1 /*-
2 * See the file LICENSE for redistribution information.
3 *
4 * Copyright (c) 1996, 1997, 1998
5 * Sleepycat Software. All rights reserved.
6 */
7
8 #include "config.h"
9
10 #ifndef lint
11 static const char sccsid[] = "@(#)db_region.c 10.53 (Sleepycat) 11/10/98";
12 #endif /* not lint */
13
14 #ifndef NO_SYSTEM_INCLUDES
15 #include <sys/types.h>
16
17 #include <errno.h>
18 #include <string.h>
19 #include <unistd.h>
20 #endif
21
22 #include "db_int.h"
23 #include "common_ext.h"
24
25 static int __db_growregion __P((REGINFO *, size_t));
26
27 /*
28 * __db_rattach --
29 * Optionally create and attach to a shared memory region.
30 *
31 * PUBLIC: int __db_rattach __P((REGINFO *));
32 */
33 int
__db_rattach(infop)34 __db_rattach(infop)
35 REGINFO *infop;
36 {
37 RLAYOUT *rlp, rl;
38 size_t grow_region, size;
39 ssize_t nr, nw;
40 u_int32_t flags, mbytes, bytes;
41 u_int8_t *p;
42 int malloc_possible, ret, retry_cnt;
43
44 grow_region = 0;
45 malloc_possible = 1;
46 ret = retry_cnt = 0;
47
48 /* Round off the requested size to the next page boundary. */
49 DB_ROUNDOFF(infop->size, DB_VMPAGESIZE);
50
51 /* Some architectures have hard limits on the maximum region size. */
52 #ifdef DB_REGIONSIZE_MAX
53 if (infop->size > DB_REGIONSIZE_MAX) {
54 __db_err(infop->dbenv, "__db_rattach: cache size too large");
55 return (EINVAL);
56 }
57 #endif
58
59 /* Intialize the return information in the REGINFO structure. */
60 loop: infop->addr = NULL;
61 infop->fd = -1;
62 infop->segid = INVALID_SEGID;
63 if (infop->name != NULL) {
64 __os_freestr(infop->name);
65 infop->name = NULL;
66 }
67 F_CLR(infop, REGION_CANGROW | REGION_CREATED);
68
69 #ifndef HAVE_SPINLOCKS
70 /*
71 * XXX
72 * Lacking spinlocks, we must have a file descriptor for fcntl(2)
73 * locking, which implies using mmap(2) to map in a regular file.
74 * (Theoretically, we could probably get a file descriptor to lock
75 * other types of shared regions, but I don't see any reason to
76 * bother.)
77 *
78 * Since we may be using shared memory regions, e.g., shmget(2),
79 * and not mmap of regular files, the backing file may be only a
80 * few tens of bytes in length. So, this depends on the ability
81 * to fcntl lock file offsets much larger than the physical file.
82 */
83 malloc_possible = 0;
84 #endif
85
86 #ifdef __hppa
87 /*
88 * XXX
89 * HP-UX won't permit mutexes to live in anything but shared memory.
90 * Instantiate a shared region file on that architecture, regardless.
91 */
92 malloc_possible = 0;
93 #endif
94 /*
95 * If a region is truly private, malloc the memory. That's faster
96 * than either anonymous memory or a shared file.
97 */
98 if (malloc_possible && F_ISSET(infop, REGION_PRIVATE)) {
99 if ((ret = __os_malloc(infop->size, NULL, &infop->addr)) != 0)
100 return (ret);
101
102 /*
103 * It's sometimes significantly faster to page-fault in all of
104 * the region's pages before we run the application, as we see
105 * nasty side-effects when we page-fault while holding various
106 * locks, i.e., the lock takes a long time to acquire because
107 * of the underlying page fault, and the other threads convoy
108 * behind the lock holder.
109 */
110 if (DB_GLOBAL(db_region_init))
111 for (p = infop->addr;
112 p < (u_int8_t *)infop->addr + infop->size;
113 p += DB_VMPAGESIZE)
114 p[0] = '\0';
115
116 F_SET(infop, REGION_CREATED | REGION_MALLOC);
117 goto region_init;
118 }
119
120 /*
121 * Get the name of the region (creating the file if a temporary file
122 * is being used). The dbenv contains the current DB environment,
123 * including naming information. The path argument may be a file or
124 * a directory. If path is a directory, it must exist and file is the
125 * file name to be created inside the directory. If path is a file,
126 * then file must be NULL.
127 */
128 if ((ret = __db_appname(infop->dbenv, infop->appname, infop->path,
129 infop->file, infop->dbflags, &infop->fd, &infop->name)) != 0)
130 return (ret);
131 if (infop->fd != -1)
132 F_SET(infop, REGION_CREATED);
133
134 /*
135 * Try to create the file, if we have authority. We have to make sure
136 * that multiple threads/processes attempting to simultaneously create
137 * the region are properly ordered, so we open it using DB_CREATE and
138 * DB_EXCL, so two attempts to create the region will return failure in
139 * one.
140 */
141 if (infop->fd == -1 && infop->dbflags & DB_CREATE) {
142 flags = infop->dbflags;
143 LF_SET(DB_EXCL);
144 if ((ret = __db_open(infop->name,
145 flags, flags, infop->mode, &infop->fd)) == 0)
146 F_SET(infop, REGION_CREATED);
147 else
148 if (ret != EEXIST)
149 goto errmsg;
150 }
151
152 /* If we couldn't create the file, try and open it. */
153 if (infop->fd == -1) {
154 flags = infop->dbflags;
155 LF_CLR(DB_CREATE | DB_EXCL);
156 if ((ret = __db_open(infop->name,
157 flags, flags, infop->mode, &infop->fd)) != 0)
158 goto errmsg;
159 }
160
161 /*
162 * There are three cases we support:
163 * 1. Named anonymous memory (shmget(2)).
164 * 2. Unnamed anonymous memory (mmap(2): MAP_ANON/MAP_ANONYMOUS).
165 * 3. Memory backed by a regular file (mmap(2)).
166 *
167 * We instantiate a backing file in all cases, which contains at least
168 * the RLAYOUT structure, and in case #3, contains the actual region.
169 * This is necessary for a couple of reasons:
170 *
171 * First, the mpool region uses temporary files to name regions, and
172 * since you may have multiple regions in the same directory, we need
173 * a filesystem name to ensure that they don't collide.
174 *
175 * Second, applications are allowed to forcibly remove regions, even
176 * if they don't know anything about them other than the name. If a
177 * region is backed by anonymous memory, there has to be some way for
178 * the application to find out that information, and, in some cases,
179 * determine ID information for the anonymous memory.
180 */
181 if (F_ISSET(infop, REGION_CREATED)) {
182 /*
183 * If we're using anonymous memory to back this region, set
184 * the flag.
185 */
186 if (DB_GLOBAL(db_region_anon))
187 F_SET(infop, REGION_ANONYMOUS);
188
189 /*
190 * If we're using a regular file to back a region we created,
191 * grow it to the specified size.
192 */
193 if (!DB_GLOBAL(db_region_anon) &&
194 (ret = __db_growregion(infop, infop->size)) != 0)
195 goto err;
196 } else {
197 /*
198 * If we're joining a region, figure out what it looks like.
199 *
200 * XXX
201 * We have to figure out if the file is a regular file backing
202 * a region that we want to map into our address space, or a
203 * file with the information we need to find a shared anonymous
204 * region that we want to map into our address space.
205 *
206 * All this noise is because some systems don't have a coherent
207 * VM and buffer cache, and worse, if you mix operations on the
208 * VM and buffer cache, half the time you hang the system.
209 *
210 * There are two possibilities. If the file is the size of an
211 * RLAYOUT structure, then we know that the real region is in
212 * shared memory, because otherwise it would be bigger. (As
213 * the RLAYOUT structure size is smaller than a disk sector,
214 * the only way it can be this size is if deliberately written
215 * that way.) In which case, retrieve the information we need
216 * from the RLAYOUT structure and use it to acquire the shared
217 * memory.
218 *
219 * If the structure is larger than an RLAYOUT structure, then
220 * the file is backing the shared memory region, and we use
221 * the current size of the file without reading any information
222 * from the file itself so that we don't confuse the VM.
223 *
224 * And yes, this makes me want to take somebody and kill them,
225 * but I can't think of any other solution.
226 */
227 if ((ret = __os_ioinfo(infop->name,
228 infop->fd, &mbytes, &bytes, NULL)) != 0)
229 goto errmsg;
230 size = mbytes * MEGABYTE + bytes;
231
232 if (size <= sizeof(RLAYOUT)) {
233 /*
234 * If the size is too small, the read fails or the
235 * valid flag is incorrect, assume it's because the
236 * RLAYOUT information hasn't been written out yet,
237 * and retry.
238 */
239 if (size < sizeof(RLAYOUT))
240 goto retry;
241 if ((ret =
242 __os_read(infop->fd, &rl, sizeof(rl), &nr)) != 0)
243 goto retry;
244 if (rl.valid != DB_REGIONMAGIC)
245 goto retry;
246
247 /* Copy the size, memory id and characteristics. */
248 size = rl.size;
249 infop->segid = rl.segid;
250 if (F_ISSET(&rl, REGION_ANONYMOUS))
251 F_SET(infop, REGION_ANONYMOUS);
252 }
253
254 /*
255 * If the region is larger than we think, that's okay, use the
256 * current size. If it's smaller than we think, and we were
257 * just using the default size, that's okay, use the current
258 * size. If it's smaller than we think and we really care,
259 * save the size and we'll catch that further down -- we can't
260 * correct it here because we have to have a lock to grow the
261 * region.
262 */
263 if (infop->size > size && !F_ISSET(infop, REGION_SIZEDEF))
264 grow_region = infop->size;
265 infop->size = size;
266 }
267
268 /*
269 * Map the region into our address space. If we're creating it, the
270 * underlying routines will make it the right size.
271 *
272 * There are at least two cases where we can "reasonably" fail when
273 * we attempt to map in the region. On Windows/95, closing the last
274 * reference to a region causes it to be zeroed out. On UNIX, when
275 * using the shmget(2) interfaces, the region will no longer exist
276 * if the system was rebooted. In these cases, the underlying map call
277 * returns EAGAIN, and we *remove* our file and try again. There are
278 * obvious races in doing this, but it should eventually settle down
279 * to a winner and then things should proceed normally.
280 */
281 if ((ret = __db_mapregion(infop->name, infop)) != 0)
282 if (ret == EAGAIN) {
283 /*
284 * Pretend we created the region even if we didn't so
285 * that our error processing unlinks it.
286 */
287 F_SET(infop, REGION_CREATED);
288 ret = 0;
289 goto retry;
290 } else
291 goto err;
292
293 region_init:
294 /*
295 * Initialize the common region information.
296 *
297 * !!!
298 * We have to order the region creates so that two processes don't try
299 * to simultaneously create the region. This is handled by using the
300 * DB_CREATE and DB_EXCL flags when we create the "backing" region file.
301 *
302 * We also have to order region joins so that processes joining regions
303 * never see inconsistent data. We'd like to play permissions games
304 * with the backing file, but we can't because WNT filesystems won't
305 * open a file mode 0.
306 */
307 rlp = (RLAYOUT *)infop->addr;
308 if (F_ISSET(infop, REGION_CREATED)) {
309 /*
310 * The process creating the region acquires a lock before it
311 * sets the valid flag. Any processes joining the region will
312 * check the valid flag before acquiring the lock.
313 *
314 * Check the return of __db_mutex_init() and __db_mutex_lock(),
315 * even though we don't usually check elsewhere. This is the
316 * first lock we initialize and acquire, and we have to know if
317 * it fails. (It CAN fail, e.g., SunOS, when using fcntl(2)
318 * for locking, with an in-memory filesystem specified as the
319 * database home.)
320 */
321 if ((ret = __db_mutex_init(&rlp->lock,
322 MUTEX_LOCK_OFFSET(rlp, &rlp->lock))) != 0 ||
323 (ret = __db_mutex_lock(&rlp->lock, infop->fd)) != 0)
324 goto err;
325
326 /* Initialize the remaining region information. */
327 rlp->refcnt = 1;
328 rlp->size = infop->size;
329 db_version(&rlp->majver, &rlp->minver, &rlp->patch);
330 rlp->panic = 0;
331 rlp->segid = infop->segid;
332 rlp->flags = 0;
333 if (F_ISSET(infop, REGION_ANONYMOUS))
334 F_SET(rlp, REGION_ANONYMOUS);
335
336 /*
337 * Fill in the valid field last -- use a magic number, memory
338 * may not be zero-filled, and we want to minimize the chance
339 * for collision.
340 */
341 rlp->valid = DB_REGIONMAGIC;
342
343 /*
344 * If the region is anonymous, write the RLAYOUT information
345 * into the backing file so that future region join and unlink
346 * calls can find it.
347 *
348 * XXX
349 * We MUST do the seek before we do the write. On Win95, while
350 * closing the last reference to an anonymous shared region
351 * doesn't discard the region, it does zero it out. So, the
352 * REGION_CREATED may be set, but the file may have already
353 * been written and the file descriptor may be at the end of
354 * the file.
355 */
356 if (F_ISSET(infop, REGION_ANONYMOUS)) {
357 if ((ret = __os_seek(infop->fd, 0, 0, 0, 0, 0)) != 0)
358 goto err;
359 if ((ret =
360 __os_write(infop->fd, rlp, sizeof(*rlp), &nw)) != 0)
361 goto err;
362 }
363 } else {
364 /* Check to see if the region has had catastrophic failure. */
365 if (rlp->panic) {
366 ret = DB_RUNRECOVERY;
367 goto err;
368 }
369
370 /*
371 * Check the valid flag to ensure the region is initialized.
372 * If the valid flag has not been set, the mutex may not have
373 * been initialized, and an attempt to get it could lead to
374 * random behavior.
375 */
376 if (rlp->valid != DB_REGIONMAGIC)
377 goto retry;
378
379 /* Get the region lock. */
380 (void)__db_mutex_lock(&rlp->lock, infop->fd);
381
382 /*
383 * We now own the region. There are a couple of things that
384 * may have gone wrong, however.
385 *
386 * Problem #1: while we were waiting for the lock, the region
387 * was deleted. Detected by re-checking the valid flag, since
388 * it's cleared by the delete region routines.
389 */
390 if (rlp->valid != DB_REGIONMAGIC) {
391 (void)__db_mutex_unlock(&rlp->lock, infop->fd);
392 goto retry;
393 }
394
395 /*
396 * Problem #3: when we checked the size of the file, it was
397 * still growing as part of creation. Detected by the fact
398 * that infop->size isn't the same size as the region.
399 */
400 if (infop->size != rlp->size) {
401 (void)__db_mutex_unlock(&rlp->lock, infop->fd);
402 goto retry;
403 }
404
405 /* Increment the reference count. */
406 ++rlp->refcnt;
407 }
408
409 /* Return the region in a locked condition. */
410
411 if (0) {
412 errmsg: __db_err(infop->dbenv, "%s: %s", infop->name, strerror(ret));
413
414 err:
415 retry: /* Discard the region. */
416 if (infop->addr != NULL) {
417 (void)__db_unmapregion(infop);
418 infop->addr = NULL;
419 }
420
421 /* Discard the backing file. */
422 if (infop->fd != -1) {
423 (void)__os_close(infop->fd);
424 infop->fd = -1;
425
426 if (F_ISSET(infop, REGION_CREATED))
427 (void)__os_unlink(infop->name);
428 }
429
430 /* Discard the name. */
431 if (infop->name != NULL) {
432 __os_freestr(infop->name);
433 infop->name = NULL;
434 }
435
436 /*
437 * If we had a temporary error, wait a few seconds and
438 * try again.
439 */
440 if (ret == 0) {
441 if (++retry_cnt <= 3) {
442 __os_sleep(retry_cnt * 2, 0);
443 goto loop;
444 }
445 ret = EAGAIN;
446 }
447 }
448
449 /*
450 * XXX
451 * HP-UX won't permit mutexes to live in anything but shared memory.
452 * Instantiate a shared region file on that architecture, regardless.
453 *
454 * XXX
455 * There's a problem in cleaning this up on application exit, or on
456 * application failure. If an application opens a database without
457 * an environment, we create a temporary backing mpool region for it.
458 * That region is marked REGION_PRIVATE, but as HP-UX won't permit
459 * mutexes to live in anything but shared memory, we instantiate a
460 * real file plus a memory region of some form. If the application
461 * crashes, the necessary information to delete the backing file and
462 * any system region (e.g., the shmget(2) segment ID) is no longer
463 * available. We can't completely fix the problem, but we try.
464 *
465 * The underlying UNIX __db_mapregion() code preferentially uses the
466 * mmap(2) interface with the MAP_ANON/MAP_ANONYMOUS flags for regions
467 * that are marked REGION_PRIVATE. This means that we normally aren't
468 * holding any system resources when we get here, in which case we can
469 * delete the backing file. This results in a short race, from the
470 * __db_open() call above to here.
471 *
472 * If, for some reason, we are holding system resources when we get
473 * here, we don't have any choice -- we can't delete the backing file
474 * because we may need it to detach from the resources. Set the
475 * REGION_LASTDETACH flag, so that we do all necessary cleanup when
476 * the application closes the region.
477 */
478 if (F_ISSET(infop, REGION_PRIVATE) && !F_ISSET(infop, REGION_MALLOC))
479 if (F_ISSET(infop, REGION_HOLDINGSYS))
480 F_SET(infop, REGION_LASTDETACH);
481 else {
482 F_SET(infop, REGION_REMOVED);
483 F_CLR(infop, REGION_CANGROW);
484
485 (void)__os_close(infop->fd);
486 (void)__os_unlink(infop->name);
487 }
488
489 return (ret);
490 }
491
492 /*
493 * __db_rdetach --
494 * De-attach from a shared memory region.
495 *
496 * PUBLIC: int __db_rdetach __P((REGINFO *));
497 */
498 int
__db_rdetach(infop)499 __db_rdetach(infop)
500 REGINFO *infop;
501 {
502 RLAYOUT *rlp;
503 int detach, ret, t_ret;
504
505 ret = 0;
506
507 /*
508 * If the region was removed when it was created, no further action
509 * is required.
510 */
511 if (F_ISSET(infop, REGION_REMOVED))
512 goto done;
513 /*
514 * If the region was created in memory returned by malloc, the only
515 * action required is freeing the memory.
516 */
517 if (F_ISSET(infop, REGION_MALLOC)) {
518 __os_free(infop->addr, 0);
519 goto done;
520 }
521
522 /* Otherwise, attach to the region and optionally delete it. */
523 rlp = infop->addr;
524
525 /* Get the lock. */
526 (void)__db_mutex_lock(&rlp->lock, infop->fd);
527
528 /* Decrement the reference count. */
529 if (rlp->refcnt == 0)
530 __db_err(infop->dbenv,
531 "region rdetach: reference count went to zero!");
532 else
533 --rlp->refcnt;
534
535 /*
536 * If we're going to remove the region, clear the valid flag so
537 * that any region join that's blocked waiting for us will know
538 * what happened.
539 */
540 detach = 0;
541 if (F_ISSET(infop, REGION_LASTDETACH))
542 if (rlp->refcnt == 0) {
543 detach = 1;
544 rlp->valid = 0;
545 } else
546 ret = EBUSY;
547
548 /* Release the lock. */
549 (void)__db_mutex_unlock(&rlp->lock, infop->fd);
550
551 /* Close the backing file descriptor. */
552 (void)__os_close(infop->fd);
553 infop->fd = -1;
554
555 /* Discard our mapping of the region. */
556 if ((t_ret = __db_unmapregion(infop)) != 0 && ret == 0)
557 ret = t_ret;
558
559 /* Discard the region itself. */
560 if (detach) {
561 if ((t_ret =
562 __db_unlinkregion(infop->name, infop) != 0) && ret == 0)
563 ret = t_ret;
564 if ((t_ret = __os_unlink(infop->name) != 0) && ret == 0)
565 ret = t_ret;
566 }
567
568 done: /* Discard the name. */
569 if (infop->name != NULL) {
570 __os_freestr(infop->name);
571 infop->name = NULL;
572 }
573
574 return (ret);
575 }
576
577 /*
578 * __db_runlink --
579 * Remove a region.
580 *
581 * PUBLIC: int __db_runlink __P((REGINFO *, int));
582 */
583 int
__db_runlink(infop,force)584 __db_runlink(infop, force)
585 REGINFO *infop;
586 int force;
587 {
588 RLAYOUT rl, *rlp;
589 size_t size;
590 ssize_t nr;
591 u_int32_t mbytes, bytes;
592 int fd, ret, t_ret;
593 char *name;
594
595 /*
596 * XXX
597 * We assume that we've created a new REGINFO structure for this
598 * call, not used one that was already initialized. Regardless,
599 * if anyone is planning to use it after we're done, they're going
600 * to be sorely disappointed.
601 *
602 * If force isn't set, we attach to the region, set a flag to delete
603 * the region on last close, and let the region delete code do the
604 * work.
605 */
606 if (!force) {
607 if ((ret = __db_rattach(infop)) != 0)
608 return (ret);
609
610 rlp = (RLAYOUT *)infop->addr;
611 (void)__db_mutex_unlock(&rlp->lock, infop->fd);
612
613 F_SET(infop, REGION_LASTDETACH);
614
615 return (__db_rdetach(infop));
616 }
617
618 /*
619 * Otherwise, we don't want to attach to the region. We may have been
620 * called to clean up if a process died leaving a region locked and/or
621 * corrupted, which could cause the attach to hang.
622 */
623 if ((ret = __db_appname(infop->dbenv, infop->appname,
624 infop->path, infop->file, infop->dbflags, NULL, &name)) != 0)
625 return (ret);
626
627 /*
628 * An underlying file is created for all regions other than private
629 * (REGION_PRIVATE) ones, regardless of whether or not it's used to
630 * back the region. If that file doesn't exist, we're done.
631 */
632 if (__os_exists(name, NULL) != 0) {
633 __os_freestr(name);
634 return (0);
635 }
636
637 /*
638 * See the comments in __db_rattach -- figure out if this is a regular
639 * file backing a region or if it's a regular file with information
640 * about a region.
641 */
642 if ((ret = __db_open(name, DB_RDONLY, DB_RDONLY, 0, &fd)) != 0)
643 goto errmsg;
644 if ((ret = __os_ioinfo(name, fd, &mbytes, &bytes, NULL)) != 0)
645 goto errmsg;
646 size = mbytes * MEGABYTE + bytes;
647
648 if (size <= sizeof(RLAYOUT)) {
649 if ((ret = __os_read(fd, &rl, sizeof(rl), &nr)) != 0)
650 goto errmsg;
651 if (rl.valid != DB_REGIONMAGIC) {
652 __db_err(infop->dbenv,
653 "%s: illegal region magic number", name);
654 ret = EINVAL;
655 goto err;
656 }
657
658 /* Set the size, memory id and characteristics. */
659 infop->size = rl.size;
660 infop->segid = rl.segid;
661 if (F_ISSET(&rl, REGION_ANONYMOUS))
662 F_SET(infop, REGION_ANONYMOUS);
663 } else {
664 infop->size = size;
665 infop->segid = INVALID_SEGID;
666 }
667
668 /* Remove the underlying region. */
669 ret = __db_unlinkregion(name, infop);
670
671 /*
672 * Unlink the backing file. Close the open file descriptor first,
673 * because some architectures (e.g., Win32) won't unlink a file if
674 * open file descriptors remain.
675 */
676 (void)__os_close(fd);
677 if ((t_ret = __os_unlink(name)) != 0 && ret == 0)
678 ret = t_ret;
679
680 if (0) {
681 errmsg: __db_err(infop->dbenv, "%s: %s", name, strerror(ret));
682 err: (void)__os_close(fd);
683 }
684
685 __os_freestr(name);
686 return (ret);
687 }
688
689 /*
690 * __db_rgrow --
691 * Extend a region.
692 *
693 * PUBLIC: int __db_rgrow __P((REGINFO *, size_t));
694 */
695 int
__db_rgrow(infop,new_size)696 __db_rgrow(infop, new_size)
697 REGINFO *infop;
698 size_t new_size;
699 {
700 RLAYOUT *rlp;
701 size_t increment;
702 int ret;
703
704 /*
705 * !!!
706 * This routine MUST be called with the region already locked.
707 */
708
709 /* The underlying routines have flagged if this region can grow. */
710 if (!F_ISSET(infop, REGION_CANGROW))
711 return (EINVAL);
712
713 /*
714 * Round off the requested size to the next page boundary, and
715 * determine the additional space required.
716 */
717 rlp = (RLAYOUT *)infop->addr;
718 DB_ROUNDOFF(new_size, DB_VMPAGESIZE);
719 increment = new_size - rlp->size;
720
721 if ((ret = __db_growregion(infop, increment)) != 0)
722 return (ret);
723
724 /* Update the on-disk region size. */
725 rlp->size = new_size;
726
727 /* Detach from and reattach to the region. */
728 return (__db_rreattach(infop, new_size));
729 }
730
731 /*
732 * __db_growregion --
733 * Grow a shared memory region.
734 */
735 static int
__db_growregion(infop,increment)736 __db_growregion(infop, increment)
737 REGINFO *infop;
738 size_t increment;
739 {
740 db_pgno_t pages;
741 size_t i;
742 ssize_t nr, nw;
743 u_int32_t relative;
744 int ret;
745 char buf[DB_VMPAGESIZE];
746
747 /* Seek to the end of the region. */
748 if ((ret = __os_seek(infop->fd, 0, 0, 0, 0, SEEK_END)) != 0)
749 goto err;
750
751 /* Write nuls to the new bytes. */
752 memset(buf, 0, sizeof(buf));
753
754 /*
755 * Some systems require that all of the bytes of the region be
756 * written before it can be mapped and accessed randomly, and
757 * other systems don't zero out the pages.
758 */
759 if (__db_mapinit())
760 /* Extend the region by writing each new page. */
761 for (i = 0; i < increment; i += DB_VMPAGESIZE) {
762 if ((ret =
763 __os_write(infop->fd, buf, sizeof(buf), &nw)) != 0)
764 goto err;
765 if (nw != sizeof(buf))
766 goto eio;
767 }
768 else {
769 /*
770 * Extend the region by writing the last page. If the region
771 * is >4Gb, increment may be larger than the maximum possible
772 * seek "relative" argument, as it's an unsigned 32-bit value.
773 * Break the offset into pages of 1MB each so that we don't
774 * overflow (2^20 + 2^32 is bigger than any memory I expect
775 * to see for awhile).
776 */
777 pages = (increment - DB_VMPAGESIZE) / MEGABYTE;
778 relative = (increment - DB_VMPAGESIZE) % MEGABYTE;
779 if ((ret = __os_seek(infop->fd,
780 MEGABYTE, pages, relative, 0, SEEK_CUR)) != 0)
781 goto err;
782 if ((ret = __os_write(infop->fd, buf, sizeof(buf), &nw)) != 0)
783 goto err;
784 if (nw != sizeof(buf))
785 goto eio;
786
787 /*
788 * It's sometimes significantly faster to page-fault in all of
789 * the region's pages before we run the application, as we see
790 * nasty side-effects when we page-fault while holding various
791 * locks, i.e., the lock takes a long time to acquire because
792 * of the underlying page fault, and the other threads convoy
793 * behind the lock holder.
794 *
795 * We also use REGION_INIT to guarantee that there is enough
796 * disk space for the region, so we also write a byte to each
797 * page. Reading the byte is insufficient as some systems
798 * (e.g., Solaris) do not instantiate disk pages to satisfy
799 * a read, and so we don't know if there is enough disk space
800 * or not.
801 */
802 if (DB_GLOBAL(db_region_init)) {
803 pages = increment / MEGABYTE;
804 relative = increment % MEGABYTE;
805 if ((ret = __os_seek(infop->fd,
806 MEGABYTE, pages, relative, 1, SEEK_END)) != 0)
807 goto err;
808
809 /* Write a byte to each page. */
810 for (i = 0; i < increment; i += DB_VMPAGESIZE) {
811 if ((ret =
812 __os_write(infop->fd, buf, 1, &nr)) != 0)
813 goto err;
814 if (nr != 1)
815 goto eio;
816 if ((ret = __os_seek(infop->fd,
817 0, 0, DB_VMPAGESIZE - 1, 0, SEEK_CUR)) != 0)
818 goto err;
819 }
820 }
821 }
822 return (0);
823
824 eio: ret = EIO;
825 err: __db_err(infop->dbenv, "region grow: %s", strerror(ret));
826 return (ret);
827 }
828
829 /*
830 * __db_rreattach --
831 * Detach from and reattach to a region.
832 *
833 * PUBLIC: int __db_rreattach __P((REGINFO *, size_t));
834 */
835 int
__db_rreattach(infop,new_size)836 __db_rreattach(infop, new_size)
837 REGINFO *infop;
838 size_t new_size;
839 {
840 int ret;
841
842 #ifdef DIAGNOSTIC
843 if (infop->name == NULL) {
844 __db_err(infop->dbenv, "__db_rreattach: name was NULL");
845 return (EINVAL);
846 }
847 #endif
848 /*
849 * If we're growing an already mapped region, we have to unmap it
850 * and get it back. We have it locked, so nobody else can get in,
851 * which makes it fairly straight-forward to do, as everybody else
852 * is going to block while we do the unmap/remap. NB: if we fail
853 * to get it back, the pooch is genuinely screwed, because we can
854 * never release the lock we're holding.
855 *
856 * Detach from the region. We have to do this first so architectures
857 * that don't permit a file to be mapped into different places in the
858 * address space simultaneously, e.g., HP's PaRisc, will work.
859 */
860 if ((ret = __db_unmapregion(infop)) != 0)
861 return (ret);
862
863 /* Update the caller's REGINFO size to the new map size. */
864 infop->size = new_size;
865
866 /* Attach to the region. */
867 ret = __db_mapregion(infop->name, infop);
868
869 return (ret);
870 }
871