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code.delx.au - gnu-emacs/blob - src/filelock.c
1 /* Copyright (C) 1985, 1986, 1987, 1993 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>
42 extern char *egetenv ();
43 extern char *strcpy ();
46 extern struct passwd
*getpwuid ();
49 #ifdef CLASH_DETECTION
51 /* If system does not have symbolic links, it does not have lstat.
52 In that case, use ordinary stat instead. */
59 /* The name of the directory in which we keep lock files, with a '/'
63 /* The name of the file in the lock directory which is used to
64 arbitrate access to the entire directory. */
65 #define SUPERLOCK_NAME "!!!SuperLock!!!"
67 /* The path to the superlock file. This is SUPERLOCK_NAME appended to
71 /* Set LOCK to the name of the lock file for the filename FILE.
72 char *LOCK; Lisp_Object FILE; */
74 #ifndef HAVE_LONG_FILE_NAMES
76 #define MAKE_LOCK_PATH(lock, file) \
77 (lock = (char *) alloca (14 + strlen (lock_path) + 1), \
78 fill_in_lock_short_file_name (lock, (file)))
81 fill_in_lock_short_file_name (lockfile
, fn
)
82 register char *lockfile
;
83 register Lisp_Object fn
;
87 unsigned int word
[2];
88 unsigned char byte
[8];
90 register unsigned char *p
, new;
92 /* 7-bytes cyclic code for burst correction on byte-by-byte basis.
93 the used polynomial is D^7 + D^6 + D^3 +1. pot@cnuce.cnr.it */
95 crc
.word
[0] = crc
.word
[1] = 0;
97 for (p
= XSTRING (fn
)->data
; new = *p
++; )
100 crc
.byte
[7] = crc
.byte
[6];
101 crc
.byte
[6] = crc
.byte
[5] + new;
102 crc
.byte
[5] = crc
.byte
[4];
103 crc
.byte
[4] = crc
.byte
[3];
104 crc
.byte
[3] = crc
.byte
[2] + new;
105 crc
.byte
[2] = crc
.byte
[1];
106 crc
.byte
[1] = crc
.byte
[0];
109 sprintf (lockfile
, "%s%.2x%.2x%.2x%.2x%.2x%.2x%.2x", lock_path
,
110 crc
.byte
[0], crc
.byte
[1], crc
.byte
[2], crc
.byte
[3],
111 crc
.byte
[4], crc
.byte
[5], crc
.byte
[6]);
114 #else /* defined HAVE_LONG_FILE_NAMES */
116 #define MAKE_LOCK_PATH(lock, file) \
117 (lock = (char *) alloca (XSTRING (file)->size + strlen (lock_path) + 1), \
118 fill_in_lock_file_name (lock, (file)))
121 fill_in_lock_file_name (lockfile
, fn
)
122 register char *lockfile
;
123 register Lisp_Object fn
;
127 strcpy (lockfile
, lock_path
);
129 p
= lockfile
+ strlen (lockfile
);
131 strcpy (p
, XSTRING (fn
)->data
);
139 #endif /* !defined HAVE_LONG_FILE_NAMES */
142 lock_file_owner_name (lfname
)
146 struct passwd
*the_pw
;
148 if (lstat (lfname
, &s
) == 0)
149 the_pw
= getpwuid (s
.st_uid
);
150 return (the_pw
== 0 ? Qnil
: build_string (the_pw
->pw_name
));
154 /* lock_file locks file fn,
155 meaning it serves notice on the world that you intend to edit that file.
156 This should be done only when about to modify a file-visiting
157 buffer previously unmodified.
158 Do not (normally) call lock_buffer for a buffer already modified,
159 as either the file is already locked, or the user has already
160 decided to go ahead without locking.
162 When lock_buffer returns, either the lock is locked for us,
163 or the user has said to go ahead without locking.
165 If the file is locked by someone else, lock_buffer calls
166 ask-user-about-lock (a Lisp function) with two arguments,
167 the file name and the name of the user who did the locking.
168 This function can signal an error, or return t meaning
169 take away the lock, or return nil meaning ignore the lock. */
171 /* The lock file name is the file name with "/" replaced by "!"
172 and put in the Emacs lock directory. */
173 /* (ie., /ka/king/junk.tex -> /!/!ka!king!junk.tex). */
175 /* If HAVE_LONG_FILE_NAMES is not defined, the lock file name is the hex
176 representation of a 14-bytes CRC generated from the file name
177 and put in the Emacs lock directory (not very nice, but it works).
178 (ie., /ka/king/junk.tex -> /!/ec92d3ed24a8f0). */
182 register Lisp_Object fn
;
184 register Lisp_Object attack
;
185 register char *lfname
;
187 MAKE_LOCK_PATH (lfname
, fn
);
189 /* See if this file is visited and has changed on disk since it was
192 register Lisp_Object subject_buf
= Fget_file_buffer (fn
);
193 if (!NILP (subject_buf
)
194 && NILP (Fverify_visited_file_modtime (subject_buf
))
195 && !NILP (Ffile_exists_p (fn
)))
196 call1 (intern ("ask-user-about-supersession-threat"), fn
);
199 /* Try to lock the lock. */
200 if (lock_if_free (lfname
) <= 0)
201 /* Return now if we have locked it, or if lock dir does not exist */
204 /* Else consider breaking the lock */
205 attack
= call2 (intern ("ask-user-about-lock"), fn
,
206 lock_file_owner_name (lfname
));
208 /* User says take the lock */
210 lock_superlock (lfname
);
211 lock_file_1 (lfname
, O_WRONLY
) ;
212 unlink (superlock_path
);
215 /* User says ignore the lock */
218 /* Lock the lock file named LFNAME.
219 If MODE is O_WRONLY, we do so even if it is already locked.
220 If MODE is O_WRONLY | O_EXCL | O_CREAT, we do so only if it is free.
221 Return 1 if successful, 0 if not. */
224 lock_file_1 (lfname
, mode
)
225 int mode
; char *lfname
;
230 if ((fd
= open (lfname
, mode
, 0666)) >= 0)
233 chmod (lfname
, 0666);
237 sprintf (buf
, "%d ", getpid ());
238 write (fd
, buf
, strlen (buf
));
246 /* Lock the lock named LFNAME if possible.
247 Return 0 in that case.
248 Return positive if lock is really locked by someone else.
249 Return -1 if cannot lock for any other reason. */
252 lock_if_free (lfname
)
253 register char *lfname
;
255 register int clasher
;
257 while (lock_file_1 (lfname
, O_WRONLY
| O_EXCL
| O_CREAT
) == 0)
261 clasher
= current_lock_owner (lfname
);
263 if (clasher
!= getpid ())
266 /* Try again to lock it */
271 /* Return the pid of the process that claims to own the lock file LFNAME,
272 or 0 if nobody does or the lock is obsolete,
273 or -1 if something is wrong with the locking mechanism. */
276 current_lock_owner (lfname
)
279 int owner
= current_lock_owner_1 (lfname
);
280 if (owner
== 0 && errno
== ENOENT
)
282 /* Is it locked by a process that exists? */
283 if (owner
!= 0 && (kill (owner
, 0) >= 0 || errno
== EPERM
))
285 if (unlink (lfname
) < 0)
291 current_lock_owner_1 (lfname
)
298 fd
= open (lfname
, O_RDONLY
, 0666);
301 tem
= read (fd
, buf
, sizeof buf
);
303 return (tem
<= 0 ? 0 : atoi (buf
));
309 register Lisp_Object fn
;
311 register char *lfname
;
313 MAKE_LOCK_PATH (lfname
, fn
);
315 lock_superlock (lfname
);
317 if (current_lock_owner_1 (lfname
) == getpid ())
320 unlink (superlock_path
);
323 lock_superlock (lfname
)
328 for (i
= -20; i
< 0 && (fd
= open (superlock_path
,
329 O_WRONLY
| O_EXCL
| O_CREAT
, 0666)) < 0;
339 chmod (superlock_path
, 0666);
343 write (fd
, lfname
, strlen (lfname
));
351 register Lisp_Object tail
;
352 register struct buffer
*b
;
354 for (tail
= Vbuffer_alist
; XGCTYPE (tail
) == Lisp_Cons
;
355 tail
= XCONS (tail
)->cdr
)
357 b
= XBUFFER (XCONS (XCONS (tail
)->car
)->cdr
);
358 if (XTYPE (b
->filename
) == Lisp_String
&&
359 b
->save_modified
< BUF_MODIFF (b
))
360 unlock_file (b
->filename
);
365 DEFUN ("lock-buffer", Flock_buffer
, Slock_buffer
,
367 "Lock FILE, if current buffer is modified.\n\
368 FILE defaults to current buffer's visited file,\n\
369 or else nothing is done if current buffer isn't visiting a file.")
374 fn
= current_buffer
->filename
;
376 CHECK_STRING (fn
, 0);
377 if (current_buffer
->save_modified
< MODIFF
383 DEFUN ("unlock-buffer", Funlock_buffer
, Sunlock_buffer
,
385 "Unlock the file visited in the current buffer,\n\
386 if it should normally be locked.")
389 if (current_buffer
->save_modified
< MODIFF
&&
390 XTYPE (current_buffer
->filename
) == Lisp_String
)
391 unlock_file (current_buffer
->filename
);
396 /* Unlock the file visited in buffer BUFFER. */
398 unlock_buffer (buffer
)
399 struct buffer
*buffer
;
401 if (buffer
->save_modified
< BUF_MODIFF (buffer
) &&
402 XTYPE (buffer
->filename
) == Lisp_String
)
403 unlock_file (buffer
->filename
);
406 DEFUN ("file-locked-p", Ffile_locked_p
, Sfile_locked_p
, 0, 1, 0,
407 "Return nil if the FILENAME is not locked,\n\
408 t if it is locked by you, else a string of the name of the locker.")
412 register char *lfname
;
415 fn
= Fexpand_file_name (fn
, Qnil
);
417 MAKE_LOCK_PATH (lfname
, fn
);
419 owner
= current_lock_owner (lfname
);
422 else if (owner
== getpid ())
425 return (lock_file_owner_name (lfname
));
429 /* Initialization functions. */
433 lock_path
= egetenv ("EMACSLOCKDIR");
435 lock_path
= PATH_LOCK
;
437 /* Make sure it ends with a slash. */
438 if (lock_path
[strlen (lock_path
) - 1] != '/')
440 lock_path
= strcpy ((char *) xmalloc (strlen (lock_path
) + 2),
442 strcat (lock_path
, "/");
445 superlock_path
= (char *) xmalloc ((strlen (lock_path
)
446 + sizeof (SUPERLOCK_NAME
)));
447 strcpy (superlock_path
, lock_path
);
448 strcat (superlock_path
, SUPERLOCK_NAME
);
453 defsubr (&Sunlock_buffer
);
454 defsubr (&Slock_buffer
);
455 defsubr (&Sfile_locked_p
);
458 #endif /* CLASH_DETECTION */