276 RS |
43 | #endif |
44 | ||
8489eb67 RS |
45 | #ifdef CLASH_DETECTION |
46 | ||
8dbbc384 RS |
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. | |
50 | ||
51 | When the host in the lock data is the current host, we can check if | |
52 | the pid is valid with kill. | |
53 | ||
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 | |
1c4f857c | 61 | environment, it seems such stale locks arise fairly infrequently, and |
8dbbc384 RS |
62 | Emacs' standard methods of dealing with clashes suffice. |
63 | ||
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 | |
1c4f857c | 68 | files to be useful on old systems lacking symlinks, nowadays |
8dbbc384 RS |
69 | virtually all such systems are probably single-user anyway, so it |
70 | didn't seem worth the complication. | |
71 | ||
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 | |
74 | symlinks. | |
75 | ||
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. | |
79 | ||
80 | --karl@cs.umb.edu/karl@hq.ileaf.com. */ | |
8489eb67 | 81 | |
8dbbc384 RS |
82 | \f |
83 | /* Here is the structure that stores information about a lock. */ | |
32676c08 | 84 | |
8dbbc384 RS |
85 | typedef struct |
86 | { | |
87 | char *user; | |
88 | char *host; | |
9005cb4f | 89 | unsigned long pid; |
8dbbc384 | 90 | } lock_info_type; |
32676c08 | 91 | |
49b6d120 RS |
92 | /* When we read the info back, we might need this much more, |
93 | enough for decimal representation plus null. */ | |
94 | #define LOCK_PID_MAX (4 * sizeof (unsigned long)) | |
32676c08 | 95 | |
8dbbc384 RS |
96 | /* Free the two dynamically-allocated pieces in PTR. */ |
97 | #define FREE_LOCK_INFO(i) do { xfree ((i).user); xfree ((i).host); } while (0) | |
e31fbc7a | 98 | |
e31fbc7a | 99 | |
8dbbc384 RS |
100 | /* Write the name of the lock file for FN into LFNAME. Length will be |
101 | that of FN plus two more for the leading `.#' plus one for the null. */ | |
7b92975f | 102 | #define MAKE_LOCK_NAME(lock, file) \ |
8dbbc384 RS |
103 | (lock = (char *) alloca (XSTRING (file)->size + 2 + 1), \ |
104 | fill_in_lock_file_name (lock, (file))) | |
e31fbc7a | 105 | |
8dbbc384 RS |
106 | static void |
107 | fill_in_lock_file_name (lockfile, fn) | |
e31fbc7a RS |
108 | register char *lockfile; |
109 | register Lisp_Object fn; | |
110 | { | |
8dbbc384 RS |
111 | register char *p; |
112 | ||
113 | strcpy (lockfile, XSTRING (fn)->data); | |
114 | ||
115 | /* Shift the nondirectory part of the file name (including the null) | |
116 | right two characters. Here is one of the places where we'd have to | |
117 | do something to support 14-character-max file names. */ | |
118 | for (p = lockfile + strlen (lockfile); p != lockfile && *p != '/'; p--) | |
119 | p[2] = *p; | |
e31fbc7a | 120 | |
8dbbc384 RS |
121 | /* Insert the `.#'. */ |
122 | p[1] = '.'; | |
123 | p[2] = '#'; | |
124 | } | |
e31fbc7a | 125 | |
8dbbc384 RS |
126 | /* Lock the lock file named LFNAME. |
127 | If FORCE is nonzero, we do so even if it is already locked. | |
128 | Return 1 if successful, 0 if not. */ | |
e31fbc7a | 129 | |
8dbbc384 RS |
130 | static int |
131 | lock_file_1 (lfname, force) | |
132 | char *lfname; | |
133 | int force; | |
134 | { | |
135 | register int err; | |
3609a53b RS |
136 | char *user_name = (char *) XSTRING (Fuser_login_name (Qnil))->data; |
137 | char *host_name = (char *) XSTRING (Fsystem_name ())->data; | |
49b6d120 RS |
138 | char *lock_info_str = alloca (strlen (user_name) + strlen (host_name) |
139 | + LOCK_PID_MAX + 5); | |
8dbbc384 | 140 | |
9005cb4f RS |
141 | sprintf (lock_info_str, "%s@%s.%lu", user_name, host_name, |
142 | (unsigned long) getpid ()); | |
8dbbc384 RS |
143 | |
144 | err = symlink (lock_info_str, lfname); | |
145 | if (errno == EEXIST && force) | |
e31fbc7a | 146 | { |
8dbbc384 RS |
147 | unlink (lfname); |
148 | err = symlink (lock_info_str, lfname); | |
e31fbc7a | 149 | } |
e31fbc7a | 150 | |
8dbbc384 RS |
151 | return err == 0; |
152 | } | |
e31fbc7a | 153 | |
32676c08 | 154 | |
8dbbc384 RS |
155 | \f |
156 | /* Return 0 if nobody owns the lock file LFNAME or the lock is obsolete, | |
157 | 1 if another process owns it (and set OWNER (if non-null) to info), | |
158 | 2 if the current process owns it, | |
159 | or -1 if something is wrong with the locking mechanism. */ | |
e31fbc7a | 160 | |
8dbbc384 RS |
161 | static int |
162 | current_lock_owner (owner, lfname) | |
163 | lock_info_type *owner; | |
164 | char *lfname; | |
32676c08 | 165 | { |
8dbbc384 RS |
166 | #ifndef index |
167 | extern char *rindex (), *index (); | |
168 | #endif | |
169 | int o, p, len, ret; | |
170 | int local_owner = 0; | |
171 | char *at, *dot; | |
172 | char *lfinfo = 0; | |
173 | int bufsize = 50; | |
174 | /* Read arbitrarily-long contents of symlink. Similar code in | |
175 | file-symlink-p in fileio.c. */ | |
176 | do | |
177 | { | |
178 | bufsize *= 2; | |
179 | lfinfo = (char *) xrealloc (lfinfo, bufsize); | |
180 | len = readlink (lfname, lfinfo, bufsize); | |
181 | } | |
182 | while (len >= bufsize); | |
183 | ||
184 | /* If nonexistent lock file, all is well; otherwise, got strange error. */ | |
185 | if (len == -1) | |
186 | { | |
187 | xfree (lfinfo); | |
188 | return errno == ENOENT ? 0 : -1; | |
189 | } | |
32676c08 | 190 | |
8dbbc384 RS |
191 | /* Link info exists, so `len' is its length. Null terminate. */ |
192 | lfinfo[len] = 0; | |
193 | ||
194 | /* Even if the caller doesn't want the owner info, we still have to | |
195 | read it to determine return value, so allocate it. */ | |
196 | if (!owner) | |
197 | { | |
3609a53b | 198 | owner = (lock_info_type *) alloca (sizeof (lock_info_type)); |
8dbbc384 RS |
199 | local_owner = 1; |
200 | } | |
201 | ||
202 | /* Parse USER@HOST.PID. If can't parse, return -1. */ | |
203 | /* The USER is everything before the first @. */ | |
204 | at = index (lfinfo, '@'); | |
205 | dot = rindex (lfinfo, '.'); | |
206 | if (!at || !dot) { | |
207 | xfree (lfinfo); | |
208 | return -1; | |
209 | } | |
210 | len = at - lfinfo; | |
211 | owner->user = (char *) xmalloc (len + 1); | |
212 | strncpy (owner->user, lfinfo, len); | |
213 | owner->user[len] = 0; | |
214 | ||
215 | /* The PID is everything after the last `.'. */ | |
216 | owner->pid = atoi (dot + 1); | |
32676c08 | 217 | |
8dbbc384 RS |
218 | /* The host is everything in between. */ |
219 | len = dot - at - 1; | |
220 | owner->host = (char *) xmalloc (len + 1); | |
221 | strncpy (owner->host, at + 1, len); | |
222 | owner->host[len] = 0; | |
32676c08 | 223 | |
8dbbc384 RS |
224 | /* We're done looking at the link info. */ |
225 | xfree (lfinfo); | |
226 | ||
227 | /* On current host? */ | |
228 | if (strcmp (owner->host, XSTRING (Fsystem_name ())->data) == 0) | |
32676c08 | 229 | { |
8dbbc384 RS |
230 | if (owner->pid == getpid ()) |
231 | ret = 2; /* We own it. */ | |
232 | ||
233 | if (owner->pid > 0 | |
234 | && (kill (owner->pid, 0) >= 0 || errno == EPERM)) | |
235 | ret = 1; /* An existing process on this machine owns it. */ | |
236 | ||
237 | /* The owner process is dead or has a strange pid (<=0), so try to | |
238 | zap the lockfile. */ | |
239 | if (unlink (lfname) < 0) | |
240 | ret = -1; | |
241 | ||
242 | ret = 0; | |
32676c08 | 243 | } |
8dbbc384 RS |
244 | else |
245 | { /* If we wanted to support the check for stale locks on remote machines, | |
246 | here's where we'd do it. */ | |
247 | ret = 1; | |
248 | } | |
249 | ||
250 | /* Avoid garbage. */ | |
251 | if (local_owner || ret <= 0) | |
252 | { | |
253 | FREE_LOCK_INFO (*owner); | |
254 | } | |
255 | return ret; | |
32676c08 JB |
256 | } |
257 | ||
8dbbc384 RS |
258 | \f |
259 | /* Lock the lock named LFNAME if possible. | |
260 | Return 0 in that case. | |
261 | Return positive if some other process owns the lock, and info about | |
262 | that process in CLASHER. | |
263 | Return -1 if cannot lock for any other reason. */ | |
8489eb67 | 264 | |
8dbbc384 RS |
265 | static int |
266 | lock_if_free (clasher, lfname) | |
267 | lock_info_type *clasher; | |
268 | register char *lfname; | |
269 | { | |
270 | while (lock_file_1 (lfname, 0) == 0) | |
271 | { | |
272 | int locker; | |
e0e0205b | 273 | |
8dbbc384 RS |
274 | if (errno != EEXIST) |
275 | return -1; | |
276 | ||
277 | locker = current_lock_owner (clasher, lfname); | |
278 | if (locker == 2) | |
279 | { | |
280 | FREE_LOCK_INFO (*clasher); | |
281 | return 0; /* We ourselves locked it. */ | |
282 | } | |
283 | else if (locker == 1) | |
284 | return 1; /* Someone else has it. */ | |
285 | else if (locker == -1) | |
286 | return -1; /* Something's wrong. */ | |
287 | ||
288 | /* If some other error, or no such lock, try to lock again. */ | |
289 | /* Is there a case where we loop forever? */ | |
290 | } | |
291 | return 0; | |
8489eb67 RS |
292 | } |
293 | ||
8dbbc384 | 294 | /* lock_file locks file FN, |
8489eb67 RS |
295 | meaning it serves notice on the world that you intend to edit that file. |
296 | This should be done only when about to modify a file-visiting | |
297 | buffer previously unmodified. | |
8dbbc384 | 298 | Do not (normally) call this for a buffer already modified, |
8489eb67 RS |
299 | as either the file is already locked, or the user has already |
300 | decided to go ahead without locking. | |
301 | ||
8dbbc384 | 302 | When this returns, either the lock is locked for us, |
8489eb67 RS |
303 | or the user has said to go ahead without locking. |
304 | ||
8dbbc384 | 305 | If the file is locked by someone else, this calls |
8489eb67 | 306 | ask-user-about-lock (a Lisp function) with two arguments, |
8dbbc384 | 307 | the file name and info about the user who did the locking. |
8489eb67 RS |
308 | This function can signal an error, or return t meaning |
309 | take away the lock, or return nil meaning ignore the lock. */ | |
310 | ||
8489eb67 RS |
311 | void |
312 | lock_file (fn) | |
8dbbc384 | 313 | register Lisp_Object fn; |
8489eb67 | 314 | { |
5383bc6d | 315 | register Lisp_Object attack, orig_fn; |
8dbbc384 RS |
316 | register char *lfname, *locker; |
317 | lock_info_type lock_info; | |
8489eb67 | 318 | |
5383bc6d | 319 | orig_fn = fn; |
1e89de84 KH |
320 | fn = Fexpand_file_name (fn, Qnil); |
321 | ||
8dbbc384 | 322 | /* Create the name of the lock-file for file fn */ |
7b92975f | 323 | MAKE_LOCK_NAME (lfname, fn); |
8489eb67 | 324 | |
32676c08 JB |
325 | /* See if this file is visited and has changed on disk since it was |
326 | visited. */ | |
8489eb67 | 327 | { |
a57bc488 | 328 | register Lisp_Object subject_buf; |
5383bc6d | 329 | subject_buf = get_truename_buffer (orig_fn); |
265a9e55 JB |
330 | if (!NILP (subject_buf) |
331 | && NILP (Fverify_visited_file_modtime (subject_buf)) | |
332 | && !NILP (Ffile_exists_p (fn))) | |
8489eb67 RS |
333 | call1 (intern ("ask-user-about-supersession-threat"), fn); |
334 | } | |
335 | ||
336 | /* Try to lock the lock. */ | |
8dbbc384 RS |
337 | if (lock_if_free (&lock_info, lfname) <= 0) |
338 | /* Return now if we have locked it, or if lock creation failed */ | |
8489eb67 RS |
339 | return; |
340 | ||
341 | /* Else consider breaking the lock */ | |
8dbbc384 RS |
342 | locker = alloca (strlen (lock_info.user) + strlen (lock_info.host) |
343 | + LOCK_PID_MAX + 9); | |
344 | sprintf (locker, "%s@%s (pid %d)", lock_info.user, lock_info.host, | |
345 | lock_info.pid); | |
346 | FREE_LOCK_INFO (lock_info); | |
347 | ||
348 | attack = call2 (intern ("ask-user-about-lock"), fn, build_string (locker)); | |
265a9e55 | 349 | if (!NILP (attack)) |
8489eb67 RS |
350 | /* User says take the lock */ |
351 | { | |
8dbbc384 | 352 | lock_file_1 (lfname, 1); |
8489eb67 RS |
353 | return; |
354 | } | |
355 | /* User says ignore the lock */ | |
356 | } | |
357 | ||
8489eb67 RS |
358 | void |
359 | unlock_file (fn) | |
360 | register Lisp_Object fn; | |
361 | { | |
362 | register char *lfname; | |
363 | ||
1e89de84 KH |
364 | fn = Fexpand_file_name (fn, Qnil); |
365 | ||
7b92975f | 366 | MAKE_LOCK_NAME (lfname, fn); |
8489eb67 | 367 | |
8dbbc384 | 368 | if (current_lock_owner (0, lfname) == 2) |
8489eb67 | 369 | unlink (lfname); |
8489eb67 RS |
370 | } |
371 | ||
372 | void | |
373 | unlock_all_files () | |
374 | { | |
375 | register Lisp_Object tail; | |
376 | register struct buffer *b; | |
377 | ||
4e6c9d9e | 378 | for (tail = Vbuffer_alist; GC_CONSP (tail); tail = XCONS (tail)->cdr) |
8489eb67 RS |
379 | { |
380 | b = XBUFFER (XCONS (XCONS (tail)->car)->cdr); | |
5757b805 RS |
381 | if (STRINGP (b->file_truename) && BUF_SAVE_MODIFF (b) < BUF_MODIFF (b)) |
382 | unlock_file (b->file_truename); | |
8489eb67 RS |
383 | } |
384 | } | |
8489eb67 RS |
385 | \f |
386 | DEFUN ("lock-buffer", Flock_buffer, Slock_buffer, | |
387 | 0, 1, 0, | |
388 | "Lock FILE, if current buffer is modified.\n\ | |
389 | FILE defaults to current buffer's visited file,\n\ | |
390 | or else nothing is done if current buffer isn't visiting a file.") | |
e9319ef2 EN |
391 | (file) |
392 | Lisp_Object file; | |
8489eb67 | 393 | { |
e9319ef2 EN |
394 | if (NILP (file)) |
395 | file = current_buffer->file_truename; | |
8489eb67 | 396 | else |
e9319ef2 | 397 | CHECK_STRING (file, 0); |
6a140159 | 398 | if (SAVE_MODIFF < MODIFF |
e9319ef2 EN |
399 | && !NILP (file)) |
400 | lock_file (file); | |
8489eb67 RS |
401 | return Qnil; |
402 | } | |
403 | ||
404 | DEFUN ("unlock-buffer", Funlock_buffer, Sunlock_buffer, | |
405 | 0, 0, 0, | |
406 | "Unlock the file visited in the current buffer,\n\ | |
407 | if it should normally be locked.") | |
408 | () | |
409 | { | |
6a140159 | 410 | if (SAVE_MODIFF < MODIFF |
5757b805 RS |
411 | && STRINGP (current_buffer->file_truename)) |
412 | unlock_file (current_buffer->file_truename); | |
8489eb67 RS |
413 | return Qnil; |
414 | } | |
415 | ||
8489eb67 RS |
416 | /* Unlock the file visited in buffer BUFFER. */ |
417 | ||
418 | unlock_buffer (buffer) | |
419 | struct buffer *buffer; | |
420 | { | |
6a140159 | 421 | if (BUF_SAVE_MODIFF (buffer) < BUF_MODIFF (buffer) |
5757b805 RS |
422 | && STRINGP (buffer->file_truename)) |
423 | unlock_file (buffer->file_truename); | |
8489eb67 RS |
424 | } |
425 | ||
426 | DEFUN ("file-locked-p", Ffile_locked_p, Sfile_locked_p, 0, 1, 0, | |
427 | "Return nil if the FILENAME is not locked,\n\ | |
428 | t if it is locked by you, else a string of the name of the locker.") | |
e9319ef2 EN |
429 | (filename) |
430 | Lisp_Object filename; | |
8489eb67 | 431 | { |
8dbbc384 | 432 | Lisp_Object ret; |
8489eb67 RS |
433 | register char *lfname; |
434 | int owner; | |
8dbbc384 | 435 | lock_info_type locker; |
8489eb67 | 436 | |
e9319ef2 | 437 | filename = Fexpand_file_name (filename, Qnil); |
8489eb67 | 438 | |
e9319ef2 | 439 | MAKE_LOCK_NAME (lfname, filename); |
8489eb67 | 440 | |
8dbbc384 | 441 | owner = current_lock_owner (&locker, lfname); |
8489eb67 | 442 | if (owner <= 0) |
8dbbc384 RS |
443 | ret = Qnil; |
444 | else if (owner == 2) | |
445 | ret = Qt; | |
446 | else | |
447 | ret = build_string (locker.user); | |
448 | ||
449 | if (owner > 0) | |
450 | FREE_LOCK_INFO (locker); | |
451 | ||
452 | return ret; | |
8489eb67 RS |
453 | } |
454 | ||
32676c08 JB |
455 | \f |
456 | /* Initialization functions. */ | |
457 | ||
458 | init_filelock () | |
459 | { | |
8dbbc384 | 460 | #if 0 |
66e7fd46 | 461 | char *new_name; |
8600e6ed | 462 | |
7b92975f RS |
463 | lock_dir = egetenv ("EMACSLOCKDIR"); |
464 | if (! lock_dir) | |
465 | lock_dir = PATH_LOCK; | |
32676c08 | 466 | |
7b92975f RS |
467 | /* Copy the name in case egetenv got it from a Lisp string. */ |
468 | new_name = (char *) xmalloc (strlen (lock_dir) + 2); | |
469 | strcpy (new_name, lock_dir); | |
470 | lock_dir = new_name; | |
8600e6ed | 471 | |
32676c08 | 472 | /* Make sure it ends with a slash. */ |
7b92975f RS |
473 | if (lock_dir[strlen (lock_dir) - 1] != '/') |
474 | strcat (lock_dir, "/"); | |
32676c08 | 475 | |
7b92975f | 476 | superlock_file = (char *) xmalloc ((strlen (lock_dir) |
32676c08 | 477 | + sizeof (SUPERLOCK_NAME))); |
7b92975f RS |
478 | strcpy (superlock_file, lock_dir); |
479 | strcat (superlock_file, SUPERLOCK_NAME); | |
8dbbc384 | 480 | #endif |
32676c08 JB |
481 | } |
482 | ||
8489eb67 RS |
483 | syms_of_filelock () |
484 | { | |
485 | defsubr (&Sunlock_buffer); | |
486 | defsubr (&Slock_buffer); | |
487 | defsubr (&Sfile_locked_p); | |
488 | } | |
489 | ||
490 | #endif /* CLASH_DETECTION */ |