1 /*
2 * dm-exception-store.c
3 *
4 * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
5 * Copyright (C) 2006 Red Hat GmbH
6 *
7 * This file is released under the GPL.
8 */
9
10 #include "dm.h"
11 #include "dm-snap.h"
12 #include "dm-io.h"
13 #include "kcopyd.h"
14
15 #include <linux/mm.h>
16 #include <linux/pagemap.h>
17 #include <linux/vmalloc.h>
18 #include <linux/slab.h>
19
20 #define DM_MSG_PREFIX "snapshots"
21 #define DM_CHUNK_SIZE_DEFAULT_SECTORS 32 /* 16KB */
22
23 /*-----------------------------------------------------------------
24 * Persistent snapshots, by persistent we mean that the snapshot
25 * will survive a reboot.
26 *---------------------------------------------------------------*/
27
28 /*
29 * We need to store a record of which parts of the origin have
30 * been copied to the snapshot device. The snapshot code
31 * requires that we copy exception chunks to chunk aligned areas
32 * of the COW store. It makes sense therefore, to store the
33 * metadata in chunk size blocks.
34 *
35 * There is no backward or forward compatibility implemented,
36 * snapshots with different disk versions than the kernel will
37 * not be usable. It is expected that "lvcreate" will blank out
38 * the start of a fresh COW device before calling the snapshot
39 * constructor.
40 *
41 * The first chunk of the COW device just contains the header.
42 * After this there is a chunk filled with exception metadata,
43 * followed by as many exception chunks as can fit in the
44 * metadata areas.
45 *
46 * All on disk structures are in little-endian format. The end
47 * of the exceptions info is indicated by an exception with a
48 * new_chunk of 0, which is invalid since it would point to the
49 * header chunk.
50 */
51
52 /*
53 * Magic for persistent snapshots: "SnAp" - Feeble isn't it.
54 */
55 #define SNAP_MAGIC 0x70416e53
56
57 /*
58 * The on-disk version of the metadata.
59 */
60 #define SNAPSHOT_DISK_VERSION 1
61
62 struct disk_header {
63 uint32_t magic;
64
65 /*
66 * Is this snapshot valid. There is no way of recovering
67 * an invalid snapshot.
68 */
69 uint32_t valid;
70
71 /*
72 * Simple, incrementing version. no backward
73 * compatibility.
74 */
75 uint32_t version;
76
77 /* In sectors */
78 uint32_t chunk_size;
79 };
80
81 struct disk_exception {
82 uint64_t old_chunk;
83 uint64_t new_chunk;
84 };
85
86 struct commit_callback {
87 void (*callback)(void *, int success);
88 void *context;
89 };
90
91 /*
92 * The top level structure for a persistent exception store.
93 */
94 struct pstore {
95 struct dm_snapshot *snap; /* up pointer to my snapshot */
96 int version;
97 int valid;
98 uint32_t exceptions_per_area;
99
100 /*
101 * Now that we have an asynchronous kcopyd there is no
102 * need for large chunk sizes, so it wont hurt to have a
103 * whole chunks worth of metadata in memory at once.
104 */
105 void *area;
106
107 /*
108 * Used to keep track of which metadata area the data in
109 * 'chunk' refers to.
110 */
111 uint32_t current_area;
112
113 /*
114 * The next free chunk for an exception.
115 */
116 uint32_t next_free;
117
118 /*
119 * The index of next free exception in the current
120 * metadata area.
121 */
122 uint32_t current_committed;
123
124 atomic_t pending_count;
125 uint32_t callback_count;
126 struct commit_callback *callbacks;
127 struct dm_io_client *io_client;
128
129 struct workqueue_struct *metadata_wq;
130 };
131
132 static unsigned sectors_to_pages(unsigned sectors)
133 {
134 return DIV_ROUND_UP(sectors, PAGE_SIZE >> 9);
135 }
136
137 static int alloc_area(struct pstore *ps)
138 {
139 int r = -ENOMEM;
140 size_t len;
141
142 len = ps->snap->chunk_size << SECTOR_SHIFT;
143
144 /*
145 * Allocate the chunk_size block of memory that will hold
146 * a single metadata area.
147 */
148 ps->area = vmalloc(len);
149 if (!ps->area)
150 return r;
151
152 return 0;
153 }
154
155 static void free_area(struct pstore *ps)
156 {
157 vfree(ps->area);
158 ps->area = NULL;
159 }
160
161 struct mdata_req {
162 struct io_region *where;
163 struct dm_io_request *io_req;
164 struct work_struct work;
165 int result;
166 };
167
168 static void do_metadata(struct work_struct *work)
169 {
170 struct mdata_req *req = container_of(work, struct mdata_req, work);
171
172 req->result = dm_io(req->io_req, 1, req->where, NULL);
173 }
174
175 /*
176 * Read or write a chunk aligned and sized block of data from a device.
177 */
178 static int chunk_io(struct pstore *ps, uint32_t chunk, int rw, int metadata)
179 {
180 struct io_region where = {
181 .bdev = ps->snap->cow->bdev,
182 .sector = ps->snap->chunk_size * chunk,
183 .count = ps->snap->chunk_size,
184 };
185 struct dm_io_request io_req = {
186 .bi_rw = rw,
187 .mem.type = DM_IO_VMA,
188 .mem.ptr.vma = ps->area,
189 .client = ps->io_client,
190 .notify.fn = NULL,
191 };
192 struct mdata_req req;
193
194 if (!metadata)
195 return dm_io(&io_req, 1, &where, NULL);
196
197 req.where = &where;
198 req.io_req = &io_req;
199
200 /*
201 * Issue the synchronous I/O from a different thread
202 * to avoid generic_make_request recursion.
203 */
204 INIT_WORK(&req.work, do_metadata);
205 queue_work(ps->metadata_wq, &req.work);
206 flush_workqueue(ps->metadata_wq);
207
208 return req.result;
209 }
210
211 /*
212 * Read or write a metadata area. Remembering to skip the first
213 * chunk which holds the header.
214 */
215 static int area_io(struct pstore *ps, uint32_t area, int rw)
216 {
217 int r;
218 uint32_t chunk;
219
220 /* convert a metadata area index to a chunk index */
221 chunk = 1 + ((ps->exceptions_per_area + 1) * area);
222
223 r = chunk_io(ps, chunk, rw, 0);
224 if (r)
225 return r;
226
227 ps->current_area = area;
228 return 0;
229 }
230
231 static int zero_area(struct pstore *ps, uint32_t area)
232 {
233 memset(ps->area, 0, ps->snap->chunk_size << SECTOR_SHIFT);
234 return area_io(ps, area, WRITE);
235 }
236
237 static int read_header(struct pstore *ps, int *new_snapshot)
238 {
239 int r;
240 struct disk_header *dh;
241 chunk_t chunk_size;
242 int chunk_size_supplied = 1;
243
244 /*
245 * Use default chunk size (or hardsect_size, if larger) if none supplied
246 */
247 if (!ps->snap->chunk_size) {
248 ps->snap->chunk_size = max(DM_CHUNK_SIZE_DEFAULT_SECTORS,
249 bdev_hardsect_size(ps->snap->cow->bdev) >> 9);
250 ps->snap->chunk_mask = ps->snap->chunk_size - 1;
251 ps->snap->chunk_shift = ffs(ps->snap->chunk_size) - 1;
252 chunk_size_supplied = 0;
253 }
254
255 ps->io_client = dm_io_client_create(sectors_to_pages(ps->snap->
256 chunk_size));
257 if (IS_ERR(ps->io_client))
258 return PTR_ERR(ps->io_client);
259
260 r = alloc_area(ps);
261 if (r)
262 return r;
263
264 r = chunk_io(ps, 0, READ, 1);
265 if (r)
266 goto bad;
267
268 dh = (struct disk_header *) ps->area;
269
270 if (le32_to_cpu(dh->magic) == 0) {
271 *new_snapshot = 1;
272 return 0;
273 }
274
275 if (le32_to_cpu(dh->magic) != SNAP_MAGIC) {
276 DMWARN("Invalid or corrupt snapshot");
277 r = -ENXIO;
278 goto bad;
279 }
280
281 *new_snapshot = 0;
282 ps->valid = le32_to_cpu(dh->valid);
283 ps->version = le32_to_cpu(dh->version);
284 chunk_size = le32_to_cpu(dh->chunk_size);
285
286 if (!chunk_size_supplied || ps->snap->chunk_size == chunk_size)
287 return 0;
288
289 DMWARN("chunk size %llu in device metadata overrides "
290 "table chunk size of %llu.",
291 (unsigned long long)chunk_size,
292 (unsigned long long)ps->snap->chunk_size);
293
294 /* We had a bogus chunk_size. Fix stuff up. */
295 free_area(ps);
296
297 ps->snap->chunk_size = chunk_size;
298 ps->snap->chunk_mask = chunk_size - 1;
299 ps->snap->chunk_shift = ffs(chunk_size) - 1;
300
301 r = dm_io_client_resize(sectors_to_pages(ps->snap->chunk_size),
302 ps->io_client);
303 if (r)
304 return r;
305
306 r = alloc_area(ps);
307 return r;
308
309 bad:
310 free_area(ps);
311 return r;
312 }
313
314 static int write_header(struct pstore *ps)
315 {
316 struct disk_header *dh;
317
318 memset(ps->area, 0, ps->snap->chunk_size << SECTOR_SHIFT);
319
320 dh = (struct disk_header *) ps->area;
321 dh->magic = cpu_to_le32(SNAP_MAGIC);
322 dh->valid = cpu_to_le32(ps->valid);
323 dh->version = cpu_to_le32(ps->version);
324 dh->chunk_size = cpu_to_le32(ps->snap->chunk_size);
325
326 return chunk_io(ps, 0, WRITE, 1);
327 }
328
329 /*
330 * Access functions for the disk exceptions, these do the endian conversions.
331 */
332 static struct disk_exception *get_exception(struct pstore *ps, uint32_t index)
333 {
334 BUG_ON(index >= ps->exceptions_per_area);
335
336 return ((struct disk_exception *) ps->area) + index;
337 }
338
339 static void read_exception(struct pstore *ps,
340 uint32_t index, struct disk_exception *result)
341 {
342 struct disk_exception *e = get_exception(ps, index);
343
344 /* copy it */
345 result->old_chunk = le64_to_cpu(e->old_chunk);
346 result->new_chunk = le64_to_cpu(e->new_chunk);
347 }
348
349 static void write_exception(struct pstore *ps,
350 uint32_t index, struct disk_exception *de)
351 {
352 struct disk_exception *e = get_exception(ps, index);
353
354 /* copy it */
355 e->old_chunk = cpu_to_le64(de->old_chunk);
356 e->new_chunk = cpu_to_le64(de->new_chunk);
357 }
358
359 /*
360 * Registers the exceptions that are present in the current area.
361 * 'full' is filled in to indicate if the area has been
362 * filled.
363 */
364 static int insert_exceptions(struct pstore *ps, int *full)
365 {
366 int r;
367 unsigned int i;
368 struct disk_exception de;
369
370 /* presume the area is full */
371 *full = 1;
372
373 for (i = 0; i < ps->exceptions_per_area; i++) {
374 read_exception(ps, i, &de);
375
376 /*
377 * If the new_chunk is pointing at the start of
378 * the COW device, where the first metadata area
379 * is we know that we've hit the end of the
380 * exceptions. Therefore the area is not full.
381 */
382 if (de.new_chunk == 0LL) {
383 ps->current_committed = i;
384 *full = 0;
385 break;
386 }
387
388 /*
389 * Keep track of the start of the free chunks.
390 */
391 if (ps->next_free <= de.new_chunk)
392 ps->next_free = de.new_chunk + 1;
393
394 /*
395 * Otherwise we add the exception to the snapshot.
396 */
397 r = dm_add_exception(ps->snap, de.old_chunk, de.new_chunk);
398 if (r)
399 return r;
400 }
401
402 return 0;
403 }
404
405 static int read_exceptions(struct pstore *ps)
406 {
407 uint32_t area;
408 int r, full = 1;
409
410 /*
411 * Keeping reading chunks and inserting exceptions until
412 * we find a partially full area.
413 */
414 for (area = 0; full; area++) {
415 r = area_io(ps, area, READ);
416 if (r)
417 return r;
418
419 r = insert_exceptions(ps, &full);
420 if (r)
421 return r;
422 }
423
424 return 0;
425 }
426
427 static struct pstore *get_info(struct exception_store *store)
428 {
429 return (struct pstore *) store->context;
430 }
431
432 static void persistent_fraction_full(struct exception_store *store,
433 sector_t *numerator, sector_t *denominator)
434 {
435 *numerator = get_info(store)->next_free * store->snap->chunk_size;
436 *denominator = get_dev_size(store->snap->cow->bdev);
437 }
438
439 static void persistent_destroy(struct exception_store *store)
440 {
441 struct pstore *ps = get_info(store);
442
443 destroy_workqueue(ps->metadata_wq);
444 dm_io_client_destroy(ps->io_client);
445 vfree(ps->callbacks);
446 free_area(ps);
447 kfree(ps);
448 }
449
450 static int persistent_read_metadata(struct exception_store *store)
451 {
452 int r, uninitialized_var(new_snapshot);
453 struct pstore *ps = get_info(store);
454
455 /*
456 * Read the snapshot header.
457 */
458 r = read_header(ps, &new_snapshot);
459 if (r)
460 return r;
461
462 /*
463 * Now we know correct chunk_size, complete the initialisation.
464 */
465 ps->exceptions_per_area = (ps->snap->chunk_size << SECTOR_SHIFT) /
466 sizeof(struct disk_exception);
467 ps->callbacks = dm_vcalloc(ps->exceptions_per_area,
468 sizeof(*ps->callbacks));
469 if (!ps->callbacks)
470 return -ENOMEM;
471
472 /*
473 * Do we need to setup a new snapshot ?
474 */
475 if (new_snapshot) {
476 r = write_header(ps);
477 if (r) {
478 DMWARN("write_header failed");
479 return r;
480 }
481
482 r = zero_area(ps, 0);
483 if (r) {
484 DMWARN("zero_area(0) failed");
485 return r;
486 }
487
488 } else {
489 /*
490 * Sanity checks.
491 */
492 if (ps->version != SNAPSHOT_DISK_VERSION) {
493 DMWARN("unable to handle snapshot disk version %d",
494 ps->version);
495 return -EINVAL;
496 }
497
498 /*
499 * Metadata are valid, but snapshot is invalidated
500 */
501 if (!ps->valid)
502 return 1;
503
504 /*
505 * Read the metadata.
506 */
507 r = read_exceptions(ps);
508 if (r)
509 return r;
510 }
511
512 return 0;
513 }
514
515 static int persistent_prepare(struct exception_store *store,
516 struct dm_snap_exception *e)
517 {
518 struct pstore *ps = get_info(store);
519 uint32_t stride;
520 sector_t size = get_dev_size(store->snap->cow->bdev);
521
522 /* Is there enough room ? */
523 if (size < ((ps->next_free + 1) * store->snap->chunk_size))
524 return -ENOSPC;
525
526 e->new_chunk = ps->next_free;
527
528 /*
529 * Move onto the next free pending, making sure to take
530 * into account the location of the metadata chunks.
531 */
532 stride = (ps->exceptions_per_area + 1);
533 if ((++ps->next_free % stride) == 1)
534 ps->next_free++;
535
536 atomic_inc(&ps->pending_count);
537 return 0;
538 }
539
540 static void persistent_commit(struct exception_store *store,
541 struct dm_snap_exception *e,
542 void (*callback) (void *, int success),
543 void *callback_context)
544 {
545 int r;
546 unsigned int i;
547 struct pstore *ps = get_info(store);
548 struct disk_exception de;
549 struct commit_callback *cb;
550
551 de.old_chunk = e->old_chunk;
552 de.new_chunk = e->new_chunk;
553 write_exception(ps, ps->current_committed++, &de);
554
555 /*
556 * Add the callback to the back of the array. This code
557 * is the only place where the callback array is
558 * manipulated, and we know that it will never be called
559 * multiple times concurrently.
560 */
561 cb = ps->callbacks + ps->callback_count++;
562 cb->callback = callback;
563 cb->context = callback_context;
564
565 /*
566 * If there are no more exceptions in flight, or we have
567 * filled this metadata area we commit the exceptions to
568 * disk.
569 */
570 if (atomic_dec_and_test(&ps->pending_count) ||
571 (ps->current_committed == ps->exceptions_per_area)) {
572 r = area_io(ps, ps->current_area, WRITE);
573 if (r)
574 ps->valid = 0;
575
576 /*
577 * Have we completely filled the current area ?
578 */
579 if (ps->current_committed == ps->exceptions_per_area) {
580 ps->current_committed = 0;
581 r = zero_area(ps, ps->current_area + 1);
582 if (r)
583 ps->valid = 0;
584 }
585
586 for (i = 0; i < ps->callback_count; i++) {
587 cb = ps->callbacks + i;
588 cb->callback(cb->context, r == 0 ? 1 : 0);
589 }
590
591 ps->callback_count = 0;
592 }
593 }
594
595 static void persistent_drop(struct exception_store *store)
596 {
597 struct pstore *ps = get_info(store);
598
599 ps->valid = 0;
600 if (write_header(ps))
601 DMWARN("write header failed");
602 }
603
604 int dm_create_persistent(struct exception_store *store)
605 {
606 struct pstore *ps;
607
608 /* allocate the pstore */
609 ps = kmalloc(sizeof(*ps), GFP_KERNEL);
610 if (!ps)
611 return -ENOMEM;
612
613 ps->snap = store->snap;
614 ps->valid = 1;
615 ps->version = SNAPSHOT_DISK_VERSION;
616 ps->area = NULL;
617 ps->next_free = 2; /* skipping the header and first area */
618 ps->current_committed = 0;
619
620 ps->callback_count = 0;
621 atomic_set(&ps->pending_count, 0);
622 ps->callbacks = NULL;
623
624 ps->metadata_wq = create_singlethread_workqueue("ksnaphd");
625 if (!ps->metadata_wq) {
626 kfree(ps);
627 DMERR("couldn't start header metadata update thread");
628 return -ENOMEM;
629 }
630
631 store->destroy = persistent_destroy;
632 store->read_metadata = persistent_read_metadata;
633 store->prepare_exception = persistent_prepare;
634 store->commit_exception = persistent_commit;
635 store->drop_snapshot = persistent_drop;
636 store->fraction_full = persistent_fraction_full;
637 store->context = ps;
638
639 return 0;
640 }
641
642 /*-----------------------------------------------------------------
643 * Implementation of the store for non-persistent snapshots.
644 *---------------------------------------------------------------*/
645 struct transient_c {
646 sector_t next_free;
647 };
648
649 static void transient_destroy(struct exception_store *store)
650 {
651 kfree(store->context);
652 }
653
654 static int transient_read_metadata(struct exception_store *store)
655 {
656 return 0;
657 }
658
659 static int transient_prepare(struct exception_store *store,
660 struct dm_snap_exception *e)
661 {
662 struct transient_c *tc = (struct transient_c *) store->context;
663 sector_t size = get_dev_size(store->snap->cow->bdev);
664
665 if (size < (tc->next_free + store->snap->chunk_size))
666 return -1;
667
668 e->new_chunk = sector_to_chunk(store->snap, tc->next_free);
669 tc->next_free += store->snap->chunk_size;
670
671 return 0;
672 }
673
674 static void transient_commit(struct exception_store *store,
675 struct dm_snap_exception *e,
676 void (*callback) (void *, int success),
677 void *callback_context)
678 {
679 /* Just succeed */
680 callback(callback_context, 1);
681 }
682
683 static void transient_fraction_full(struct exception_store *store,
684 sector_t *numerator, sector_t *denominator)
685 {
686 *numerator = ((struct transient_c *) store->context)->next_free;
687 *denominator = get_dev_size(store->snap->cow->bdev);
688 }
689
690 int dm_create_transient(struct exception_store *store)
691 {
692 struct transient_c *tc;
693
694 store->destroy = transient_destroy;
695 store->read_metadata = transient_read_metadata;
696 store->prepare_exception = transient_prepare;
697 store->commit_exception = transient_commit;
698 store->drop_snapshot = NULL;
699 store->fraction_full = transient_fraction_full;
700
701 tc = kmalloc(sizeof(struct transient_c), GFP_KERNEL);
702 if (!tc)
703 return -ENOMEM;
704
705 tc->next_free = 0;
706 store->context = tc;
707
708 return 0;
709 }
710
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