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  * Creates a new bitset populated with values provided by a callback
  97  * function.  This is more efficient than creating an empty bitset,
  98  * resizing, and then setting values since that process incurs a lot of
  99  * copying.
 100  *
 101  * info - describes the array
 102  * root - the root block of the array on disk
 103  * size - the number of entries in the array
 104  * fn - the callback
 105  * context - passed to the callback
 106  */
 107 typedef int (*bit_value_fn)(uint32_t index, bool *value, void *context);
 108 int dm_bitset_new(struct dm_disk_bitset *info, dm_block_t *root,
 109                   uint32_t size, bit_value_fn fn, void *context);
 110
 111 /*
 112  * Resize the bitset.
 113  *
 114  * info - describes the bitset
 115  * old_root - the root block of the array on disk
 116  * old_nr_entries - the number of bits in the old bitset
 117  * new_nr_entries - the number of bits you want in the new bitset
 118  * default_value - the value for any new bits
 119  * new_root - on success, points to the new root block
 120  */
 121 int dm_bitset_resize(struct dm_disk_bitset *info, dm_block_t old_root,
 122                      uint32_t old_nr_entries, uint32_t new_nr_entries,
 123                      bool default_value, dm_block_t *new_root);
 124
 125 /*
 126  * Frees the bitset.
 127  */
 128 int dm_bitset_del(struct dm_disk_bitset *info, dm_block_t root);
 129
 130 /*
 131  * Set a bit.
 132  *
 133  * info - describes the bitset
 134  * root - the root block of the bitset
 135  * index - the bit index
 136  * new_root - on success, points to the new root block
 137  *
 138  * -ENODATA will be returned if the index is out of bounds.
 139  */
 140 int dm_bitset_set_bit(struct dm_disk_bitset *info, dm_block_t root,
 141                       uint32_t index, dm_block_t *new_root);
 142
 143 /*
 144  * Clears a bit.
 145  *
 146  * info - describes the bitset
 147  * root - the root block of the bitset
 148  * index - the bit index
 149  * new_root - on success, points to the new root block
 150  *
 151  * -ENODATA will be returned if the index is out of bounds.
 152  */
 153 int dm_bitset_clear_bit(struct dm_disk_bitset *info, dm_block_t root,
 154                         uint32_t index, dm_block_t *new_root);
 155
 156 /*
 157  * Tests a bit.
 158  *
 159  * info - describes the bitset
 160  * root - the root block of the bitset
 161  * index - the bit index
 162  * new_root - on success, points to the new root block (cached values may have been written)
 163  * result - the bit value you're after
 164  *
 165  * -ENODATA will be returned if the index is out of bounds.
 166  */
 167 int dm_bitset_test_bit(struct dm_disk_bitset *info, dm_block_t root,
 168                        uint32_t index, dm_block_t *new_root, bool *result);
 169
 170 /*
 171  * Flush any cached changes to disk.
 172  *
 173  * info - describes the bitset
 174  * root - the root block of the bitset
 175  * new_root - on success, points to the new root block
 176  */
 177 int dm_bitset_flush(struct dm_disk_bitset *info, dm_block_t root,
 178                     dm_block_t *new_root);
 179
 180 struct dm_bitset_cursor {
 181         struct dm_disk_bitset *info;
 182         struct dm_array_cursor cursor;
 183
 184         uint32_t entries_remaining;
 185         uint32_t array_index;
 186         uint32_t bit_index;
 187         uint64_t current_bits;
 188 };
 189
 190 /*
 191  * Make sure you've flush any dm_disk_bitset and updated the root before
 192  * using this.
 193  */
 194 int dm_bitset_cursor_begin(struct dm_disk_bitset *info,
 195                            dm_block_t root, uint32_t nr_entries,
 196                            struct dm_bitset_cursor *c);
 197 void dm_bitset_cursor_end(struct dm_bitset_cursor *c);
 198
 199 int dm_bitset_cursor_next(struct dm_bitset_cursor *c);
 200 int dm_bitset_cursor_skip(struct dm_bitset_cursor *c, uint32_t count);
 201 bool dm_bitset_cursor_get_value(struct dm_bitset_cursor *c);
 202
 203 /*----------------------------------------------------------------*/
 204
 205 #endif /* _LINUX_DM_BITSET_H */