| 1 | /* Lock files for editing. |
| 2 | |
| 3 | Copyright (C) 1985-1987, 1993-1994, 1996, 1998-2014 |
| 4 | Free Software Foundation, Inc. |
| 5 | |
| 6 | Author: Richard King |
| 7 | (according to authors.el) |
| 8 | |
| 9 | This file is part of GNU Emacs. |
| 10 | |
| 11 | GNU Emacs is free software: you can redistribute it and/or modify |
| 12 | it under the terms of the GNU General Public License as published by |
| 13 | the Free Software Foundation, either version 3 of the License, or |
| 14 | (at your option) any later version. |
| 15 | |
| 16 | GNU Emacs is distributed in the hope that it will be useful, |
| 17 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 18 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 19 | GNU General Public License for more details. |
| 20 | |
| 21 | You should have received a copy of the GNU General Public License |
| 22 | along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>. */ |
| 23 | |
| 24 | |
| 25 | #include <config.h> |
| 26 | #include <sys/types.h> |
| 27 | #include <sys/stat.h> |
| 28 | #include <signal.h> |
| 29 | #include <stdio.h> |
| 30 | |
| 31 | #ifdef HAVE_PWD_H |
| 32 | #include <pwd.h> |
| 33 | #endif |
| 34 | |
| 35 | #include <sys/file.h> |
| 36 | #include <fcntl.h> |
| 37 | #include <unistd.h> |
| 38 | |
| 39 | #ifdef __FreeBSD__ |
| 40 | #include <sys/sysctl.h> |
| 41 | #endif /* __FreeBSD__ */ |
| 42 | |
| 43 | #include <errno.h> |
| 44 | |
| 45 | #include <c-ctype.h> |
| 46 | |
| 47 | #include "lisp.h" |
| 48 | #include "character.h" |
| 49 | #include "buffer.h" |
| 50 | #include "coding.h" |
| 51 | #include "systime.h" |
| 52 | #ifdef WINDOWSNT |
| 53 | #include <share.h> |
| 54 | #include <sys/socket.h> /* for fcntl */ |
| 55 | #include "w32.h" /* for dostounix_filename */ |
| 56 | #endif |
| 57 | |
| 58 | #ifdef HAVE_UTMP_H |
| 59 | #include <utmp.h> |
| 60 | #endif |
| 61 | |
| 62 | /* A file whose last-modified time is just after the most recent boot. |
| 63 | Define this to be NULL to disable checking for this file. */ |
| 64 | #ifndef BOOT_TIME_FILE |
| 65 | #define BOOT_TIME_FILE "/var/run/random-seed" |
| 66 | #endif |
| 67 | |
| 68 | #ifndef WTMP_FILE |
| 69 | #define WTMP_FILE "/var/log/wtmp" |
| 70 | #endif |
| 71 | |
| 72 | /* Normally use a symbolic link to represent a lock. |
| 73 | The strategy: to lock a file FN, create a symlink .#FN in FN's |
| 74 | directory, with link data `user@host.pid'. This avoids a single |
| 75 | mount (== failure) point for lock files. |
| 76 | |
| 77 | When the host in the lock data is the current host, we can check if |
| 78 | the pid is valid with kill. |
| 79 | |
| 80 | Otherwise, we could look at a separate file that maps hostnames to |
| 81 | reboot times to see if the remote pid can possibly be valid, since we |
| 82 | don't want Emacs to have to communicate via pipes or sockets or |
| 83 | whatever to other processes, either locally or remotely; rms says |
| 84 | that's too unreliable. Hence the separate file, which could |
| 85 | theoretically be updated by daemons running separately -- but this |
| 86 | whole idea is unimplemented; in practice, at least in our |
| 87 | environment, it seems such stale locks arise fairly infrequently, and |
| 88 | Emacs' standard methods of dealing with clashes suffice. |
| 89 | |
| 90 | We use symlinks instead of normal files because (1) they can be |
| 91 | stored more efficiently on the filesystem, since the kernel knows |
| 92 | they will be small, and (2) all the info about the lock can be read |
| 93 | in a single system call (readlink). Although we could use regular |
| 94 | files to be useful on old systems lacking symlinks, nowadays |
| 95 | virtually all such systems are probably single-user anyway, so it |
| 96 | didn't seem worth the complication. |
| 97 | |
| 98 | Similarly, we don't worry about a possible 14-character limit on |
| 99 | file names, because those are all the same systems that don't have |
| 100 | symlinks. |
| 101 | |
| 102 | This is compatible with the locking scheme used by Interleaf (which |
| 103 | has contributed this implementation for Emacs), and was designed by |
| 104 | Ethan Jacobson, Kimbo Mundy, and others. |
| 105 | |
| 106 | --karl@cs.umb.edu/karl@hq.ileaf.com. |
| 107 | |
| 108 | On some file systems, notably those of MS-Windows, symbolic links |
| 109 | do not work well, so instead of a symlink .#FN -> 'user@host.pid', |
| 110 | the lock is a regular file .#FN with contents 'user@host.pid'. To |
| 111 | establish a lock, a nonce file is created and then renamed to .#FN. |
| 112 | On MS-Windows this renaming is atomic unless the lock is forcibly |
| 113 | acquired. On other systems the renaming is atomic if the lock is |
| 114 | forcibly acquired; if not, the renaming is done via hard links, |
| 115 | which is good enough for lock-file purposes. |
| 116 | |
| 117 | To summarize, race conditions can occur with either: |
| 118 | |
| 119 | * Forced locks on MS-Windows systems. |
| 120 | |
| 121 | * Non-forced locks on non-MS-Windows systems that support neither |
| 122 | hard nor symbolic links. */ |
| 123 | |
| 124 | \f |
| 125 | /* Return the time of the last system boot. */ |
| 126 | |
| 127 | static time_t boot_time; |
| 128 | static bool boot_time_initialized; |
| 129 | |
| 130 | #ifdef BOOT_TIME |
| 131 | static void get_boot_time_1 (const char *, bool); |
| 132 | #endif |
| 133 | |
| 134 | static time_t |
| 135 | get_boot_time (void) |
| 136 | { |
| 137 | #if defined (BOOT_TIME) |
| 138 | int counter; |
| 139 | #endif |
| 140 | |
| 141 | if (boot_time_initialized) |
| 142 | return boot_time; |
| 143 | boot_time_initialized = 1; |
| 144 | |
| 145 | #if defined (CTL_KERN) && defined (KERN_BOOTTIME) |
| 146 | { |
| 147 | int mib[2]; |
| 148 | size_t size; |
| 149 | struct timeval boottime_val; |
| 150 | |
| 151 | mib[0] = CTL_KERN; |
| 152 | mib[1] = KERN_BOOTTIME; |
| 153 | size = sizeof (boottime_val); |
| 154 | |
| 155 | if (sysctl (mib, 2, &boottime_val, &size, NULL, 0) >= 0) |
| 156 | { |
| 157 | boot_time = boottime_val.tv_sec; |
| 158 | return boot_time; |
| 159 | } |
| 160 | } |
| 161 | #endif /* defined (CTL_KERN) && defined (KERN_BOOTTIME) */ |
| 162 | |
| 163 | if (BOOT_TIME_FILE) |
| 164 | { |
| 165 | struct stat st; |
| 166 | if (stat (BOOT_TIME_FILE, &st) == 0) |
| 167 | { |
| 168 | boot_time = st.st_mtime; |
| 169 | return boot_time; |
| 170 | } |
| 171 | } |
| 172 | |
| 173 | #if defined (BOOT_TIME) |
| 174 | #ifndef CANNOT_DUMP |
| 175 | /* The utmp routines maintain static state. |
| 176 | Don't touch that state unless we are initialized, |
| 177 | since it might not survive dumping. */ |
| 178 | if (! initialized) |
| 179 | return boot_time; |
| 180 | #endif /* not CANNOT_DUMP */ |
| 181 | |
| 182 | /* Try to get boot time from utmp before wtmp, |
| 183 | since utmp is typically much smaller than wtmp. |
| 184 | Passing a null pointer causes get_boot_time_1 |
| 185 | to inspect the default file, namely utmp. */ |
| 186 | get_boot_time_1 (0, 0); |
| 187 | if (boot_time) |
| 188 | return boot_time; |
| 189 | |
| 190 | /* Try to get boot time from the current wtmp file. */ |
| 191 | get_boot_time_1 (WTMP_FILE, 1); |
| 192 | |
| 193 | /* If we did not find a boot time in wtmp, look at wtmp, and so on. */ |
| 194 | for (counter = 0; counter < 20 && ! boot_time; counter++) |
| 195 | { |
| 196 | char cmd_string[sizeof WTMP_FILE ".19.gz"]; |
| 197 | Lisp_Object tempname, filename; |
| 198 | bool delete_flag = 0; |
| 199 | |
| 200 | filename = Qnil; |
| 201 | |
| 202 | tempname = make_formatted_string |
| 203 | (cmd_string, "%s.%d", WTMP_FILE, counter); |
| 204 | if (! NILP (Ffile_exists_p (tempname))) |
| 205 | filename = tempname; |
| 206 | else |
| 207 | { |
| 208 | tempname = make_formatted_string (cmd_string, "%s.%d.gz", |
| 209 | WTMP_FILE, counter); |
| 210 | if (! NILP (Ffile_exists_p (tempname))) |
| 211 | { |
| 212 | Lisp_Object args[6]; |
| 213 | |
| 214 | /* The utmp functions on mescaline.gnu.org accept only |
| 215 | file names up to 8 characters long. Choose a 2 |
| 216 | character long prefix, and call make_temp_file with |
| 217 | second arg non-zero, so that it will add not more |
| 218 | than 6 characters to the prefix. */ |
| 219 | filename = Fexpand_file_name (build_string ("wt"), |
| 220 | Vtemporary_file_directory); |
| 221 | filename = make_temp_name (filename, 1); |
| 222 | args[0] = build_string ("gzip"); |
| 223 | args[1] = Qnil; |
| 224 | args[2] = list2 (QCfile, filename); |
| 225 | args[3] = Qnil; |
| 226 | args[4] = build_string ("-cd"); |
| 227 | args[5] = tempname; |
| 228 | Fcall_process (6, args); |
| 229 | delete_flag = 1; |
| 230 | } |
| 231 | } |
| 232 | |
| 233 | if (! NILP (filename)) |
| 234 | { |
| 235 | get_boot_time_1 (SSDATA (filename), 1); |
| 236 | if (delete_flag) |
| 237 | unlink (SSDATA (filename)); |
| 238 | } |
| 239 | } |
| 240 | |
| 241 | return boot_time; |
| 242 | #else |
| 243 | return 0; |
| 244 | #endif |
| 245 | } |
| 246 | |
| 247 | #ifdef BOOT_TIME |
| 248 | /* Try to get the boot time from wtmp file FILENAME. |
| 249 | This succeeds if that file contains a reboot record. |
| 250 | |
| 251 | If FILENAME is zero, use the same file as before; |
| 252 | if no FILENAME has ever been specified, this is the utmp file. |
| 253 | Use the newest reboot record if NEWEST, |
| 254 | the first reboot record otherwise. |
| 255 | Ignore all reboot records on or before BOOT_TIME. |
| 256 | Success is indicated by setting BOOT_TIME to a larger value. */ |
| 257 | |
| 258 | void |
| 259 | get_boot_time_1 (const char *filename, bool newest) |
| 260 | { |
| 261 | struct utmp ut, *utp; |
| 262 | |
| 263 | if (filename) |
| 264 | { |
| 265 | /* On some versions of IRIX, opening a nonexistent file name |
| 266 | is likely to crash in the utmp routines. */ |
| 267 | if (faccessat (AT_FDCWD, filename, R_OK, AT_EACCESS) != 0) |
| 268 | return; |
| 269 | |
| 270 | utmpname (filename); |
| 271 | } |
| 272 | |
| 273 | setutent (); |
| 274 | |
| 275 | while (1) |
| 276 | { |
| 277 | /* Find the next reboot record. */ |
| 278 | ut.ut_type = BOOT_TIME; |
| 279 | utp = getutid (&ut); |
| 280 | if (! utp) |
| 281 | break; |
| 282 | /* Compare reboot times and use the newest one. */ |
| 283 | if (utp->ut_time > boot_time) |
| 284 | { |
| 285 | boot_time = utp->ut_time; |
| 286 | if (! newest) |
| 287 | break; |
| 288 | } |
| 289 | /* Advance on element in the file |
| 290 | so that getutid won't repeat the same one. */ |
| 291 | utp = getutent (); |
| 292 | if (! utp) |
| 293 | break; |
| 294 | } |
| 295 | endutent (); |
| 296 | } |
| 297 | #endif /* BOOT_TIME */ |
| 298 | \f |
| 299 | /* An arbitrary limit on lock contents length. 8 K should be plenty |
| 300 | big enough in practice. */ |
| 301 | enum { MAX_LFINFO = 8 * 1024 }; |
| 302 | |
| 303 | /* Here is the structure that stores information about a lock. */ |
| 304 | |
| 305 | typedef struct |
| 306 | { |
| 307 | /* Location of '@', '.', ':' in USER. If there's no colon, COLON |
| 308 | points to the end of USER. */ |
| 309 | char *at, *dot, *colon; |
| 310 | |
| 311 | /* Lock file contents USER@HOST.PID with an optional :BOOT_TIME |
| 312 | appended. This memory is used as a lock file contents buffer, so |
| 313 | it needs room for MAX_LFINFO + 1 bytes. A string " (pid NNNN)" |
| 314 | may be appended to the USER@HOST while generating a diagnostic, |
| 315 | so make room for its extra bytes (as opposed to ".NNNN") too. */ |
| 316 | char user[MAX_LFINFO + 1 + sizeof " (pid )" - sizeof "."]; |
| 317 | } lock_info_type; |
| 318 | |
| 319 | /* Write the name of the lock file for FNAME into LOCKNAME. Length |
| 320 | will be that of FNAME plus two more for the leading ".#", plus one |
| 321 | for the null. */ |
| 322 | #define MAKE_LOCK_NAME(lockname, fname) \ |
| 323 | (lockname = SAFE_ALLOCA (SBYTES (fname) + 2 + 1), \ |
| 324 | fill_in_lock_file_name (lockname, fname)) |
| 325 | |
| 326 | static void |
| 327 | fill_in_lock_file_name (char *lockfile, Lisp_Object fn) |
| 328 | { |
| 329 | char *last_slash = memrchr (SSDATA (fn), '/', SBYTES (fn)); |
| 330 | char *base = last_slash + 1; |
| 331 | ptrdiff_t dirlen = base - SSDATA (fn); |
| 332 | memcpy (lockfile, SSDATA (fn), dirlen); |
| 333 | lockfile[dirlen] = '.'; |
| 334 | lockfile[dirlen + 1] = '#'; |
| 335 | strcpy (lockfile + dirlen + 2, base); |
| 336 | } |
| 337 | |
| 338 | /* For some reason Linux kernels return EPERM on file systems that do |
| 339 | not support hard or symbolic links. This symbol documents the quirk. |
| 340 | There is no way to tell whether a symlink call fails due to |
| 341 | permissions issues or because links are not supported, but luckily |
| 342 | the lock file code should work either way. */ |
| 343 | enum { LINKS_MIGHT_NOT_WORK = EPERM }; |
| 344 | |
| 345 | /* Rename OLD to NEW. If FORCE, replace any existing NEW. |
| 346 | It is OK if there are temporarily two hard links to OLD. |
| 347 | Return 0 if successful, -1 (setting errno) otherwise. */ |
| 348 | static int |
| 349 | rename_lock_file (char const *old, char const *new, bool force) |
| 350 | { |
| 351 | #ifdef WINDOWSNT |
| 352 | return sys_rename_replace (old, new, force); |
| 353 | #else |
| 354 | if (! force) |
| 355 | { |
| 356 | struct stat st; |
| 357 | |
| 358 | if (link (old, new) == 0) |
| 359 | return unlink (old) == 0 || errno == ENOENT ? 0 : -1; |
| 360 | if (errno != ENOSYS && errno != LINKS_MIGHT_NOT_WORK) |
| 361 | return -1; |
| 362 | |
| 363 | /* 'link' does not work on this file system. This can occur on |
| 364 | a GNU/Linux host mounting a FAT32 file system. Fall back on |
| 365 | 'rename' after checking that NEW does not exist. There is a |
| 366 | potential race condition since some other process may create |
| 367 | NEW immediately after the existence check, but it's the best |
| 368 | we can portably do here. */ |
| 369 | if (lstat (new, &st) == 0 || errno == EOVERFLOW) |
| 370 | { |
| 371 | errno = EEXIST; |
| 372 | return -1; |
| 373 | } |
| 374 | if (errno != ENOENT) |
| 375 | return -1; |
| 376 | } |
| 377 | |
| 378 | return rename (old, new); |
| 379 | #endif |
| 380 | } |
| 381 | |
| 382 | /* Create the lock file LFNAME with contents LOCK_INFO_STR. Return 0 if |
| 383 | successful, an errno value on failure. If FORCE, remove any |
| 384 | existing LFNAME if necessary. */ |
| 385 | |
| 386 | static int |
| 387 | create_lock_file (char *lfname, char *lock_info_str, bool force) |
| 388 | { |
| 389 | #ifdef WINDOWSNT |
| 390 | /* Symlinks are supported only by later versions of Windows, and |
| 391 | creating them is a privileged operation that often triggers |
| 392 | User Account Control elevation prompts. Avoid the problem by |
| 393 | pretending that 'symlink' does not work. */ |
| 394 | int err = ENOSYS; |
| 395 | #else |
| 396 | int err = symlink (lock_info_str, lfname) == 0 ? 0 : errno; |
| 397 | #endif |
| 398 | |
| 399 | if (err == EEXIST && force) |
| 400 | { |
| 401 | unlink (lfname); |
| 402 | err = symlink (lock_info_str, lfname) == 0 ? 0 : errno; |
| 403 | } |
| 404 | |
| 405 | if (err == ENOSYS || err == LINKS_MIGHT_NOT_WORK || err == ENAMETOOLONG) |
| 406 | { |
| 407 | static char const nonce_base[] = ".#-emacsXXXXXX"; |
| 408 | char *last_slash = strrchr (lfname, '/'); |
| 409 | ptrdiff_t lfdirlen = last_slash + 1 - lfname; |
| 410 | USE_SAFE_ALLOCA; |
| 411 | char *nonce = SAFE_ALLOCA (lfdirlen + sizeof nonce_base); |
| 412 | int fd; |
| 413 | memcpy (nonce, lfname, lfdirlen); |
| 414 | strcpy (nonce + lfdirlen, nonce_base); |
| 415 | |
| 416 | fd = mkostemp (nonce, O_BINARY | O_CLOEXEC); |
| 417 | if (fd < 0) |
| 418 | err = errno; |
| 419 | else |
| 420 | { |
| 421 | ptrdiff_t lock_info_len; |
| 422 | if (! O_CLOEXEC) |
| 423 | fcntl (fd, F_SETFD, FD_CLOEXEC); |
| 424 | lock_info_len = strlen (lock_info_str); |
| 425 | err = 0; |
| 426 | /* Use 'write', not 'emacs_write', as garbage collection |
| 427 | might signal an error, which would leak FD. */ |
| 428 | if (write (fd, lock_info_str, lock_info_len) != lock_info_len |
| 429 | || fchmod (fd, S_IRUSR | S_IRGRP | S_IROTH) != 0) |
| 430 | err = errno; |
| 431 | /* There is no need to call fsync here, as the contents of |
| 432 | the lock file need not survive system crashes. */ |
| 433 | if (emacs_close (fd) != 0) |
| 434 | err = errno; |
| 435 | if (!err && rename_lock_file (nonce, lfname, force) != 0) |
| 436 | err = errno; |
| 437 | if (err) |
| 438 | unlink (nonce); |
| 439 | } |
| 440 | |
| 441 | SAFE_FREE (); |
| 442 | } |
| 443 | |
| 444 | return err; |
| 445 | } |
| 446 | |
| 447 | /* Lock the lock file named LFNAME. |
| 448 | If FORCE, do so even if it is already locked. |
| 449 | Return 0 if successful, an error number on failure. */ |
| 450 | |
| 451 | static int |
| 452 | lock_file_1 (char *lfname, bool force) |
| 453 | { |
| 454 | /* Call this first because it can GC. */ |
| 455 | printmax_t boot = get_boot_time (); |
| 456 | |
| 457 | Lisp_Object luser_name = Fuser_login_name (Qnil); |
| 458 | char const *user_name = STRINGP (luser_name) ? SSDATA (luser_name) : ""; |
| 459 | Lisp_Object lhost_name = Fsystem_name (); |
| 460 | char const *host_name = STRINGP (lhost_name) ? SSDATA (lhost_name) : ""; |
| 461 | char lock_info_str[MAX_LFINFO + 1]; |
| 462 | printmax_t pid = getpid (); |
| 463 | |
| 464 | if (boot) |
| 465 | { |
| 466 | if (sizeof lock_info_str |
| 467 | <= snprintf (lock_info_str, sizeof lock_info_str, |
| 468 | "%s@%s.%"pMd":%"pMd, |
| 469 | user_name, host_name, pid, boot)) |
| 470 | return ENAMETOOLONG; |
| 471 | } |
| 472 | else if (sizeof lock_info_str |
| 473 | <= snprintf (lock_info_str, sizeof lock_info_str, |
| 474 | "%s@%s.%"pMd, |
| 475 | user_name, host_name, pid)) |
| 476 | return ENAMETOOLONG; |
| 477 | |
| 478 | return create_lock_file (lfname, lock_info_str, force); |
| 479 | } |
| 480 | |
| 481 | /* Return true if times A and B are no more than one second apart. */ |
| 482 | |
| 483 | static bool |
| 484 | within_one_second (time_t a, time_t b) |
| 485 | { |
| 486 | return (a - b >= -1 && a - b <= 1); |
| 487 | } |
| 488 | \f |
| 489 | /* On systems lacking ELOOP, test for an errno value that shouldn't occur. */ |
| 490 | #ifndef ELOOP |
| 491 | # define ELOOP (-1) |
| 492 | #endif |
| 493 | |
| 494 | /* Read the data for the lock file LFNAME into LFINFO. Read at most |
| 495 | MAX_LFINFO + 1 bytes. Return the number of bytes read, or -1 |
| 496 | (setting errno) on error. */ |
| 497 | |
| 498 | static ptrdiff_t |
| 499 | read_lock_data (char *lfname, char lfinfo[MAX_LFINFO + 1]) |
| 500 | { |
| 501 | ptrdiff_t nbytes; |
| 502 | |
| 503 | while ((nbytes = readlinkat (AT_FDCWD, lfname, lfinfo, MAX_LFINFO + 1)) < 0 |
| 504 | && errno == EINVAL) |
| 505 | { |
| 506 | int fd = emacs_open (lfname, O_RDONLY | O_BINARY | O_NOFOLLOW, 0); |
| 507 | if (0 <= fd) |
| 508 | { |
| 509 | /* Use read, not emacs_read, since FD isn't unwind-protected. */ |
| 510 | ptrdiff_t read_bytes = read (fd, lfinfo, MAX_LFINFO + 1); |
| 511 | int read_errno = errno; |
| 512 | if (emacs_close (fd) != 0) |
| 513 | return -1; |
| 514 | errno = read_errno; |
| 515 | return read_bytes; |
| 516 | } |
| 517 | |
| 518 | if (errno != ELOOP) |
| 519 | return -1; |
| 520 | |
| 521 | /* readlinkat saw a non-symlink, but emacs_open saw a symlink. |
| 522 | The former must have been removed and replaced by the latter. |
| 523 | Try again. */ |
| 524 | QUIT; |
| 525 | } |
| 526 | |
| 527 | return nbytes; |
| 528 | } |
| 529 | |
| 530 | /* Return 0 if nobody owns the lock file LFNAME or the lock is obsolete, |
| 531 | 1 if another process owns it (and set OWNER (if non-null) to info), |
| 532 | 2 if the current process owns it, |
| 533 | or -1 if something is wrong with the locking mechanism. */ |
| 534 | |
| 535 | static int |
| 536 | current_lock_owner (lock_info_type *owner, char *lfname) |
| 537 | { |
| 538 | int ret; |
| 539 | lock_info_type local_owner; |
| 540 | ptrdiff_t lfinfolen; |
| 541 | intmax_t pid, boot_time; |
| 542 | char *at, *dot, *lfinfo_end; |
| 543 | |
| 544 | /* Even if the caller doesn't want the owner info, we still have to |
| 545 | read it to determine return value. */ |
| 546 | if (!owner) |
| 547 | owner = &local_owner; |
| 548 | |
| 549 | /* If nonexistent lock file, all is well; otherwise, got strange error. */ |
| 550 | lfinfolen = read_lock_data (lfname, owner->user); |
| 551 | if (lfinfolen < 0) |
| 552 | return errno == ENOENT ? 0 : -1; |
| 553 | if (MAX_LFINFO < lfinfolen) |
| 554 | return -1; |
| 555 | owner->user[lfinfolen] = 0; |
| 556 | |
| 557 | /* Parse USER@HOST.PID:BOOT_TIME. If can't parse, return -1. */ |
| 558 | /* The USER is everything before the last @. */ |
| 559 | owner->at = at = memrchr (owner->user, '@', lfinfolen); |
| 560 | if (!at) |
| 561 | return -1; |
| 562 | owner->dot = dot = strrchr (at, '.'); |
| 563 | if (!dot) |
| 564 | return -1; |
| 565 | |
| 566 | /* The PID is everything from the last `.' to the `:'. */ |
| 567 | if (! c_isdigit (dot[1])) |
| 568 | return -1; |
| 569 | errno = 0; |
| 570 | pid = strtoimax (dot + 1, &owner->colon, 10); |
| 571 | if (errno == ERANGE) |
| 572 | pid = -1; |
| 573 | |
| 574 | /* After the `:', if there is one, comes the boot time. */ |
| 575 | switch (owner->colon[0]) |
| 576 | { |
| 577 | case 0: |
| 578 | boot_time = 0; |
| 579 | lfinfo_end = owner->colon; |
| 580 | break; |
| 581 | |
| 582 | case ':': |
| 583 | if (! c_isdigit (owner->colon[1])) |
| 584 | return -1; |
| 585 | boot_time = strtoimax (owner->colon + 1, &lfinfo_end, 10); |
| 586 | break; |
| 587 | |
| 588 | default: |
| 589 | return -1; |
| 590 | } |
| 591 | if (lfinfo_end != owner->user + lfinfolen) |
| 592 | return -1; |
| 593 | |
| 594 | /* On current host? */ |
| 595 | if (STRINGP (Vsystem_name) |
| 596 | && dot - (at + 1) == SBYTES (Vsystem_name) |
| 597 | && memcmp (at + 1, SSDATA (Vsystem_name), SBYTES (Vsystem_name)) == 0) |
| 598 | { |
| 599 | if (pid == getpid ()) |
| 600 | ret = 2; /* We own it. */ |
| 601 | else if (0 < pid && pid <= TYPE_MAXIMUM (pid_t) |
| 602 | && (kill (pid, 0) >= 0 || errno == EPERM) |
| 603 | && (boot_time == 0 |
| 604 | || (boot_time <= TYPE_MAXIMUM (time_t) |
| 605 | && within_one_second (boot_time, get_boot_time ())))) |
| 606 | ret = 1; /* An existing process on this machine owns it. */ |
| 607 | /* The owner process is dead or has a strange pid, so try to |
| 608 | zap the lockfile. */ |
| 609 | else |
| 610 | return unlink (lfname); |
| 611 | } |
| 612 | else |
| 613 | { /* If we wanted to support the check for stale locks on remote machines, |
| 614 | here's where we'd do it. */ |
| 615 | ret = 1; |
| 616 | } |
| 617 | |
| 618 | return ret; |
| 619 | } |
| 620 | |
| 621 | \f |
| 622 | /* Lock the lock named LFNAME if possible. |
| 623 | Return 0 in that case. |
| 624 | Return positive if some other process owns the lock, and info about |
| 625 | that process in CLASHER. |
| 626 | Return -1 if cannot lock for any other reason. */ |
| 627 | |
| 628 | static int |
| 629 | lock_if_free (lock_info_type *clasher, char *lfname) |
| 630 | { |
| 631 | int err; |
| 632 | while ((err = lock_file_1 (lfname, 0)) == EEXIST) |
| 633 | { |
| 634 | switch (current_lock_owner (clasher, lfname)) |
| 635 | { |
| 636 | case 2: |
| 637 | return 0; /* We ourselves locked it. */ |
| 638 | case 1: |
| 639 | return 1; /* Someone else has it. */ |
| 640 | case -1: |
| 641 | return -1; /* current_lock_owner returned strange error. */ |
| 642 | } |
| 643 | |
| 644 | /* We deleted a stale lock; try again to lock the file. */ |
| 645 | } |
| 646 | |
| 647 | return err ? -1 : 0; |
| 648 | } |
| 649 | |
| 650 | /* lock_file locks file FN, |
| 651 | meaning it serves notice on the world that you intend to edit that file. |
| 652 | This should be done only when about to modify a file-visiting |
| 653 | buffer previously unmodified. |
| 654 | Do not (normally) call this for a buffer already modified, |
| 655 | as either the file is already locked, or the user has already |
| 656 | decided to go ahead without locking. |
| 657 | |
| 658 | When this returns, either the lock is locked for us, |
| 659 | or lock creation failed, |
| 660 | or the user has said to go ahead without locking. |
| 661 | |
| 662 | If the file is locked by someone else, this calls |
| 663 | ask-user-about-lock (a Lisp function) with two arguments, |
| 664 | the file name and info about the user who did the locking. |
| 665 | This function can signal an error, or return t meaning |
| 666 | take away the lock, or return nil meaning ignore the lock. */ |
| 667 | |
| 668 | void |
| 669 | lock_file (Lisp_Object fn) |
| 670 | { |
| 671 | Lisp_Object orig_fn, encoded_fn; |
| 672 | char *lfname; |
| 673 | lock_info_type lock_info; |
| 674 | struct gcpro gcpro1; |
| 675 | USE_SAFE_ALLOCA; |
| 676 | |
| 677 | /* Don't do locking if the user has opted out. */ |
| 678 | if (! create_lockfiles) |
| 679 | return; |
| 680 | |
| 681 | /* Don't do locking while dumping Emacs. |
| 682 | Uncompressing wtmp files uses call-process, which does not work |
| 683 | in an uninitialized Emacs. */ |
| 684 | if (! NILP (Vpurify_flag)) |
| 685 | return; |
| 686 | |
| 687 | orig_fn = fn; |
| 688 | GCPRO1 (fn); |
| 689 | fn = Fexpand_file_name (fn, Qnil); |
| 690 | #ifdef WINDOWSNT |
| 691 | /* Ensure we have only '/' separators, to avoid problems with |
| 692 | looking (inside fill_in_lock_file_name) for backslashes in file |
| 693 | names encoded by some DBCS codepage. */ |
| 694 | dostounix_filename (SSDATA (fn)); |
| 695 | #endif |
| 696 | encoded_fn = ENCODE_FILE (fn); |
| 697 | |
| 698 | /* Create the name of the lock-file for file fn */ |
| 699 | MAKE_LOCK_NAME (lfname, encoded_fn); |
| 700 | |
| 701 | /* See if this file is visited and has changed on disk since it was |
| 702 | visited. */ |
| 703 | { |
| 704 | register Lisp_Object subject_buf; |
| 705 | |
| 706 | subject_buf = get_truename_buffer (orig_fn); |
| 707 | |
| 708 | if (!NILP (subject_buf) |
| 709 | && NILP (Fverify_visited_file_modtime (subject_buf)) |
| 710 | && !NILP (Ffile_exists_p (fn))) |
| 711 | call1 (intern ("ask-user-about-supersession-threat"), fn); |
| 712 | |
| 713 | } |
| 714 | |
| 715 | /* Try to lock the lock. */ |
| 716 | if (0 < lock_if_free (&lock_info, lfname)) |
| 717 | { |
| 718 | /* Someone else has the lock. Consider breaking it. */ |
| 719 | Lisp_Object attack; |
| 720 | char *dot = lock_info.dot; |
| 721 | ptrdiff_t pidlen = lock_info.colon - (dot + 1); |
| 722 | static char const replacement[] = " (pid "; |
| 723 | int replacementlen = sizeof replacement - 1; |
| 724 | memmove (dot + replacementlen, dot + 1, pidlen); |
| 725 | strcpy (dot + replacementlen + pidlen, ")"); |
| 726 | memcpy (dot, replacement, replacementlen); |
| 727 | attack = call2 (intern ("ask-user-about-lock"), fn, |
| 728 | build_string (lock_info.user)); |
| 729 | /* Take the lock if the user said so. */ |
| 730 | if (!NILP (attack)) |
| 731 | lock_file_1 (lfname, 1); |
| 732 | } |
| 733 | |
| 734 | UNGCPRO; |
| 735 | SAFE_FREE (); |
| 736 | } |
| 737 | |
| 738 | void |
| 739 | unlock_file (Lisp_Object fn) |
| 740 | { |
| 741 | char *lfname; |
| 742 | USE_SAFE_ALLOCA; |
| 743 | |
| 744 | fn = Fexpand_file_name (fn, Qnil); |
| 745 | fn = ENCODE_FILE (fn); |
| 746 | |
| 747 | MAKE_LOCK_NAME (lfname, fn); |
| 748 | |
| 749 | if (current_lock_owner (0, lfname) == 2) |
| 750 | unlink (lfname); |
| 751 | |
| 752 | SAFE_FREE (); |
| 753 | } |
| 754 | |
| 755 | void |
| 756 | unlock_all_files (void) |
| 757 | { |
| 758 | register Lisp_Object tail, buf; |
| 759 | register struct buffer *b; |
| 760 | |
| 761 | FOR_EACH_LIVE_BUFFER (tail, buf) |
| 762 | { |
| 763 | b = XBUFFER (buf); |
| 764 | if (STRINGP (BVAR (b, file_truename)) |
| 765 | && BUF_SAVE_MODIFF (b) < BUF_MODIFF (b)) |
| 766 | unlock_file (BVAR (b, file_truename)); |
| 767 | } |
| 768 | } |
| 769 | \f |
| 770 | DEFUN ("lock-buffer", Flock_buffer, Slock_buffer, |
| 771 | 0, 1, 0, |
| 772 | doc: /* Lock FILE, if current buffer is modified. |
| 773 | FILE defaults to current buffer's visited file, |
| 774 | or else nothing is done if current buffer isn't visiting a file. |
| 775 | |
| 776 | If the option `create-lockfiles' is nil, this does nothing. */) |
| 777 | (Lisp_Object file) |
| 778 | { |
| 779 | if (NILP (file)) |
| 780 | file = BVAR (current_buffer, file_truename); |
| 781 | else |
| 782 | CHECK_STRING (file); |
| 783 | if (SAVE_MODIFF < MODIFF |
| 784 | && !NILP (file)) |
| 785 | lock_file (file); |
| 786 | return Qnil; |
| 787 | } |
| 788 | |
| 789 | DEFUN ("unlock-buffer", Funlock_buffer, Sunlock_buffer, |
| 790 | 0, 0, 0, |
| 791 | doc: /* Unlock the file visited in the current buffer. |
| 792 | If the buffer is not modified, this does nothing because the file |
| 793 | should not be locked in that case. */) |
| 794 | (void) |
| 795 | { |
| 796 | if (SAVE_MODIFF < MODIFF |
| 797 | && STRINGP (BVAR (current_buffer, file_truename))) |
| 798 | unlock_file (BVAR (current_buffer, file_truename)); |
| 799 | return Qnil; |
| 800 | } |
| 801 | |
| 802 | /* Unlock the file visited in buffer BUFFER. */ |
| 803 | |
| 804 | void |
| 805 | unlock_buffer (struct buffer *buffer) |
| 806 | { |
| 807 | if (BUF_SAVE_MODIFF (buffer) < BUF_MODIFF (buffer) |
| 808 | && STRINGP (BVAR (buffer, file_truename))) |
| 809 | unlock_file (BVAR (buffer, file_truename)); |
| 810 | } |
| 811 | |
| 812 | DEFUN ("file-locked-p", Ffile_locked_p, Sfile_locked_p, 1, 1, 0, |
| 813 | doc: /* Return a value indicating whether FILENAME is locked. |
| 814 | The value is nil if the FILENAME is not locked, |
| 815 | t if it is locked by you, else a string saying which user has locked it. */) |
| 816 | (Lisp_Object filename) |
| 817 | { |
| 818 | Lisp_Object ret; |
| 819 | char *lfname; |
| 820 | int owner; |
| 821 | lock_info_type locker; |
| 822 | USE_SAFE_ALLOCA; |
| 823 | |
| 824 | filename = Fexpand_file_name (filename, Qnil); |
| 825 | |
| 826 | MAKE_LOCK_NAME (lfname, filename); |
| 827 | |
| 828 | owner = current_lock_owner (&locker, lfname); |
| 829 | if (owner <= 0) |
| 830 | ret = Qnil; |
| 831 | else if (owner == 2) |
| 832 | ret = Qt; |
| 833 | else |
| 834 | ret = make_string (locker.user, locker.at - locker.user); |
| 835 | |
| 836 | SAFE_FREE (); |
| 837 | return ret; |
| 838 | } |
| 839 | |
| 840 | void |
| 841 | syms_of_filelock (void) |
| 842 | { |
| 843 | #include "filelock.x" |
| 844 | |
| 845 | DEFVAR_LISP ("temporary-file-directory", Vtemporary_file_directory, |
| 846 | doc: /* The directory for writing temporary files. */); |
| 847 | Vtemporary_file_directory = Qnil; |
| 848 | |
| 849 | DEFVAR_BOOL ("create-lockfiles", create_lockfiles, |
| 850 | doc: /* Non-nil means use lockfiles to avoid editing collisions. */); |
| 851 | create_lockfiles = 1; |
| 852 | } |