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/device-mapper.h>
15
16/*
17 * The snapshot code deals with largish chunks of the disk at a
18 * time. Typically 32k - 512k.
19 */
20typedef sector_t chunk_t;
21
22/*
23 * An exception is used where an old chunk of data has been
24 * replaced by a new one.
25 * If chunk_t is 64 bits in size, the top 8 bits of new_chunk hold the number
26 * of chunks that follow contiguously. Remaining bits hold the number of the
27 * chunk within the device.
28 */
29struct dm_exception {
30 struct list_head hash_list;
31
32 chunk_t old_chunk;
33 chunk_t new_chunk;
34};
35
36/*
37 * Abstraction to handle the meta/layout of exception stores (the
38 * COW device).
39 */
40struct dm_exception_store;
41struct dm_exception_store_type {
42 const char *name;
43 struct module *module;
44
45 int (*ctr) (struct dm_exception_store *store, char *options);
46
47 /*
48 * Destroys this object when you've finished with it.
49 */
50 void (*dtr) (struct dm_exception_store *store);
51
52 /*
53 * The target shouldn't read the COW device until this is
54 * called. As exceptions are read from the COW, they are
55 * reported back via the callback.
56 */
57 int (*read_metadata) (struct dm_exception_store *store,
58 int (*callback)(void *callback_context,
59 chunk_t old, chunk_t new),
60 void *callback_context);
61
62 /*
63 * Find somewhere to store the next exception.
64 */
65 int (*prepare_exception) (struct dm_exception_store *store,
66 struct dm_exception *e);
67
68 /*
69 * Update the metadata with this exception.
70 */
71 void (*commit_exception) (struct dm_exception_store *store,
72 struct dm_exception *e, int valid,
73 void (*callback) (void *, int success),
74 void *callback_context);
75
76 /*
77 * Returns 0 if the exception store is empty.
78 *
79 * If there are exceptions still to be merged, sets
80 * *last_old_chunk and *last_new_chunk to the most recent
81 * still-to-be-merged chunk and returns the number of
82 * consecutive previous ones.
83 */
84 int (*prepare_merge) (struct dm_exception_store *store,
85 chunk_t *last_old_chunk, chunk_t *last_new_chunk);
86
87 /*
88 * Clear the last n exceptions.
89 * nr_merged must be <= the value returned by prepare_merge.
90 */
91 int (*commit_merge) (struct dm_exception_store *store, int nr_merged);
92
93 /*
94 * The snapshot is invalid, note this in the metadata.
95 */
96 void (*drop_snapshot) (struct dm_exception_store *store);
97
98 unsigned (*status) (struct dm_exception_store *store,
99 status_type_t status, char *result,
100 unsigned maxlen);
101
102 /*
103 * Return how full the snapshot is.
104 */
105 void (*usage) (struct dm_exception_store *store,
106 sector_t *total_sectors, sector_t *sectors_allocated,
107 sector_t *metadata_sectors);
108
109 /* For internal device-mapper use only. */
110 struct list_head list;
111};
112
113struct dm_snapshot;
114
115struct dm_exception_store {
116 struct dm_exception_store_type *type;
117 struct dm_snapshot *snap;
118
119 /* Size of data blocks saved - must be a power of 2 */
120 unsigned chunk_size;
121 unsigned chunk_mask;
122 unsigned chunk_shift;
123
124 void *context;
125
126 bool userspace_supports_overflow;
127};
128
129/*
130 * Obtain the origin or cow device used by a given snapshot.
131 */
132struct dm_dev *dm_snap_origin(struct dm_snapshot *snap);
133struct dm_dev *dm_snap_cow(struct dm_snapshot *snap);
134
135/*
136 * Funtions to manipulate consecutive chunks
137 */
138# if defined(CONFIG_LBDAF) || (BITS_PER_LONG == 64)
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# else
167# define DM_CHUNK_CONSECUTIVE_BITS 0
168
169static inline chunk_t dm_chunk_number(chunk_t chunk)
170{
171 return chunk;
172}
173
174static inline unsigned dm_consecutive_chunk_count(struct dm_exception *e)
175{
176 return 0;
177}
178
179static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
180{
181}
182
183static inline void dm_consecutive_chunk_count_dec(struct dm_exception *e)
184{
185}
186
187# endif
188
189/*
190 * Return the number of sectors in the device.
191 */
192static inline sector_t get_dev_size(struct block_device *bdev)
193{
194 return i_size_read(bdev->bd_inode) >> SECTOR_SHIFT;
195}
196
197static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
198 sector_t sector)
199{
200 return sector >> store->chunk_shift;
201}
202
203int dm_exception_store_type_register(struct dm_exception_store_type *type);
204int dm_exception_store_type_unregister(struct dm_exception_store_type *type);
205
206int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
207 unsigned chunk_size,
208 char **error);
209
210int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
211 struct dm_snapshot *snap,
212 unsigned *args_used,
213 struct dm_exception_store **store);
214void dm_exception_store_destroy(struct dm_exception_store *store);
215
216int dm_exception_store_init(void);
217void dm_exception_store_exit(void);
218
219/*
220 * Two exception store implementations.
221 */
222int dm_persistent_snapshot_init(void);
223void dm_persistent_snapshot_exit(void);
224
225int dm_transient_snapshot_init(void);
226void dm_transient_snapshot_exit(void);
227
228#endif /* _LINUX_DM_EXCEPTION_STORE */
229