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code.delx.au - gnu-emacs/blob - src/filelock.c
1 /* Copyright (C) 1985, 1986, 1987, 1993, 1994 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, 675 Mass Ave, Cambridge, MA 02139, USA. */
20 #include <sys/types.h>
40 #ifdef SYSV_SYSTEM_DIR
42 #else /* not SYSV_SYSTEM_DIR */
43 #ifdef NONSYSTEM_DIR_LIBRARY
45 #else /* not NONSYSTEM_DIR_LIBRARY */
51 #endif /* not NONSYSTEM_DIR_LIBRARY */
53 extern DIR *opendir ();
54 #endif /* not MSDOS */
55 #endif /* not SYSV_SYSTEM_DIR */
59 extern char *egetenv ();
60 extern char *strcpy ();
62 #ifdef DECLARE_GETPWUID_WITH_UID_T
63 extern struct passwd
*getpwuid (uid_t
);
65 extern struct passwd
*getpwuid ();
68 #ifdef CLASH_DETECTION
70 /* If system does not have symbolic links, it does not have lstat.
71 In that case, use ordinary stat instead. */
78 /* The name of the directory in which we keep lock files, with a '/'
82 /* The name of the file in the lock directory which is used to
83 arbitrate access to the entire directory. */
84 #define SUPERLOCK_NAME "!!!SuperLock!!!"
86 /* The name of the superlock file. This is SUPERLOCK_NAME appended to
90 /* Set LOCK to the name of the lock file for the filename FILE.
91 char *LOCK; Lisp_Object FILE; */
93 #ifndef HAVE_LONG_FILE_NAMES
95 #define MAKE_LOCK_NAME(lock, file) \
96 (lock = (char *) alloca (14 + strlen (lock_dir) + 1), \
97 fill_in_lock_short_file_name (lock, (file)))
100 fill_in_lock_short_file_name (lockfile
, fn
)
101 register char *lockfile
;
102 register Lisp_Object fn
;
106 unsigned int word
[2];
107 unsigned char byte
[8];
109 register unsigned char *p
, new;
111 /* 7-bytes cyclic code for burst correction on byte-by-byte basis.
112 the used polynomial is D^7 + D^6 + D^3 +1. pot@cnuce.cnr.it */
114 crc
.word
[0] = crc
.word
[1] = 0;
116 for (p
= XSTRING (fn
)->data
; new = *p
++; )
119 crc
.byte
[6] = crc
.byte
[5] + new;
120 crc
.byte
[5] = crc
.byte
[4];
121 crc
.byte
[4] = crc
.byte
[3];
122 crc
.byte
[3] = crc
.byte
[2] + new;
123 crc
.byte
[2] = crc
.byte
[1];
124 crc
.byte
[1] = crc
.byte
[0];
127 sprintf (lockfile
, "%s%.2x%.2x%.2x%.2x%.2x%.2x%.2x", lock_dir
,
128 crc
.byte
[0], crc
.byte
[1], crc
.byte
[2], crc
.byte
[3],
129 crc
.byte
[4], crc
.byte
[5], crc
.byte
[6]);
132 #else /* defined HAVE_LONG_FILE_NAMES */
134 #define MAKE_LOCK_NAME(lock, file) \
135 (lock = (char *) alloca (XSTRING (file)->size + strlen (lock_dir) + 1), \
136 fill_in_lock_file_name (lock, (file)))
139 fill_in_lock_file_name (lockfile
, fn
)
140 register char *lockfile
;
141 register Lisp_Object fn
;
145 strcpy (lockfile
, lock_dir
);
147 p
= lockfile
+ strlen (lockfile
);
149 strcpy (p
, XSTRING (fn
)->data
);
157 #endif /* !defined HAVE_LONG_FILE_NAMES */
160 lock_file_owner_name (lfname
)
164 struct passwd
*the_pw
;
166 if (lstat (lfname
, &s
) == 0)
167 the_pw
= getpwuid (s
.st_uid
);
168 return (the_pw
== 0 ? Qnil
: build_string (the_pw
->pw_name
));
172 /* lock_file locks file fn,
173 meaning it serves notice on the world that you intend to edit that file.
174 This should be done only when about to modify a file-visiting
175 buffer previously unmodified.
176 Do not (normally) call lock_buffer for a buffer already modified,
177 as either the file is already locked, or the user has already
178 decided to go ahead without locking.
180 When lock_buffer returns, either the lock is locked for us,
181 or the user has said to go ahead without locking.
183 If the file is locked by someone else, lock_buffer calls
184 ask-user-about-lock (a Lisp function) with two arguments,
185 the file name and the name of the user who did the locking.
186 This function can signal an error, or return t meaning
187 take away the lock, or return nil meaning ignore the lock. */
189 /* The lock file name is the file name with "/" replaced by "!"
190 and put in the Emacs lock directory. */
191 /* (ie., /ka/king/junk.tex -> /!/!ka!king!junk.tex). */
193 /* If HAVE_LONG_FILE_NAMES is not defined, the lock file name is the hex
194 representation of a 14-bytes CRC generated from the file name
195 and put in the Emacs lock directory (not very nice, but it works).
196 (ie., /ka/king/junk.tex -> /!/12a82c62f1c6da). */
200 register Lisp_Object fn
;
202 register Lisp_Object attack
, orig_fn
;
203 register char *lfname
;
206 fn
= Fexpand_file_name (fn
, Qnil
);
208 MAKE_LOCK_NAME (lfname
, fn
);
210 /* See if this file is visited and has changed on disk since it was
213 register Lisp_Object subject_buf
;
214 subject_buf
= get_truename_buffer (orig_fn
);
215 if (!NILP (subject_buf
)
216 && NILP (Fverify_visited_file_modtime (subject_buf
))
217 && !NILP (Ffile_exists_p (fn
)))
218 call1 (intern ("ask-user-about-supersession-threat"), fn
);
221 /* Try to lock the lock. */
222 if (lock_if_free (lfname
) <= 0)
223 /* Return now if we have locked it, or if lock dir does not exist */
226 /* Else consider breaking the lock */
227 attack
= call2 (intern ("ask-user-about-lock"), fn
,
228 lock_file_owner_name (lfname
));
230 /* User says take the lock */
232 lock_superlock (lfname
);
233 lock_file_1 (lfname
, O_WRONLY
) ;
234 unlink (superlock_file
);
237 /* User says ignore the lock */
240 /* Lock the lock file named LFNAME.
241 If MODE is O_WRONLY, we do so even if it is already locked.
242 If MODE is O_WRONLY | O_EXCL | O_CREAT, we do so only if it is free.
243 Return 1 if successful, 0 if not. */
246 lock_file_1 (lfname
, mode
)
247 int mode
; char *lfname
;
252 if ((fd
= open (lfname
, mode
, 0666)) >= 0)
255 chmod (lfname
, 0666);
259 sprintf (buf
, "%d ", getpid ());
260 write (fd
, buf
, strlen (buf
));
268 /* Lock the lock named LFNAME if possible.
269 Return 0 in that case.
270 Return positive if lock is really locked by someone else.
271 Return -1 if cannot lock for any other reason. */
274 lock_if_free (lfname
)
275 register char *lfname
;
277 register int clasher
;
279 while (lock_file_1 (lfname
, O_WRONLY
| O_EXCL
| O_CREAT
) == 0)
283 clasher
= current_lock_owner (lfname
);
285 if (clasher
!= getpid ())
288 /* Try again to lock it */
293 /* Return the pid of the process that claims to own the lock file LFNAME,
294 or 0 if nobody does or the lock is obsolete,
295 or -1 if something is wrong with the locking mechanism. */
298 current_lock_owner (lfname
)
301 int owner
= current_lock_owner_1 (lfname
);
302 if (owner
== 0 && errno
== ENOENT
)
304 /* Is it locked by a process that exists? */
305 if (owner
!= 0 && (kill (owner
, 0) >= 0 || errno
== EPERM
))
307 if (unlink (lfname
) < 0)
313 current_lock_owner_1 (lfname
)
320 fd
= open (lfname
, O_RDONLY
, 0666);
323 tem
= read (fd
, buf
, sizeof buf
);
325 return (tem
<= 0 ? 0 : atoi (buf
));
331 register Lisp_Object fn
;
333 register char *lfname
;
335 fn
= Fexpand_file_name (fn
, Qnil
);
337 MAKE_LOCK_NAME (lfname
, fn
);
339 lock_superlock (lfname
);
341 if (current_lock_owner_1 (lfname
) == getpid ())
344 unlink (superlock_file
);
347 lock_superlock (lfname
)
353 for (i
= -20; i
< 0 && (fd
= open (superlock_file
,
354 O_WRONLY
| O_EXCL
| O_CREAT
, 0666)) < 0;
360 /* This seems to be necessary to prevent Emacs from hanging when the
361 competing process has already deleted the superlock, but it's still
362 in the NFS cache. So we force NFS to synchronize the cache. */
363 if (lockdir
= opendir (lock_dir
))
371 chmod (superlock_file
, 0666);
375 write (fd
, lfname
, strlen (lfname
));
383 register Lisp_Object tail
;
384 register struct buffer
*b
;
386 for (tail
= Vbuffer_alist
; GC_CONSP (tail
); tail
= XCONS (tail
)->cdr
)
388 b
= XBUFFER (XCONS (XCONS (tail
)->car
)->cdr
);
389 if (STRINGP (b
->file_truename
) && BUF_SAVE_MODIFF (b
) < BUF_MODIFF (b
))
390 unlock_file (b
->file_truename
);
395 DEFUN ("lock-buffer", Flock_buffer
, Slock_buffer
,
397 "Lock FILE, if current buffer is modified.\n\
398 FILE defaults to current buffer's visited file,\n\
399 or else nothing is done if current buffer isn't visiting a file.")
404 fn
= current_buffer
->file_truename
;
406 CHECK_STRING (fn
, 0);
407 if (SAVE_MODIFF
< MODIFF
413 DEFUN ("unlock-buffer", Funlock_buffer
, Sunlock_buffer
,
415 "Unlock the file visited in the current buffer,\n\
416 if it should normally be locked.")
419 if (SAVE_MODIFF
< MODIFF
420 && STRINGP (current_buffer
->file_truename
))
421 unlock_file (current_buffer
->file_truename
);
426 /* Unlock the file visited in buffer BUFFER. */
428 unlock_buffer (buffer
)
429 struct buffer
*buffer
;
431 if (BUF_SAVE_MODIFF (buffer
) < BUF_MODIFF (buffer
)
432 && STRINGP (buffer
->file_truename
))
433 unlock_file (buffer
->file_truename
);
436 DEFUN ("file-locked-p", Ffile_locked_p
, Sfile_locked_p
, 0, 1, 0,
437 "Return nil if the FILENAME is not locked,\n\
438 t if it is locked by you, else a string of the name of the locker.")
442 register char *lfname
;
445 fn
= Fexpand_file_name (fn
, Qnil
);
447 MAKE_LOCK_NAME (lfname
, fn
);
449 owner
= current_lock_owner (lfname
);
452 else if (owner
== getpid ())
455 return (lock_file_owner_name (lfname
));
459 /* Initialization functions. */
465 lock_dir
= egetenv ("EMACSLOCKDIR");
467 lock_dir
= PATH_LOCK
;
469 /* Copy the name in case egetenv got it from a Lisp string. */
470 new_name
= (char *) xmalloc (strlen (lock_dir
) + 2);
471 strcpy (new_name
, lock_dir
);
474 /* Make sure it ends with a slash. */
475 if (lock_dir
[strlen (lock_dir
) - 1] != '/')
476 strcat (lock_dir
, "/");
478 superlock_file
= (char *) xmalloc ((strlen (lock_dir
)
479 + sizeof (SUPERLOCK_NAME
)));
480 strcpy (superlock_file
, lock_dir
);
481 strcat (superlock_file
, SUPERLOCK_NAME
);
486 defsubr (&Sunlock_buffer
);
487 defsubr (&Slock_buffer
);
488 defsubr (&Sfile_locked_p
);
491 #endif /* CLASH_DETECTION */