Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * dsm_impl.c
4 : * manage dynamic shared memory segments
5 : *
6 : * This file provides low-level APIs for creating and destroying shared
7 : * memory segments using several different possible techniques. We refer
8 : * to these segments as dynamic because they can be created, altered, and
9 : * destroyed at any point during the server life cycle. This is unlike
10 : * the main shared memory segment, of which there is always exactly one
11 : * and which is always mapped at a fixed address in every PostgreSQL
12 : * background process.
13 : *
14 : * Because not all systems provide the same primitives in this area, nor
15 : * do all primitives behave the same way on all systems, we provide
16 : * several implementations of this facility. Many systems implement
17 : * POSIX shared memory (shm_open etc.), which is well-suited to our needs
18 : * in this area, with the exception that shared memory identifiers live
19 : * in a flat system-wide namespace, raising the uncomfortable prospect of
20 : * name collisions with other processes (including other copies of
21 : * PostgreSQL) running on the same system. Some systems only support
22 : * the older System V shared memory interface (shmget etc.) which is
23 : * also usable; however, the default allocation limits are often quite
24 : * small, and the namespace is even more restricted.
25 : *
26 : * We also provide an mmap-based shared memory implementation. This may
27 : * be useful on systems that provide shared memory via a special-purpose
28 : * filesystem; by opting for this implementation, the user can even
29 : * control precisely where their shared memory segments are placed. It
30 : * can also be used as a fallback for systems where shm_open and shmget
31 : * are not available or can't be used for some reason. Of course,
32 : * mapping a file residing on an actual spinning disk is a fairly poor
33 : * approximation for shared memory because writeback may hurt performance
34 : * substantially, but there should be few systems where we must make do
35 : * with such poor tools.
36 : *
37 : * As ever, Windows requires its own implementation.
38 : *
39 : * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
40 : * Portions Copyright (c) 1994, Regents of the University of California
41 : *
42 : *
43 : * IDENTIFICATION
44 : * src/backend/storage/ipc/dsm_impl.c
45 : *
46 : *-------------------------------------------------------------------------
47 : */
48 :
49 : #include "postgres.h"
50 : #include "miscadmin.h"
51 :
52 : #include <fcntl.h>
53 : #include <unistd.h>
54 : #ifndef WIN32
55 : #include <sys/mman.h>
56 : #endif
57 : #include <sys/stat.h>
58 : #ifdef HAVE_SYS_IPC_H
59 : #include <sys/ipc.h>
60 : #endif
61 : #ifdef HAVE_SYS_SHM_H
62 : #include <sys/shm.h>
63 : #endif
64 : #include "common/file_perm.h"
65 : #include "pgstat.h"
66 :
67 : #include "portability/mem.h"
68 : #include "storage/dsm_impl.h"
69 : #include "storage/fd.h"
70 : #include "utils/guc.h"
71 : #include "utils/memutils.h"
72 : #include "postmaster/postmaster.h"
73 :
74 : #ifdef USE_DSM_POSIX
75 : static bool dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
76 : void **impl_private, void **mapped_address,
77 : Size *mapped_size, int elevel);
78 : static int dsm_impl_posix_resize(int fd, off_t size);
79 : #endif
80 : #ifdef USE_DSM_SYSV
81 : static bool dsm_impl_sysv(dsm_op op, dsm_handle handle, Size request_size,
82 : void **impl_private, void **mapped_address,
83 : Size *mapped_size, int elevel);
84 : #endif
85 : #ifdef USE_DSM_WINDOWS
86 : static bool dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
87 : void **impl_private, void **mapped_address,
88 : Size *mapped_size, int elevel);
89 : #endif
90 : #ifdef USE_DSM_MMAP
91 : static bool dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
92 : void **impl_private, void **mapped_address,
93 : Size *mapped_size, int elevel);
94 : #endif
95 : static int errcode_for_dynamic_shared_memory(void);
96 :
97 : const struct config_enum_entry dynamic_shared_memory_options[] = {
98 : #ifdef USE_DSM_POSIX
99 : {"posix", DSM_IMPL_POSIX, false},
100 : #endif
101 : #ifdef USE_DSM_SYSV
102 : {"sysv", DSM_IMPL_SYSV, false},
103 : #endif
104 : #ifdef USE_DSM_WINDOWS
105 : {"windows", DSM_IMPL_WINDOWS, false},
106 : #endif
107 : #ifdef USE_DSM_MMAP
108 : {"mmap", DSM_IMPL_MMAP, false},
109 : #endif
110 : {NULL, 0, false}
111 : };
112 :
113 : /* Implementation selector. */
114 : int dynamic_shared_memory_type;
115 :
116 : /* Size of buffer to be used for zero-filling. */
117 : #define ZBUFFER_SIZE 8192
118 :
119 : #define SEGMENT_NAME_PREFIX "Global/PostgreSQL"
120 :
121 : /*------
122 : * Perform a low-level shared memory operation in a platform-specific way,
123 : * as dictated by the selected implementation. Each implementation is
124 : * required to implement the following primitives.
125 : *
126 : * DSM_OP_CREATE. Create a segment whose size is the request_size and
127 : * map it.
128 : *
129 : * DSM_OP_ATTACH. Map the segment, whose size must be the request_size.
130 : *
131 : * DSM_OP_DETACH. Unmap the segment.
132 : *
133 : * DSM_OP_DESTROY. Unmap the segment, if it is mapped. Destroy the
134 : * segment.
135 : *
136 : * Arguments:
137 : * op: The operation to be performed.
138 : * handle: The handle of an existing object, or for DSM_OP_CREATE, the
139 : * a new handle the caller wants created.
140 : * request_size: For DSM_OP_CREATE, the requested size. Otherwise, 0.
141 : * impl_private: Private, implementation-specific data. Will be a pointer
142 : * to NULL for the first operation on a shared memory segment within this
143 : * backend; thereafter, it will point to the value to which it was set
144 : * on the previous call.
145 : * mapped_address: Pointer to start of current mapping; pointer to NULL
146 : * if none. Updated with new mapping address.
147 : * mapped_size: Pointer to size of current mapping; pointer to 0 if none.
148 : * Updated with new mapped size.
149 : * elevel: Level at which to log errors.
150 : *
151 : * Return value: true on success, false on failure. When false is returned,
152 : * a message should first be logged at the specified elevel, except in the
153 : * case where DSM_OP_CREATE experiences a name collision, which should
154 : * silently return false.
155 : *-----
156 : */
157 : bool
158 13600 : dsm_impl_op(dsm_op op, dsm_handle handle, Size request_size,
159 : void **impl_private, void **mapped_address, Size *mapped_size,
160 : int elevel)
161 : {
162 : Assert(op == DSM_OP_CREATE || request_size == 0);
163 : Assert((op != DSM_OP_CREATE && op != DSM_OP_ATTACH) ||
164 : (*mapped_address == NULL && *mapped_size == 0));
165 :
166 13600 : switch (dynamic_shared_memory_type)
167 : {
168 : #ifdef USE_DSM_POSIX
169 : case DSM_IMPL_POSIX:
170 13600 : return dsm_impl_posix(op, handle, request_size, impl_private,
171 : mapped_address, mapped_size, elevel);
172 : #endif
173 : #ifdef USE_DSM_SYSV
174 : case DSM_IMPL_SYSV:
175 0 : return dsm_impl_sysv(op, handle, request_size, impl_private,
176 : mapped_address, mapped_size, elevel);
177 : #endif
178 : #ifdef USE_DSM_WINDOWS
179 : case DSM_IMPL_WINDOWS:
180 : return dsm_impl_windows(op, handle, request_size, impl_private,
181 : mapped_address, mapped_size, elevel);
182 : #endif
183 : #ifdef USE_DSM_MMAP
184 : case DSM_IMPL_MMAP:
185 0 : return dsm_impl_mmap(op, handle, request_size, impl_private,
186 : mapped_address, mapped_size, elevel);
187 : #endif
188 : default:
189 0 : elog(ERROR, "unexpected dynamic shared memory type: %d",
190 : dynamic_shared_memory_type);
191 : return false;
192 : }
193 : }
194 :
195 : #ifdef USE_DSM_POSIX
196 : /*
197 : * Operating system primitives to support POSIX shared memory.
198 : *
199 : * POSIX shared memory segments are created and attached using shm_open()
200 : * and shm_unlink(); other operations, such as sizing or mapping the
201 : * segment, are performed as if the shared memory segments were files.
202 : *
203 : * Indeed, on some platforms, they may be implemented that way. While
204 : * POSIX shared memory segments seem intended to exist in a flat namespace,
205 : * some operating systems may implement them as files, even going so far
206 : * to treat a request for /xyz as a request to create a file by that name
207 : * in the root directory. Users of such broken platforms should select
208 : * a different shared memory implementation.
209 : */
210 : static bool
211 13600 : dsm_impl_posix(dsm_op op, dsm_handle handle, Size request_size,
212 : void **impl_private, void **mapped_address, Size *mapped_size,
213 : int elevel)
214 : {
215 : char name[64];
216 : int flags;
217 : int fd;
218 : char *address;
219 :
220 13600 : snprintf(name, 64, "/PostgreSQL.%u", handle);
221 :
222 : /* Handle teardown cases. */
223 13600 : if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
224 : {
225 7414 : if (*mapped_address != NULL
226 6770 : && munmap(*mapped_address, *mapped_size) != 0)
227 : {
228 0 : ereport(elevel,
229 : (errcode_for_dynamic_shared_memory(),
230 : errmsg("could not unmap shared memory segment \"%s\": %m",
231 : name)));
232 0 : return false;
233 : }
234 7414 : *mapped_address = NULL;
235 7414 : *mapped_size = 0;
236 7414 : if (op == DSM_OP_DESTROY && shm_unlink(name) != 0)
237 : {
238 0 : ereport(elevel,
239 : (errcode_for_dynamic_shared_memory(),
240 : errmsg("could not remove shared memory segment \"%s\": %m",
241 : name)));
242 0 : return false;
243 : }
244 7414 : return true;
245 : }
246 :
247 : /*
248 : * Create new segment or open an existing one for attach.
249 : *
250 : * Even though we're not going through fd.c, we should be safe against
251 : * running out of file descriptors, because of NUM_RESERVED_FDS. We're
252 : * only opening one extra descriptor here, and we'll close it before
253 : * returning.
254 : */
255 6186 : flags = O_RDWR | (op == DSM_OP_CREATE ? O_CREAT | O_EXCL : 0);
256 6186 : if ((fd = shm_open(name, flags, PG_FILE_MODE_OWNER)) == -1)
257 : {
258 0 : if (errno != EEXIST)
259 0 : ereport(elevel,
260 : (errcode_for_dynamic_shared_memory(),
261 : errmsg("could not open shared memory segment \"%s\": %m",
262 : name)));
263 0 : return false;
264 : }
265 :
266 : /*
267 : * If we're attaching the segment, determine the current size; if we are
268 : * creating the segment, set the size to the requested value.
269 : */
270 6186 : if (op == DSM_OP_ATTACH)
271 : {
272 : struct stat st;
273 :
274 3694 : if (fstat(fd, &st) != 0)
275 : {
276 : int save_errno;
277 :
278 : /* Back out what's already been done. */
279 0 : save_errno = errno;
280 0 : close(fd);
281 0 : errno = save_errno;
282 :
283 0 : ereport(elevel,
284 : (errcode_for_dynamic_shared_memory(),
285 : errmsg("could not stat shared memory segment \"%s\": %m",
286 : name)));
287 0 : return false;
288 : }
289 3694 : request_size = st.st_size;
290 : }
291 2492 : else if (dsm_impl_posix_resize(fd, request_size) != 0)
292 : {
293 : int save_errno;
294 :
295 : /* Back out what's already been done. */
296 0 : save_errno = errno;
297 0 : close(fd);
298 0 : shm_unlink(name);
299 0 : errno = save_errno;
300 :
301 : /*
302 : * If we received a query cancel or termination signal, we will have
303 : * EINTR set here. If the caller said that errors are OK here, check
304 : * for interrupts immediately.
305 : */
306 0 : if (errno == EINTR && elevel >= ERROR)
307 0 : CHECK_FOR_INTERRUPTS();
308 :
309 0 : ereport(elevel,
310 : (errcode_for_dynamic_shared_memory(),
311 : errmsg("could not resize shared memory segment \"%s\" to %zu bytes: %m",
312 : name, request_size)));
313 0 : return false;
314 : }
315 :
316 : /* Map it. */
317 6186 : address = mmap(NULL, request_size, PROT_READ | PROT_WRITE,
318 : MAP_SHARED | MAP_HASSEMAPHORE | MAP_NOSYNC, fd, 0);
319 6186 : if (address == MAP_FAILED)
320 : {
321 : int save_errno;
322 :
323 : /* Back out what's already been done. */
324 0 : save_errno = errno;
325 0 : close(fd);
326 0 : if (op == DSM_OP_CREATE)
327 0 : shm_unlink(name);
328 0 : errno = save_errno;
329 :
330 0 : ereport(elevel,
331 : (errcode_for_dynamic_shared_memory(),
332 : errmsg("could not map shared memory segment \"%s\": %m",
333 : name)));
334 0 : return false;
335 : }
336 6186 : *mapped_address = address;
337 6186 : *mapped_size = request_size;
338 6186 : close(fd);
339 :
340 6186 : return true;
341 : }
342 :
343 : /*
344 : * Set the size of a virtual memory region associated with a file descriptor.
345 : * If necessary, also ensure that virtual memory is actually allocated by the
346 : * operating system, to avoid nasty surprises later.
347 : *
348 : * Returns non-zero if either truncation or allocation fails, and sets errno.
349 : */
350 : static int
351 2492 : dsm_impl_posix_resize(int fd, off_t size)
352 : {
353 : int rc;
354 :
355 : /* Truncate (or extend) the file to the requested size. */
356 2492 : rc = ftruncate(fd, size);
357 :
358 : /*
359 : * On Linux, a shm_open fd is backed by a tmpfs file. After resizing with
360 : * ftruncate, the file may contain a hole. Accessing memory backed by a
361 : * hole causes tmpfs to allocate pages, which fails with SIGBUS if there
362 : * is no more tmpfs space available. So we ask tmpfs to allocate pages
363 : * here, so we can fail gracefully with ENOSPC now rather than risking
364 : * SIGBUS later.
365 : */
366 : #if defined(HAVE_POSIX_FALLOCATE) && defined(__linux__)
367 2492 : if (rc == 0)
368 : {
369 : /*
370 : * We may get interrupted. If so, just retry unless there is an
371 : * interrupt pending. This avoids the possibility of looping forever
372 : * if another backend is repeatedly trying to interrupt us.
373 : */
374 : do
375 : {
376 2492 : rc = posix_fallocate(fd, 0, size);
377 2492 : } while (rc == EINTR && !(ProcDiePending || QueryCancelPending));
378 :
379 : /*
380 : * The caller expects errno to be set, but posix_fallocate() doesn't
381 : * set it. Instead it returns error numbers directly. So set errno,
382 : * even though we'll also return rc to indicate success or failure.
383 : */
384 2492 : errno = rc;
385 : }
386 : #endif /* HAVE_POSIX_FALLOCATE && __linux__ */
387 :
388 2492 : return rc;
389 : }
390 :
391 : #endif /* USE_DSM_POSIX */
392 :
393 : #ifdef USE_DSM_SYSV
394 : /*
395 : * Operating system primitives to support System V shared memory.
396 : *
397 : * System V shared memory segments are manipulated using shmget(), shmat(),
398 : * shmdt(), and shmctl(). As the default allocation limits for System V
399 : * shared memory are usually quite low, the POSIX facilities may be
400 : * preferable; but those are not supported everywhere.
401 : */
402 : static bool
403 0 : dsm_impl_sysv(dsm_op op, dsm_handle handle, Size request_size,
404 : void **impl_private, void **mapped_address, Size *mapped_size,
405 : int elevel)
406 : {
407 : key_t key;
408 : int ident;
409 : char *address;
410 : char name[64];
411 : int *ident_cache;
412 :
413 : /*
414 : * POSIX shared memory and mmap-based shared memory identify segments with
415 : * names. To avoid needless error message variation, we use the handle as
416 : * the name.
417 : */
418 0 : snprintf(name, 64, "%u", handle);
419 :
420 : /*
421 : * The System V shared memory namespace is very restricted; names are of
422 : * type key_t, which is expected to be some sort of integer data type, but
423 : * not necessarily the same one as dsm_handle. Since we use dsm_handle to
424 : * identify shared memory segments across processes, this might seem like
425 : * a problem, but it's really not. If dsm_handle is bigger than key_t,
426 : * the cast below might truncate away some bits from the handle the
427 : * user-provided, but it'll truncate exactly the same bits away in exactly
428 : * the same fashion every time we use that handle, which is all that
429 : * really matters. Conversely, if dsm_handle is smaller than key_t, we
430 : * won't use the full range of available key space, but that's no big deal
431 : * either.
432 : *
433 : * We do make sure that the key isn't negative, because that might not be
434 : * portable.
435 : */
436 0 : key = (key_t) handle;
437 0 : if (key < 1) /* avoid compiler warning if type is unsigned */
438 0 : key = -key;
439 :
440 : /*
441 : * There's one special key, IPC_PRIVATE, which can't be used. If we end
442 : * up with that value by chance during a create operation, just pretend it
443 : * already exists, so that caller will retry. If we run into it anywhere
444 : * else, the caller has passed a handle that doesn't correspond to
445 : * anything we ever created, which should not happen.
446 : */
447 0 : if (key == IPC_PRIVATE)
448 : {
449 0 : if (op != DSM_OP_CREATE)
450 0 : elog(DEBUG4, "System V shared memory key may not be IPC_PRIVATE");
451 0 : errno = EEXIST;
452 0 : return false;
453 : }
454 :
455 : /*
456 : * Before we can do anything with a shared memory segment, we have to map
457 : * the shared memory key to a shared memory identifier using shmget(). To
458 : * avoid repeated lookups, we store the key using impl_private.
459 : */
460 0 : if (*impl_private != NULL)
461 : {
462 0 : ident_cache = *impl_private;
463 0 : ident = *ident_cache;
464 : }
465 : else
466 : {
467 0 : int flags = IPCProtection;
468 : size_t segsize;
469 :
470 : /*
471 : * Allocate the memory BEFORE acquiring the resource, so that we don't
472 : * leak the resource if memory allocation fails.
473 : */
474 0 : ident_cache = MemoryContextAlloc(TopMemoryContext, sizeof(int));
475 :
476 : /*
477 : * When using shmget to find an existing segment, we must pass the
478 : * size as 0. Passing a non-zero size which is greater than the
479 : * actual size will result in EINVAL.
480 : */
481 0 : segsize = 0;
482 :
483 0 : if (op == DSM_OP_CREATE)
484 : {
485 0 : flags |= IPC_CREAT | IPC_EXCL;
486 0 : segsize = request_size;
487 : }
488 :
489 0 : if ((ident = shmget(key, segsize, flags)) == -1)
490 : {
491 0 : if (errno != EEXIST)
492 : {
493 0 : int save_errno = errno;
494 :
495 0 : pfree(ident_cache);
496 0 : errno = save_errno;
497 0 : ereport(elevel,
498 : (errcode_for_dynamic_shared_memory(),
499 : errmsg("could not get shared memory segment: %m")));
500 : }
501 0 : return false;
502 : }
503 :
504 0 : *ident_cache = ident;
505 0 : *impl_private = ident_cache;
506 : }
507 :
508 : /* Handle teardown cases. */
509 0 : if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
510 : {
511 0 : pfree(ident_cache);
512 0 : *impl_private = NULL;
513 0 : if (*mapped_address != NULL && shmdt(*mapped_address) != 0)
514 : {
515 0 : ereport(elevel,
516 : (errcode_for_dynamic_shared_memory(),
517 : errmsg("could not unmap shared memory segment \"%s\": %m",
518 : name)));
519 0 : return false;
520 : }
521 0 : *mapped_address = NULL;
522 0 : *mapped_size = 0;
523 0 : if (op == DSM_OP_DESTROY && shmctl(ident, IPC_RMID, NULL) < 0)
524 : {
525 0 : ereport(elevel,
526 : (errcode_for_dynamic_shared_memory(),
527 : errmsg("could not remove shared memory segment \"%s\": %m",
528 : name)));
529 0 : return false;
530 : }
531 0 : return true;
532 : }
533 :
534 : /* If we're attaching it, we must use IPC_STAT to determine the size. */
535 0 : if (op == DSM_OP_ATTACH)
536 : {
537 : struct shmid_ds shm;
538 :
539 0 : if (shmctl(ident, IPC_STAT, &shm) != 0)
540 : {
541 0 : ereport(elevel,
542 : (errcode_for_dynamic_shared_memory(),
543 : errmsg("could not stat shared memory segment \"%s\": %m",
544 : name)));
545 0 : return false;
546 : }
547 0 : request_size = shm.shm_segsz;
548 : }
549 :
550 : /* Map it. */
551 0 : address = shmat(ident, NULL, PG_SHMAT_FLAGS);
552 0 : if (address == (void *) -1)
553 : {
554 : int save_errno;
555 :
556 : /* Back out what's already been done. */
557 0 : save_errno = errno;
558 0 : if (op == DSM_OP_CREATE)
559 0 : shmctl(ident, IPC_RMID, NULL);
560 0 : errno = save_errno;
561 :
562 0 : ereport(elevel,
563 : (errcode_for_dynamic_shared_memory(),
564 : errmsg("could not map shared memory segment \"%s\": %m",
565 : name)));
566 0 : return false;
567 : }
568 0 : *mapped_address = address;
569 0 : *mapped_size = request_size;
570 :
571 0 : return true;
572 : }
573 : #endif
574 :
575 : #ifdef USE_DSM_WINDOWS
576 : /*
577 : * Operating system primitives to support Windows shared memory.
578 : *
579 : * Windows shared memory implementation is done using file mapping
580 : * which can be backed by either physical file or system paging file.
581 : * Current implementation uses system paging file as other effects
582 : * like performance are not clear for physical file and it is used in similar
583 : * way for main shared memory in windows.
584 : *
585 : * A memory mapping object is a kernel object - they always get deleted when
586 : * the last reference to them goes away, either explicitly via a CloseHandle or
587 : * when the process containing the reference exits.
588 : */
589 : static bool
590 : dsm_impl_windows(dsm_op op, dsm_handle handle, Size request_size,
591 : void **impl_private, void **mapped_address,
592 : Size *mapped_size, int elevel)
593 : {
594 : char *address;
595 : HANDLE hmap;
596 : char name[64];
597 : MEMORY_BASIC_INFORMATION info;
598 :
599 : /*
600 : * Storing the shared memory segment in the Global\ namespace, can allow
601 : * any process running in any session to access that file mapping object
602 : * provided that the caller has the required access rights. But to avoid
603 : * issues faced in main shared memory, we are using the naming convention
604 : * similar to main shared memory. We can change here once issue mentioned
605 : * in GetSharedMemName is resolved.
606 : */
607 : snprintf(name, 64, "%s.%u", SEGMENT_NAME_PREFIX, handle);
608 :
609 : /*
610 : * Handle teardown cases. Since Windows automatically destroys the object
611 : * when no references remain, we can treat it the same as detach.
612 : */
613 : if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
614 : {
615 : if (*mapped_address != NULL
616 : && UnmapViewOfFile(*mapped_address) == 0)
617 : {
618 : _dosmaperr(GetLastError());
619 : ereport(elevel,
620 : (errcode_for_dynamic_shared_memory(),
621 : errmsg("could not unmap shared memory segment \"%s\": %m",
622 : name)));
623 : return false;
624 : }
625 : if (*impl_private != NULL
626 : && CloseHandle(*impl_private) == 0)
627 : {
628 : _dosmaperr(GetLastError());
629 : ereport(elevel,
630 : (errcode_for_dynamic_shared_memory(),
631 : errmsg("could not remove shared memory segment \"%s\": %m",
632 : name)));
633 : return false;
634 : }
635 :
636 : *impl_private = NULL;
637 : *mapped_address = NULL;
638 : *mapped_size = 0;
639 : return true;
640 : }
641 :
642 : /* Create new segment or open an existing one for attach. */
643 : if (op == DSM_OP_CREATE)
644 : {
645 : DWORD size_high;
646 : DWORD size_low;
647 : DWORD errcode;
648 :
649 : /* Shifts >= the width of the type are undefined. */
650 : #ifdef _WIN64
651 : size_high = request_size >> 32;
652 : #else
653 : size_high = 0;
654 : #endif
655 : size_low = (DWORD) request_size;
656 :
657 : /* CreateFileMapping might not clear the error code on success */
658 : SetLastError(0);
659 :
660 : hmap = CreateFileMapping(INVALID_HANDLE_VALUE, /* Use the pagefile */
661 : NULL, /* Default security attrs */
662 : PAGE_READWRITE, /* Memory is read/write */
663 : size_high, /* Upper 32 bits of size */
664 : size_low, /* Lower 32 bits of size */
665 : name);
666 :
667 : errcode = GetLastError();
668 : if (errcode == ERROR_ALREADY_EXISTS || errcode == ERROR_ACCESS_DENIED)
669 : {
670 : /*
671 : * On Windows, when the segment already exists, a handle for the
672 : * existing segment is returned. We must close it before
673 : * returning. However, if the existing segment is created by a
674 : * service, then it returns ERROR_ACCESS_DENIED. We don't do
675 : * _dosmaperr here, so errno won't be modified.
676 : */
677 : if (hmap)
678 : CloseHandle(hmap);
679 : return false;
680 : }
681 :
682 : if (!hmap)
683 : {
684 : _dosmaperr(errcode);
685 : ereport(elevel,
686 : (errcode_for_dynamic_shared_memory(),
687 : errmsg("could not create shared memory segment \"%s\": %m",
688 : name)));
689 : return false;
690 : }
691 : }
692 : else
693 : {
694 : hmap = OpenFileMapping(FILE_MAP_WRITE | FILE_MAP_READ,
695 : FALSE, /* do not inherit the name */
696 : name); /* name of mapping object */
697 : if (!hmap)
698 : {
699 : _dosmaperr(GetLastError());
700 : ereport(elevel,
701 : (errcode_for_dynamic_shared_memory(),
702 : errmsg("could not open shared memory segment \"%s\": %m",
703 : name)));
704 : return false;
705 : }
706 : }
707 :
708 : /* Map it. */
709 : address = MapViewOfFile(hmap, FILE_MAP_WRITE | FILE_MAP_READ,
710 : 0, 0, 0);
711 : if (!address)
712 : {
713 : int save_errno;
714 :
715 : _dosmaperr(GetLastError());
716 : /* Back out what's already been done. */
717 : save_errno = errno;
718 : CloseHandle(hmap);
719 : errno = save_errno;
720 :
721 : ereport(elevel,
722 : (errcode_for_dynamic_shared_memory(),
723 : errmsg("could not map shared memory segment \"%s\": %m",
724 : name)));
725 : return false;
726 : }
727 :
728 : /*
729 : * VirtualQuery gives size in page_size units, which is 4K for Windows. We
730 : * need size only when we are attaching, but it's better to get the size
731 : * when creating new segment to keep size consistent both for
732 : * DSM_OP_CREATE and DSM_OP_ATTACH.
733 : */
734 : if (VirtualQuery(address, &info, sizeof(info)) == 0)
735 : {
736 : int save_errno;
737 :
738 : _dosmaperr(GetLastError());
739 : /* Back out what's already been done. */
740 : save_errno = errno;
741 : UnmapViewOfFile(address);
742 : CloseHandle(hmap);
743 : errno = save_errno;
744 :
745 : ereport(elevel,
746 : (errcode_for_dynamic_shared_memory(),
747 : errmsg("could not stat shared memory segment \"%s\": %m",
748 : name)));
749 : return false;
750 : }
751 :
752 : *mapped_address = address;
753 : *mapped_size = info.RegionSize;
754 : *impl_private = hmap;
755 :
756 : return true;
757 : }
758 : #endif
759 :
760 : #ifdef USE_DSM_MMAP
761 : /*
762 : * Operating system primitives to support mmap-based shared memory.
763 : *
764 : * Calling this "shared memory" is somewhat of a misnomer, because what
765 : * we're really doing is creating a bunch of files and mapping them into
766 : * our address space. The operating system may feel obliged to
767 : * synchronize the contents to disk even if nothing is being paged out,
768 : * which will not serve us well. The user can relocate the pg_dynshmem
769 : * directory to a ramdisk to avoid this problem, if available.
770 : */
771 : static bool
772 0 : dsm_impl_mmap(dsm_op op, dsm_handle handle, Size request_size,
773 : void **impl_private, void **mapped_address, Size *mapped_size,
774 : int elevel)
775 : {
776 : char name[64];
777 : int flags;
778 : int fd;
779 : char *address;
780 :
781 0 : snprintf(name, 64, PG_DYNSHMEM_DIR "/" PG_DYNSHMEM_MMAP_FILE_PREFIX "%u",
782 : handle);
783 :
784 : /* Handle teardown cases. */
785 0 : if (op == DSM_OP_DETACH || op == DSM_OP_DESTROY)
786 : {
787 0 : if (*mapped_address != NULL
788 0 : && munmap(*mapped_address, *mapped_size) != 0)
789 : {
790 0 : ereport(elevel,
791 : (errcode_for_dynamic_shared_memory(),
792 : errmsg("could not unmap shared memory segment \"%s\": %m",
793 : name)));
794 0 : return false;
795 : }
796 0 : *mapped_address = NULL;
797 0 : *mapped_size = 0;
798 0 : if (op == DSM_OP_DESTROY && unlink(name) != 0)
799 : {
800 0 : ereport(elevel,
801 : (errcode_for_dynamic_shared_memory(),
802 : errmsg("could not remove shared memory segment \"%s\": %m",
803 : name)));
804 0 : return false;
805 : }
806 0 : return true;
807 : }
808 :
809 : /* Create new segment or open an existing one for attach. */
810 0 : flags = O_RDWR | (op == DSM_OP_CREATE ? O_CREAT | O_EXCL : 0);
811 0 : if ((fd = OpenTransientFile(name, flags)) == -1)
812 : {
813 0 : if (errno != EEXIST)
814 0 : ereport(elevel,
815 : (errcode_for_dynamic_shared_memory(),
816 : errmsg("could not open shared memory segment \"%s\": %m",
817 : name)));
818 0 : return false;
819 : }
820 :
821 : /*
822 : * If we're attaching the segment, determine the current size; if we are
823 : * creating the segment, set the size to the requested value.
824 : */
825 0 : if (op == DSM_OP_ATTACH)
826 : {
827 : struct stat st;
828 :
829 0 : if (fstat(fd, &st) != 0)
830 : {
831 : int save_errno;
832 :
833 : /* Back out what's already been done. */
834 0 : save_errno = errno;
835 0 : CloseTransientFile(fd);
836 0 : errno = save_errno;
837 :
838 0 : ereport(elevel,
839 : (errcode_for_dynamic_shared_memory(),
840 : errmsg("could not stat shared memory segment \"%s\": %m",
841 : name)));
842 0 : return false;
843 : }
844 0 : request_size = st.st_size;
845 : }
846 : else
847 : {
848 : /*
849 : * Allocate a buffer full of zeros.
850 : *
851 : * Note: palloc zbuffer, instead of just using a local char array, to
852 : * ensure it is reasonably well-aligned; this may save a few cycles
853 : * transferring data to the kernel.
854 : */
855 0 : char *zbuffer = (char *) palloc0(ZBUFFER_SIZE);
856 0 : uint32 remaining = request_size;
857 0 : bool success = true;
858 :
859 : /*
860 : * Zero-fill the file. We have to do this the hard way to ensure that
861 : * all the file space has really been allocated, so that we don't
862 : * later seg fault when accessing the memory mapping. This is pretty
863 : * pessimal.
864 : */
865 0 : while (success && remaining > 0)
866 : {
867 0 : Size goal = remaining;
868 :
869 0 : if (goal > ZBUFFER_SIZE)
870 0 : goal = ZBUFFER_SIZE;
871 0 : pgstat_report_wait_start(WAIT_EVENT_DSM_FILL_ZERO_WRITE);
872 0 : if (write(fd, zbuffer, goal) == goal)
873 0 : remaining -= goal;
874 : else
875 0 : success = false;
876 0 : pgstat_report_wait_end();
877 : }
878 :
879 0 : if (!success)
880 : {
881 : int save_errno;
882 :
883 : /* Back out what's already been done. */
884 0 : save_errno = errno;
885 0 : CloseTransientFile(fd);
886 0 : unlink(name);
887 0 : errno = save_errno ? save_errno : ENOSPC;
888 :
889 0 : ereport(elevel,
890 : (errcode_for_dynamic_shared_memory(),
891 : errmsg("could not resize shared memory segment \"%s\" to %zu bytes: %m",
892 : name, request_size)));
893 0 : return false;
894 : }
895 : }
896 :
897 : /* Map it. */
898 0 : address = mmap(NULL, request_size, PROT_READ | PROT_WRITE,
899 : MAP_SHARED | MAP_HASSEMAPHORE | MAP_NOSYNC, fd, 0);
900 0 : if (address == MAP_FAILED)
901 : {
902 : int save_errno;
903 :
904 : /* Back out what's already been done. */
905 0 : save_errno = errno;
906 0 : CloseTransientFile(fd);
907 0 : if (op == DSM_OP_CREATE)
908 0 : unlink(name);
909 0 : errno = save_errno;
910 :
911 0 : ereport(elevel,
912 : (errcode_for_dynamic_shared_memory(),
913 : errmsg("could not map shared memory segment \"%s\": %m",
914 : name)));
915 0 : return false;
916 : }
917 0 : *mapped_address = address;
918 0 : *mapped_size = request_size;
919 :
920 0 : if (CloseTransientFile(fd))
921 : {
922 0 : ereport(elevel,
923 : (errcode_for_file_access(),
924 : errmsg("could not close shared memory segment \"%s\": %m",
925 : name)));
926 0 : return false;
927 : }
928 :
929 0 : return true;
930 : }
931 : #endif
932 :
933 : /*
934 : * Implementation-specific actions that must be performed when a segment is to
935 : * be preserved even when no backend has it attached.
936 : *
937 : * Except on Windows, we don't need to do anything at all. But since Windows
938 : * cleans up segments automatically when no references remain, we duplicate
939 : * the segment handle into the postmaster process. The postmaster needn't
940 : * do anything to receive the handle; Windows transfers it automatically.
941 : */
942 : void
943 108 : dsm_impl_pin_segment(dsm_handle handle, void *impl_private,
944 : void **impl_private_pm_handle)
945 : {
946 108 : switch (dynamic_shared_memory_type)
947 : {
948 : #ifdef USE_DSM_WINDOWS
949 : case DSM_IMPL_WINDOWS:
950 : {
951 : HANDLE hmap;
952 :
953 : if (!DuplicateHandle(GetCurrentProcess(), impl_private,
954 : PostmasterHandle, &hmap, 0, FALSE,
955 : DUPLICATE_SAME_ACCESS))
956 : {
957 : char name[64];
958 :
959 : snprintf(name, 64, "%s.%u", SEGMENT_NAME_PREFIX, handle);
960 : _dosmaperr(GetLastError());
961 : ereport(ERROR,
962 : (errcode_for_dynamic_shared_memory(),
963 : errmsg("could not duplicate handle for \"%s\": %m",
964 : name)));
965 : }
966 :
967 : /*
968 : * Here, we remember the handle that we created in the
969 : * postmaster process. This handle isn't actually usable in
970 : * any process other than the postmaster, but that doesn't
971 : * matter. We're just holding onto it so that, if the segment
972 : * is unpinned, dsm_impl_unpin_segment can close it.
973 : */
974 : *impl_private_pm_handle = hmap;
975 : break;
976 : }
977 : #endif
978 : default:
979 108 : break;
980 : }
981 108 : }
982 :
983 : /*
984 : * Implementation-specific actions that must be performed when a segment is no
985 : * longer to be preserved, so that it will be cleaned up when all backends
986 : * have detached from it.
987 : *
988 : * Except on Windows, we don't need to do anything at all. For Windows, we
989 : * close the extra handle that dsm_impl_pin_segment created in the
990 : * postmaster's process space.
991 : */
992 : void
993 108 : dsm_impl_unpin_segment(dsm_handle handle, void **impl_private)
994 : {
995 108 : switch (dynamic_shared_memory_type)
996 : {
997 : #ifdef USE_DSM_WINDOWS
998 : case DSM_IMPL_WINDOWS:
999 : {
1000 : if (*impl_private &&
1001 : !DuplicateHandle(PostmasterHandle, *impl_private,
1002 : NULL, NULL, 0, FALSE,
1003 : DUPLICATE_CLOSE_SOURCE))
1004 : {
1005 : char name[64];
1006 :
1007 : snprintf(name, 64, "%s.%u", SEGMENT_NAME_PREFIX, handle);
1008 : _dosmaperr(GetLastError());
1009 : ereport(ERROR,
1010 : (errcode_for_dynamic_shared_memory(),
1011 : errmsg("could not duplicate handle for \"%s\": %m",
1012 : name)));
1013 : }
1014 :
1015 : *impl_private = NULL;
1016 : break;
1017 : }
1018 : #endif
1019 : default:
1020 108 : break;
1021 : }
1022 108 : }
1023 :
1024 : static int
1025 0 : errcode_for_dynamic_shared_memory(void)
1026 : {
1027 0 : if (errno == EFBIG || errno == ENOMEM)
1028 0 : return errcode(ERRCODE_OUT_OF_MEMORY);
1029 : else
1030 0 : return errcode_for_file_access();
1031 : }
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