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