1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3  * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
4  * Copyright (C) 2008 Red Hat, Inc. All rights reserved.
5  *
6  * Device-mapper snapshot exception store.
7  *
8  * This file is released under the GPL.
9  */
10 
11 #ifndef _LINUX_DM_EXCEPTION_STORE
12 #define _LINUX_DM_EXCEPTION_STORE
13 
14 #include <linux/blkdev.h>
15 #include <linux/list_bl.h>
16 #include <linux/device-mapper.h>
17 
18 /*
19  * The snapshot code deals with largish chunks of the disk at a
20  * time. Typically 32k - 512k.
21  */
22 typedef sector_t chunk_t;
23 
24 /*
25  * An exception is used where an old chunk of data has been
26  * replaced by a new one.
27  * If chunk_t is 64 bits in size, the top 8 bits of new_chunk hold the number
28  * of chunks that follow contiguously.  Remaining bits hold the number of the
29  * chunk within the device.
30  */
31 struct dm_exception {
32 	struct hlist_bl_node hash_list;
33 
34 	chunk_t old_chunk;
35 	chunk_t new_chunk;
36 };
37 
38 /*
39  * Abstraction to handle the meta/layout of exception stores (the
40  * COW device).
41  */
42 struct dm_exception_store;
43 struct dm_exception_store_type {
44 	const char *name;
45 	struct module *module;
46 
47 	int (*ctr)(struct dm_exception_store *store, char *options);
48 
49 	/*
50 	 * Destroys this object when you've finished with it.
51 	 */
52 	void (*dtr)(struct dm_exception_store *store);
53 
54 	/*
55 	 * The target shouldn't read the COW device until this is
56 	 * called.  As exceptions are read from the COW, they are
57 	 * reported back via the callback.
58 	 */
59 	int (*read_metadata)(struct dm_exception_store *store,
60 			     int (*callback)(void *callback_context,
61 					     chunk_t old, chunk_t new),
62 			     void *callback_context);
63 
64 	/*
65 	 * Find somewhere to store the next exception.
66 	 */
67 	int (*prepare_exception)(struct dm_exception_store *store,
68 				 struct dm_exception *e);
69 
70 	/*
71 	 * Update the metadata with this exception.
72 	 */
73 	void (*commit_exception)(struct dm_exception_store *store,
74 				 struct dm_exception *e, int valid,
75 				 void (*callback)(void *, int success),
76 				 void *callback_context);
77 
78 	/*
79 	 * Returns 0 if the exception store is empty.
80 	 *
81 	 * If there are exceptions still to be merged, sets
82 	 * *last_old_chunk and *last_new_chunk to the most recent
83 	 * still-to-be-merged chunk and returns the number of
84 	 * consecutive previous ones.
85 	 */
86 	int (*prepare_merge)(struct dm_exception_store *store,
87 			     chunk_t *last_old_chunk, chunk_t *last_new_chunk);
88 
89 	/*
90 	 * Clear the last n exceptions.
91 	 * nr_merged must be <= the value returned by prepare_merge.
92 	 */
93 	int (*commit_merge)(struct dm_exception_store *store, int nr_merged);
94 
95 	/*
96 	 * The snapshot is invalid, note this in the metadata.
97 	 */
98 	void (*drop_snapshot)(struct dm_exception_store *store);
99 
100 	unsigned int (*status)(struct dm_exception_store *store,
101 			       status_type_t status, char *result,
102 			       unsigned int maxlen);
103 
104 	/*
105 	 * Return how full the snapshot is.
106 	 */
107 	void (*usage)(struct dm_exception_store *store,
108 		      sector_t *total_sectors, sector_t *sectors_allocated,
109 		      sector_t *metadata_sectors);
110 
111 	/* For internal device-mapper use only. */
112 	struct list_head list;
113 };
114 
115 struct dm_snapshot;
116 
117 struct dm_exception_store {
118 	struct dm_exception_store_type *type;
119 	struct dm_snapshot *snap;
120 
121 	/* Size of data blocks saved - must be a power of 2 */
122 	unsigned int chunk_size;
123 	unsigned int chunk_mask;
124 	unsigned int chunk_shift;
125 
126 	void *context;
127 
128 	bool userspace_supports_overflow;
129 };
130 
131 /*
132  * Obtain the origin or cow device used by a given snapshot.
133  */
134 struct dm_dev *dm_snap_origin(struct dm_snapshot *snap);
135 struct dm_dev *dm_snap_cow(struct dm_snapshot *snap);
136 
137 /*
138  * Funtions to manipulate consecutive chunks
139  */
140 #define DM_CHUNK_CONSECUTIVE_BITS 8
141 #define DM_CHUNK_NUMBER_BITS 56
142 
143 static inline chunk_t dm_chunk_number(chunk_t chunk)
144 {
145 	return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL);
146 }
147 
148 static inline unsigned int dm_consecutive_chunk_count(struct dm_exception *e)
149 {
150 	return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
151 }
152 
153 static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
154 {
155 	e->new_chunk += (1ULL << DM_CHUNK_NUMBER_BITS);
156 
157 	BUG_ON(!dm_consecutive_chunk_count(e));
158 }
159 
160 static inline void dm_consecutive_chunk_count_dec(struct dm_exception *e)
161 {
162 	BUG_ON(!dm_consecutive_chunk_count(e));
163 
164 	e->new_chunk -= (1ULL << DM_CHUNK_NUMBER_BITS);
165 }
166 
167 /*
168  * Return the number of sectors in the device.
169  */
170 static inline sector_t get_dev_size(struct block_device *bdev)
171 {
172 	return bdev_nr_sectors(bdev);
173 }
174 
175 static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
176 				      sector_t sector)
177 {
178 	return sector >> store->chunk_shift;
179 }
180 
181 int dm_exception_store_type_register(struct dm_exception_store_type *type);
182 int dm_exception_store_type_unregister(struct dm_exception_store_type *type);
183 
184 int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
185 				      unsigned int chunk_size,
186 				      char **error);
187 
188 int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
189 			      struct dm_snapshot *snap,
190 			      unsigned int *args_used,
191 			      struct dm_exception_store **store);
192 void dm_exception_store_destroy(struct dm_exception_store *store);
193 
194 int dm_exception_store_init(void);
195 void dm_exception_store_exit(void);
196 
197 /*
198  * Two exception store implementations.
199  */
200 int dm_persistent_snapshot_init(void);
201 void dm_persistent_snapshot_exit(void);
202 
203 int dm_transient_snapshot_init(void);
204 void dm_transient_snapshot_exit(void);
205 
206 #endif /* _LINUX_DM_EXCEPTION_STORE */
207