git.ozlabs.org Git - ccan/blob - ccan/tdb2/tdb1_lock.c

   1  /*
   2    Unix SMB/CIFS implementation.
   3
   4    trivial database library
   5
   6    Copyright (C) Andrew Tridgell              1999-2005
   7    Copyright (C) Paul `Rusty' Russell              2000
   8    Copyright (C) Jeremy Allison                    2000-2003
   9
  10      ** NOTE! The following LGPL license applies to the tdb
  11      ** library. This does NOT imply that all of Samba is released
  12      ** under the LGPL
  13
  14    This library is free software; you can redistribute it and/or
  15    modify it under the terms of the GNU Lesser General Public
  16    License as published by the Free Software Foundation; either
  17    version 3 of the License, or (at your option) any later version.
  18
  19    This library is distributed in the hope that it will be useful,
  20    but WITHOUT ANY WARRANTY; without even the implied warranty of
  21    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  22    Lesser General Public License for more details.
  23
  24    You should have received a copy of the GNU Lesser General Public
  25    License along with this library; if not, see <http://www.gnu.org/licenses/>.
  26 */
  27
  28 #include "tdb1_private.h"
  29
  30 /* list -1 is the alloc list, otherwise a hash chain. */
  31 static tdb1_off_t lock_offset(int list)
  32 {
  33         return TDB1_FREELIST_TOP + 4*list;
  34 }
  35
  36 /* a byte range locking function - return 0 on success
  37    this functions locks/unlocks 1 byte at the specified offset.
  38
  39    On error, errno is also set so that errors are passed back properly
  40    through tdb1_open().
  41
  42    note that a len of zero means lock to end of file
  43 */
  44 int tdb1_brlock(struct tdb_context *tdb,
  45                int rw_type, tdb1_off_t offset, size_t len,
  46                enum tdb_lock_flags flags)
  47 {
  48         enum TDB_ERROR ecode = tdb_brlock(tdb, rw_type, offset, len, flags
  49                                           | TDB_LOCK_NOCHECK);
  50         if (ecode == TDB_SUCCESS)
  51                 return 0;
  52         tdb->last_error = ecode;
  53         return -1;
  54 }
  55
  56 int tdb1_brunlock(struct tdb_context *tdb,
  57                  int rw_type, tdb1_off_t offset, size_t len)
  58 {
  59         enum TDB_ERROR ecode = tdb_brunlock(tdb, rw_type, offset, len);
  60         if (ecode == TDB_SUCCESS)
  61                 return 0;
  62         tdb->last_error = ecode;
  63         return -1;
  64 }
  65
  66 int tdb1_allrecord_upgrade(struct tdb_context *tdb)
  67 {
  68         enum TDB_ERROR ecode = tdb_allrecord_upgrade(tdb, TDB1_FREELIST_TOP);
  69         if (ecode == TDB_SUCCESS)
  70                 return 0;
  71         tdb->last_error = ecode;
  72         return -1;
  73 }
  74
  75 static struct tdb_lock *tdb1_find_nestlock(struct tdb_context *tdb,
  76                                            tdb1_off_t offset)
  77 {
  78         unsigned int i;
  79
  80         for (i=0; i<tdb->file->num_lockrecs; i++) {
  81                 if (tdb->file->lockrecs[i].off == offset) {
  82                         return &tdb->file->lockrecs[i];
  83                 }
  84         }
  85         return NULL;
  86 }
  87
  88 /* lock an offset in the database. */
  89 int tdb1_nest_lock(struct tdb_context *tdb, uint32_t offset, int ltype,
  90                   enum tdb_lock_flags flags)
  91 {
  92         enum TDB_ERROR ecode;
  93
  94         if (offset >= lock_offset(tdb->tdb1.header.hash_size)) {
  95                 tdb->last_error = tdb_logerr(tdb, TDB_ERR_LOCK, TDB_LOG_ERROR,
  96                                         "tdb1_lock: invalid offset %u for"
  97                                         " ltype=%d",
  98                                         offset, ltype);
  99                 return -1;
 100         }
 101
 102         ecode = tdb_nest_lock(tdb, offset, ltype, flags | TDB_LOCK_NOCHECK);
 103         if (unlikely(ecode != TDB_SUCCESS)) {
 104                 tdb->last_error = ecode;
 105                 return -1;
 106         }
 107         return 0;
 108 }
 109
 110 static int tdb1_lock_and_recover(struct tdb_context *tdb)
 111 {
 112         int ret;
 113
 114         /* We need to match locking order in transaction commit. */
 115         if (tdb1_brlock(tdb, F_WRLCK, TDB1_FREELIST_TOP, 0,
 116                         TDB_LOCK_WAIT|TDB_LOCK_NOCHECK)) {
 117                 return -1;
 118         }
 119
 120         if (tdb1_brlock(tdb, F_WRLCK, TDB1_OPEN_LOCK, 1,
 121                         TDB_LOCK_WAIT|TDB_LOCK_NOCHECK)) {
 122                 tdb1_brunlock(tdb, F_WRLCK, TDB1_FREELIST_TOP, 0);
 123                 return -1;
 124         }
 125
 126         ret = tdb1_transaction_recover(tdb);
 127
 128         tdb1_brunlock(tdb, F_WRLCK, TDB1_OPEN_LOCK, 1);
 129         tdb1_brunlock(tdb, F_WRLCK, TDB1_FREELIST_TOP, 0);
 130
 131         return ret;
 132 }
 133
 134 static bool have_data_locks(const struct tdb_context *tdb)
 135 {
 136         unsigned int i;
 137
 138         for (i = 0; i < tdb->file->num_lockrecs; i++) {
 139                 if (tdb->file->lockrecs[i].off >= lock_offset(-1))
 140                         return true;
 141         }
 142         return false;
 143 }
 144
 145 static int tdb1_lock_list(struct tdb_context *tdb, int list, int ltype,
 146                          enum tdb_lock_flags waitflag)
 147 {
 148         int ret;
 149         bool check = false;
 150
 151         /* a allrecord lock allows us to avoid per chain locks */
 152         if (tdb->file->allrecord_lock.count &&
 153             (ltype == tdb->file->allrecord_lock.ltype || ltype == F_RDLCK)) {
 154                 return 0;
 155         }
 156
 157         if (tdb->file->allrecord_lock.count) {
 158                 tdb->last_error = TDB_ERR_LOCK;
 159                 ret = -1;
 160         } else {
 161                 /* Only check when we grab first data lock. */
 162                 check = !have_data_locks(tdb);
 163                 ret = tdb1_nest_lock(tdb, lock_offset(list), ltype, waitflag);
 164
 165                 if (ret == 0 && check) {
 166                         tdb_bool_err berr = tdb1_needs_recovery(tdb);
 167
 168                         if (berr < 0) {
 169                                 return -1;
 170                         }
 171                         if (berr == true) {
 172                                 tdb1_nest_unlock(tdb, lock_offset(list), ltype);
 173
 174                                 if (tdb1_lock_and_recover(tdb) == -1) {
 175                                         return -1;
 176                                 }
 177                                 return tdb1_lock_list(tdb, list, ltype,
 178                                                       waitflag);
 179                         }
 180                 }
 181         }
 182         return ret;
 183 }
 184
 185 /* lock a list in the database. list -1 is the alloc list */
 186 int tdb1_lock(struct tdb_context *tdb, int list, int ltype)
 187 {
 188         int ret;
 189
 190         ret = tdb1_lock_list(tdb, list, ltype, TDB_LOCK_WAIT);
 191         /* Don't log for EAGAIN and EINTR: they could have overridden lock fns */
 192         if (ret && errno != EAGAIN && errno != EINTR) {
 193                 tdb_logerr(tdb, tdb->last_error, TDB_LOG_ERROR,
 194                            "tdb1_lock failed on list %d "
 195                            "ltype=%d (%s)",  list, ltype, strerror(errno));
 196         }
 197         return ret;
 198 }
 199
 200 int tdb1_nest_unlock(struct tdb_context *tdb, uint32_t offset, int ltype)
 201 {
 202         enum TDB_ERROR ecode;
 203
 204         /* Sanity checks */
 205         if (offset >= lock_offset(tdb->tdb1.header.hash_size)) {
 206                 tdb->last_error = tdb_logerr(tdb, TDB_ERR_LOCK, TDB_LOG_ERROR,
 207                                         "tdb1_unlock: offset %u invalid (%d)",
 208                                         offset, tdb->tdb1.header.hash_size);
 209                 return -1;
 210         }
 211
 212         ecode = tdb_nest_unlock(tdb, offset, ltype);
 213         if (unlikely(ecode != TDB_SUCCESS)) {
 214                 tdb->last_error = ecode;
 215                 return -1;
 216         }
 217         return 0;
 218 }
 219
 220 int tdb1_unlock(struct tdb_context *tdb, int list, int ltype)
 221 {
 222         /* a global lock allows us to avoid per chain locks */
 223         if (tdb->file->allrecord_lock.count &&
 224             (ltype == tdb->file->allrecord_lock.ltype || ltype == F_RDLCK)) {
 225                 return 0;
 226         }
 227
 228         if (tdb->file->allrecord_lock.count) {
 229                 tdb->last_error = TDB_ERR_LOCK;
 230                 return -1;
 231         }
 232
 233         return tdb1_nest_unlock(tdb, lock_offset(list), ltype);
 234 }
 235
 236 /*
 237   get the transaction lock
 238  */
 239 int tdb1_transaction_lock(struct tdb_context *tdb, int ltype,
 240                          enum tdb_lock_flags lockflags)
 241 {
 242         return tdb1_nest_lock(tdb, TDB1_TRANSACTION_LOCK, ltype, lockflags);
 243 }
 244
 245 /*
 246   release the transaction lock
 247  */
 248 int tdb1_transaction_unlock(struct tdb_context *tdb, int ltype)
 249 {
 250         return tdb1_nest_unlock(tdb, TDB1_TRANSACTION_LOCK, ltype);
 251 }
 252
 253 /* lock/unlock entire database.  It can only be upgradable if you have some
 254  * other way of guaranteeing exclusivity (ie. transaction write lock).
 255  * We do the locking gradually to avoid being starved by smaller locks. */
 256 int tdb1_allrecord_lock(struct tdb_context *tdb, int ltype,
 257                        enum tdb_lock_flags flags, bool upgradable)
 258 {
 259         enum TDB_ERROR ecode;
 260         tdb_bool_err berr;
 261
 262         /* tdb_lock_gradual() doesn't know about tdb->tdb1.traverse_read. */
 263         if (tdb->tdb1.traverse_read && !(tdb->flags & TDB_NOLOCK)) {
 264                 tdb->last_error = tdb_logerr(tdb, TDB_ERR_LOCK,
 265                                              TDB_LOG_USE_ERROR,
 266                                              "tdb1_allrecord_lock during"
 267                                              " tdb1_read_traverse");
 268                 return -1;
 269         }
 270
 271         if (tdb->file->allrecord_lock.count
 272             && tdb->file->allrecord_lock.ltype == ltype) {
 273                 tdb->file->allrecord_lock.count++;
 274                 return 0;
 275         }
 276
 277         if (tdb1_have_extra_locks(tdb)) {
 278                 /* can't combine global and chain locks */
 279                 tdb->last_error = tdb_logerr(tdb, TDB_ERR_LOCK,
 280                                              TDB_LOG_USE_ERROR,
 281                                              "tdb1_allrecord_lock holding"
 282                                              " other locks");
 283                 return -1;
 284         }
 285
 286         if (upgradable && ltype != F_RDLCK) {
 287                 /* tdb error: you can't upgrade a write lock! */
 288                 tdb->last_error = tdb_logerr(tdb, TDB_ERR_LOCK,
 289                                              TDB_LOG_ERROR,
 290                                              "tdb1_allrecord_lock cannot"
 291                                              " have upgradable write lock");
 292                 return -1;
 293         }
 294
 295         /* We cover two kinds of locks:
 296          * 1) Normal chain locks.  Taken for almost all operations.
 297          * 3) Individual records locks.  Taken after normal or free
 298          *    chain locks.
 299          *
 300          * It is (1) which cause the starvation problem, so we're only
 301          * gradual for that. */
 302         ecode = tdb_lock_gradual(tdb, ltype, flags | TDB_LOCK_NOCHECK,
 303                                  TDB1_FREELIST_TOP, tdb->tdb1.header.hash_size * 4);
 304         if (ecode != TDB_SUCCESS) {
 305                 tdb->last_error = ecode;
 306                 return -1;
 307         }
 308
 309         /* Grab individual record locks. */
 310         if (tdb1_brlock(tdb, ltype, lock_offset(tdb->tdb1.header.hash_size), 0,
 311                        flags) == -1) {
 312                 tdb1_brunlock(tdb, ltype, TDB1_FREELIST_TOP,
 313                              tdb->tdb1.header.hash_size * 4);
 314                 return -1;
 315         }
 316
 317         /* FIXME: Temporary cast. */
 318         tdb->file->allrecord_lock.owner = (void *)(struct tdb_context *)tdb;
 319         tdb->file->allrecord_lock.count = 1;
 320         /* If it's upgradable, it's actually exclusive so we can treat
 321          * it as a write lock. */
 322         tdb->file->allrecord_lock.ltype = upgradable ? F_WRLCK : ltype;
 323         tdb->file->allrecord_lock.off = upgradable;
 324
 325         berr = tdb1_needs_recovery(tdb);
 326         if (berr < 0) {
 327                 return -1;
 328         }
 329
 330         if (berr == true) {
 331                 tdb1_allrecord_unlock(tdb, ltype);
 332                 if (tdb1_lock_and_recover(tdb) == -1) {
 333                         return -1;
 334                 }
 335                 return tdb1_allrecord_lock(tdb, ltype, flags, upgradable);
 336         }
 337
 338         return 0;
 339 }
 340
 341
 342
 343 /* unlock entire db */
 344 int tdb1_allrecord_unlock(struct tdb_context *tdb, int ltype)
 345 {
 346         /* Don't try this during r/o traversal! */
 347         if (tdb->tdb1.traverse_read) {
 348                 tdb->last_error = TDB_ERR_LOCK;
 349                 return -1;
 350         }
 351
 352         if (tdb->file->allrecord_lock.count == 0) {
 353                 tdb->last_error = TDB_ERR_LOCK;
 354                 return -1;
 355         }
 356
 357         /* Upgradable locks are marked as write locks. */
 358         if (tdb->file->allrecord_lock.ltype != ltype
 359             && (!tdb->file->allrecord_lock.off || ltype != F_RDLCK)) {
 360                 tdb->last_error = TDB_ERR_LOCK;
 361                 return -1;
 362         }
 363
 364         if (tdb->file->allrecord_lock.count > 1) {
 365                 tdb->file->allrecord_lock.count--;
 366                 return 0;
 367         }
 368
 369         if (tdb1_brunlock(tdb, ltype, TDB1_FREELIST_TOP, 0)) {
 370                 tdb_logerr(tdb, tdb->last_error, TDB_LOG_ERROR,
 371                            "tdb1_unlockall failed (%s)", strerror(errno));
 372                 return -1;
 373         }
 374
 375         tdb->file->allrecord_lock.count = 0;
 376         tdb->file->allrecord_lock.ltype = 0;
 377
 378         return 0;
 379 }
 380
 381 /* lock/unlock one hash chain. This is meant to be used to reduce
 382    contention - it cannot guarantee how many records will be locked */
 383 int tdb1_chainlock(struct tdb_context *tdb, TDB_DATA key)
 384 {
 385         int ret = tdb1_lock(tdb,
 386                             TDB1_BUCKET(tdb_hash(tdb, key.dptr, key.dsize)),
 387                             F_WRLCK);
 388         return ret;
 389 }
 390
 391 int tdb1_chainunlock(struct tdb_context *tdb, TDB_DATA key)
 392 {
 393         return tdb1_unlock(tdb, TDB1_BUCKET(tdb_hash(tdb, key.dptr, key.dsize)),
 394                            F_WRLCK);
 395 }
 396
 397 int tdb1_chainlock_read(struct tdb_context *tdb, TDB_DATA key)
 398 {
 399         int ret;
 400         ret = tdb1_lock(tdb, TDB1_BUCKET(tdb_hash(tdb, key.dptr, key.dsize)),
 401                         F_RDLCK);
 402         return ret;
 403 }
 404
 405 int tdb1_chainunlock_read(struct tdb_context *tdb, TDB_DATA key)
 406 {
 407         return tdb1_unlock(tdb, TDB1_BUCKET(tdb_hash(tdb, key.dptr, key.dsize)),
 408                            F_RDLCK);
 409 }
 410
 411 /* record lock stops delete underneath */
 412 int tdb1_lock_record(struct tdb_context *tdb, tdb1_off_t off)
 413 {
 414         if (tdb->file->allrecord_lock.count) {
 415                 return 0;
 416         }
 417         return off ? tdb1_brlock(tdb, F_RDLCK, off, 1, TDB_LOCK_WAIT) : 0;
 418 }
 419
 420 /*
 421   Write locks override our own fcntl readlocks, so check it here.
 422   Note this is meant to be F_SETLK, *not* F_SETLKW, as it's not
 423   an error to fail to get the lock here.
 424 */
 425 int tdb1_write_lock_record(struct tdb_context *tdb, tdb1_off_t off)
 426 {
 427         struct tdb1_traverse_lock *i;
 428         for (i = &tdb->tdb1.travlocks; i; i = i->next)
 429                 if (i->off == off)
 430                         return -1;
 431         if (tdb->file->allrecord_lock.count) {
 432                 if (tdb->file->allrecord_lock.ltype == F_WRLCK) {
 433                         return 0;
 434                 }
 435                 return -1;
 436         }
 437         return tdb1_brlock(tdb, F_WRLCK, off, 1, TDB_LOCK_NOWAIT|TDB_LOCK_PROBE);
 438 }
 439
 440 int tdb1_write_unlock_record(struct tdb_context *tdb, tdb1_off_t off)
 441 {
 442         if (tdb->file->allrecord_lock.count) {
 443                 return 0;
 444         }
 445         return tdb1_brunlock(tdb, F_WRLCK, off, 1);
 446 }
 447
 448 /* fcntl locks don't stack: avoid unlocking someone else's */
 449 int tdb1_unlock_record(struct tdb_context *tdb, tdb1_off_t off)
 450 {
 451         struct tdb1_traverse_lock *i;
 452         uint32_t count = 0;
 453
 454         if (tdb->file->allrecord_lock.count) {
 455                 return 0;
 456         }
 457
 458         if (off == 0)
 459                 return 0;
 460         for (i = &tdb->tdb1.travlocks; i; i = i->next)
 461                 if (i->off == off)
 462                         count++;
 463         return (count == 1 ? tdb1_brunlock(tdb, F_RDLCK, off, 1) : 0);
 464 }
 465
 466 bool tdb1_have_extra_locks(struct tdb_context *tdb)
 467 {
 468         unsigned int extra = tdb->file->num_lockrecs;
 469
 470         /* A transaction holds the lock for all records. */
 471         if (!tdb->tdb1.transaction && tdb->file->allrecord_lock.count) {
 472                 return true;
 473         }
 474
 475         /* We always hold the active lock if CLEAR_IF_FIRST. */
 476         if (tdb1_find_nestlock(tdb, TDB1_ACTIVE_LOCK)) {
 477                 extra--;
 478         }
 479
 480         /* In a transaction, we expect to hold the transaction lock */
 481         if (tdb->tdb1.transaction
 482             && tdb1_find_nestlock(tdb, TDB1_TRANSACTION_LOCK)) {
 483                 extra--;
 484         }
 485
 486         return extra;
 487 }
 488
 489 /* The transaction code uses this to remove all locks. */
 490 void tdb1_release_transaction_locks(struct tdb_context *tdb)
 491 {
 492         unsigned int i, active = 0;
 493
 494         if (tdb->file->allrecord_lock.count != 0) {
 495                 tdb1_brunlock(tdb, tdb->file->allrecord_lock.ltype, TDB1_FREELIST_TOP, 0);
 496                 tdb->file->allrecord_lock.count = 0;
 497         }
 498
 499         for (i=0;i<tdb->file->num_lockrecs;i++) {
 500                 struct tdb_lock *lck = &tdb->file->lockrecs[i];
 501
 502                 /* Don't release the active lock!  Copy it to first entry. */
 503                 if (lck->off == TDB1_ACTIVE_LOCK) {
 504                         tdb->file->lockrecs[active++] = *lck;
 505                 } else {
 506                         tdb1_brunlock(tdb, lck->ltype, lck->off, 1);
 507                 }
 508         }
 509         tdb->file->num_lockrecs = active;
 510         if (tdb->file->num_lockrecs == 0) {
 511                 SAFE_FREE(tdb->file->lockrecs);
 512         }
 513 }