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
  15 /*
  16  * The snapshot code deals with largish chunks of the disk at a
  17  * time. Typically 32k - 512k.
  18  */
  19 typedef sector_t chunk_t;
  20
  21 /*
  22  * An exception is used where an old chunk of data has been
  23  * replaced by a new one.
  24  * If chunk_t is 64 bits in size, the top 8 bits of new_chunk hold the number
  25  * of chunks that follow contiguously.  Remaining bits hold the number of the
  26  * chunk within the device.
  27  */
  28 struct dm_snap_exception {
  29         struct list_head hash_list;
  30
  31         chunk_t old_chunk;
  32         chunk_t new_chunk;
  33 };
  34
  35 /*
  36  * Abstraction to handle the meta/layout of exception stores (the
  37  * COW device).
  38  */
  39 struct dm_exception_store {
  40
  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.
  49          */
  50         int (*read_metadata) (struct dm_exception_store *store);
  51
  52         /*
  53          * Find somewhere to store the next exception.
  54          */
  55         int (*prepare_exception) (struct dm_exception_store *store,
  56                                   struct dm_snap_exception *e);
  57
  58         /*
  59          * Update the metadata with this exception.
  60          */
  61         void (*commit_exception) (struct dm_exception_store *store,
  62                                   struct dm_snap_exception *e,
  63                                   void (*callback) (void *, int success),
  64                                   void *callback_context);
  65
  66         /*
  67          * The snapshot is invalid, note this in the metadata.
  68          */
  69         void (*drop_snapshot) (struct dm_exception_store *store);
  70
  71         /*
  72          * Return how full the snapshot is.
  73          */
  74         void (*fraction_full) (struct dm_exception_store *store,
  75                                sector_t *numerator,
  76                                sector_t *denominator);
  77
  78         struct dm_snapshot *snap;
  79         void *context;
  80 };
  81
  82 /*
  83  * Funtions to manipulate consecutive chunks
  84  */
  85 #  if defined(CONFIG_LBD) || (BITS_PER_LONG == 64)
  86 #    define DM_CHUNK_CONSECUTIVE_BITS 8
  87 #    define DM_CHUNK_NUMBER_BITS 56
  88
  89 static inline chunk_t dm_chunk_number(chunk_t chunk)
  90 {
  91         return chunk & (chunk_t)((1ULL << DM_CHUNK_NUMBER_BITS) - 1ULL);
  92 }
  93
  94 static inline unsigned dm_consecutive_chunk_count(struct dm_snap_exception *e)
  95 {
  96         return e->new_chunk >> DM_CHUNK_NUMBER_BITS;
  97 }
  98
  99 static inline void dm_consecutive_chunk_count_inc(struct dm_snap_exception *e)
 100 {
 101         e->new_chunk += (1ULL << DM_CHUNK_NUMBER_BITS);
 102
 103         BUG_ON(!dm_consecutive_chunk_count(e));
 104 }
 105
 106 #  else
 107 #    define DM_CHUNK_CONSECUTIVE_BITS 0
 108
 109 static inline chunk_t dm_chunk_number(chunk_t chunk)
 110 {
 111         return chunk;
 112 }
 113
 114 static inline unsigned dm_consecutive_chunk_count(struct dm_snap_exception *e)
 115 {
 116         return 0;
 117 }
 118
 119 static inline void dm_consecutive_chunk_count_inc(struct dm_snap_exception *e)
 120 {
 121 }
 122
 123 #  endif
 124
 125 /*
 126  * Two exception store implementations.
 127  */
 128 int dm_create_persistent(struct dm_exception_store *store);
 129
 130 int dm_create_transient(struct dm_exception_store *store);
 131
 132 #endif /* _LINUX_DM_EXCEPTION_STORE */