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 */
21 typedef 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 */
30 struct 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 */
41 struct dm_exception_store;
42 struct 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
114 struct dm_snapshot;
115
116 struct 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 */
133 struct dm_dev *dm_snap_origin(struct dm_snapshot *snap);
134 struct 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
dm_chunk_number(chunk_t chunk)142 static inline chunk_t dm_chunk_number(chunk_t chunk)
143 {
144 return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL);
145 }
146
dm_consecutive_chunk_count(struct dm_exception * e)147 static inline unsigned dm_consecutive_chunk_count(struct dm_exception *e)
148 {
149 return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
150 }
151
dm_consecutive_chunk_count_inc(struct dm_exception * e)152 static 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
dm_consecutive_chunk_count_dec(struct dm_exception * e)159 static 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 */
get_dev_size(struct block_device * bdev)169 static inline sector_t get_dev_size(struct block_device *bdev)
170 {
171 return i_size_read(bdev->bd_inode) >> SECTOR_SHIFT;
172 }
173
sector_to_chunk(struct dm_exception_store * store,sector_t sector)174 static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
175 sector_t sector)
176 {
177 return sector >> store->chunk_shift;
178 }
179
180 int dm_exception_store_type_register(struct dm_exception_store_type *type);
181 int dm_exception_store_type_unregister(struct dm_exception_store_type *type);
182
183 int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
184 unsigned chunk_size,
185 char **error);
186
187 int 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);
191 void dm_exception_store_destroy(struct dm_exception_store *store);
192
193 int dm_exception_store_init(void);
194 void dm_exception_store_exit(void);
195
196 /*
197 * Two exception store implementations.
198 */
199 int dm_persistent_snapshot_init(void);
200 void dm_persistent_snapshot_exit(void);
201
202 int dm_transient_snapshot_init(void);
203 void dm_transient_snapshot_exit(void);
204
205 #endif /* _LINUX_DM_EXCEPTION_STORE */
206