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 */
166