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 
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 /*
167  * Return the number of sectors in the device.
168  */
169 static inline sector_t get_dev_size(struct block_device *bdev)
170 {
171 	return bdev_nr_sectors(bdev);
172 }
173 
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