LXR linux/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 */
  67struct 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 */
  84void 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 */
  93int 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 */
 105int 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 */
 112int 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 */
 124int 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 */
 137int 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 */
 151int 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 */
 161int 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 */
 167