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          * The snapshot is invalid, note this in the metadata.
  79          */
  80         void (*drop_snapshot) (struct dm_exception_store *store);
  81
  82         unsigned (*status) (struct dm_exception_store *store,
  83                             status_type_t status, char *result,
  84                             unsigned maxlen);
  85
  86         /*
  87          * Return how full the snapshot is.
  88          */
  89         void (*usage) (struct dm_exception_store *store,
  90                        sector_t *total_sectors, sector_t *sectors_allocated,
  91                        sector_t *metadata_sectors);
  92
  93         /* For internal device-mapper use only. */
  94         struct list_head list;
  95 };
  96
  97 struct dm_snapshot;
  98
  99 struct dm_exception_store {
 100         struct dm_exception_store_type *type;
 101         struct dm_snapshot *snap;
 102
 103         /* Size of data blocks saved - must be a power of 2 */
 104         unsigned chunk_size;
 105         unsigned chunk_mask;
 106         unsigned chunk_shift;
 107
 108         void *context;
 109 };
 110
 111 /*
 112  * Obtain the cow device used by a given snapshot.
 113  */
 114 struct dm_dev *dm_snap_cow(struct dm_snapshot *snap);
 115
 116 /*
 117  * Funtions to manipulate consecutive chunks
 118  */
 119 #  if defined(CONFIG_LBDAF) || (BITS_PER_LONG == 64)
 120 #    define DM_CHUNK_CONSECUTIVE_BITS 8
 121 #    define DM_CHUNK_NUMBER_BITS 56
 122
 123 static inline chunk_t dm_chunk_number(chunk_t chunk)
 124 {
 125         return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL);
 126 }
 127
 128 static inline unsigned dm_consecutive_chunk_count(struct dm_exception *e)
 129 {
 130         return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
 131 }
 132
 133 static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
 134 {
 135         e->new_chunk += (1ULL << DM_CHUNK_NUMBER_BITS);
 136
 137         BUG_ON(!dm_consecutive_chunk_count(e));
 138 }
 139
 140 #  else
 141 #    define DM_CHUNK_CONSECUTIVE_BITS 0
 142
 143 static inline chunk_t dm_chunk_number(chunk_t chunk)
 144 {
 145         return chunk;
 146 }
 147
 148 static inline unsigned dm_consecutive_chunk_count(struct dm_exception *e)
 149 {
 150         return 0;
 151 }
 152
 153 static inline void dm_consecutive_chunk_count_inc(struct dm_exception *e)
 154 {
 155 }
 156
 157 #  endif
 158
 159 /*
 160  * Return the number of sectors in the device.
 161  */
 162 static inline sector_t get_dev_size(struct block_device *bdev)
 163 {
 164         return i_size_read(bdev->bd_inode) >> SECTOR_SHIFT;
 165 }
 166
 167 static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
 168                                       sector_t sector)
 169 {
 170         return sector >> store->chunk_shift;
 171 }
 172
 173 int dm_exception_store_type_register(struct dm_exception_store_type *type);
 174 int dm_exception_store_type_unregister(struct dm_exception_store_type *type);
 175
 176 int dm_exception_store_set_chunk_size(struct dm_exception_store *store,
 177                                       unsigned chunk_size,
 178                                       char **error);
 179
 180 int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
 181                               struct dm_snapshot *snap,
 182                               unsigned *args_used,
 183                               struct dm_exception_store **store);
 184 void dm_exception_store_destroy(struct dm_exception_store *store);
 185
 186 int dm_exception_store_init(void);
 187 void dm_exception_store_exit(void);
 188
 189 /*
 190  * Two exception store implementations.
 191  */
 192 int dm_persistent_snapshot_init(void);
 193 void dm_persistent_snapshot_exit(void);
 194
 195 int dm_transient_snapshot_init(void);
 196 void dm_transient_snapshot_exit(void);
 197
 198 #endif /* _LINUX_DM_EXCEPTION_STORE */