drivers/md/persistent-data/dm-bitset.h

   1 /*
   2  * Copyright (C) 2012 Red Hat, Inc.
   3  *
   4  * This file is released under the GPL.
   5  */
   6 #ifndef _LINUX_DM_BITSET_H
   7 #define _LINUX_DM_BITSET_H
   8
   9 #include "dm-array.h"
  10
  11 /*----------------------------------------------------------------*/
  12
  13 /*
  14  * This bitset type is a thin wrapper round a dm_array of 64bit words.  It
  15  * uses a tiny, one word cache to reduce the number of array lookups and so
  16  * increase performance.
  17  *
  18  * Like the dm-array that it's based on, the caller needs to keep track of
  19  * the size of the bitset separately.  The underlying dm-array implicitly
  20  * knows how many words it's storing and will return -ENODATA if you try
  21  * and access an out of bounds word.  However, an out of bounds bit in the
  22  * final word will _not_ be detected, you have been warned.
  23  *
  24  * Bits are indexed from zero.
  25
  26  * Typical use:
  27  *
  28  * a) Initialise a dm_disk_bitset structure with dm_disk_bitset_init().
  29  *    This describes the bitset and includes the cache.  It's not called it
  30  *    dm_bitset_info in line with other data structures because it does
  31  *    include instance data.
  32  *
  33  * b) Get yourself a root.  The root is the index of a block of data on the
  34  *    disk that holds a particular instance of an bitset.  You may have a
  35  *    pre existing root in your metadata that you wish to use, or you may
  36  *    want to create a brand new, empty bitset with dm_bitset_empty().
  37  *
  38  * Like the other data structures in this library, dm_bitset objects are
  39  * immutable between transactions.  Update functions will return you the
  40  * root for a _new_ array.  If you've incremented the old root, via
  41  * dm_tm_inc(), before calling the update function you may continue to use
  42  * it in parallel with the new root.
  43  *
  44  * Even read operations may trigger the cache to be flushed and as such
  45  * return a root for a new, updated bitset.
  46  *
  47  * c) resize a bitset with dm_bitset_resize().
  48  *
  49  * d) Set a bit with dm_bitset_set_bit().
  50  *
  51  * e) Clear a bit with dm_bitset_clear_bit().
  52  *
  53  * f) Test a bit with dm_bitset_test_bit().
  54  *
  55  * g) Flush all updates from the cache with dm_bitset_flush().
  56  *
  57  * h) Destroy the bitset with dm_bitset_del().  This tells the transaction
  58  *    manager that you're no longer using this data structure so it can
  59  *    recycle it's blocks.  (dm_bitset_dec() would be a better name for it,
  60  *    but del is in keeping with dm_btree_del()).
  61  */
  62
  63 /*
  64  * Opaque object.  Unlike dm_array_info, you should have one of these per
  65  * bitset.  Initialise with dm_disk_bitset_init().
  66  */
  67 struct dm_disk_bitset {
  68         struct dm_array_info array_info;
  69
  70         uint32_t current_index;
  71         uint64_t current_bits;
  72
  73         bool current_index_set:1;
  74         bool dirty:1;
  75 };
  76
  77 /*
  78  * Sets up a dm_disk_bitset structure.  You don't need to do anything with
  79  * this structure when you finish using it.
  80  *
  81  * tm - the transaction manager that should supervise this structure
  82  * info - the structure being initialised
  83  */
  84 void dm_disk_bitset_init(struct dm_transaction_manager *tm,
  85                          struct dm_disk_bitset *info);
  86
  87 /*
  88  * Create an empty, zero length bitset.
  89  *
  90  * info - describes the bitset
  91  * new_root - on success, points to the new root block
  92  */
  93 int dm_bitset_empty(struct dm_disk_bitset *info, dm_block_t *new_root);
  94
  95 /*
  96  * Resize the bitset.
  97  *
  98  * info - describes the bitset
  99  * old_root - the root block of the array on disk
 100  * old_nr_entries - the number of bits in the old bitset
 101  * new_nr_entries - the number of bits you want in the new bitset
 102  * default_value - the value for any new bits
 103  * new_root - on success, points to the new root block
 104  */
 105 int dm_bitset_resize(struct dm_disk_bitset *info, dm_block_t old_root,
 106                      uint32_t old_nr_entries, uint32_t new_nr_entries,
 107                      bool default_value, dm_block_t *new_root);
 108
 109 /*
 110  * Frees the bitset.
 111  */
 112 int dm_bitset_del(struct dm_disk_bitset *info, dm_block_t root);
 113
 114 /*
 115  * Set a bit.
 116  *
 117  * info - describes the bitset
 118  * root - the root block of the bitset
 119  * index - the bit index
 120  * new_root - on success, points to the new root block
 121  *
 122  * -ENODATA will be returned if the index is out of bounds.
 123  */
 124 int dm_bitset_set_bit(struct dm_disk_bitset *info, dm_block_t root,
 125                       uint32_t index, dm_block_t *new_root);
 126
 127 /*
 128  * Clears a bit.
 129  *
 130  * info - describes the bitset
 131  * root - the root block of the bitset
 132  * index - the bit index
 133  * new_root - on success, points to the new root block
 134  *
 135  * -ENODATA will be returned if the index is out of bounds.
 136  */
 137 int dm_bitset_clear_bit(struct dm_disk_bitset *info, dm_block_t root,
 138                         uint32_t index, dm_block_t *new_root);
 139
 140 /*
 141  * Tests a bit.
 142  *
 143  * info - describes the bitset
 144  * root - the root block of the bitset
 145  * index - the bit index
 146  * new_root - on success, points to the new root block (cached values may have been written)
 147  * result - the bit value you're after
 148  *
 149  * -ENODATA will be returned if the index is out of bounds.
 150  */
 151 int dm_bitset_test_bit(struct dm_disk_bitset *info, dm_block_t root,
 152                        uint32_t index, dm_block_t *new_root, bool *result);
 153
 154 /*
 155  * Flush any cached changes to disk.
 156  *
 157  * info - describes the bitset
 158  * root - the root block of the bitset
 159  * new_root - on success, points to the new root block
 160  */
 161 int dm_bitset_flush(struct dm_disk_bitset *info, dm_block_t root,
 162                     dm_block_t *new_root);
 163
 164 /*----------------------------------------------------------------*/
 165
 166 #endif /* _LINUX_DM_BITSET_H */