2 * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
3 * Copyright (C) 2006-2008 Red Hat GmbH
5 * This file is released under the GPL.
8 #include "dm-exception-store.h"
11 #include <linux/pagemap.h>
12 #include <linux/vmalloc.h>
13 #include <linux/export.h>
14 #include <linux/slab.h>
15 #include <linux/dm-io.h>
18 #define DM_MSG_PREFIX "persistent snapshot"
19 #define DM_CHUNK_SIZE_DEFAULT_SECTORS 32 /* 16KB */
21 #define DM_PREFETCH_CHUNKS 12
23 /*-----------------------------------------------------------------
24 * Persistent snapshots, by persistent we mean that the snapshot
25 * will survive a reboot.
26 *---------------------------------------------------------------*/
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.
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
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
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
53 * Magic for persistent snapshots: "SnAp" - Feeble isn't it.
55 #define SNAP_MAGIC 0x70416e53
58 * The on-disk version of the metadata.
60 #define SNAPSHOT_DISK_VERSION 1
62 #define NUM_SNAPSHOT_HDR_CHUNKS 1
68 * Is this snapshot valid. There is no way of recovering
69 * an invalid snapshot.
74 * Simple, incrementing version. no backward
83 struct disk_exception {
88 struct core_exception {
93 struct commit_callback {
94 void (*callback)(void *, int success);
99 * The top level structure for a persistent exception store.
102 struct dm_exception_store *store;
105 uint32_t exceptions_per_area;
108 * Now that we have an asynchronous kcopyd there is no
109 * need for large chunk sizes, so it wont hurt to have a
110 * whole chunks worth of metadata in memory at once.
115 * An area of zeros used to clear the next area.
120 * An area used for header. The header can be written
121 * concurrently with metadata (when invalidating the snapshot),
122 * so it needs a separate buffer.
127 * Used to keep track of which metadata area the data in
130 chunk_t current_area;
133 * The next free chunk for an exception.
135 * When creating exceptions, all the chunks here and above are
136 * free. It holds the next chunk to be allocated. On rare
137 * occasions (e.g. after a system crash) holes can be left in
138 * the exception store because chunks can be committed out of
141 * When merging exceptions, it does not necessarily mean all the
142 * chunks here and above are free. It holds the value it would
143 * have held if all chunks had been committed in order of
144 * allocation. Consequently the value may occasionally be
145 * slightly too low, but since it's only used for 'status' and
146 * it can never reach its minimum value too early this doesn't
153 * The index of next free exception in the current
156 uint32_t current_committed;
158 atomic_t pending_count;
159 uint32_t callback_count;
160 struct commit_callback *callbacks;
161 struct dm_io_client *io_client;
163 struct workqueue_struct *metadata_wq;
166 static int alloc_area(struct pstore *ps)
171 len = ps->store->chunk_size << SECTOR_SHIFT;
174 * Allocate the chunk_size block of memory that will hold
175 * a single metadata area.
177 ps->area = vmalloc(len);
181 ps->zero_area = vzalloc(len);
185 ps->header_area = vmalloc(len);
186 if (!ps->header_area)
187 goto err_header_area;
192 vfree(ps->zero_area);
201 static void free_area(struct pstore *ps)
208 vfree(ps->zero_area);
209 ps->zero_area = NULL;
212 vfree(ps->header_area);
213 ps->header_area = NULL;
217 struct dm_io_region *where;
218 struct dm_io_request *io_req;
219 struct work_struct work;
223 static void do_metadata(struct work_struct *work)
225 struct mdata_req *req = container_of(work, struct mdata_req, work);
227 req->result = dm_io(req->io_req, 1, req->where, NULL);
231 * Read or write a chunk aligned and sized block of data from a device.
233 static int chunk_io(struct pstore *ps, void *area, chunk_t chunk, int rw,
236 struct dm_io_region where = {
237 .bdev = dm_snap_cow(ps->store->snap)->bdev,
238 .sector = ps->store->chunk_size * chunk,
239 .count = ps->store->chunk_size,
241 struct dm_io_request io_req = {
243 .mem.type = DM_IO_VMA,
245 .client = ps->io_client,
248 struct mdata_req req;
251 return dm_io(&io_req, 1, &where, NULL);
254 req.io_req = &io_req;
257 * Issue the synchronous I/O from a different thread
258 * to avoid generic_make_request recursion.
260 INIT_WORK_ONSTACK(&req.work, do_metadata);
261 queue_work(ps->metadata_wq, &req.work);
262 flush_workqueue(ps->metadata_wq);
263 destroy_work_on_stack(&req.work);
269 * Convert a metadata area index to a chunk index.
271 static chunk_t area_location(struct pstore *ps, chunk_t area)
273 return NUM_SNAPSHOT_HDR_CHUNKS + ((ps->exceptions_per_area + 1) * area);
276 static void skip_metadata(struct pstore *ps)
278 uint32_t stride = ps->exceptions_per_area + 1;
279 chunk_t next_free = ps->next_free;
280 if (sector_div(next_free, stride) == NUM_SNAPSHOT_HDR_CHUNKS)
285 * Read or write a metadata area. Remembering to skip the first
286 * chunk which holds the header.
288 static int area_io(struct pstore *ps, int rw)
293 chunk = area_location(ps, ps->current_area);
295 r = chunk_io(ps, ps->area, chunk, rw, 0);
302 static void zero_memory_area(struct pstore *ps)
304 memset(ps->area, 0, ps->store->chunk_size << SECTOR_SHIFT);
307 static int zero_disk_area(struct pstore *ps, chunk_t area)
309 return chunk_io(ps, ps->zero_area, area_location(ps, area), WRITE, 0);
312 static int read_header(struct pstore *ps, int *new_snapshot)
315 struct disk_header *dh;
317 int chunk_size_supplied = 1;
321 * Use default chunk size (or logical_block_size, if larger)
324 if (!ps->store->chunk_size) {
325 ps->store->chunk_size = max(DM_CHUNK_SIZE_DEFAULT_SECTORS,
326 bdev_logical_block_size(dm_snap_cow(ps->store->snap)->
328 ps->store->chunk_mask = ps->store->chunk_size - 1;
329 ps->store->chunk_shift = ffs(ps->store->chunk_size) - 1;
330 chunk_size_supplied = 0;
333 ps->io_client = dm_io_client_create();
334 if (IS_ERR(ps->io_client))
335 return PTR_ERR(ps->io_client);
341 r = chunk_io(ps, ps->header_area, 0, READ, 1);
345 dh = ps->header_area;
347 if (le32_to_cpu(dh->magic) == 0) {
352 if (le32_to_cpu(dh->magic) != SNAP_MAGIC) {
353 DMWARN("Invalid or corrupt snapshot");
359 ps->valid = le32_to_cpu(dh->valid);
360 ps->version = le32_to_cpu(dh->version);
361 chunk_size = le32_to_cpu(dh->chunk_size);
363 if (ps->store->chunk_size == chunk_size)
366 if (chunk_size_supplied)
367 DMWARN("chunk size %u in device metadata overrides "
368 "table chunk size of %u.",
369 chunk_size, ps->store->chunk_size);
371 /* We had a bogus chunk_size. Fix stuff up. */
374 r = dm_exception_store_set_chunk_size(ps->store, chunk_size,
377 DMERR("invalid on-disk chunk size %u: %s.",
378 chunk_size, chunk_err);
390 static int write_header(struct pstore *ps)
392 struct disk_header *dh;
394 memset(ps->header_area, 0, ps->store->chunk_size << SECTOR_SHIFT);
396 dh = ps->header_area;
397 dh->magic = cpu_to_le32(SNAP_MAGIC);
398 dh->valid = cpu_to_le32(ps->valid);
399 dh->version = cpu_to_le32(ps->version);
400 dh->chunk_size = cpu_to_le32(ps->store->chunk_size);
402 return chunk_io(ps, ps->header_area, 0, WRITE, 1);
406 * Access functions for the disk exceptions, these do the endian conversions.
408 static struct disk_exception *get_exception(struct pstore *ps, void *ps_area,
411 BUG_ON(index >= ps->exceptions_per_area);
413 return ((struct disk_exception *) ps_area) + index;
416 static void read_exception(struct pstore *ps, void *ps_area,
417 uint32_t index, struct core_exception *result)
419 struct disk_exception *de = get_exception(ps, ps_area, index);
422 result->old_chunk = le64_to_cpu(de->old_chunk);
423 result->new_chunk = le64_to_cpu(de->new_chunk);
426 static void write_exception(struct pstore *ps,
427 uint32_t index, struct core_exception *e)
429 struct disk_exception *de = get_exception(ps, ps->area, index);
432 de->old_chunk = cpu_to_le64(e->old_chunk);
433 de->new_chunk = cpu_to_le64(e->new_chunk);
436 static void clear_exception(struct pstore *ps, uint32_t index)
438 struct disk_exception *de = get_exception(ps, ps->area, index);
446 * Registers the exceptions that are present in the current area.
447 * 'full' is filled in to indicate if the area has been
450 static int insert_exceptions(struct pstore *ps, void *ps_area,
451 int (*callback)(void *callback_context,
452 chunk_t old, chunk_t new),
453 void *callback_context,
458 struct core_exception e;
460 /* presume the area is full */
463 for (i = 0; i < ps->exceptions_per_area; i++) {
464 read_exception(ps, ps_area, i, &e);
467 * If the new_chunk is pointing at the start of
468 * the COW device, where the first metadata area
469 * is we know that we've hit the end of the
470 * exceptions. Therefore the area is not full.
472 if (e.new_chunk == 0LL) {
473 ps->current_committed = i;
479 * Keep track of the start of the free chunks.
481 if (ps->next_free <= e.new_chunk)
482 ps->next_free = e.new_chunk + 1;
485 * Otherwise we add the exception to the snapshot.
487 r = callback(callback_context, e.old_chunk, e.new_chunk);
495 static int read_exceptions(struct pstore *ps,
496 int (*callback)(void *callback_context, chunk_t old,
498 void *callback_context)
501 struct dm_bufio_client *client;
502 chunk_t prefetch_area = 0;
504 client = dm_bufio_client_create(dm_snap_cow(ps->store->snap)->bdev,
505 ps->store->chunk_size << SECTOR_SHIFT,
509 return PTR_ERR(client);
512 * Setup for one current buffer + desired readahead buffers.
514 dm_bufio_set_minimum_buffers(client, 1 + DM_PREFETCH_CHUNKS);
517 * Keeping reading chunks and inserting exceptions until
518 * we find a partially full area.
520 for (ps->current_area = 0; full; ps->current_area++) {
521 struct dm_buffer *bp;
525 if (unlikely(prefetch_area < ps->current_area))
526 prefetch_area = ps->current_area;
528 if (DM_PREFETCH_CHUNKS) do {
529 chunk_t pf_chunk = area_location(ps, prefetch_area);
530 if (unlikely(pf_chunk >= dm_bufio_get_device_size(client)))
532 dm_bufio_prefetch(client, pf_chunk, 1);
534 if (unlikely(!prefetch_area))
536 } while (prefetch_area <= ps->current_area + DM_PREFETCH_CHUNKS);
538 chunk = area_location(ps, ps->current_area);
540 area = dm_bufio_read(client, chunk, &bp);
541 if (unlikely(IS_ERR(area))) {
543 goto ret_destroy_bufio;
546 r = insert_exceptions(ps, area, callback, callback_context,
550 memcpy(ps->area, area, ps->store->chunk_size << SECTOR_SHIFT);
552 dm_bufio_release(bp);
554 dm_bufio_forget(client, chunk);
557 goto ret_destroy_bufio;
567 dm_bufio_client_destroy(client);
572 static struct pstore *get_info(struct dm_exception_store *store)
574 return (struct pstore *) store->context;
577 static void persistent_usage(struct dm_exception_store *store,
578 sector_t *total_sectors,
579 sector_t *sectors_allocated,
580 sector_t *metadata_sectors)
582 struct pstore *ps = get_info(store);
584 *sectors_allocated = ps->next_free * store->chunk_size;
585 *total_sectors = get_dev_size(dm_snap_cow(store->snap)->bdev);
588 * First chunk is the fixed header.
589 * Then there are (ps->current_area + 1) metadata chunks, each one
590 * separated from the next by ps->exceptions_per_area data chunks.
592 *metadata_sectors = (ps->current_area + 1 + NUM_SNAPSHOT_HDR_CHUNKS) *
596 static void persistent_dtr(struct dm_exception_store *store)
598 struct pstore *ps = get_info(store);
600 destroy_workqueue(ps->metadata_wq);
602 /* Created in read_header */
604 dm_io_client_destroy(ps->io_client);
607 /* Allocated in persistent_read_metadata */
609 vfree(ps->callbacks);
614 static int persistent_read_metadata(struct dm_exception_store *store,
615 int (*callback)(void *callback_context,
616 chunk_t old, chunk_t new),
617 void *callback_context)
619 int r, uninitialized_var(new_snapshot);
620 struct pstore *ps = get_info(store);
623 * Read the snapshot header.
625 r = read_header(ps, &new_snapshot);
630 * Now we know correct chunk_size, complete the initialisation.
632 ps->exceptions_per_area = (ps->store->chunk_size << SECTOR_SHIFT) /
633 sizeof(struct disk_exception);
634 ps->callbacks = dm_vcalloc(ps->exceptions_per_area,
635 sizeof(*ps->callbacks));
640 * Do we need to setup a new snapshot ?
643 r = write_header(ps);
645 DMWARN("write_header failed");
649 ps->current_area = 0;
650 zero_memory_area(ps);
651 r = zero_disk_area(ps, 0);
653 DMWARN("zero_disk_area(0) failed");
659 if (ps->version != SNAPSHOT_DISK_VERSION) {
660 DMWARN("unable to handle snapshot disk version %d",
666 * Metadata are valid, but snapshot is invalidated
674 r = read_exceptions(ps, callback, callback_context);
679 static int persistent_prepare_exception(struct dm_exception_store *store,
680 struct dm_exception *e)
682 struct pstore *ps = get_info(store);
683 sector_t size = get_dev_size(dm_snap_cow(store->snap)->bdev);
685 /* Is there enough room ? */
686 if (size < ((ps->next_free + 1) * store->chunk_size))
689 e->new_chunk = ps->next_free;
692 * Move onto the next free pending, making sure to take
693 * into account the location of the metadata chunks.
698 atomic_inc(&ps->pending_count);
702 static void persistent_commit_exception(struct dm_exception_store *store,
703 struct dm_exception *e,
704 void (*callback) (void *, int success),
705 void *callback_context)
708 struct pstore *ps = get_info(store);
709 struct core_exception ce;
710 struct commit_callback *cb;
712 ce.old_chunk = e->old_chunk;
713 ce.new_chunk = e->new_chunk;
714 write_exception(ps, ps->current_committed++, &ce);
717 * Add the callback to the back of the array. This code
718 * is the only place where the callback array is
719 * manipulated, and we know that it will never be called
720 * multiple times concurrently.
722 cb = ps->callbacks + ps->callback_count++;
723 cb->callback = callback;
724 cb->context = callback_context;
727 * If there are exceptions in flight and we have not yet
728 * filled this metadata area there's nothing more to do.
730 if (!atomic_dec_and_test(&ps->pending_count) &&
731 (ps->current_committed != ps->exceptions_per_area))
735 * If we completely filled the current area, then wipe the next one.
737 if ((ps->current_committed == ps->exceptions_per_area) &&
738 zero_disk_area(ps, ps->current_area + 1))
742 * Commit exceptions to disk.
744 if (ps->valid && area_io(ps, WRITE_FLUSH_FUA))
748 * Advance to the next area if this one is full.
750 if (ps->current_committed == ps->exceptions_per_area) {
751 ps->current_committed = 0;
753 zero_memory_area(ps);
756 for (i = 0; i < ps->callback_count; i++) {
757 cb = ps->callbacks + i;
758 cb->callback(cb->context, ps->valid);
761 ps->callback_count = 0;
764 static int persistent_prepare_merge(struct dm_exception_store *store,
765 chunk_t *last_old_chunk,
766 chunk_t *last_new_chunk)
768 struct pstore *ps = get_info(store);
769 struct core_exception ce;
774 * When current area is empty, move back to preceding area.
776 if (!ps->current_committed) {
780 if (!ps->current_area)
784 r = area_io(ps, READ);
787 ps->current_committed = ps->exceptions_per_area;
790 read_exception(ps, ps->area, ps->current_committed - 1, &ce);
791 *last_old_chunk = ce.old_chunk;
792 *last_new_chunk = ce.new_chunk;
795 * Find number of consecutive chunks within the current area,
798 for (nr_consecutive = 1; nr_consecutive < ps->current_committed;
800 read_exception(ps, ps->area,
801 ps->current_committed - 1 - nr_consecutive, &ce);
802 if (ce.old_chunk != *last_old_chunk - nr_consecutive ||
803 ce.new_chunk != *last_new_chunk - nr_consecutive)
807 return nr_consecutive;
810 static int persistent_commit_merge(struct dm_exception_store *store,
814 struct pstore *ps = get_info(store);
816 BUG_ON(nr_merged > ps->current_committed);
818 for (i = 0; i < nr_merged; i++)
819 clear_exception(ps, ps->current_committed - 1 - i);
821 r = area_io(ps, WRITE_FLUSH_FUA);
825 ps->current_committed -= nr_merged;
828 * At this stage, only persistent_usage() uses ps->next_free, so
829 * we make no attempt to keep ps->next_free strictly accurate
830 * as exceptions may have been committed out-of-order originally.
831 * Once a snapshot has become merging, we set it to the value it
832 * would have held had all the exceptions been committed in order.
834 * ps->current_area does not get reduced by prepare_merge() until
835 * after commit_merge() has removed the nr_merged previous exceptions.
837 ps->next_free = area_location(ps, ps->current_area) +
838 ps->current_committed + 1;
843 static void persistent_drop_snapshot(struct dm_exception_store *store)
845 struct pstore *ps = get_info(store);
848 if (write_header(ps))
849 DMWARN("write header failed");
852 static int persistent_ctr(struct dm_exception_store *store,
853 unsigned argc, char **argv)
857 /* allocate the pstore */
858 ps = kzalloc(sizeof(*ps), GFP_KERNEL);
864 ps->version = SNAPSHOT_DISK_VERSION;
866 ps->zero_area = NULL;
867 ps->header_area = NULL;
868 ps->next_free = NUM_SNAPSHOT_HDR_CHUNKS + 1; /* header and 1st area */
869 ps->current_committed = 0;
871 ps->callback_count = 0;
872 atomic_set(&ps->pending_count, 0);
873 ps->callbacks = NULL;
875 ps->metadata_wq = alloc_workqueue("ksnaphd", WQ_MEM_RECLAIM, 0);
876 if (!ps->metadata_wq) {
878 DMERR("couldn't start header metadata update thread");
887 static unsigned persistent_status(struct dm_exception_store *store,
888 status_type_t status, char *result,
894 case STATUSTYPE_INFO:
896 case STATUSTYPE_TABLE:
897 DMEMIT(" P %llu", (unsigned long long)store->chunk_size);
903 static struct dm_exception_store_type _persistent_type = {
904 .name = "persistent",
905 .module = THIS_MODULE,
906 .ctr = persistent_ctr,
907 .dtr = persistent_dtr,
908 .read_metadata = persistent_read_metadata,
909 .prepare_exception = persistent_prepare_exception,
910 .commit_exception = persistent_commit_exception,
911 .prepare_merge = persistent_prepare_merge,
912 .commit_merge = persistent_commit_merge,
913 .drop_snapshot = persistent_drop_snapshot,
914 .usage = persistent_usage,
915 .status = persistent_status,
918 static struct dm_exception_store_type _persistent_compat_type = {
920 .module = THIS_MODULE,
921 .ctr = persistent_ctr,
922 .dtr = persistent_dtr,
923 .read_metadata = persistent_read_metadata,
924 .prepare_exception = persistent_prepare_exception,
925 .commit_exception = persistent_commit_exception,
926 .prepare_merge = persistent_prepare_merge,
927 .commit_merge = persistent_commit_merge,
928 .drop_snapshot = persistent_drop_snapshot,
929 .usage = persistent_usage,
930 .status = persistent_status,
933 int dm_persistent_snapshot_init(void)
937 r = dm_exception_store_type_register(&_persistent_type);
939 DMERR("Unable to register persistent exception store type");
943 r = dm_exception_store_type_register(&_persistent_compat_type);
945 DMERR("Unable to register old-style persistent exception "
947 dm_exception_store_type_unregister(&_persistent_type);
954 void dm_persistent_snapshot_exit(void)
956 dm_exception_store_type_unregister(&_persistent_type);
957 dm_exception_store_type_unregister(&_persistent_compat_type);