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 */
20 typedef 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 */
29 struct dm_snap_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 */
40 struct dm_exception_store {
41 /*
42 * Destroys this object when you've finished with it.
43 */
44 void (*destroy) (struct dm_exception_store *store);
45
46 /*
47 * The target shouldn't read the COW device until this is
48 * called. As exceptions are read from the COW, they are
49 * reported back via the callback.
50 */
51 int (*read_metadata) (struct dm_exception_store *store,
52 int (*callback)(void *callback_context,
53 chunk_t old, chunk_t new),
54 void *callback_context);
55
56 /*
57 * Find somewhere to store the next exception.
58 */
59 int (*prepare_exception) (struct dm_exception_store *store,
60 struct dm_snap_exception *e);
61
62 /*
63 * Update the metadata with this exception.
64 */
65 void (*commit_exception) (struct dm_exception_store *store,
66 struct dm_snap_exception *e,
67 void (*callback) (void *, int success),
68 void *callback_context);
69
70 /*
71 * The snapshot is invalid, note this in the metadata.
72 */
73 void (*drop_snapshot) (struct dm_exception_store *store);
74
75 int (*status) (struct dm_exception_store *store, status_type_t status,
76 char *result, unsigned int maxlen);
77
78 /*
79 * Return how full the snapshot is.
80 */
81 void (*fraction_full) (struct dm_exception_store *store,
82 sector_t *numerator,
83 sector_t *denominator);
84
85 struct dm_snapshot *snap;
86 void *context;
87 };
88
89 /*
90 * Funtions to manipulate consecutive chunks
91 */
92 # if defined(CONFIG_LBD) || (BITS_PER_LONG == 64)
93 # define DM_CHUNK_CONSECUTIVE_BITS 8
94 # define DM_CHUNK_NUMBER_BITS 56
95
dm_chunk_number(chunk_t chunk)96 static inline chunk_t dm_chunk_number(chunk_t chunk)
97 {
98 return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL);
99 }
100
dm_consecutive_chunk_count(struct dm_snap_exception * e)101 static inline unsigned dm_consecutive_chunk_count(struct dm_snap_exception *e)
102 {
103 return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
104 }
105
dm_consecutive_chunk_count_inc(struct dm_snap_exception * e)106 static inline void dm_consecutive_chunk_count_inc(struct dm_snap_exception *e)
107 {
108 e->new_chunk += (1ULL << DM_CHUNK_NUMBER_BITS);
109
110 BUG_ON(!dm_consecutive_chunk_count(e));
111 }
112
113 # else
114 # define DM_CHUNK_CONSECUTIVE_BITS 0
115
dm_chunk_number(chunk_t chunk)116 static inline chunk_t dm_chunk_number(chunk_t chunk)
117 {
118 return chunk;
119 }
120
dm_consecutive_chunk_count(struct dm_snap_exception * e)121 static inline unsigned dm_consecutive_chunk_count(struct dm_snap_exception *e)
122 {
123 return 0;
124 }
125
dm_consecutive_chunk_count_inc(struct dm_snap_exception * e)126 static inline void dm_consecutive_chunk_count_inc(struct dm_snap_exception *e)
127 {
128 }
129
130 # endif
131
132 int dm_exception_store_init(void);
133 void dm_exception_store_exit(void);
134
135 /*
136 * Two exception store implementations.
137 */
138 int dm_persistent_snapshot_init(void);
139 void dm_persistent_snapshot_exit(void);
140
141 int dm_transient_snapshot_init(void);
142 void dm_transient_snapshot_exit(void);
143
144 int dm_create_persistent(struct dm_exception_store *store);
145
146 int dm_create_transient(struct dm_exception_store *store);
147
148 #endif /* _LINUX_DM_EXCEPTION_STORE */
149