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, int valid, 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 #define DM_CHUNK_CONSECUTIVE_BITS 8 139 #define DM_CHUNK_NUMBER_BITS 56 140 141 static inline chunk_t dm_chunk_number(chunk_t chunk) 142 { 143 return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL); 144 } 145 146 static inline unsigned dm_consecutive_chunk_count(struct dm_exception *e) 147 { 148 return e->new_chunk >> DM_CHUNK_NUMBER_BITS; 149 } 150 151 static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e) 152 { 153 e->new_chunk += (1ULL << DM_CHUNK_NUMBER_BITS); 154 155 BUG_ON(!dm_consecutive_chunk_count(e)); 156 } 157 158 static inline void dm_consecutive_chunk_count_dec(struct dm_exception *e) 159 { 160 BUG_ON(!dm_consecutive_chunk_count(e)); 161 162 e->new_chunk -= (1ULL << DM_CHUNK_NUMBER_BITS); 163 } 164 165 /* 166 * Return the number of sectors in the device. 167 */ 168 static inline sector_t get_dev_size(struct block_device *bdev) 169 { 170 return i_size_read(bdev->bd_inode) >> SECTOR_SHIFT; 171 } 172 173 static inline chunk_t sector_to_chunk(struct dm_exception_store *store, 174 sector_t sector) 175 { 176 return sector >> store->chunk_shift; 177 } 178 179 int dm_exception_store_type_register(struct dm_exception_store_type *type); 180 int dm_exception_store_type_unregister(struct dm_exception_store_type *type); 181 182 int dm_exception_store_set_chunk_size(struct dm_exception_store *store, 183 unsigned chunk_size, 184 char **error); 185 186 int dm_exception_store_create(struct dm_target *ti, int argc, char **argv, 187 struct dm_snapshot *snap, 188 unsigned *args_used, 189 struct dm_exception_store **store); 190 void dm_exception_store_destroy(struct dm_exception_store *store); 191 192 int dm_exception_store_init(void); 193 void dm_exception_store_exit(void); 194 195 /* 196 * Two exception store implementations. 197 */ 198 int dm_persistent_snapshot_init(void); 199 void dm_persistent_snapshot_exit(void); 200 201 int dm_transient_snapshot_init(void); 202 void dm_transient_snapshot_exit(void); 203 204 #endif /* _LINUX_DM_EXCEPTION_STORE */ 205