drivers/md/dm-exception-store.h

   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,
  46                     unsigned argc, char **argv);
  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,
  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
 128 /*
 129  * Obtain the cow device used by a given snapshot.
 130  */
 131 struct dm_dev *dm_snap_cow(struct dm_snapshot *snap);
 132
 133 /*
 134  * Funtions to manipulate consecutive chunks
 135  */
 136 #  if defined(CONFIG_LBDAF) || (BITS_PER_LONG == 64)
 137 #    define DM_CHUNK_CONSECUTIVE_BITS 8
 138 #    define DM_CHUNK_NUMBER_BITS 56
 139
 140 static inline chunk_t dm_chunk_number(chunk_t chunk)
 141 {
 142         return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL);
 143 }
 144
 145 static inline unsigned dm_consecutive_chunk_count(struct dm_exception *e)
 146 {
 147         return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
 148 }
 149
 150 static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
 151 {
 152         e->new_chunk += (1ULL << DM_CHUNK_NUMBER_BITS);
 153
 154         BUG_ON(!dm_consecutive_chunk_count(e));
 155 }
 156
 157 static inline void dm_consecutive_chunk_count_dec(struct dm_exception *e)
 158 {
 159         BUG_ON(!dm_consecutive_chunk_count(e));
 160
 161         e->new_chunk -= (1ULL << DM_CHUNK_NUMBER_BITS);
 162 }
 163
 164 #  else
 165 #    define DM_CHUNK_CONSECUTIVE_BITS 0
 166
 167 static inline chunk_t dm_chunk_number(chunk_t chunk)
 168 {
 169         return chunk;
 170 }
 171
 172 static inline unsigned dm_consecutive_chunk_count(struct dm_exception *e)
 173 {
 174         return 0;
 175 }
 176
 177 static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
 178 {
 179 }
 180
 181 static inline void dm_consecutive_chunk_count_dec(struct dm_exception *e)
 182 {
 183 }
 184
 185 #  endif
 186
 187 /*
 188  * Return the number of sectors in the device.
 189  */
 190 static inline sector_t get_dev_size(struct block_device *bdev)
 191 {
 192         return i_size_read(bdev->bd_inode) >> SECTOR_SHIFT;
 193 }
 194
 195 static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
 196                                       sector_t sector)
 197 {
 198         return sector >> store->chunk_shift;
 199 }
 200
 201 int dm_exception_store_type_register(struct dm_exception_store_type *type);
 202 int dm_exception_store_type_unregister(struct dm_exception_store_type *type);
 203
 204 int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
 205                                       unsigned chunk_size,
 206                                       char **error);
 207
 208 int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
 209                               struct dm_snapshot *snap,
 210                               unsigned *args_used,
 211                               struct dm_exception_store **store);
 212 void dm_exception_store_destroy(struct dm_exception_store *store);
 213
 214 int dm_exception_store_init(void);
 215 void dm_exception_store_exit(void);
 216
 217 /*
 218  * Two exception store implementations.
 219  */
 220 int dm_persistent_snapshot_init(void);
 221 void dm_persistent_snapshot_exit(void);
 222
 223 int dm_transient_snapshot_init(void);
 224 void dm_transient_snapshot_exit(void);
 225
 226 #endif /* _LINUX_DM_EXCEPTION_STORE */