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_snap_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_snap_exception *e);
  68
  69         /*
  70          * Update the metadata with this exception.
  71          */
  72         void (*commit_exception) (struct dm_exception_store *store,
  73                                   struct dm_snap_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 (*fraction_full) (struct dm_exception_store *store,
  90                                sector_t *numerator,
  91                                sector_t *denominator);
  92
  93         /* For internal device-mapper use only. */
  94         struct list_head list;
  95 };
  96
  97 struct dm_exception_store {
  98         struct dm_exception_store_type *type;
  99         struct dm_target *ti;
 100
 101         struct dm_dev *cow;
 102
 103         /* Size of data blocks saved - must be a power of 2 */
 104         chunk_t chunk_size;
 105         chunk_t chunk_mask;
 106         chunk_t chunk_shift;
 107
 108         void *context;
 109 };
 110
 111 /*
 112  * Funtions to manipulate consecutive chunks
 113  */
 114 #  if defined(CONFIG_LBD) || (BITS_PER_LONG == 64)
 115 #    define DM_CHUNK_CONSECUTIVE_BITS 8
 116 #    define DM_CHUNK_NUMBER_BITS 56
 117
 118 static inline chunk_t dm_chunk_number(chunk_t chunk)
 119 {
 120         return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL);
 121 }
 122
 123 static inline unsigned dm_consecutive_chunk_count(struct dm_snap_exception *e)
 124 {
 125         return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
 126 }
 127
 128 static inline void dm_consecutive_chunk_count_inc(struct dm_snap_exception *e)
 129 {
 130         e->new_chunk += (1ULL << DM_CHUNK_NUMBER_BITS);
 131
 132         BUG_ON(!dm_consecutive_chunk_count(e));
 133 }
 134
 135 #  else
 136 #    define DM_CHUNK_CONSECUTIVE_BITS 0
 137
 138 static inline chunk_t dm_chunk_number(chunk_t chunk)
 139 {
 140         return chunk;
 141 }
 142
 143 static inline unsigned dm_consecutive_chunk_count(struct dm_snap_exception *e)
 144 {
 145         return 0;
 146 }
 147
 148 static inline void dm_consecutive_chunk_count_inc(struct dm_snap_exception *e)
 149 {
 150 }
 151
 152 #  endif
 153
 154 /*
 155  * Return the number of sectors in the device.
 156  */
 157 static inline sector_t get_dev_size(struct block_device *bdev)
 158 {
 159         return bdev->bd_inode->i_size >> SECTOR_SHIFT;
 160 }
 161
 162 static inline chunk_t sector_to_chunk(struct dm_exception_store *store,
 163                                       sector_t sector)
 164 {
 165         return (sector & ~store->chunk_mask) >> store->chunk_shift;
 166 }
 167
 168 int dm_exception_store_type_register(struct dm_exception_store_type *type);
 169 int dm_exception_store_type_unregister(struct dm_exception_store_type *type);
 170
 171 int dm_exception_store_create(struct dm_target *ti, int argc, char **argv,
 172                               unsigned *args_used,
 173                               struct dm_exception_store **store);
 174 void dm_exception_store_destroy(struct dm_exception_store *store);
 175
 176 int dm_exception_store_init(void);
 177 void dm_exception_store_exit(void);
 178
 179 /*
 180  * Two exception store implementations.
 181  */
 182 int dm_persistent_snapshot_init(void);
 183 void dm_persistent_snapshot_exit(void);
 184
 185 int dm_transient_snapshot_init(void);
 186 void dm_transient_snapshot_exit(void);
 187
 188 #endif /* _LINUX_DM_EXCEPTION_STORE */