| 1 | /* Lock files for editing. |
| 2 | Copyright (C) 1985-1987, 1993-1994, 1996, 1998-2013 Free Software |
| 3 | Foundation, Inc. |
| 4 | |
| 5 | This file is part of GNU Emacs. |
| 6 | |
| 7 | GNU Emacs is free software: you can redistribute it and/or modify |
| 8 | it under the terms of the GNU General Public License as published by |
| 9 | the Free Software Foundation, either version 3 of the License, or |
| 10 | (at your option) any later version. |
| 11 | |
| 12 | GNU Emacs is distributed in the hope that it will be useful, |
| 13 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 15 | GNU General Public License for more details. |
| 16 | |
| 17 | You should have received a copy of the GNU General Public License |
| 18 | along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>. */ |
| 19 | |
| 20 | |
| 21 | #include <config.h> |
| 22 | #include <sys/types.h> |
| 23 | #include <sys/stat.h> |
| 24 | #include <signal.h> |
| 25 | #include <stdio.h> |
| 26 | |
| 27 | #ifdef HAVE_PWD_H |
| 28 | #include <pwd.h> |
| 29 | #endif |
| 30 | |
| 31 | #include <sys/file.h> |
| 32 | #include <fcntl.h> |
| 33 | #include <unistd.h> |
| 34 | |
| 35 | #ifdef __FreeBSD__ |
| 36 | #include <sys/sysctl.h> |
| 37 | #endif /* __FreeBSD__ */ |
| 38 | |
| 39 | #include <errno.h> |
| 40 | |
| 41 | #include "lisp.h" |
| 42 | #include "character.h" |
| 43 | #include "buffer.h" |
| 44 | #include "coding.h" |
| 45 | #include "systime.h" |
| 46 | #ifdef WINDOWSNT |
| 47 | #include <share.h> |
| 48 | #include "w32.h" /* for dostounix_filename */ |
| 49 | #endif |
| 50 | |
| 51 | #ifdef CLASH_DETECTION |
| 52 | |
| 53 | #ifdef HAVE_UTMP_H |
| 54 | #include <utmp.h> |
| 55 | #endif |
| 56 | |
| 57 | /* A file whose last-modified time is just after the most recent boot. |
| 58 | Define this to be NULL to disable checking for this file. */ |
| 59 | #ifndef BOOT_TIME_FILE |
| 60 | #define BOOT_TIME_FILE "/var/run/random-seed" |
| 61 | #endif |
| 62 | |
| 63 | #ifndef WTMP_FILE |
| 64 | #define WTMP_FILE "/var/log/wtmp" |
| 65 | #endif |
| 66 | |
| 67 | /* The strategy: to lock a file FN, create a symlink .#FN in FN's |
| 68 | directory, with link data `user@host.pid'. This avoids a single |
| 69 | mount (== failure) point for lock files. |
| 70 | |
| 71 | When the host in the lock data is the current host, we can check if |
| 72 | the pid is valid with kill. |
| 73 | |
| 74 | Otherwise, we could look at a separate file that maps hostnames to |
| 75 | reboot times to see if the remote pid can possibly be valid, since we |
| 76 | don't want Emacs to have to communicate via pipes or sockets or |
| 77 | whatever to other processes, either locally or remotely; rms says |
| 78 | that's too unreliable. Hence the separate file, which could |
| 79 | theoretically be updated by daemons running separately -- but this |
| 80 | whole idea is unimplemented; in practice, at least in our |
| 81 | environment, it seems such stale locks arise fairly infrequently, and |
| 82 | Emacs' standard methods of dealing with clashes suffice. |
| 83 | |
| 84 | We use symlinks instead of normal files because (1) they can be |
| 85 | stored more efficiently on the filesystem, since the kernel knows |
| 86 | they will be small, and (2) all the info about the lock can be read |
| 87 | in a single system call (readlink). Although we could use regular |
| 88 | files to be useful on old systems lacking symlinks, nowadays |
| 89 | virtually all such systems are probably single-user anyway, so it |
| 90 | didn't seem worth the complication. |
| 91 | |
| 92 | Similarly, we don't worry about a possible 14-character limit on |
| 93 | file names, because those are all the same systems that don't have |
| 94 | symlinks. |
| 95 | |
| 96 | This is compatible with the locking scheme used by Interleaf (which |
| 97 | has contributed this implementation for Emacs), and was designed by |
| 98 | Ethan Jacobson, Kimbo Mundy, and others. |
| 99 | |
| 100 | --karl@cs.umb.edu/karl@hq.ileaf.com. */ |
| 101 | |
| 102 | \f |
| 103 | /* Return the time of the last system boot. */ |
| 104 | |
| 105 | static time_t boot_time; |
| 106 | static bool boot_time_initialized; |
| 107 | |
| 108 | #ifdef BOOT_TIME |
| 109 | static void get_boot_time_1 (const char *, bool); |
| 110 | #endif |
| 111 | |
| 112 | static time_t |
| 113 | get_boot_time (void) |
| 114 | { |
| 115 | #if defined (BOOT_TIME) |
| 116 | int counter; |
| 117 | #endif |
| 118 | |
| 119 | if (boot_time_initialized) |
| 120 | return boot_time; |
| 121 | boot_time_initialized = 1; |
| 122 | |
| 123 | #if defined (CTL_KERN) && defined (KERN_BOOTTIME) |
| 124 | { |
| 125 | int mib[2]; |
| 126 | size_t size; |
| 127 | struct timeval boottime_val; |
| 128 | |
| 129 | mib[0] = CTL_KERN; |
| 130 | mib[1] = KERN_BOOTTIME; |
| 131 | size = sizeof (boottime_val); |
| 132 | |
| 133 | if (sysctl (mib, 2, &boottime_val, &size, NULL, 0) >= 0) |
| 134 | { |
| 135 | boot_time = boottime_val.tv_sec; |
| 136 | return boot_time; |
| 137 | } |
| 138 | } |
| 139 | #endif /* defined (CTL_KERN) && defined (KERN_BOOTTIME) */ |
| 140 | |
| 141 | if (BOOT_TIME_FILE) |
| 142 | { |
| 143 | struct stat st; |
| 144 | if (stat (BOOT_TIME_FILE, &st) == 0) |
| 145 | { |
| 146 | boot_time = st.st_mtime; |
| 147 | return boot_time; |
| 148 | } |
| 149 | } |
| 150 | |
| 151 | #if defined (BOOT_TIME) |
| 152 | #ifndef CANNOT_DUMP |
| 153 | /* The utmp routines maintain static state. |
| 154 | Don't touch that state unless we are initialized, |
| 155 | since it might not survive dumping. */ |
| 156 | if (! initialized) |
| 157 | return boot_time; |
| 158 | #endif /* not CANNOT_DUMP */ |
| 159 | |
| 160 | /* Try to get boot time from utmp before wtmp, |
| 161 | since utmp is typically much smaller than wtmp. |
| 162 | Passing a null pointer causes get_boot_time_1 |
| 163 | to inspect the default file, namely utmp. */ |
| 164 | get_boot_time_1 ((char *) 0, 0); |
| 165 | if (boot_time) |
| 166 | return boot_time; |
| 167 | |
| 168 | /* Try to get boot time from the current wtmp file. */ |
| 169 | get_boot_time_1 (WTMP_FILE, 1); |
| 170 | |
| 171 | /* If we did not find a boot time in wtmp, look at wtmp, and so on. */ |
| 172 | for (counter = 0; counter < 20 && ! boot_time; counter++) |
| 173 | { |
| 174 | char cmd_string[sizeof WTMP_FILE ".19.gz"]; |
| 175 | Lisp_Object tempname, filename; |
| 176 | bool delete_flag = 0; |
| 177 | |
| 178 | filename = Qnil; |
| 179 | |
| 180 | tempname = make_formatted_string |
| 181 | (cmd_string, "%s.%d", WTMP_FILE, counter); |
| 182 | if (! NILP (Ffile_exists_p (tempname))) |
| 183 | filename = tempname; |
| 184 | else |
| 185 | { |
| 186 | tempname = make_formatted_string (cmd_string, "%s.%d.gz", |
| 187 | WTMP_FILE, counter); |
| 188 | if (! NILP (Ffile_exists_p (tempname))) |
| 189 | { |
| 190 | Lisp_Object args[6]; |
| 191 | |
| 192 | /* The utmp functions on mescaline.gnu.org accept only |
| 193 | file names up to 8 characters long. Choose a 2 |
| 194 | character long prefix, and call make_temp_file with |
| 195 | second arg non-zero, so that it will add not more |
| 196 | than 6 characters to the prefix. */ |
| 197 | filename = Fexpand_file_name (build_string ("wt"), |
| 198 | Vtemporary_file_directory); |
| 199 | filename = make_temp_name (filename, 1); |
| 200 | args[0] = build_string ("gzip"); |
| 201 | args[1] = Qnil; |
| 202 | args[2] = list2 (QCfile, filename); |
| 203 | args[3] = Qnil; |
| 204 | args[4] = build_string ("-cd"); |
| 205 | args[5] = tempname; |
| 206 | Fcall_process (6, args); |
| 207 | delete_flag = 1; |
| 208 | } |
| 209 | } |
| 210 | |
| 211 | if (! NILP (filename)) |
| 212 | { |
| 213 | get_boot_time_1 (SSDATA (filename), 1); |
| 214 | if (delete_flag) |
| 215 | unlink (SSDATA (filename)); |
| 216 | } |
| 217 | } |
| 218 | |
| 219 | return boot_time; |
| 220 | #else |
| 221 | return 0; |
| 222 | #endif |
| 223 | } |
| 224 | |
| 225 | #ifdef BOOT_TIME |
| 226 | /* Try to get the boot time from wtmp file FILENAME. |
| 227 | This succeeds if that file contains a reboot record. |
| 228 | |
| 229 | If FILENAME is zero, use the same file as before; |
| 230 | if no FILENAME has ever been specified, this is the utmp file. |
| 231 | Use the newest reboot record if NEWEST, |
| 232 | the first reboot record otherwise. |
| 233 | Ignore all reboot records on or before BOOT_TIME. |
| 234 | Success is indicated by setting BOOT_TIME to a larger value. */ |
| 235 | |
| 236 | void |
| 237 | get_boot_time_1 (const char *filename, bool newest) |
| 238 | { |
| 239 | struct utmp ut, *utp; |
| 240 | int desc; |
| 241 | |
| 242 | if (filename) |
| 243 | { |
| 244 | /* On some versions of IRIX, opening a nonexistent file name |
| 245 | is likely to crash in the utmp routines. */ |
| 246 | desc = emacs_open (filename, O_RDONLY, 0); |
| 247 | if (desc < 0) |
| 248 | return; |
| 249 | |
| 250 | emacs_close (desc); |
| 251 | |
| 252 | utmpname (filename); |
| 253 | } |
| 254 | |
| 255 | setutent (); |
| 256 | |
| 257 | while (1) |
| 258 | { |
| 259 | /* Find the next reboot record. */ |
| 260 | ut.ut_type = BOOT_TIME; |
| 261 | utp = getutid (&ut); |
| 262 | if (! utp) |
| 263 | break; |
| 264 | /* Compare reboot times and use the newest one. */ |
| 265 | if (utp->ut_time > boot_time) |
| 266 | { |
| 267 | boot_time = utp->ut_time; |
| 268 | if (! newest) |
| 269 | break; |
| 270 | } |
| 271 | /* Advance on element in the file |
| 272 | so that getutid won't repeat the same one. */ |
| 273 | utp = getutent (); |
| 274 | if (! utp) |
| 275 | break; |
| 276 | } |
| 277 | endutent (); |
| 278 | } |
| 279 | #endif /* BOOT_TIME */ |
| 280 | \f |
| 281 | /* Here is the structure that stores information about a lock. */ |
| 282 | |
| 283 | typedef struct |
| 284 | { |
| 285 | char *user; |
| 286 | char *host; |
| 287 | pid_t pid; |
| 288 | time_t boot_time; |
| 289 | } lock_info_type; |
| 290 | |
| 291 | /* Free the two dynamically-allocated pieces in PTR. */ |
| 292 | #define FREE_LOCK_INFO(i) do { xfree ((i).user); xfree ((i).host); } while (0) |
| 293 | |
| 294 | |
| 295 | /* Write the name of the lock file for FNAME into LOCKNAME. Length |
| 296 | will be that of FN plus two more for the leading `.#' plus 1 for |
| 297 | the trailing period plus one for the digit after it plus one for |
| 298 | the null. */ |
| 299 | #define MAKE_LOCK_NAME(LOCKNAME, FNAME) \ |
| 300 | (LOCKNAME = alloca (SBYTES (FNAME) + 2 + 1 + 1 + 1), \ |
| 301 | fill_in_lock_file_name (LOCKNAME, (FNAME))) |
| 302 | |
| 303 | #ifdef WINDOWSNT |
| 304 | /* 256 chars for user, 1024 chars for host, 10 digits for each of 2 int's. */ |
| 305 | #define MAX_LFINFO (256 + 1024 + 10 + 10 + 2) |
| 306 | /* min size: .@PID */ |
| 307 | #define IS_LOCK_FILE(ST) (MAX_LFINFO >= (ST).st_size && (ST).st_size >= 3) |
| 308 | #else |
| 309 | #define IS_LOCK_FILE(ST) S_ISLNK ((ST).st_mode) |
| 310 | #endif |
| 311 | |
| 312 | static void |
| 313 | fill_in_lock_file_name (register char *lockfile, register Lisp_Object fn) |
| 314 | { |
| 315 | ptrdiff_t length = SBYTES (fn); |
| 316 | register char *p; |
| 317 | struct stat st; |
| 318 | int count = 0; |
| 319 | |
| 320 | strcpy (lockfile, SSDATA (fn)); |
| 321 | |
| 322 | /* Shift the nondirectory part of the file name (including the null) |
| 323 | right two characters. Here is one of the places where we'd have to |
| 324 | do something to support 14-character-max file names. */ |
| 325 | for (p = lockfile + length; p != lockfile && *p != '/'; p--) |
| 326 | p[2] = *p; |
| 327 | |
| 328 | /* Insert the `.#'. */ |
| 329 | p[1] = '.'; |
| 330 | p[2] = '#'; |
| 331 | |
| 332 | p = lockfile + length + 2; |
| 333 | |
| 334 | while (lstat (lockfile, &st) == 0 && !IS_LOCK_FILE (st)) |
| 335 | { |
| 336 | if (count > 9) |
| 337 | { |
| 338 | *p = '\0'; |
| 339 | return; |
| 340 | } |
| 341 | sprintf (p, ".%d", count++); |
| 342 | } |
| 343 | } |
| 344 | |
| 345 | static int |
| 346 | create_lock_file (char *lfname, char *lock_info_str, bool force) |
| 347 | { |
| 348 | int err; |
| 349 | |
| 350 | #ifdef WINDOWSNT |
| 351 | /* Symlinks are supported only by latest versions of Windows, and |
| 352 | creating them is a privileged operation that often triggers UAC |
| 353 | elevation prompts. Therefore, instead of using symlinks, we |
| 354 | create a regular file with the lock info written as its |
| 355 | contents. */ |
| 356 | { |
| 357 | /* Deny everybody else any kind of access to the file until we are |
| 358 | done writing it and close the handle. This makes the entire |
| 359 | open/write/close operation atomic, as far as other processes |
| 360 | are concerned. */ |
| 361 | int fd = _sopen (lfname, |
| 362 | _O_WRONLY | _O_BINARY | _O_CREAT | _O_EXCL | _O_NOINHERIT, |
| 363 | _SH_DENYRW, S_IREAD | S_IWRITE); |
| 364 | |
| 365 | if (fd < 0 && errno == EEXIST && force) |
| 366 | fd = _sopen (lfname, _O_WRONLY | _O_BINARY | _O_TRUNC |_O_NOINHERIT, |
| 367 | _SH_DENYRW, S_IREAD | S_IWRITE); |
| 368 | if (fd >= 0) |
| 369 | { |
| 370 | ssize_t lock_info_len = strlen (lock_info_str); |
| 371 | |
| 372 | err = 0; |
| 373 | if (emacs_write (fd, lock_info_str, lock_info_len) != lock_info_len) |
| 374 | err = -1; |
| 375 | if (emacs_close (fd)) |
| 376 | err = -1; |
| 377 | } |
| 378 | else |
| 379 | err = -1; |
| 380 | } |
| 381 | #else |
| 382 | err = symlink (lock_info_str, lfname); |
| 383 | if (errno == EEXIST && force) |
| 384 | { |
| 385 | unlink (lfname); |
| 386 | err = symlink (lock_info_str, lfname); |
| 387 | } |
| 388 | #endif |
| 389 | |
| 390 | return err; |
| 391 | } |
| 392 | |
| 393 | /* Lock the lock file named LFNAME. |
| 394 | If FORCE, do so even if it is already locked. |
| 395 | Return true if successful. */ |
| 396 | |
| 397 | static bool |
| 398 | lock_file_1 (char *lfname, bool force) |
| 399 | { |
| 400 | int err; |
| 401 | int symlink_errno; |
| 402 | USE_SAFE_ALLOCA; |
| 403 | |
| 404 | /* Call this first because it can GC. */ |
| 405 | printmax_t boot = get_boot_time (); |
| 406 | |
| 407 | Lisp_Object luser_name = Fuser_login_name (Qnil); |
| 408 | char const *user_name = STRINGP (luser_name) ? SSDATA (luser_name) : ""; |
| 409 | Lisp_Object lhost_name = Fsystem_name (); |
| 410 | char const *host_name = STRINGP (lhost_name) ? SSDATA (lhost_name) : ""; |
| 411 | ptrdiff_t lock_info_size = (strlen (user_name) + strlen (host_name) |
| 412 | + 2 * INT_STRLEN_BOUND (printmax_t) |
| 413 | + sizeof "@.:"); |
| 414 | char *lock_info_str = SAFE_ALLOCA (lock_info_size); |
| 415 | printmax_t pid = getpid (); |
| 416 | |
| 417 | esprintf (lock_info_str, boot ? "%s@%s.%"pMd":%"pMd : "%s@%s.%"pMd, |
| 418 | user_name, host_name, pid, boot); |
| 419 | err = create_lock_file (lfname, lock_info_str, force); |
| 420 | |
| 421 | symlink_errno = errno; |
| 422 | SAFE_FREE (); |
| 423 | errno = symlink_errno; |
| 424 | return err == 0; |
| 425 | } |
| 426 | |
| 427 | /* Return true if times A and B are no more than one second apart. */ |
| 428 | |
| 429 | static bool |
| 430 | within_one_second (time_t a, time_t b) |
| 431 | { |
| 432 | return (a - b >= -1 && a - b <= 1); |
| 433 | } |
| 434 | \f |
| 435 | static Lisp_Object |
| 436 | read_lock_data (char *lfname) |
| 437 | { |
| 438 | #ifndef WINDOWSNT |
| 439 | return emacs_readlinkat (AT_FDCWD, lfname); |
| 440 | #else |
| 441 | int fd = emacs_open (lfname, O_RDONLY | O_BINARY, S_IREAD); |
| 442 | ssize_t nbytes; |
| 443 | char lfinfo[MAX_LFINFO + 1]; |
| 444 | |
| 445 | if (fd < 0) |
| 446 | return Qnil; |
| 447 | |
| 448 | nbytes = emacs_read (fd, lfinfo, MAX_LFINFO); |
| 449 | emacs_close (fd); |
| 450 | |
| 451 | if (nbytes > 0) |
| 452 | { |
| 453 | lfinfo[nbytes] = '\0'; |
| 454 | return build_string (lfinfo); |
| 455 | } |
| 456 | else |
| 457 | return Qnil; |
| 458 | #endif |
| 459 | } |
| 460 | |
| 461 | /* Return 0 if nobody owns the lock file LFNAME or the lock is obsolete, |
| 462 | 1 if another process owns it (and set OWNER (if non-null) to info), |
| 463 | 2 if the current process owns it, |
| 464 | or -1 if something is wrong with the locking mechanism. */ |
| 465 | |
| 466 | static int |
| 467 | current_lock_owner (lock_info_type *owner, char *lfname) |
| 468 | { |
| 469 | int ret; |
| 470 | ptrdiff_t len; |
| 471 | lock_info_type local_owner; |
| 472 | intmax_t n; |
| 473 | char *at, *dot, *colon; |
| 474 | Lisp_Object lfinfo_object = read_lock_data (lfname); |
| 475 | char *lfinfo; |
| 476 | struct gcpro gcpro1; |
| 477 | |
| 478 | /* If nonexistent lock file, all is well; otherwise, got strange error. */ |
| 479 | if (NILP (lfinfo_object)) |
| 480 | return errno == ENOENT ? 0 : -1; |
| 481 | lfinfo = SSDATA (lfinfo_object); |
| 482 | |
| 483 | /* Even if the caller doesn't want the owner info, we still have to |
| 484 | read it to determine return value. */ |
| 485 | if (!owner) |
| 486 | owner = &local_owner; |
| 487 | |
| 488 | /* Parse USER@HOST.PID:BOOT_TIME. If can't parse, return -1. */ |
| 489 | /* The USER is everything before the last @. */ |
| 490 | at = strrchr (lfinfo, '@'); |
| 491 | dot = strrchr (lfinfo, '.'); |
| 492 | if (!at || !dot) |
| 493 | return -1; |
| 494 | len = at - lfinfo; |
| 495 | GCPRO1 (lfinfo_object); |
| 496 | owner->user = xmalloc (len + 1); |
| 497 | memcpy (owner->user, lfinfo, len); |
| 498 | owner->user[len] = 0; |
| 499 | |
| 500 | /* The PID is everything from the last `.' to the `:'. */ |
| 501 | errno = 0; |
| 502 | n = strtoimax (dot + 1, NULL, 10); |
| 503 | owner->pid = |
| 504 | ((0 <= n && n <= TYPE_MAXIMUM (pid_t) |
| 505 | && (TYPE_MAXIMUM (pid_t) < INTMAX_MAX || errno != ERANGE)) |
| 506 | ? n : 0); |
| 507 | |
| 508 | colon = strchr (dot + 1, ':'); |
| 509 | /* After the `:', if there is one, comes the boot time. */ |
| 510 | n = 0; |
| 511 | if (colon) |
| 512 | { |
| 513 | errno = 0; |
| 514 | n = strtoimax (colon + 1, NULL, 10); |
| 515 | } |
| 516 | owner->boot_time = |
| 517 | ((0 <= n && n <= TYPE_MAXIMUM (time_t) |
| 518 | && (TYPE_MAXIMUM (time_t) < INTMAX_MAX || errno != ERANGE)) |
| 519 | ? n : 0); |
| 520 | |
| 521 | /* The host is everything in between. */ |
| 522 | len = dot - at - 1; |
| 523 | owner->host = xmalloc (len + 1); |
| 524 | memcpy (owner->host, at + 1, len); |
| 525 | owner->host[len] = 0; |
| 526 | |
| 527 | /* We're done looking at the link info. */ |
| 528 | UNGCPRO; |
| 529 | |
| 530 | /* On current host? */ |
| 531 | if (STRINGP (Fsystem_name ()) |
| 532 | && strcmp (owner->host, SSDATA (Fsystem_name ())) == 0) |
| 533 | { |
| 534 | if (owner->pid == getpid ()) |
| 535 | ret = 2; /* We own it. */ |
| 536 | else if (owner->pid > 0 |
| 537 | && (kill (owner->pid, 0) >= 0 || errno == EPERM) |
| 538 | && (owner->boot_time == 0 |
| 539 | || within_one_second (owner->boot_time, get_boot_time ()))) |
| 540 | ret = 1; /* An existing process on this machine owns it. */ |
| 541 | /* The owner process is dead or has a strange pid (<=0), so try to |
| 542 | zap the lockfile. */ |
| 543 | else if (unlink (lfname) < 0) |
| 544 | ret = -1; |
| 545 | else |
| 546 | ret = 0; |
| 547 | } |
| 548 | else |
| 549 | { /* If we wanted to support the check for stale locks on remote machines, |
| 550 | here's where we'd do it. */ |
| 551 | ret = 1; |
| 552 | } |
| 553 | |
| 554 | /* Avoid garbage. */ |
| 555 | if (owner == &local_owner || ret <= 0) |
| 556 | { |
| 557 | FREE_LOCK_INFO (*owner); |
| 558 | } |
| 559 | return ret; |
| 560 | } |
| 561 | |
| 562 | \f |
| 563 | /* Lock the lock named LFNAME if possible. |
| 564 | Return 0 in that case. |
| 565 | Return positive if some other process owns the lock, and info about |
| 566 | that process in CLASHER. |
| 567 | Return -1 if cannot lock for any other reason. */ |
| 568 | |
| 569 | static int |
| 570 | lock_if_free (lock_info_type *clasher, register char *lfname) |
| 571 | { |
| 572 | while (! lock_file_1 (lfname, 0)) |
| 573 | { |
| 574 | int locker; |
| 575 | |
| 576 | if (errno != EEXIST) |
| 577 | return -1; |
| 578 | |
| 579 | locker = current_lock_owner (clasher, lfname); |
| 580 | if (locker == 2) |
| 581 | { |
| 582 | FREE_LOCK_INFO (*clasher); |
| 583 | return 0; /* We ourselves locked it. */ |
| 584 | } |
| 585 | else if (locker == 1) |
| 586 | return 1; /* Someone else has it. */ |
| 587 | else if (locker == -1) |
| 588 | return -1; /* current_lock_owner returned strange error. */ |
| 589 | |
| 590 | /* We deleted a stale lock; try again to lock the file. */ |
| 591 | } |
| 592 | return 0; |
| 593 | } |
| 594 | |
| 595 | /* lock_file locks file FN, |
| 596 | meaning it serves notice on the world that you intend to edit that file. |
| 597 | This should be done only when about to modify a file-visiting |
| 598 | buffer previously unmodified. |
| 599 | Do not (normally) call this for a buffer already modified, |
| 600 | as either the file is already locked, or the user has already |
| 601 | decided to go ahead without locking. |
| 602 | |
| 603 | When this returns, either the lock is locked for us, |
| 604 | or the user has said to go ahead without locking. |
| 605 | |
| 606 | If the file is locked by someone else, this calls |
| 607 | ask-user-about-lock (a Lisp function) with two arguments, |
| 608 | the file name and info about the user who did the locking. |
| 609 | This function can signal an error, or return t meaning |
| 610 | take away the lock, or return nil meaning ignore the lock. */ |
| 611 | |
| 612 | void |
| 613 | lock_file (Lisp_Object fn) |
| 614 | { |
| 615 | register Lisp_Object attack, orig_fn, encoded_fn; |
| 616 | register char *lfname, *locker; |
| 617 | ptrdiff_t locker_size; |
| 618 | lock_info_type lock_info; |
| 619 | printmax_t pid; |
| 620 | struct gcpro gcpro1; |
| 621 | USE_SAFE_ALLOCA; |
| 622 | |
| 623 | /* Don't do locking if the user has opted out. */ |
| 624 | if (! create_lockfiles) |
| 625 | return; |
| 626 | |
| 627 | /* Don't do locking while dumping Emacs. |
| 628 | Uncompressing wtmp files uses call-process, which does not work |
| 629 | in an uninitialized Emacs. */ |
| 630 | if (! NILP (Vpurify_flag)) |
| 631 | return; |
| 632 | |
| 633 | orig_fn = fn; |
| 634 | GCPRO1 (fn); |
| 635 | fn = Fexpand_file_name (fn, Qnil); |
| 636 | #ifdef WINDOWSNT |
| 637 | /* Ensure we have only '/' separators, to avoid problems with |
| 638 | looking (inside fill_in_lock_file_name) for backslashes in file |
| 639 | names encoded by some DBCS codepage. */ |
| 640 | dostounix_filename (SSDATA (fn), 1); |
| 641 | #endif |
| 642 | encoded_fn = ENCODE_FILE (fn); |
| 643 | |
| 644 | /* Create the name of the lock-file for file fn */ |
| 645 | MAKE_LOCK_NAME (lfname, encoded_fn); |
| 646 | |
| 647 | /* See if this file is visited and has changed on disk since it was |
| 648 | visited. */ |
| 649 | { |
| 650 | register Lisp_Object subject_buf; |
| 651 | |
| 652 | subject_buf = get_truename_buffer (orig_fn); |
| 653 | |
| 654 | if (!NILP (subject_buf) |
| 655 | && NILP (Fverify_visited_file_modtime (subject_buf)) |
| 656 | && !NILP (Ffile_exists_p (fn))) |
| 657 | call1 (intern ("ask-user-about-supersession-threat"), fn); |
| 658 | |
| 659 | } |
| 660 | UNGCPRO; |
| 661 | |
| 662 | /* Try to lock the lock. */ |
| 663 | if (lock_if_free (&lock_info, lfname) <= 0) |
| 664 | /* Return now if we have locked it, or if lock creation failed */ |
| 665 | return; |
| 666 | |
| 667 | /* Else consider breaking the lock */ |
| 668 | locker_size = (strlen (lock_info.user) + strlen (lock_info.host) |
| 669 | + INT_STRLEN_BOUND (printmax_t) |
| 670 | + sizeof "@ (pid )"); |
| 671 | locker = SAFE_ALLOCA (locker_size); |
| 672 | pid = lock_info.pid; |
| 673 | esprintf (locker, "%s@%s (pid %"pMd")", |
| 674 | lock_info.user, lock_info.host, pid); |
| 675 | FREE_LOCK_INFO (lock_info); |
| 676 | |
| 677 | attack = call2 (intern ("ask-user-about-lock"), fn, build_string (locker)); |
| 678 | SAFE_FREE (); |
| 679 | if (!NILP (attack)) |
| 680 | /* User says take the lock */ |
| 681 | { |
| 682 | lock_file_1 (lfname, 1); |
| 683 | return; |
| 684 | } |
| 685 | /* User says ignore the lock */ |
| 686 | } |
| 687 | |
| 688 | void |
| 689 | unlock_file (register Lisp_Object fn) |
| 690 | { |
| 691 | register char *lfname; |
| 692 | |
| 693 | fn = Fexpand_file_name (fn, Qnil); |
| 694 | fn = ENCODE_FILE (fn); |
| 695 | |
| 696 | MAKE_LOCK_NAME (lfname, fn); |
| 697 | |
| 698 | if (current_lock_owner (0, lfname) == 2) |
| 699 | unlink (lfname); |
| 700 | } |
| 701 | |
| 702 | void |
| 703 | unlock_all_files (void) |
| 704 | { |
| 705 | register Lisp_Object tail; |
| 706 | register struct buffer *b; |
| 707 | |
| 708 | for (tail = Vbuffer_alist; CONSP (tail); tail = XCDR (tail)) |
| 709 | { |
| 710 | b = XBUFFER (XCDR (XCAR (tail))); |
| 711 | if (STRINGP (BVAR (b, file_truename)) && BUF_SAVE_MODIFF (b) < BUF_MODIFF (b)) |
| 712 | { |
| 713 | unlock_file (BVAR (b, file_truename)); |
| 714 | } |
| 715 | } |
| 716 | } |
| 717 | \f |
| 718 | DEFUN ("lock-buffer", Flock_buffer, Slock_buffer, |
| 719 | 0, 1, 0, |
| 720 | doc: /* Lock FILE, if current buffer is modified. |
| 721 | FILE defaults to current buffer's visited file, |
| 722 | or else nothing is done if current buffer isn't visiting a file. */) |
| 723 | (Lisp_Object file) |
| 724 | { |
| 725 | if (NILP (file)) |
| 726 | file = BVAR (current_buffer, file_truename); |
| 727 | else |
| 728 | CHECK_STRING (file); |
| 729 | if (SAVE_MODIFF < MODIFF |
| 730 | && !NILP (file)) |
| 731 | lock_file (file); |
| 732 | return Qnil; |
| 733 | } |
| 734 | |
| 735 | DEFUN ("unlock-buffer", Funlock_buffer, Sunlock_buffer, |
| 736 | 0, 0, 0, |
| 737 | doc: /* Unlock the file visited in the current buffer. |
| 738 | If the buffer is not modified, this does nothing because the file |
| 739 | should not be locked in that case. */) |
| 740 | (void) |
| 741 | { |
| 742 | if (SAVE_MODIFF < MODIFF |
| 743 | && STRINGP (BVAR (current_buffer, file_truename))) |
| 744 | unlock_file (BVAR (current_buffer, file_truename)); |
| 745 | return Qnil; |
| 746 | } |
| 747 | |
| 748 | /* Unlock the file visited in buffer BUFFER. */ |
| 749 | |
| 750 | void |
| 751 | unlock_buffer (struct buffer *buffer) |
| 752 | { |
| 753 | if (BUF_SAVE_MODIFF (buffer) < BUF_MODIFF (buffer) |
| 754 | && STRINGP (BVAR (buffer, file_truename))) |
| 755 | unlock_file (BVAR (buffer, file_truename)); |
| 756 | } |
| 757 | |
| 758 | DEFUN ("file-locked-p", Ffile_locked_p, Sfile_locked_p, 1, 1, 0, |
| 759 | doc: /* Return a value indicating whether FILENAME is locked. |
| 760 | The value is nil if the FILENAME is not locked, |
| 761 | t if it is locked by you, else a string saying which user has locked it. */) |
| 762 | (Lisp_Object filename) |
| 763 | { |
| 764 | Lisp_Object ret; |
| 765 | register char *lfname; |
| 766 | int owner; |
| 767 | lock_info_type locker; |
| 768 | |
| 769 | filename = Fexpand_file_name (filename, Qnil); |
| 770 | |
| 771 | MAKE_LOCK_NAME (lfname, filename); |
| 772 | |
| 773 | owner = current_lock_owner (&locker, lfname); |
| 774 | if (owner <= 0) |
| 775 | ret = Qnil; |
| 776 | else if (owner == 2) |
| 777 | ret = Qt; |
| 778 | else |
| 779 | ret = build_string (locker.user); |
| 780 | |
| 781 | if (owner > 0) |
| 782 | FREE_LOCK_INFO (locker); |
| 783 | |
| 784 | return ret; |
| 785 | } |
| 786 | |
| 787 | #endif /* CLASH_DETECTION */ |
| 788 | |
| 789 | void |
| 790 | syms_of_filelock (void) |
| 791 | { |
| 792 | DEFVAR_LISP ("temporary-file-directory", Vtemporary_file_directory, |
| 793 | doc: /* The directory for writing temporary files. */); |
| 794 | Vtemporary_file_directory = Qnil; |
| 795 | |
| 796 | DEFVAR_BOOL ("create-lockfiles", create_lockfiles, |
| 797 | doc: /* Non-nil means use lockfiles to avoid editing collisions. */); |
| 798 | create_lockfiles = 1; |
| 799 | |
| 800 | #ifdef CLASH_DETECTION |
| 801 | defsubr (&Sunlock_buffer); |
| 802 | defsubr (&Slock_buffer); |
| 803 | defsubr (&Sfile_locked_p); |
| 804 | #endif |
| 805 | } |