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2c37ca7c | 1 | /* SPDX-License-Identifier: LGPL-2.1-or-later */ |
27c6d415 | 2 | /* |
2c37ca7c | 3 | * This file is part of libmount from util-linux project. |
27c6d415 | 4 | * |
2c37ca7c KZ |
5 | * Copyright (C) 2009-2018 Karel Zak <kzak@redhat.com> |
6 | * | |
7 | * libmount is free software; you can redistribute it and/or modify it | |
8 | * under the terms of the GNU Lesser General Public License as published by | |
9 | * the Free Software Foundation; either version 2.1 of the License, or | |
10 | * (at your option) any later version. | |
27c6d415 | 11 | */ |
192c6aad KZ |
12 | |
13 | /** | |
14 | * SECTION: lock | |
63de90d4 | 15 | * @title: Locking |
5eb00eb4 | 16 | * @short_description: locking methods for /etc/mtab or another libmount files |
192c6aad | 17 | * |
d58b3157 | 18 | * The mtab lock is backwards compatible with the standard linux /etc/mtab |
5eb00eb4 | 19 | * locking. Note, it's necessary to use the same locking schema in all |
d58b3157 | 20 | * applications that access the file. |
192c6aad | 21 | */ |
27c6d415 KZ |
22 | #include <sys/time.h> |
23 | #include <time.h> | |
24 | #include <signal.h> | |
25 | #include <fcntl.h> | |
26 | #include <limits.h> | |
5eb00eb4 | 27 | #include <sys/file.h> |
27c6d415 | 28 | |
60f25dea | 29 | #include "strutils.h" |
69f1cad4 | 30 | #include "closestream.h" |
27c6d415 | 31 | #include "pathnames.h" |
27c6d415 | 32 | #include "mountP.h" |
cd2876d2 | 33 | #include "monotonic.h" |
27c6d415 KZ |
34 | |
35 | /* | |
36 | * lock handler | |
37 | */ | |
68164f6c | 38 | struct libmnt_lock { |
27c6d415 KZ |
39 | char *lockfile; /* path to lock file (e.g. /etc/mtab~) */ |
40 | char *linkfile; /* path to link file (e.g. /etc/mtab~.<id>) */ | |
41 | int lockfile_fd; /* lock file descriptor */ | |
5976114f | 42 | |
88d7d36f KZ |
43 | unsigned int locked :1, /* do we own the lock? */ |
44 | sigblock :1, /* block signals when locked */ | |
45 | simplelock :1; /* use flock rather than normal mtab lock */ | |
5976114f KZ |
46 | |
47 | sigset_t oldsigmask; | |
27c6d415 KZ |
48 | }; |
49 | ||
50 | ||
51 | /** | |
52 | * mnt_new_lock: | |
0f32f1e2 | 53 | * @datafile: the file that should be covered by the lock |
27c6d415 KZ |
54 | * @id: unique linkfile identifier or 0 (default is getpid()) |
55 | * | |
192c6aad | 56 | * Returns: newly allocated lock handler or NULL on case of error. |
27c6d415 | 57 | */ |
68164f6c | 58 | struct libmnt_lock *mnt_new_lock(const char *datafile, pid_t id) |
27c6d415 | 59 | { |
68164f6c | 60 | struct libmnt_lock *ml = NULL; |
66c33aab | 61 | char *lo = NULL, *ln = NULL; |
5eb00eb4 | 62 | size_t losz; |
27c6d415 | 63 | |
37290a53 KZ |
64 | if (!datafile) |
65 | return NULL; | |
4569bbea | 66 | |
5eb00eb4 KZ |
67 | /* for flock we use "foo.lock, for mtab "foo~" |
68 | */ | |
69 | losz = strlen(datafile) + sizeof(".lock"); | |
70 | lo = malloc(losz); | |
71 | if (!lo) | |
66c33aab | 72 | goto err; |
5eb00eb4 KZ |
73 | |
74 | /* default is mtab~ lock */ | |
75 | snprintf(lo, losz, "%s~", datafile); | |
76 | ||
66c33aab KZ |
77 | if (asprintf(&ln, "%s~.%d", datafile, id ? : getpid()) == -1) { |
78 | ln = NULL; | |
79 | goto err; | |
27c6d415 | 80 | } |
68164f6c | 81 | ml = calloc(1, sizeof(*ml) ); |
66c33aab KZ |
82 | if (!ml) |
83 | goto err; | |
84 | ||
85 | ml->lockfile_fd = -1; | |
86 | ml->linkfile = ln; | |
87 | ml->lockfile = lo; | |
3f31a959 | 88 | |
83a78332 | 89 | DBG(LOCKS, ul_debugobj(ml, "alloc: default linkfile=%s, lockfile=%s", ln, lo)); |
27c6d415 | 90 | return ml; |
66c33aab KZ |
91 | err: |
92 | free(lo); | |
93 | free(ln); | |
94 | free(ml); | |
95 | return NULL; | |
27c6d415 KZ |
96 | } |
97 | ||
66c33aab | 98 | |
27c6d415 KZ |
99 | /** |
100 | * mnt_free_lock: | |
68164f6c | 101 | * @ml: struct libmnt_lock handler |
27c6d415 KZ |
102 | * |
103 | * Deallocates mnt_lock. | |
104 | */ | |
68164f6c | 105 | void mnt_free_lock(struct libmnt_lock *ml) |
27c6d415 KZ |
106 | { |
107 | if (!ml) | |
108 | return; | |
83a78332 | 109 | DBG(LOCKS, ul_debugobj(ml, "free%s", ml->locked ? " !!! LOCKED !!!" : "")); |
27c6d415 KZ |
110 | free(ml->lockfile); |
111 | free(ml->linkfile); | |
112 | free(ml); | |
113 | } | |
114 | ||
5976114f KZ |
115 | /** |
116 | * mnt_lock_block_signals: | |
117 | * @ml: struct libmnt_lock handler | |
118 | * @enable: TRUE/FALSE | |
119 | * | |
120 | * Block/unblock signals when the lock is locked, the signals are not blocked | |
121 | * by default. | |
122 | * | |
123 | * Returns: <0 on error, 0 on success. | |
124 | */ | |
125 | int mnt_lock_block_signals(struct libmnt_lock *ml, int enable) | |
126 | { | |
127 | if (!ml) | |
128 | return -EINVAL; | |
83a78332 | 129 | DBG(LOCKS, ul_debugobj(ml, "signals: %s", enable ? "BLOCKED" : "UNBLOCKED")); |
6f5788c5 | 130 | ml->sigblock = enable ? 1 : 0; |
5976114f KZ |
131 | return 0; |
132 | } | |
133 | ||
5eb00eb4 KZ |
134 | /* don't export this to API |
135 | */ | |
136 | int mnt_lock_use_simplelock(struct libmnt_lock *ml, int enable) | |
137 | { | |
138 | size_t sz; | |
139 | ||
140 | if (!ml) | |
141 | return -EINVAL; | |
142 | ||
143 | assert(ml->lockfile); | |
144 | ||
83a78332 | 145 | DBG(LOCKS, ul_debugobj(ml, "flock: %s", enable ? "ENABLED" : "DISABLED")); |
5eb00eb4 KZ |
146 | ml->simplelock = enable ? 1 : 0; |
147 | ||
148 | sz = strlen(ml->lockfile); | |
9d670a2a KZ |
149 | assert(sz); |
150 | ||
151 | if (sz < 1) | |
152 | return -EINVAL; | |
5eb00eb4 KZ |
153 | |
154 | /* Change lock name: | |
155 | * | |
156 | * flock: "<name>.lock" | |
157 | * mtab lock: "<name>~" | |
158 | */ | |
159 | if (ml->simplelock && endswith(ml->lockfile, "~")) | |
160 | memcpy(ml->lockfile + sz - 1, ".lock", 6); | |
161 | ||
162 | else if (!ml->simplelock && endswith(ml->lockfile, ".lock")) | |
163 | memcpy(ml->lockfile + sz - 5, "~", 2); | |
164 | ||
83a78332 | 165 | DBG(LOCKS, ul_debugobj(ml, "new lock filename: '%s'", ml->lockfile)); |
5eb00eb4 KZ |
166 | return 0; |
167 | } | |
168 | ||
0f32f1e2 KZ |
169 | /* |
170 | * Returns path to lockfile. | |
27c6d415 | 171 | */ |
68164f6c | 172 | static const char *mnt_lock_get_lockfile(struct libmnt_lock *ml) |
27c6d415 | 173 | { |
66c33aab | 174 | return ml ? ml->lockfile : NULL; |
27c6d415 KZ |
175 | } |
176 | ||
0f32f1e2 | 177 | /* |
66c33aab KZ |
178 | * Note that the filename is generated by mnt_new_lock() and depends on |
179 | * getpid() or 'id' argument of the mnt_new_lock() function. | |
180 | * | |
181 | * Returns: unique (per process/thread) path to linkfile. | |
27c6d415 | 182 | */ |
68164f6c | 183 | static const char *mnt_lock_get_linkfile(struct libmnt_lock *ml) |
27c6d415 | 184 | { |
66c33aab | 185 | return ml ? ml->linkfile : NULL; |
27c6d415 KZ |
186 | } |
187 | ||
5eb00eb4 KZ |
188 | /* |
189 | * Simple flocking | |
190 | */ | |
191 | static void unlock_simplelock(struct libmnt_lock *ml) | |
192 | { | |
193 | assert(ml); | |
194 | assert(ml->simplelock); | |
195 | ||
196 | if (ml->lockfile_fd >= 0) { | |
83a78332 | 197 | DBG(LOCKS, ul_debugobj(ml, "%s: unflocking", |
5eb00eb4 KZ |
198 | mnt_lock_get_lockfile(ml))); |
199 | close(ml->lockfile_fd); | |
200 | } | |
201 | } | |
202 | ||
203 | static int lock_simplelock(struct libmnt_lock *ml) | |
204 | { | |
205 | const char *lfile; | |
206 | int rc; | |
207 | ||
208 | assert(ml); | |
209 | assert(ml->simplelock); | |
210 | ||
211 | lfile = mnt_lock_get_lockfile(ml); | |
212 | ||
83a78332 | 213 | DBG(LOCKS, ul_debugobj(ml, "%s: locking", lfile)); |
5eb00eb4 KZ |
214 | |
215 | if (ml->sigblock) { | |
216 | sigset_t sigs; | |
217 | sigemptyset(&ml->oldsigmask); | |
218 | sigfillset(&sigs); | |
219 | sigprocmask(SIG_BLOCK, &sigs, &ml->oldsigmask); | |
220 | } | |
221 | ||
222 | ml->lockfile_fd = open(lfile, O_RDONLY|O_CREAT|O_CLOEXEC, | |
223 | S_IWUSR|S_IRUSR|S_IRGRP|S_IROTH); | |
224 | if (ml->lockfile_fd < 0) { | |
225 | rc = -errno; | |
226 | goto err; | |
227 | } | |
ecfeae90 SB |
228 | rc = fchmod(ml->lockfile_fd, S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH); |
229 | if (rc < 0) { | |
230 | rc = -errno; | |
231 | goto err; | |
232 | } | |
5eb00eb4 KZ |
233 | |
234 | while (flock(ml->lockfile_fd, LOCK_EX) < 0) { | |
235 | int errsv; | |
236 | if ((errno == EAGAIN) || (errno == EINTR)) | |
237 | continue; | |
238 | errsv = errno; | |
239 | close(ml->lockfile_fd); | |
240 | ml->lockfile_fd = -1; | |
241 | rc = -errsv; | |
242 | goto err; | |
243 | } | |
86cd5870 | 244 | ml->locked = 1; |
5eb00eb4 KZ |
245 | return 0; |
246 | err: | |
247 | if (ml->sigblock) | |
248 | sigprocmask(SIG_SETMASK, &ml->oldsigmask, NULL); | |
249 | return rc; | |
250 | } | |
251 | ||
252 | /* | |
253 | * traditional mtab locking | |
254 | */ | |
255 | ||
7fc6d2b8 | 256 | static void mnt_lockalrm_handler(int sig __attribute__((__unused__))) |
27c6d415 KZ |
257 | { |
258 | /* do nothing, say nothing, be nothing */ | |
259 | } | |
260 | ||
261 | /* | |
262 | * Waits for F_SETLKW, unfortunately we have to use SIGALRM here to interrupt | |
d58b3157 | 263 | * fcntl() to avoid neverending waiting. |
27c6d415 | 264 | * |
192c6aad | 265 | * Returns: 0 on success, 1 on timeout, -errno on error. |
27c6d415 | 266 | */ |
5eb00eb4 | 267 | static int mnt_wait_mtab_lock(struct libmnt_lock *ml, struct flock *fl, time_t maxtime) |
27c6d415 KZ |
268 | { |
269 | struct timeval now; | |
270 | struct sigaction sa, osa; | |
271 | int ret = 0; | |
272 | ||
700031ad | 273 | gettime_monotonic(&now); |
3df1a79a KZ |
274 | DBG(LOCKS, ul_debugobj(ml, "(%d) waiting for F_SETLKW (now=%lu, maxtime=%lu, diff=%lu)", |
275 | getpid(), | |
276 | (unsigned long) now.tv_sec, | |
277 | (unsigned long) maxtime, | |
278 | (unsigned long) (maxtime - now.tv_sec))); | |
27c6d415 KZ |
279 | |
280 | if (now.tv_sec >= maxtime) | |
281 | return 1; /* timeout */ | |
282 | ||
283 | /* setup ALARM handler -- we don't want to wait forever */ | |
284 | sa.sa_flags = 0; | |
285 | sa.sa_handler = mnt_lockalrm_handler; | |
286 | sigfillset (&sa.sa_mask); | |
287 | ||
288 | sigaction(SIGALRM, &sa, &osa); | |
289 | ||
27c6d415 KZ |
290 | |
291 | alarm(maxtime - now.tv_sec); | |
292 | if (fcntl(ml->lockfile_fd, F_SETLKW, fl) == -1) | |
293 | ret = errno == EINTR ? 1 : -errno; | |
294 | alarm(0); | |
295 | ||
296 | /* restore old sigaction */ | |
297 | sigaction(SIGALRM, &osa, NULL); | |
298 | ||
83a78332 | 299 | DBG(LOCKS, ul_debugobj(ml, "(%d) leaving mnt_wait_setlkw(), rc=%d", |
3f31a959 | 300 | getpid(), ret)); |
27c6d415 KZ |
301 | return ret; |
302 | } | |
303 | ||
304 | /* | |
5eb00eb4 | 305 | * Create the mtab lock file. |
27c6d415 KZ |
306 | * |
307 | * The old code here used flock on a lock file /etc/mtab~ and deleted | |
308 | * this lock file afterwards. However, as rgooch remarks, that has a | |
309 | * race: a second mount may be waiting on the lock and proceed as | |
310 | * soon as the lock file is deleted by the first mount, and immediately | |
311 | * afterwards a third mount comes, creates a new /etc/mtab~, applies | |
312 | * flock to that, and also proceeds, so that the second and third mount | |
d58b3157 | 313 | * are now both scribbling in /etc/mtab. |
27c6d415 KZ |
314 | * |
315 | * The new code uses a link() instead of a creat(), where we proceed | |
316 | * only if it was us that created the lock, and hence we always have | |
317 | * to delete the lock afterwards. Now the use of flock() is in principle | |
318 | * superfluous, but avoids an arbitrary sleep(). | |
319 | * | |
320 | * Where does the link point to? Obvious choices are mtab and mtab~~. | |
321 | * HJLu points out that the latter leads to races. Right now we use | |
ee314075 | 322 | * mtab~.pid instead. |
27c6d415 KZ |
323 | * |
324 | * | |
325 | * The original mount locking code has used sleep(1) between attempts and | |
326 | * maximal number of attempts has been 5. | |
327 | * | |
d58b3157 | 328 | * There was a very small number of attempts and extremely long waiting (1s) |
27c6d415 KZ |
329 | * that is useless on machines with large number of mount processes. |
330 | * | |
d58b3157 OO |
331 | * Now we wait for a few thousand microseconds between attempts and we have a global |
332 | * time limit (30s) rather than a limit for the number of attempts. The advantage | |
27c6d415 | 333 | * is that this method also counts time which we spend in fcntl(F_SETLKW) and |
d58b3157 | 334 | * the number of attempts is not restricted. |
27c6d415 KZ |
335 | * -- kzak@redhat.com [Mar-2007] |
336 | * | |
337 | * | |
338 | * This mtab locking code has been refactored and moved to libmount. The mtab | |
339 | * locking is really not perfect (e.g. SIGALRM), but it's stable, reliable and | |
66c33aab KZ |
340 | * backwardly compatible code. |
341 | * | |
342 | * Don't forget that this code has to be compatible with 3rd party mounts | |
ee314075 | 343 | * (/sbin/mount.foo) and has to work with NFS. |
27c6d415 KZ |
344 | * -- kzak@redhat.com [May-2009] |
345 | */ | |
346 | ||
d58b3157 | 347 | /* maximum seconds between the first and the last attempt */ |
27c6d415 KZ |
348 | #define MOUNTLOCK_MAXTIME 30 |
349 | ||
350 | /* sleep time (in microseconds, max=999999) between attempts */ | |
351 | #define MOUNTLOCK_WAITTIME 5000 | |
352 | ||
5eb00eb4 | 353 | static void unlock_mtab(struct libmnt_lock *ml) |
27c6d415 KZ |
354 | { |
355 | if (!ml) | |
356 | return; | |
357 | ||
6f5788c5 | 358 | if (!ml->locked && ml->lockfile && ml->linkfile) |
27c6d415 | 359 | { |
d58b3157 | 360 | /* We (probably) have all the files, but we don't own the lock, |
27c6d415 | 361 | * Really? Check it! Maybe ml->locked wasn't set properly |
d58b3157 | 362 | * because the code was interrupted by a signal. Paranoia? Yes. |
27c6d415 KZ |
363 | * |
364 | * We own the lock when linkfile == lockfile. | |
365 | */ | |
366 | struct stat lo, li; | |
367 | ||
368 | if (!stat(ml->lockfile, &lo) && !stat(ml->linkfile, &li) && | |
369 | lo.st_dev == li.st_dev && lo.st_ino == li.st_ino) | |
370 | ml->locked = 1; | |
371 | } | |
3a5b1b1d | 372 | |
27c6d415 KZ |
373 | if (ml->linkfile) |
374 | unlink(ml->linkfile); | |
375 | if (ml->lockfile_fd >= 0) | |
376 | close(ml->lockfile_fd); | |
6f5788c5 | 377 | if (ml->locked && ml->lockfile) { |
27c6d415 | 378 | unlink(ml->lockfile); |
83a78332 | 379 | DBG(LOCKS, ul_debugobj(ml, "unlink %s", ml->lockfile)); |
6f5788c5 | 380 | } |
27c6d415 KZ |
381 | } |
382 | ||
5eb00eb4 | 383 | static int lock_mtab(struct libmnt_lock *ml) |
27c6d415 | 384 | { |
03a8029b | 385 | int i, rc = -1; |
27c6d415 KZ |
386 | struct timespec waittime; |
387 | struct timeval maxtime; | |
388 | const char *lockfile, *linkfile; | |
389 | ||
390 | if (!ml) | |
03a8029b | 391 | return -EINVAL; |
27c6d415 KZ |
392 | if (ml->locked) |
393 | return 0; | |
394 | ||
395 | lockfile = mnt_lock_get_lockfile(ml); | |
396 | if (!lockfile) | |
03a8029b | 397 | return -EINVAL; |
27c6d415 KZ |
398 | linkfile = mnt_lock_get_linkfile(ml); |
399 | if (!linkfile) | |
03a8029b | 400 | return -EINVAL; |
27c6d415 | 401 | |
5976114f KZ |
402 | if (ml->sigblock) { |
403 | /* | |
404 | * Block all signals when locked, mnt_unlock_file() will | |
405 | * restore the old mask. | |
406 | */ | |
407 | sigset_t sigs; | |
408 | ||
409 | sigemptyset(&ml->oldsigmask); | |
410 | sigfillset(&sigs); | |
411 | sigdelset(&sigs, SIGTRAP); | |
412 | sigdelset(&sigs, SIGALRM); | |
413 | sigprocmask(SIG_BLOCK, &sigs, &ml->oldsigmask); | |
414 | } | |
415 | ||
d39c2b43 | 416 | i = open(linkfile, O_WRONLY|O_CREAT|O_CLOEXEC, S_IRUSR|S_IWUSR); |
03a8029b KZ |
417 | if (i < 0) { |
418 | /* linkfile does not exist (as a file) and we cannot create it. | |
419 | * Read-only or full filesystem? Too many files open in the system? | |
420 | */ | |
421 | if (errno > 0) | |
422 | rc = -errno; | |
27c6d415 | 423 | goto failed; |
03a8029b | 424 | } |
27c6d415 KZ |
425 | close(i); |
426 | ||
700031ad | 427 | gettime_monotonic(&maxtime); |
27c6d415 KZ |
428 | maxtime.tv_sec += MOUNTLOCK_MAXTIME; |
429 | ||
430 | waittime.tv_sec = 0; | |
431 | waittime.tv_nsec = (1000 * MOUNTLOCK_WAITTIME); | |
432 | ||
433 | /* Repeat until it was us who made the link */ | |
6f5788c5 | 434 | while (!ml->locked) { |
27c6d415 KZ |
435 | struct timeval now; |
436 | struct flock flock; | |
437 | int j; | |
438 | ||
439 | j = link(linkfile, lockfile); | |
440 | if (j == 0) | |
441 | ml->locked = 1; | |
442 | ||
03a8029b KZ |
443 | if (j < 0 && errno != EEXIST) { |
444 | if (errno > 0) | |
445 | rc = -errno; | |
27c6d415 | 446 | goto failed; |
03a8029b | 447 | } |
d39c2b43 | 448 | ml->lockfile_fd = open(lockfile, O_WRONLY|O_CLOEXEC); |
27c6d415 KZ |
449 | |
450 | if (ml->lockfile_fd < 0) { | |
451 | /* Strange... Maybe the file was just deleted? */ | |
452 | int errsv = errno; | |
700031ad | 453 | gettime_monotonic(&now); |
27c6d415 KZ |
454 | if (errsv == ENOENT && now.tv_sec < maxtime.tv_sec) { |
455 | ml->locked = 0; | |
456 | continue; | |
457 | } | |
03a8029b KZ |
458 | if (errsv > 0) |
459 | rc = -errsv; | |
27c6d415 KZ |
460 | goto failed; |
461 | } | |
462 | ||
463 | flock.l_type = F_WRLCK; | |
464 | flock.l_whence = SEEK_SET; | |
465 | flock.l_start = 0; | |
466 | flock.l_len = 0; | |
467 | ||
468 | if (ml->locked) { | |
469 | /* We made the link. Now claim the lock. */ | |
470 | if (fcntl (ml->lockfile_fd, F_SETLK, &flock) == -1) { | |
83a78332 | 471 | DBG(LOCKS, ul_debugobj(ml, |
27c6d415 KZ |
472 | "%s: can't F_SETLK lockfile, errno=%d\n", |
473 | lockfile, errno)); | |
474 | /* proceed, since it was us who created the lockfile anyway */ | |
475 | } | |
476 | break; | |
042f62df | 477 | } |
27c6d415 | 478 | |
042f62df RP |
479 | /* Someone else made the link. Wait. */ |
480 | int err = mnt_wait_mtab_lock(ml, &flock, maxtime.tv_sec); | |
481 | ||
482 | if (err == 1) { | |
483 | DBG(LOCKS, ul_debugobj(ml, | |
484 | "%s: can't create link: time out (perhaps " | |
485 | "there is a stale lock file?)", lockfile)); | |
486 | rc = -ETIMEDOUT; | |
487 | goto failed; | |
488 | ||
489 | } else if (err < 0) { | |
490 | rc = err; | |
491 | goto failed; | |
27c6d415 | 492 | } |
042f62df RP |
493 | nanosleep(&waittime, NULL); |
494 | close(ml->lockfile_fd); | |
495 | ml->lockfile_fd = -1; | |
27c6d415 | 496 | } |
83a78332 | 497 | DBG(LOCKS, ul_debugobj(ml, "%s: (%d) successfully locked", |
6f5788c5 | 498 | lockfile, getpid())); |
27c6d415 KZ |
499 | unlink(linkfile); |
500 | return 0; | |
501 | ||
502 | failed: | |
503 | mnt_unlock_file(ml); | |
03a8029b | 504 | return rc; |
27c6d415 KZ |
505 | } |
506 | ||
5eb00eb4 KZ |
507 | |
508 | /** | |
509 | * mnt_lock_file | |
510 | * @ml: pointer to struct libmnt_lock instance | |
511 | * | |
d58b3157 | 512 | * Creates a lock file (e.g. /etc/mtab~). Note that this function may |
5eb00eb4 KZ |
513 | * use alarm(). |
514 | * | |
d58b3157 | 515 | * Your application always has to call mnt_unlock_file() before exit. |
5eb00eb4 KZ |
516 | * |
517 | * Traditional mtab locking scheme: | |
518 | * | |
519 | * 1. create linkfile (e.g. /etc/mtab~.$PID) | |
520 | * 2. link linkfile --> lockfile (e.g. /etc/mtab~.$PID --> /etc/mtab~) | |
9e930041 | 521 | * 3. a) link() success: setups F_SETLK lock (see fcntl(2)) |
5eb00eb4 KZ |
522 | * b) link() failed: wait (max 30s) on F_SETLKW lock, goto 2. |
523 | * | |
398f7f9d | 524 | * Note that when the lock is used by mnt_update_table() interface then libmount |
9e930041 | 525 | * uses flock() for private library file /run/mount/utab. The fcntl(2) is used only |
398f7f9d KZ |
526 | * for backwardly compatible stuff like /etc/mtab. |
527 | * | |
5eb00eb4 KZ |
528 | * Returns: 0 on success or negative number in case of error (-ETIMEOUT is case |
529 | * of stale lock file). | |
530 | */ | |
531 | int mnt_lock_file(struct libmnt_lock *ml) | |
532 | { | |
533 | if (!ml) | |
534 | return -EINVAL; | |
535 | ||
536 | if (ml->simplelock) | |
537 | return lock_simplelock(ml); | |
538 | ||
539 | return lock_mtab(ml); | |
540 | } | |
541 | ||
542 | /** | |
543 | * mnt_unlock_file: | |
544 | * @ml: lock struct | |
545 | * | |
d58b3157 | 546 | * Unlocks the file. The function could be called independently of the |
5eb00eb4 KZ |
547 | * lock status (for example from exit(3)). |
548 | */ | |
549 | void mnt_unlock_file(struct libmnt_lock *ml) | |
550 | { | |
551 | if (!ml) | |
552 | return; | |
553 | ||
83a78332 | 554 | DBG(LOCKS, ul_debugobj(ml, "(%d) %s", getpid(), |
5eb00eb4 KZ |
555 | ml->locked ? "unlocking" : "cleaning")); |
556 | ||
557 | if (ml->simplelock) | |
558 | unlock_simplelock(ml); | |
559 | else | |
560 | unlock_mtab(ml); | |
561 | ||
562 | ml->locked = 0; | |
563 | ml->lockfile_fd = -1; | |
564 | ||
565 | if (ml->sigblock) { | |
83a78332 | 566 | DBG(LOCKS, ul_debugobj(ml, "restoring sigmask")); |
5eb00eb4 KZ |
567 | sigprocmask(SIG_SETMASK, &ml->oldsigmask, NULL); |
568 | } | |
569 | } | |
570 | ||
27c6d415 | 571 | #ifdef TEST_PROGRAM |
27c6d415 | 572 | |
41427f97 | 573 | static struct libmnt_lock *lock; |
27c6d415 KZ |
574 | |
575 | /* | |
576 | * read number from @filename, increment the number and | |
577 | * write the number back to the file | |
578 | */ | |
5fde1d9f | 579 | static void increment_data(const char *filename, int verbose, int loopno) |
27c6d415 KZ |
580 | { |
581 | long num; | |
582 | FILE *f; | |
583 | char buf[256]; | |
584 | ||
1eb8539d | 585 | if (!(f = fopen(filename, "r" UL_CLOEXECSTR))) |
27c6d415 KZ |
586 | err(EXIT_FAILURE, "%d: failed to open: %s", getpid(), filename); |
587 | ||
588 | if (!fgets(buf, sizeof(buf), f)) | |
589 | err(EXIT_FAILURE, "%d failed read: %s", getpid(), filename); | |
590 | ||
591 | fclose(f); | |
592 | num = atol(buf) + 1; | |
593 | ||
1eb8539d | 594 | if (!(f = fopen(filename, "w" UL_CLOEXECSTR))) |
27c6d415 KZ |
595 | err(EXIT_FAILURE, "%d: failed to open: %s", getpid(), filename); |
596 | ||
597 | fprintf(f, "%ld", num); | |
69f1cad4 SK |
598 | |
599 | if (close_stream(f) != 0) | |
600 | err(EXIT_FAILURE, "write failed: %s", filename); | |
27c6d415 KZ |
601 | |
602 | if (verbose) | |
603 | fprintf(stderr, "%d: %s: %ld --> %ld (loop=%d)\n", getpid(), | |
604 | filename, num - 1, num, loopno); | |
605 | } | |
606 | ||
5fde1d9f | 607 | static void clean_lock(void) |
27c6d415 | 608 | { |
27c6d415 KZ |
609 | if (!lock) |
610 | return; | |
611 | mnt_unlock_file(lock); | |
612 | mnt_free_lock(lock); | |
613 | } | |
614 | ||
5fde1d9f | 615 | static void __attribute__((__noreturn__)) sig_handler(int sig) |
27c6d415 KZ |
616 | { |
617 | errx(EXIT_FAILURE, "\n%d: catch signal: %s\n", getpid(), strsignal(sig)); | |
618 | } | |
619 | ||
5fde1d9f | 620 | static int test_lock(struct libmnt_test *ts, int argc, char *argv[]) |
27c6d415 | 621 | { |
9e10ad3d KZ |
622 | time_t synctime = 0; |
623 | unsigned int usecs; | |
9e10ad3d KZ |
624 | const char *datafile = NULL; |
625 | int verbose = 0, loops = 0, l, idx = 1; | |
27c6d415 | 626 | |
66c33aab | 627 | if (argc < 3) |
9e10ad3d | 628 | return -EINVAL; |
27c6d415 | 629 | |
9e10ad3d KZ |
630 | if (strcmp(argv[idx], "--synctime") == 0) { |
631 | synctime = (time_t) atol(argv[idx + 1]); | |
632 | idx += 2; | |
633 | } | |
634 | if (idx < argc && strcmp(argv[idx], "--verbose") == 0) { | |
27c6d415 | 635 | verbose = 1; |
9e10ad3d KZ |
636 | idx++; |
637 | } | |
638 | ||
639 | if (idx < argc) | |
640 | datafile = argv[idx++]; | |
641 | if (idx < argc) | |
642 | loops = atoi(argv[idx++]); | |
643 | ||
644 | if (!datafile || !loops) | |
645 | return -EINVAL; | |
646 | ||
3a5b1b1d KZ |
647 | if (verbose) |
648 | fprintf(stderr, "%d: start: synctime=%u, datafile=%s, loops=%d\n", | |
649 | getpid(), (int) synctime, datafile, loops); | |
27c6d415 KZ |
650 | |
651 | atexit(clean_lock); | |
652 | ||
653 | /* be paranoid and call exit() (=clean_lock()) for all signals */ | |
654 | { | |
655 | int sig = 0; | |
656 | struct sigaction sa; | |
657 | ||
658 | sa.sa_handler = sig_handler; | |
659 | sa.sa_flags = 0; | |
660 | sigfillset(&sa.sa_mask); | |
661 | ||
662 | while (sigismember(&sa.sa_mask, ++sig) != -1 && sig != SIGCHLD) | |
663 | sigaction (sig, &sa, (struct sigaction *) 0); | |
664 | } | |
665 | ||
9e10ad3d KZ |
666 | /* start the test in exactly defined time */ |
667 | if (synctime) { | |
bbf0ff70 KZ |
668 | struct timeval tv; |
669 | ||
670 | gettimeofday(&tv, NULL); | |
9e10ad3d KZ |
671 | if (synctime && synctime - tv.tv_sec > 1) { |
672 | usecs = ((synctime - tv.tv_sec) * 1000000UL) - | |
673 | (1000000UL - tv.tv_usec); | |
a5bd7939 | 674 | xusleep(usecs); |
9e10ad3d KZ |
675 | } |
676 | } | |
677 | ||
27c6d415 | 678 | for (l = 0; l < loops; l++) { |
66c33aab KZ |
679 | lock = mnt_new_lock(datafile, 0); |
680 | if (!lock) | |
681 | return -1; | |
27c6d415 | 682 | |
abc3d154 | 683 | if (mnt_lock_file(lock) != 0) { |
66c33aab KZ |
684 | fprintf(stderr, "%d: failed to lock %s file\n", |
685 | getpid(), datafile); | |
27c6d415 KZ |
686 | return -1; |
687 | } | |
688 | ||
689 | increment_data(datafile, verbose, l); | |
690 | ||
691 | mnt_unlock_file(lock); | |
692 | mnt_free_lock(lock); | |
693 | lock = NULL; | |
9e10ad3d | 694 | |
d58b3157 | 695 | /* The mount command usually finishes after a mtab update. We |
9e10ad3d KZ |
696 | * simulate this via short sleep -- it's also enough to make |
697 | * concurrent processes happy. | |
698 | */ | |
699 | if (synctime) | |
a5bd7939 | 700 | xusleep(25000); |
27c6d415 KZ |
701 | } |
702 | ||
703 | return 0; | |
704 | } | |
705 | ||
192c6aad KZ |
706 | /* |
707 | * Note that this test should be executed from a script that creates many | |
708 | * parallel processes, otherwise this test does not make sense. | |
709 | */ | |
27c6d415 KZ |
710 | int main(int argc, char *argv[]) |
711 | { | |
68164f6c | 712 | struct libmnt_test tss[] = { |
9e10ad3d KZ |
713 | { "--lock", test_lock, " [--synctime <time_t>] [--verbose] <datafile> <loops> " |
714 | "increment a number in datafile" }, | |
27c6d415 KZ |
715 | { NULL } |
716 | }; | |
717 | ||
718 | return mnt_run_test(tss, argc, argv); | |
719 | } | |
720 | ||
721 | #endif /* TEST_PROGRAM */ |