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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 | |
61 | environment, it seems such stale locks arise fiarly infrequently, and | |
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 | |
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. | |
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; | |
89 | int pid; | |
90 | } lock_info_type; | |
32676c08 | 91 | |
8dbbc384 RS |
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 */ | |
32676c08 | 94 | |
8dbbc384 RS |
95 | /* Free the two dynamically-allocated pieces in PTR. */ |
96 | #define FREE_LOCK_INFO(i) do { xfree ((i).user); xfree ((i).host); } while (0) | |
e31fbc7a | 97 | |
e31fbc7a | 98 | |
8dbbc384 RS |
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. */ | |
7b92975f | 101 | #define MAKE_LOCK_NAME(lock, file) \ |
8dbbc384 RS |
102 | (lock = (char *) alloca (XSTRING (file)->size + 2 + 1), \ |
103 | fill_in_lock_file_name (lock, (file))) | |
e31fbc7a | 104 | |
8dbbc384 RS |
105 | static void |
106 | fill_in_lock_file_name (lockfile, fn) | |
e31fbc7a RS |
107 | register char *lockfile; |
108 | register Lisp_Object fn; | |
109 | { | |
8dbbc384 RS |
110 | register char *p; |
111 | ||
112 | strcpy (lockfile, XSTRING (fn)->data); | |
113 | ||
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--) | |
118 | p[2] = *p; | |
e31fbc7a | 119 | |
8dbbc384 RS |
120 | /* Insert the `.#'. */ |
121 | p[1] = '.'; | |
122 | p[2] = '#'; | |
123 | } | |
e31fbc7a | 124 | |
8dbbc384 RS |
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. */ | |
e31fbc7a | 128 | |
8dbbc384 RS |
129 | static int |
130 | lock_file_1 (lfname, force) | |
131 | char *lfname; | |
132 | int force; | |
133 | { | |
134 | register int err; | |
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); | |
138 | ||
139 | sprintf (lock_info_str, "%s@%s.%d", user_name, host_name, getpid ()); | |
140 | ||
141 | err = symlink (lock_info_str, lfname); | |
142 | if (errno == EEXIST && force) | |
e31fbc7a | 143 | { |
8dbbc384 RS |
144 | unlink (lfname); |
145 | err = symlink (lock_info_str, lfname); | |
e31fbc7a | 146 | } |
e31fbc7a | 147 | |
8dbbc384 RS |
148 | return err == 0; |
149 | } | |
e31fbc7a | 150 | |
32676c08 | 151 | |
8dbbc384 RS |
152 | \f |
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. */ | |
e31fbc7a | 157 | |
8dbbc384 RS |
158 | static int |
159 | current_lock_owner (owner, lfname) | |
160 | lock_info_type *owner; | |
161 | char *lfname; | |
32676c08 | 162 | { |
8dbbc384 RS |
163 | #ifndef index |
164 | extern char *rindex (), *index (); | |
165 | #endif | |
166 | int o, p, len, ret; | |
167 | int local_owner = 0; | |
168 | char *at, *dot; | |
169 | char *lfinfo = 0; | |
170 | int bufsize = 50; | |
171 | /* Read arbitrarily-long contents of symlink. Similar code in | |
172 | file-symlink-p in fileio.c. */ | |
173 | do | |
174 | { | |
175 | bufsize *= 2; | |
176 | lfinfo = (char *) xrealloc (lfinfo, bufsize); | |
177 | len = readlink (lfname, lfinfo, bufsize); | |
178 | } | |
179 | while (len >= bufsize); | |
180 | ||
181 | /* If nonexistent lock file, all is well; otherwise, got strange error. */ | |
182 | if (len == -1) | |
183 | { | |
184 | xfree (lfinfo); | |
185 | return errno == ENOENT ? 0 : -1; | |
186 | } | |
32676c08 | 187 | |
8dbbc384 RS |
188 | /* Link info exists, so `len' is its length. Null terminate. */ |
189 | lfinfo[len] = 0; | |
190 | ||
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. */ | |
193 | if (!owner) | |
194 | { | |
195 | owner = alloca (sizeof (lock_info_type)); | |
196 | local_owner = 1; | |
197 | } | |
198 | ||
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, '.'); | |
203 | if (!at || !dot) { | |
204 | xfree (lfinfo); | |
205 | return -1; | |
206 | } | |
207 | len = at - lfinfo; | |
208 | owner->user = (char *) xmalloc (len + 1); | |
209 | strncpy (owner->user, lfinfo, len); | |
210 | owner->user[len] = 0; | |
211 | ||
212 | /* The PID is everything after the last `.'. */ | |
213 | owner->pid = atoi (dot + 1); | |
32676c08 | 214 | |
8dbbc384 RS |
215 | /* The host is everything in between. */ |
216 | len = dot - at - 1; | |
217 | owner->host = (char *) xmalloc (len + 1); | |
218 | strncpy (owner->host, at + 1, len); | |
219 | owner->host[len] = 0; | |
32676c08 | 220 | |
8dbbc384 RS |
221 | /* We're done looking at the link info. */ |
222 | xfree (lfinfo); | |
223 | ||
224 | /* On current host? */ | |
225 | if (strcmp (owner->host, XSTRING (Fsystem_name ())->data) == 0) | |
32676c08 | 226 | { |
8dbbc384 RS |
227 | if (owner->pid == getpid ()) |
228 | ret = 2; /* We own it. */ | |
229 | ||
230 | if (owner->pid > 0 | |
231 | && (kill (owner->pid, 0) >= 0 || errno == EPERM)) | |
232 | ret = 1; /* An existing process on this machine owns it. */ | |
233 | ||
234 | /* The owner process is dead or has a strange pid (<=0), so try to | |
235 | zap the lockfile. */ | |
236 | if (unlink (lfname) < 0) | |
237 | ret = -1; | |
238 | ||
239 | ret = 0; | |
32676c08 | 240 | } |
8dbbc384 RS |
241 | else |
242 | { /* If we wanted to support the check for stale locks on remote machines, | |
243 | here's where we'd do it. */ | |
244 | ret = 1; | |
245 | } | |
246 | ||
247 | /* Avoid garbage. */ | |
248 | if (local_owner || ret <= 0) | |
249 | { | |
250 | FREE_LOCK_INFO (*owner); | |
251 | } | |
252 | return ret; | |
32676c08 JB |
253 | } |
254 | ||
8dbbc384 RS |
255 | \f |
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. */ | |
8489eb67 | 261 | |
8dbbc384 RS |
262 | static int |
263 | lock_if_free (clasher, lfname) | |
264 | lock_info_type *clasher; | |
265 | register char *lfname; | |
266 | { | |
267 | while (lock_file_1 (lfname, 0) == 0) | |
268 | { | |
269 | int locker; | |
e0e0205b | 270 | |
8dbbc384 RS |
271 | if (errno != EEXIST) |
272 | return -1; | |
273 | ||
274 | locker = current_lock_owner (clasher, lfname); | |
275 | if (locker == 2) | |
276 | { | |
277 | FREE_LOCK_INFO (*clasher); | |
278 | return 0; /* We ourselves locked it. */ | |
279 | } | |
280 | else if (locker == 1) | |
281 | return 1; /* Someone else has it. */ | |
282 | else if (locker == -1) | |
283 | return -1; /* Something's wrong. */ | |
284 | ||
285 | /* If some other error, or no such lock, try to lock again. */ | |
286 | /* Is there a case where we loop forever? */ | |
287 | } | |
288 | return 0; | |
8489eb67 RS |
289 | } |
290 | ||
8dbbc384 | 291 | /* lock_file locks file FN, |
8489eb67 RS |
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. | |
8dbbc384 | 295 | Do not (normally) call this for a buffer already modified, |
8489eb67 RS |
296 | as either the file is already locked, or the user has already |
297 | decided to go ahead without locking. | |
298 | ||
8dbbc384 | 299 | When this returns, either the lock is locked for us, |
8489eb67 RS |
300 | or the user has said to go ahead without locking. |
301 | ||
8dbbc384 | 302 | If the file is locked by someone else, this calls |
8489eb67 | 303 | ask-user-about-lock (a Lisp function) with two arguments, |
8dbbc384 | 304 | the file name and info about the user who did the locking. |
8489eb67 RS |
305 | This function can signal an error, or return t meaning |
306 | take away the lock, or return nil meaning ignore the lock. */ | |
307 | ||
8489eb67 RS |
308 | void |
309 | lock_file (fn) | |
8dbbc384 | 310 | register Lisp_Object fn; |
8489eb67 | 311 | { |
5383bc6d | 312 | register Lisp_Object attack, orig_fn; |
8dbbc384 RS |
313 | register char *lfname, *locker; |
314 | lock_info_type lock_info; | |
8489eb67 | 315 | |
5383bc6d | 316 | orig_fn = fn; |
1e89de84 KH |
317 | fn = Fexpand_file_name (fn, Qnil); |
318 | ||
8dbbc384 | 319 | /* Create the name of the lock-file for file fn */ |
7b92975f | 320 | MAKE_LOCK_NAME (lfname, fn); |
8489eb67 | 321 | |
32676c08 JB |
322 | /* See if this file is visited and has changed on disk since it was |
323 | visited. */ | |
8489eb67 | 324 | { |
a57bc488 | 325 | register Lisp_Object subject_buf; |
5383bc6d | 326 | subject_buf = get_truename_buffer (orig_fn); |
265a9e55 JB |
327 | if (!NILP (subject_buf) |
328 | && NILP (Fverify_visited_file_modtime (subject_buf)) | |
329 | && !NILP (Ffile_exists_p (fn))) | |
8489eb67 RS |
330 | call1 (intern ("ask-user-about-supersession-threat"), fn); |
331 | } | |
332 | ||
333 | /* Try to lock the lock. */ | |
8dbbc384 RS |
334 | if (lock_if_free (&lock_info, lfname) <= 0) |
335 | /* Return now if we have locked it, or if lock creation failed */ | |
8489eb67 RS |
336 | return; |
337 | ||
338 | /* Else consider breaking the lock */ | |
8dbbc384 RS |
339 | locker = alloca (strlen (lock_info.user) + strlen (lock_info.host) |
340 | + LOCK_PID_MAX + 9); | |
341 | sprintf (locker, "%s@%s (pid %d)", lock_info.user, lock_info.host, | |
342 | lock_info.pid); | |
343 | FREE_LOCK_INFO (lock_info); | |
344 | ||
345 | attack = call2 (intern ("ask-user-about-lock"), fn, build_string (locker)); | |
265a9e55 | 346 | if (!NILP (attack)) |
8489eb67 RS |
347 | /* User says take the lock */ |
348 | { | |
8dbbc384 | 349 | lock_file_1 (lfname, 1); |
8489eb67 RS |
350 | return; |
351 | } | |
352 | /* User says ignore the lock */ | |
353 | } | |
354 | ||
8489eb67 RS |
355 | void |
356 | unlock_file (fn) | |
357 | register Lisp_Object fn; | |
358 | { | |
359 | register char *lfname; | |
360 | ||
1e89de84 KH |
361 | fn = Fexpand_file_name (fn, Qnil); |
362 | ||
7b92975f | 363 | MAKE_LOCK_NAME (lfname, fn); |
8489eb67 | 364 | |
8dbbc384 | 365 | if (current_lock_owner (0, lfname) == 2) |
8489eb67 | 366 | unlink (lfname); |
8489eb67 RS |
367 | } |
368 | ||
369 | void | |
370 | unlock_all_files () | |
371 | { | |
372 | register Lisp_Object tail; | |
373 | register struct buffer *b; | |
374 | ||
4e6c9d9e | 375 | for (tail = Vbuffer_alist; GC_CONSP (tail); tail = XCONS (tail)->cdr) |
8489eb67 RS |
376 | { |
377 | b = XBUFFER (XCONS (XCONS (tail)->car)->cdr); | |
5757b805 RS |
378 | if (STRINGP (b->file_truename) && BUF_SAVE_MODIFF (b) < BUF_MODIFF (b)) |
379 | unlock_file (b->file_truename); | |
8489eb67 RS |
380 | } |
381 | } | |
8489eb67 RS |
382 | \f |
383 | DEFUN ("lock-buffer", Flock_buffer, Slock_buffer, | |
384 | 0, 1, 0, | |
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.") | |
e9319ef2 EN |
388 | (file) |
389 | Lisp_Object file; | |
8489eb67 | 390 | { |
e9319ef2 EN |
391 | if (NILP (file)) |
392 | file = current_buffer->file_truename; | |
8489eb67 | 393 | else |
e9319ef2 | 394 | CHECK_STRING (file, 0); |
6a140159 | 395 | if (SAVE_MODIFF < MODIFF |
e9319ef2 EN |
396 | && !NILP (file)) |
397 | lock_file (file); | |
8489eb67 RS |
398 | return Qnil; |
399 | } | |
400 | ||
401 | DEFUN ("unlock-buffer", Funlock_buffer, Sunlock_buffer, | |
402 | 0, 0, 0, | |
403 | "Unlock the file visited in the current buffer,\n\ | |
404 | if it should normally be locked.") | |
405 | () | |
406 | { | |
6a140159 | 407 | if (SAVE_MODIFF < MODIFF |
5757b805 RS |
408 | && STRINGP (current_buffer->file_truename)) |
409 | unlock_file (current_buffer->file_truename); | |
8489eb67 RS |
410 | return Qnil; |
411 | } | |
412 | ||
8489eb67 RS |
413 | /* Unlock the file visited in buffer BUFFER. */ |
414 | ||
415 | unlock_buffer (buffer) | |
416 | struct buffer *buffer; | |
417 | { | |
6a140159 | 418 | if (BUF_SAVE_MODIFF (buffer) < BUF_MODIFF (buffer) |
5757b805 RS |
419 | && STRINGP (buffer->file_truename)) |
420 | unlock_file (buffer->file_truename); | |
8489eb67 RS |
421 | } |
422 | ||
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.") | |
e9319ef2 EN |
426 | (filename) |
427 | Lisp_Object filename; | |
8489eb67 | 428 | { |
8dbbc384 | 429 | Lisp_Object ret; |
8489eb67 RS |
430 | register char *lfname; |
431 | int owner; | |
8dbbc384 | 432 | lock_info_type locker; |
8489eb67 | 433 | |
e9319ef2 | 434 | filename = Fexpand_file_name (filename, Qnil); |
8489eb67 | 435 | |
e9319ef2 | 436 | MAKE_LOCK_NAME (lfname, filename); |
8489eb67 | 437 | |
8dbbc384 | 438 | owner = current_lock_owner (&locker, lfname); |
8489eb67 | 439 | if (owner <= 0) |
8dbbc384 RS |
440 | ret = Qnil; |
441 | else if (owner == 2) | |
442 | ret = Qt; | |
443 | else | |
444 | ret = build_string (locker.user); | |
445 | ||
446 | if (owner > 0) | |
447 | FREE_LOCK_INFO (locker); | |
448 | ||
449 | return ret; | |
8489eb67 RS |
450 | } |
451 | ||
32676c08 JB |
452 | \f |
453 | /* Initialization functions. */ | |
454 | ||
455 | init_filelock () | |
456 | { | |
8dbbc384 | 457 | #if 0 |
66e7fd46 | 458 | char *new_name; |
8600e6ed | 459 | |
7b92975f RS |
460 | lock_dir = egetenv ("EMACSLOCKDIR"); |
461 | if (! lock_dir) | |
462 | lock_dir = PATH_LOCK; | |
32676c08 | 463 | |
7b92975f RS |
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); | |
467 | lock_dir = new_name; | |
8600e6ed | 468 | |
32676c08 | 469 | /* Make sure it ends with a slash. */ |
7b92975f RS |
470 | if (lock_dir[strlen (lock_dir) - 1] != '/') |
471 | strcat (lock_dir, "/"); | |
32676c08 | 472 | |
7b92975f | 473 | superlock_file = (char *) xmalloc ((strlen (lock_dir) |
32676c08 | 474 | + sizeof (SUPERLOCK_NAME))); |
7b92975f RS |
475 | strcpy (superlock_file, lock_dir); |
476 | strcat (superlock_file, SUPERLOCK_NAME); | |
8dbbc384 | 477 | #endif |
32676c08 JB |
478 | } |
479 | ||
8489eb67 RS |
480 | syms_of_filelock () |
481 | { | |
482 | defsubr (&Sunlock_buffer); | |
483 | defsubr (&Slock_buffer); | |
484 | defsubr (&Sfile_locked_p); | |
485 | } | |
486 | ||
487 | #endif /* CLASH_DETECTION */ |