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, 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 */