1 /* Lock files for editing.
2 Copyright (C) 1985, 86, 87, 93, 94, 96, 98, 1999 Free Software Foundation, Inc.
4 This file is part of GNU Emacs.
6 GNU Emacs is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 GNU Emacs is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GNU Emacs; see the file COPYING. If not, write to
18 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA. */
23 #include <sys/types.h>
46 #include <sys/types.h>
47 #include <sys/sysctl.h>
48 #endif /* __FreeBSD__ */
62 /* The directory for writing temporary files. */
64 Lisp_Object Vtemporary_file_directory
;
66 #ifdef CLASH_DETECTION
70 /* A file whose last-modified time is just after the most recent boot.
71 Define this to be NULL to disable checking for this file. */
72 #ifndef BOOT_TIME_FILE
73 #define BOOT_TIME_FILE "/var/run/random-seed"
77 #define WTMP_FILE "/var/log/wtmp"
80 /* The strategy: to lock a file FN, create a symlink .#FN in FN's
81 directory, with link data `user@host.pid'. This avoids a single
82 mount (== failure) point for lock files.
84 When the host in the lock data is the current host, we can check if
85 the pid is valid with kill.
87 Otherwise, we could look at a separate file that maps hostnames to
88 reboot times to see if the remote pid can possibly be valid, since we
89 don't want Emacs to have to communicate via pipes or sockets or
90 whatever to other processes, either locally or remotely; rms says
91 that's too unreliable. Hence the separate file, which could
92 theoretically be updated by daemons running separately -- but this
93 whole idea is unimplemented; in practice, at least in our
94 environment, it seems such stale locks arise fairly infrequently, and
95 Emacs' standard methods of dealing with clashes suffice.
97 We use symlinks instead of normal files because (1) they can be
98 stored more efficiently on the filesystem, since the kernel knows
99 they will be small, and (2) all the info about the lock can be read
100 in a single system call (readlink). Although we could use regular
101 files to be useful on old systems lacking symlinks, nowadays
102 virtually all such systems are probably single-user anyway, so it
103 didn't seem worth the complication.
105 Similarly, we don't worry about a possible 14-character limit on
106 file names, because those are all the same systems that don't have
109 This is compatible with the locking scheme used by Interleaf (which
110 has contributed this implementation for Emacs), and was designed by
111 Ethan Jacobson, Kimbo Mundy, and others.
113 --karl@cs.umb.edu/karl@hq.ileaf.com. */
116 /* Return the time of the last system boot. */
118 static time_t boot_time
;
119 static int boot_time_initialized
;
121 extern Lisp_Object Vshell_file_name
;
124 static void get_boot_time_1
P_ ((char *, int));
130 #if defined (BOOT_TIME) && ! defined (NO_WTMP_FILE)
134 if (boot_time_initialized
)
136 boot_time_initialized
= 1;
138 #if defined (CTL_KERN) && defined (KERN_BOOTTIME)
142 struct timeval boottime_val
;
145 mib
[1] = KERN_BOOTTIME
;
146 size
= sizeof (boottime_val
);
148 if (sysctl (mib
, 2, &boottime_val
, &size
, NULL
, 0) >= 0)
150 boot_time
= boottime_val
.tv_sec
;
154 #endif /* defined (CTL_KERN) && defined (KERN_BOOTTIME) */
159 if (stat (BOOT_TIME_FILE
, &st
) == 0)
161 boot_time
= st
.st_mtime
;
166 #if defined (BOOT_TIME) && ! defined (NO_WTMP_FILE)
168 /* The utmp routines maintain static state.
169 Don't touch that state unless we are initialized,
170 since it might not survive dumping. */
173 #endif /* not CANNOT_DUMP */
175 /* Try to get boot time from utmp before wtmp,
176 since utmp is typically much smaller than wtmp.
177 Passing a null pointer causes get_boot_time_1
178 to inspect the default file, namely utmp. */
179 get_boot_time_1 ((char *) 0, 0);
183 /* Try to get boot time from the current wtmp file. */
184 get_boot_time_1 (WTMP_FILE
, 1);
186 /* If we did not find a boot time in wtmp, look at wtmp, and so on. */
187 for (counter
= 0; counter
< 20 && ! boot_time
; counter
++)
189 char cmd_string
[100];
190 Lisp_Object tempname
, filename
;
195 sprintf (cmd_string
, "%s.%d", WTMP_FILE
, counter
);
196 tempname
= build_string (cmd_string
);
197 if (! NILP (Ffile_exists_p (tempname
)))
201 sprintf (cmd_string
, "%s.%d.gz", WTMP_FILE
, counter
);
202 tempname
= build_string (cmd_string
);
203 if (! NILP (Ffile_exists_p (tempname
)))
206 tempname
= Fexpand_file_name (build_string ("wtmp"),
207 Vtemporary_file_directory
);
208 tempname
= Fmake_temp_name (tempname
);
209 args
[0] = Vshell_file_name
;
213 args
[4] = build_string ("-c");
214 sprintf (cmd_string
, "gunzip < %s.%d.gz > %s",
215 WTMP_FILE
, counter
, XSTRING (tempname
)->data
);
216 args
[5] = build_string (cmd_string
);
217 Fcall_process (6, args
);
223 if (! NILP (filename
))
225 get_boot_time_1 (XSTRING (filename
)->data
, 1);
227 unlink (XSTRING (filename
)->data
);
238 /* Try to get the boot time from wtmp file FILENAME.
239 This succeeds if that file contains a reboot record.
241 If FILENAME is zero, use the same file as before;
242 if no FILENAME has ever been specified, this is the utmp file.
243 Use the newest reboot record if NEWEST is nonzero,
244 the first reboot record otherwise.
245 Ignore all reboot records on or before BOOT_TIME.
246 Success is indicated by setting BOOT_TIME to a larger value. */
249 get_boot_time_1 (filename
, newest
)
253 struct utmp ut
, *utp
;
258 /* On some versions of IRIX, opening a nonexistent file name
259 is likely to crash in the utmp routines. */
260 desc
= emacs_open (filename
, O_RDONLY
, 0);
273 /* Find the next reboot record. */
274 ut
.ut_type
= BOOT_TIME
;
278 /* Compare reboot times and use the newest one. */
279 if (utp
->ut_time
> boot_time
)
281 boot_time
= utp
->ut_time
;
285 /* Advance on element in the file
286 so that getutid won't repeat the same one. */
293 #endif /* BOOT_TIME */
295 /* Here is the structure that stores information about a lock. */
305 /* When we read the info back, we might need this much more,
306 enough for decimal representation plus null. */
307 #define LOCK_PID_MAX (4 * sizeof (unsigned long))
309 /* Free the two dynamically-allocated pieces in PTR. */
310 #define FREE_LOCK_INFO(i) do { xfree ((i).user); xfree ((i).host); } while (0)
313 /* Write the name of the lock file for FN into LFNAME. Length will be
314 that of FN plus two more for the leading `.#' plus 1 for the
315 trailing period plus one for the digit after it plus one for the
317 #define MAKE_LOCK_NAME(lock, file) \
318 (lock = (char *) alloca (STRING_BYTES (XSTRING (file)) + 2 + 1 + 1 + 1), \
319 fill_in_lock_file_name (lock, (file)))
322 fill_in_lock_file_name (lockfile
, fn
)
323 register char *lockfile
;
324 register Lisp_Object fn
;
330 strcpy (lockfile
, XSTRING (fn
)->data
);
332 /* Shift the nondirectory part of the file name (including the null)
333 right two characters. Here is one of the places where we'd have to
334 do something to support 14-character-max file names. */
335 for (p
= lockfile
+ strlen (lockfile
); p
!= lockfile
&& *p
!= '/'; p
--)
338 /* Insert the `.#'. */
344 while (lstat (lockfile
, &st
) == 0 && !S_ISLNK (st
.st_mode
))
351 sprintf (p
, ".%d", count
++);
355 /* Lock the lock file named LFNAME.
356 If FORCE is nonzero, we do so even if it is already locked.
357 Return 1 if successful, 0 if not. */
360 lock_file_1 (lfname
, force
)
370 if (STRINGP (Fuser_login_name (Qnil
)))
371 user_name
= (char *)XSTRING (Fuser_login_name (Qnil
))->data
;
374 if (STRINGP (Fsystem_name ()))
375 host_name
= (char *)XSTRING (Fsystem_name ())->data
;
378 lock_info_str
= (char *)alloca (strlen (user_name
) + strlen (host_name
)
381 boot_time
= get_boot_time ();
383 sprintf (lock_info_str
, "%s@%s.%lu:%lu", user_name
, host_name
,
384 (unsigned long) getpid (), (unsigned long) boot_time
);
386 sprintf (lock_info_str
, "%s@%s.%lu", user_name
, host_name
,
387 (unsigned long) getpid ());
389 err
= symlink (lock_info_str
, lfname
);
390 if (errno
== EEXIST
&& force
)
393 err
= symlink (lock_info_str
, lfname
);
399 /* Return 1 if times A and B are no more than one second apart. */
402 within_one_second (a
, b
)
405 return (a
- b
>= -1 && a
- b
<= 1);
408 /* Return 0 if nobody owns the lock file LFNAME or the lock is obsolete,
409 1 if another process owns it (and set OWNER (if non-null) to info),
410 2 if the current process owns it,
411 or -1 if something is wrong with the locking mechanism. */
414 current_lock_owner (owner
, lfname
)
415 lock_info_type
*owner
;
419 extern char *rindex (), *index ();
423 char *at
, *dot
, *colon
;
426 /* Read arbitrarily-long contents of symlink. Similar code in
427 file-symlink-p in fileio.c. */
431 lfinfo
= (char *) xrealloc (lfinfo
, bufsize
);
432 len
= readlink (lfname
, lfinfo
, bufsize
);
434 while (len
>= bufsize
);
436 /* If nonexistent lock file, all is well; otherwise, got strange error. */
440 return errno
== ENOENT
? 0 : -1;
443 /* Link info exists, so `len' is its length. Null terminate. */
446 /* Even if the caller doesn't want the owner info, we still have to
447 read it to determine return value, so allocate it. */
450 owner
= (lock_info_type
*) alloca (sizeof (lock_info_type
));
454 /* Parse USER@HOST.PID:BOOT_TIME. If can't parse, return -1. */
455 /* The USER is everything before the first @. */
456 at
= index (lfinfo
, '@');
457 dot
= rindex (lfinfo
, '.');
464 owner
->user
= (char *) xmalloc (len
+ 1);
465 strncpy (owner
->user
, lfinfo
, len
);
466 owner
->user
[len
] = 0;
468 /* The PID is everything from the last `.' to the `:'. */
469 owner
->pid
= atoi (dot
+ 1);
471 while (*colon
&& *colon
!= ':')
473 /* After the `:', if there is one, comes the boot time. */
475 owner
->boot_time
= atoi (colon
+ 1);
477 owner
->boot_time
= 0;
479 /* The host is everything in between. */
481 owner
->host
= (char *) xmalloc (len
+ 1);
482 strncpy (owner
->host
, at
+ 1, len
);
483 owner
->host
[len
] = 0;
485 /* We're done looking at the link info. */
488 /* On current host? */
489 if (STRINGP (Fsystem_name ())
490 && strcmp (owner
->host
, XSTRING (Fsystem_name ())->data
) == 0)
492 if (owner
->pid
== getpid ())
493 ret
= 2; /* We own it. */
494 else if (owner
->pid
> 0
495 && (kill (owner
->pid
, 0) >= 0 || errno
== EPERM
)
496 && (owner
->boot_time
== 0
497 || within_one_second (owner
->boot_time
, get_boot_time ())))
498 ret
= 1; /* An existing process on this machine owns it. */
499 /* The owner process is dead or has a strange pid (<=0), so try to
501 else if (unlink (lfname
) < 0)
507 { /* If we wanted to support the check for stale locks on remote machines,
508 here's where we'd do it. */
513 if (local_owner
|| ret
<= 0)
515 FREE_LOCK_INFO (*owner
);
521 /* Lock the lock named LFNAME if possible.
522 Return 0 in that case.
523 Return positive if some other process owns the lock, and info about
524 that process in CLASHER.
525 Return -1 if cannot lock for any other reason. */
528 lock_if_free (clasher
, lfname
)
529 lock_info_type
*clasher
;
530 register char *lfname
;
532 while (lock_file_1 (lfname
, 0) == 0)
539 locker
= current_lock_owner (clasher
, lfname
);
542 FREE_LOCK_INFO (*clasher
);
543 return 0; /* We ourselves locked it. */
545 else if (locker
== 1)
546 return 1; /* Someone else has it. */
547 else if (locker
== -1)
548 return -1; /* current_lock_owner returned strange error. */
550 /* We deleted a stale lock; try again to lock the file. */
555 /* lock_file locks file FN,
556 meaning it serves notice on the world that you intend to edit that file.
557 This should be done only when about to modify a file-visiting
558 buffer previously unmodified.
559 Do not (normally) call this for a buffer already modified,
560 as either the file is already locked, or the user has already
561 decided to go ahead without locking.
563 When this returns, either the lock is locked for us,
564 or the user has said to go ahead without locking.
566 If the file is locked by someone else, this calls
567 ask-user-about-lock (a Lisp function) with two arguments,
568 the file name and info about the user who did the locking.
569 This function can signal an error, or return t meaning
570 take away the lock, or return nil meaning ignore the lock. */
576 register Lisp_Object attack
, orig_fn
, encoded_fn
;
577 register char *lfname
, *locker
;
578 lock_info_type lock_info
;
581 /* Don't do locking while dumping Emacs.
582 Uncompressing wtmp files uses call-process, which does not work
583 in an uninitialized Emacs. */
584 if (! NILP (Vpurify_flag
))
589 fn
= Fexpand_file_name (fn
, Qnil
);
590 encoded_fn
= ENCODE_FILE (fn
);
592 /* Create the name of the lock-file for file fn */
593 MAKE_LOCK_NAME (lfname
, encoded_fn
);
595 /* See if this file is visited and has changed on disk since it was
598 register Lisp_Object subject_buf
;
600 subject_buf
= get_truename_buffer (orig_fn
);
602 if (!NILP (subject_buf
)
603 && NILP (Fverify_visited_file_modtime (subject_buf
))
604 && !NILP (Ffile_exists_p (fn
)))
605 call1 (intern ("ask-user-about-supersession-threat"), fn
);
610 /* Try to lock the lock. */
611 if (lock_if_free (&lock_info
, lfname
) <= 0)
612 /* Return now if we have locked it, or if lock creation failed */
615 /* Else consider breaking the lock */
616 locker
= (char *) alloca (strlen (lock_info
.user
) + strlen (lock_info
.host
)
618 sprintf (locker
, "%s@%s (pid %lu)", lock_info
.user
, lock_info
.host
,
620 FREE_LOCK_INFO (lock_info
);
622 attack
= call2 (intern ("ask-user-about-lock"), fn
, build_string (locker
));
624 /* User says take the lock */
626 lock_file_1 (lfname
, 1);
629 /* User says ignore the lock */
634 register Lisp_Object fn
;
636 register char *lfname
;
638 fn
= Fexpand_file_name (fn
, Qnil
);
639 fn
= ENCODE_FILE (fn
);
641 MAKE_LOCK_NAME (lfname
, fn
);
643 if (current_lock_owner (0, lfname
) == 2)
650 register Lisp_Object tail
;
651 register struct buffer
*b
;
653 for (tail
= Vbuffer_alist
; GC_CONSP (tail
); tail
= XCDR (tail
))
655 b
= XBUFFER (XCDR (XCAR (tail
)));
656 if (STRINGP (b
->file_truename
) && BUF_SAVE_MODIFF (b
) < BUF_MODIFF (b
))
658 register char *lfname
;
660 MAKE_LOCK_NAME (lfname
, b
->file_truename
);
662 if (current_lock_owner (0, lfname
) == 2)
668 DEFUN ("lock-buffer", Flock_buffer
, Slock_buffer
,
670 "Lock FILE, if current buffer is modified.\n\
671 FILE defaults to current buffer's visited file,\n\
672 or else nothing is done if current buffer isn't visiting a file.")
677 file
= current_buffer
->file_truename
;
679 CHECK_STRING (file
, 0);
680 if (SAVE_MODIFF
< MODIFF
686 DEFUN ("unlock-buffer", Funlock_buffer
, Sunlock_buffer
,
688 "Unlock the file visited in the current buffer,\n\
689 if it should normally be locked.")
692 if (SAVE_MODIFF
< MODIFF
693 && STRINGP (current_buffer
->file_truename
))
694 unlock_file (current_buffer
->file_truename
);
698 /* Unlock the file visited in buffer BUFFER. */
701 unlock_buffer (buffer
)
702 struct buffer
*buffer
;
704 if (BUF_SAVE_MODIFF (buffer
) < BUF_MODIFF (buffer
)
705 && STRINGP (buffer
->file_truename
))
706 unlock_file (buffer
->file_truename
);
709 DEFUN ("file-locked-p", Ffile_locked_p
, Sfile_locked_p
, 1, 1, 0,
710 "Return nil if the FILENAME is not locked,\n\
711 t if it is locked by you, else a string of the name of the locker.")
713 Lisp_Object filename
;
716 register char *lfname
;
718 lock_info_type locker
;
720 filename
= Fexpand_file_name (filename
, Qnil
);
722 MAKE_LOCK_NAME (lfname
, filename
);
724 owner
= current_lock_owner (&locker
, lfname
);
730 ret
= build_string (locker
.user
);
733 FREE_LOCK_INFO (locker
);
738 /* Initialization functions. */
744 boot_time_initialized
= 0;
750 DEFVAR_LISP ("temporary-file-directory", &Vtemporary_file_directory
,
751 "The directory for writing temporary files.");
752 Vtemporary_file_directory
= Qnil
;
754 defsubr (&Sunlock_buffer
);
755 defsubr (&Slock_buffer
);
756 defsubr (&Sfile_locked_p
);
759 #endif /* CLASH_DETECTION */