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Joe Thornber6513c292013-03-01 22:45:51 +00001/*
2 * Copyright (C) 2012 Red Hat, Inc.
3 *
4 * This file is released under the GPL.
5 */
6#ifndef _LINUX_DM_ARRAY_H
7#define _LINUX_DM_ARRAY_H
8
9#include "dm-btree.h"
10
11/*----------------------------------------------------------------*/
12
13/*
14 * The dm-array is a persistent version of an array. It packs the data
15 * more efficiently than a btree which will result in less disk space use,
16 * and a performance boost. The element get and set operations are still
17 * O(ln(n)), but with a much smaller constant.
18 *
19 * The value type structure is reused from the btree type to support proper
20 * reference counting of values.
21 *
22 * The arrays implicitly know their length, and bounds are checked for
23 * lookups and updated. It doesn't store this in an accessible place
24 * because it would waste a whole metadata block. Make sure you store the
25 * size along with the array root in your encompassing data.
26 *
27 * Array entries are indexed via an unsigned integer starting from zero.
28 * Arrays are not sparse; if you resize an array to have 'n' entries then
29 * 'n - 1' will be the last valid index.
30 *
31 * Typical use:
32 *
33 * a) initialise a dm_array_info structure. This describes the array
34 * values and ties it into a specific transaction manager. It holds no
35 * instance data; the same info can be used for many similar arrays if
36 * you wish.
37 *
38 * b) Get yourself a root. The root is the index of a block of data on the
39 * disk that holds a particular instance of an array. You may have a
40 * pre existing root in your metadata that you wish to use, or you may
41 * want to create a brand new, empty array with dm_array_empty().
42 *
43 * Like the other data structures in this library, dm_array objects are
44 * immutable between transactions. Update functions will return you the
45 * root for a _new_ array. If you've incremented the old root, via
46 * dm_tm_inc(), before calling the update function you may continue to use
47 * it in parallel with the new root.
48 *
49 * c) resize an array with dm_array_resize().
50 *
51 * d) Get a value from the array with dm_array_get_value().
52 *
53 * e) Set a value in the array with dm_array_set_value().
54 *
55 * f) Walk an array of values in index order with dm_array_walk(). More
56 * efficient than making many calls to dm_array_get_value().
57 *
58 * g) Destroy the array with dm_array_del(). This tells the transaction
59 * manager that you're no longer using this data structure so it can
60 * recycle it's blocks. (dm_array_dec() would be a better name for it,
61 * but del is in keeping with dm_btree_del()).
62 */
63
64/*
65 * Describes an array. Don't initialise this structure yourself, use the
66 * init function below.
67 */
68struct dm_array_info {
69 struct dm_transaction_manager *tm;
70 struct dm_btree_value_type value_type;
71 struct dm_btree_info btree_info;
72};
73
74/*
75 * Sets up a dm_array_info structure. You don't need to do anything with
76 * this structure when you finish using it.
77 *
78 * info - the structure being filled in.
79 * tm - the transaction manager that should supervise this structure.
80 * vt - describes the leaf values.
81 */
82void dm_array_info_init(struct dm_array_info *info,
83 struct dm_transaction_manager *tm,
84 struct dm_btree_value_type *vt);
85
86/*
87 * Create an empty, zero length array.
88 *
89 * info - describes the array
90 * root - on success this will be filled out with the root block
91 */
92int dm_array_empty(struct dm_array_info *info, dm_block_t *root);
93
94/*
95 * Resizes the array.
96 *
97 * info - describes the array
98 * root - the root block of the array on disk
99 * old_size - the caller is responsible for remembering the size of
100 * the array
101 * new_size - can be bigger or smaller than old_size
102 * value - if we're growing the array the new entries will have this value
103 * new_root - on success, points to the new root block
104 *
105 * If growing the inc function for 'value' will be called the appropriate
106 * number of times. So if the caller is holding a reference they may want
107 * to drop it.
108 */
109int dm_array_resize(struct dm_array_info *info, dm_block_t root,
110 uint32_t old_size, uint32_t new_size,
111 const void *value, dm_block_t *new_root)
112 __dm_written_to_disk(value);
113
114/*
115 * Frees a whole array. The value_type's decrement operation will be called
116 * for all values in the array
117 */
118int dm_array_del(struct dm_array_info *info, dm_block_t root);
119
120/*
121 * Lookup a value in the array
122 *
123 * info - describes the array
124 * root - root block of the array
125 * index - array index
126 * value - the value to be read. Will be in on-disk format of course.
127 *
128 * -ENODATA will be returned if the index is out of bounds.
129 */
130int dm_array_get_value(struct dm_array_info *info, dm_block_t root,
131 uint32_t index, void *value);
132
133/*
134 * Set an entry in the array.
135 *
136 * info - describes the array
137 * root - root block of the array
138 * index - array index
139 * value - value to be written to disk. Make sure you confirm the value is
140 * in on-disk format with__dm_bless_for_disk() before calling.
141 * new_root - the new root block
142 *
143 * The old value being overwritten will be decremented, the new value
144 * incremented.
145 *
146 * -ENODATA will be returned if the index is out of bounds.
147 */
148int dm_array_set_value(struct dm_array_info *info, dm_block_t root,
149 uint32_t index, const void *value, dm_block_t *new_root)
150 __dm_written_to_disk(value);
151
152/*
153 * Walk through all the entries in an array.
154 *
155 * info - describes the array
156 * root - root block of the array
157 * fn - called back for every element
158 * context - passed to the callback
159 */
160int dm_array_walk(struct dm_array_info *info, dm_block_t root,
161 int (*fn)(void *context, uint64_t key, void *leaf),
162 void *context);
163
164/*----------------------------------------------------------------*/
165
166#endif /* _LINUX_DM_ARRAY_H */