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_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 struct 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,
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 
113 struct dm_snapshot;
114 
115 struct 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  */
132 struct dm_dev *dm_snap_origin(struct dm_snapshot *snap);
133 struct 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 
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 
147 static inline unsigned dm_consecutive_chunk_count(struct dm_exception *e)
148 {
149 	return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
150 }
151 
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 
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 #  else
167 #    define DM_CHUNK_CONSECUTIVE_BITS 0
168 
169 static inline chunk_t dm_chunk_number(chunk_t chunk)
170 {
171 	return chunk;
172 }
173 
174 static inline unsigned dm_consecutive_chunk_count(struct dm_exception *e)
175 {
176 	return 0;
177 }
178 
179 static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
180 {
181 }
182 
183 static 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  */
192 static inline sector_t get_dev_size(struct block_device *bdev)
193 {
194 	return i_size_read(bdev->bd_inode) >> SECTOR_SHIFT;
195 }
196 
197 static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
198 				      sector_t sector)
199 {
200 	return sector >> store->chunk_shift;
201 }
202 
203 int dm_exception_store_type_register(struct dm_exception_store_type *type);
204 int dm_exception_store_type_unregister(struct dm_exception_store_type *type);
205 
206 int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
207 				      unsigned chunk_size,
208 				      char **error);
209 
210 int 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);
214 void dm_exception_store_destroy(struct dm_exception_store *store);
215 
216 int dm_exception_store_init(void);
217 void dm_exception_store_exit(void);
218 
219 /*
220  * Two exception store implementations.
221  */
222 int dm_persistent_snapshot_init(void);
223 void dm_persistent_snapshot_exit(void);
224 
225 int dm_transient_snapshot_init(void);
226 void dm_transient_snapshot_exit(void);
227 
228 #endif /* _LINUX_DM_EXCEPTION_STORE */
229