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 };
  75
  76 /*
  77  * Sets up a dm_disk_bitset structure.  You don't need to do anything with
  78  * this structure when you finish using it.
  79  *
  80  * tm - the transaction manager that should supervise this structure
  81  * info - the structure being initialised
  82  */
  83 void dm_disk_bitset_init(struct dm_transaction_manager *tm,
  84                          struct dm_disk_bitset *info);
  85
  86 /*
  87  * Create an empty, zero length bitset.
  88  *
  89  * info - describes the bitset
  90  * new_root - on success, points to the new root block
  91  */
  92 int dm_bitset_empty(struct dm_disk_bitset *info, dm_block_t *new_root);
  93
  94 /*
  95  * Resize the bitset.
  96  *
  97  * info - describes the bitset
  98  * old_root - the root block of the array on disk
  99  * old_nr_entries - the number of bits in the old bitset
 100  * new_nr_entries - the number of bits you want in the new bitset
 101  * default_value - the value for any new bits
 102  * new_root - on success, points to the new root block
 103  */
 104 int dm_bitset_resize(struct dm_disk_bitset *info, dm_block_t old_root,
 105                      uint32_t old_nr_entries, uint32_t new_nr_entries,
 106                      bool default_value, dm_block_t *new_root);
 107
 108 /*
 109  * Frees the bitset.
 110  */
 111 int dm_bitset_del(struct dm_disk_bitset *info, dm_block_t root);
 112
 113 /*
 114  * Set a bit.
 115  *
 116  * info - describes the bitset
 117  * root - the root block of the bitset
 118  * index - the bit index
 119  * new_root - on success, points to the new root block
 120  *
 121  * -ENODATA will be returned if the index is out of bounds.
 122  */
 123 int dm_bitset_set_bit(struct dm_disk_bitset *info, dm_block_t root,
 124                       uint32_t index, dm_block_t *new_root);
 125
 126 /*
 127  * Clears a bit.
 128  *
 129  * info - describes the bitset
 130  * root - the root block of the bitset
 131  * index - the bit index
 132  * new_root - on success, points to the new root block
 133  *
 134  * -ENODATA will be returned if the index is out of bounds.
 135  */
 136 int dm_bitset_clear_bit(struct dm_disk_bitset *info, dm_block_t root,
 137                         uint32_t index, dm_block_t *new_root);
 138
 139 /*
 140  * Tests a bit.
 141  *
 142  * info - describes the bitset
 143  * root - the root block of the bitset
 144  * index - the bit index
 145  * new_root - on success, points to the new root block (cached values may have been written)
 146  * result - the bit value you're after
 147  *
 148  * -ENODATA will be returned if the index is out of bounds.
 149  */
 150 int dm_bitset_test_bit(struct dm_disk_bitset *info, dm_block_t root,
 151                        uint32_t index, dm_block_t *new_root, bool *result);
 152
 153 /*
 154  * Flush any cached changes to disk.
 155  *
 156  * info - describes the bitset
 157  * root - the root block of the bitset
 158  * new_root - on success, points to the new root block
 159  */
 160 int dm_bitset_flush(struct dm_disk_bitset *info, dm_block_t root,
 161                     dm_block_t *new_root);
 162
 163 /*----------------------------------------------------------------*/
 164
 165 #endif /* _LINUX_DM_BITSET_H */