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         /*
  42          * Destroys this object when you've finished with it.
  43          */
  44         void (*destroy) (struct dm_exception_store *store);
  45
  46         /*
  47          * The target shouldn't read the COW device until this is
  48          * called.  As exceptions are read from the COW, they are
  49          * reported back via the callback.
  50          */
  51         int (*read_metadata) (struct dm_exception_store *store,
  52                               int (*callback)(void *callback_context,
  53                                               chunk_t old, chunk_t new),
  54                               void *callback_context);
  55
  56         /*
  57          * Find somewhere to store the next exception.
  58          */
  59         int (*prepare_exception) (struct dm_exception_store *store,
  60                                   struct dm_snap_exception *e);
  61
  62         /*
  63          * Update the metadata with this exception.
  64          */
  65         void (*commit_exception) (struct dm_exception_store *store,
  66                                   struct dm_snap_exception *e,
  67                                   void (*callback) (void *, int success),
  68                                   void *callback_context);
  69
  70         /*
  71          * The snapshot is invalid, note this in the metadata.
  72          */
  73         void (*drop_snapshot) (struct dm_exception_store *store);
  74
  75         int (*status) (struct dm_exception_store *store, status_type_t status,
  76                        char *result, unsigned int maxlen);
  77
  78         /*
  79          * Return how full the snapshot is.
  80          */
  81         void (*fraction_full) (struct dm_exception_store *store,
  82                                sector_t *numerator,
  83                                sector_t *denominator);
  84
  85         struct dm_snapshot *snap;
  86         void *context;
  87 };
  88
  89 /*
  90  * Funtions to manipulate consecutive chunks
  91  */
  92 #  if defined(CONFIG_LBD) || (BITS_PER_LONG == 64)
  93 #    define DM_CHUNK_CONSECUTIVE_BITS 8
  94 #    define DM_CHUNK_NUMBER_BITS 56
  95
  96 static inline chunk_t dm_chunk_number(chunk_t chunk)
  97 {
  98         return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL);
  99 }
 100
 101 static inline unsigned dm_consecutive_chunk_count(struct dm_snap_exception *e)
 102 {
 103         return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
 104 }
 105
 106 static inline void dm_consecutive_chunk_count_inc(struct dm_snap_exception *e)
 107 {
 108         e->new_chunk += (1ULL << DM_CHUNK_NUMBER_BITS);
 109
 110         BUG_ON(!dm_consecutive_chunk_count(e));
 111 }
 112
 113 #  else
 114 #    define DM_CHUNK_CONSECUTIVE_BITS 0
 115
 116 static inline chunk_t dm_chunk_number(chunk_t chunk)
 117 {
 118         return chunk;
 119 }
 120
 121 static inline unsigned dm_consecutive_chunk_count(struct dm_snap_exception *e)
 122 {
 123         return 0;
 124 }
 125
 126 static inline void dm_consecutive_chunk_count_inc(struct dm_snap_exception *e)
 127 {
 128 }
 129
 130 #  endif
 131
 132 int dm_exception_store_init(void);
 133 void dm_exception_store_exit(void);
 134
 135 /*
 136  * Two exception store implementations.
 137  */
 138 int dm_persistent_snapshot_init(void);
 139 void dm_persistent_snapshot_exit(void);
 140
 141 int dm_transient_snapshot_init(void);
 142 void dm_transient_snapshot_exit(void);
 143
 144 int dm_create_persistent(struct dm_exception_store *store);
 145
 146 int dm_create_transient(struct dm_exception_store *store);
 147
 148 #endif /* _LINUX_DM_EXCEPTION_STORE */