1/*
2 * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
3 * Copyright (C) 2008 Red Hat, Inc. All rights reserved.
4 *
5 * Device-mapper snapshot exception store.
6 *
7 * This file is released under the GPL.
8 */
9
10#ifndef _LINUX_DM_EXCEPTION_STORE
11#define _LINUX_DM_EXCEPTION_STORE
12
13#include <linux/blkdev.h>
14#include <linux/list_bl.h>
15#include <linux/device-mapper.h>
16
17/*
18 * The snapshot code deals with largish chunks of the disk at a
19 * time. Typically 32k - 512k.
20 */
21typedef sector_t chunk_t;
22
23/*
24 * An exception is used where an old chunk of data has been
25 * replaced by a new one.
26 * If chunk_t is 64 bits in size, the top 8 bits of new_chunk hold the number
27 * of chunks that follow contiguously.  Remaining bits hold the number of the
28 * chunk within the device.
29 */
30struct dm_exception {
31	struct hlist_bl_node hash_list;
32
33	chunk_t old_chunk;
34	chunk_t new_chunk;
35};
36
37/*
38 * Abstraction to handle the meta/layout of exception stores (the
39 * COW device).
40 */
41struct dm_exception_store;
42struct dm_exception_store_type {
43	const char *name;
44	struct module *module;
45
46	int (*ctr) (struct dm_exception_store *store, char *options);
47
48	/*
49	 * Destroys this object when you've finished with it.
50	 */
51	void (*dtr) (struct dm_exception_store *store);
52
53	/*
54	 * The target shouldn't read the COW device until this is
55	 * called.  As exceptions are read from the COW, they are
56	 * reported back via the callback.
57	 */
58	int (*read_metadata) (struct dm_exception_store *store,
59			      int (*callback)(void *callback_context,
60					      chunk_t old, chunk_t new),
61			      void *callback_context);
62
63	/*
64	 * Find somewhere to store the next exception.
65	 */
66	int (*prepare_exception) (struct dm_exception_store *store,
67				  struct dm_exception *e);
68
69	/*
70	 * Update the metadata with this exception.
71	 */
72	void (*commit_exception) (struct dm_exception_store *store,
73				  struct dm_exception *e, int valid,
74				  void (*callback) (void *, int success),
75				  void *callback_context);
76
77	/*
78	 * Returns 0 if the exception store is empty.
79	 *
80	 * If there are exceptions still to be merged, sets
81	 * *last_old_chunk and *last_new_chunk to the most recent
82	 * still-to-be-merged chunk and returns the number of
83	 * consecutive previous ones.
84	 */
85	int (*prepare_merge) (struct dm_exception_store *store,
86			      chunk_t *last_old_chunk, chunk_t *last_new_chunk);
87
88	/*
89	 * Clear the last n exceptions.
90	 * nr_merged must be <= the value returned by prepare_merge.
91	 */
92	int (*commit_merge) (struct dm_exception_store *store, int nr_merged);
93
94	/*
95	 * The snapshot is invalid, note this in the metadata.
96	 */
97	void (*drop_snapshot) (struct dm_exception_store *store);
98
99	unsigned (*status) (struct dm_exception_store *store,
100			    status_type_t status, char *result,
101			    unsigned maxlen);
102
103	/*
104	 * Return how full the snapshot is.
105	 */
106	void (*usage) (struct dm_exception_store *store,
107		       sector_t *total_sectors, sector_t *sectors_allocated,
108		       sector_t *metadata_sectors);
109
110	/* For internal device-mapper use only. */
111	struct list_head list;
112};
113
114struct dm_snapshot;
115
116struct dm_exception_store {
117	struct dm_exception_store_type *type;
118	struct dm_snapshot *snap;
119
120	/* Size of data blocks saved - must be a power of 2 */
121	unsigned chunk_size;
122	unsigned chunk_mask;
123	unsigned chunk_shift;
124
125	void *context;
126
127	bool userspace_supports_overflow;
128};
129
130/*
131 * Obtain the origin or cow device used by a given snapshot.
132 */
133struct dm_dev *dm_snap_origin(struct dm_snapshot *snap);
134struct dm_dev *dm_snap_cow(struct dm_snapshot *snap);
135
136/*
137 * Funtions to manipulate consecutive chunks
138 */
139#define DM_CHUNK_CONSECUTIVE_BITS 8
140#define DM_CHUNK_NUMBER_BITS 56
141
142static inline chunk_t dm_chunk_number(chunk_t chunk)
143{
144	return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL);
145}
146
147static inline unsigned dm_consecutive_chunk_count(struct dm_exception *e)
148{
149	return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
150}
151
152static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
153{
154	e->new_chunk += (1ULL << DM_CHUNK_NUMBER_BITS);
155
156	BUG_ON(!dm_consecutive_chunk_count(e));
157}
158
159static inline void dm_consecutive_chunk_count_dec(struct dm_exception *e)
160{
161	BUG_ON(!dm_consecutive_chunk_count(e));
162
163	e->new_chunk -= (1ULL << DM_CHUNK_NUMBER_BITS);
164}
165
166/*
167 * Return the number of sectors in the device.
168 */
169static inline sector_t get_dev_size(struct block_device *bdev)
170{
171	return i_size_read(bdev->bd_inode) >> SECTOR_SHIFT;
172}
173
174static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
175				      sector_t sector)
176{
177	return sector >> store->chunk_shift;
178}
179
180int dm_exception_store_type_register(struct dm_exception_store_type *type);
181int dm_exception_store_type_unregister(struct dm_exception_store_type *type);
182
183int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
184				      unsigned chunk_size,
185				      char **error);
186
187int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
188			      struct dm_snapshot *snap,
189			      unsigned *args_used,
190			      struct dm_exception_store **store);
191void dm_exception_store_destroy(struct dm_exception_store *store);
192
193int dm_exception_store_init(void);
194void dm_exception_store_exit(void);
195
196/*
197 * Two exception store implementations.
198 */
199int dm_persistent_snapshot_init(void);
200void dm_persistent_snapshot_exit(void);
201
202int dm_transient_snapshot_init(void);
203void dm_transient_snapshot_exit(void);
204
205#endif /* _LINUX_DM_EXCEPTION_STORE */
206