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1/*
2 * Copyright (C) 2001 Momchil Velikov
3 * Portions Copyright (C) 2001 Christoph Hellwig
4 * Copyright (C) 2006 Nick Piggin
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License as
8 * published by the Free Software Foundation; either version 2, or (at
9 * your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful, but
12 * WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
19 */
20#ifndef _LINUX_RADIX_TREE_H
21#define _LINUX_RADIX_TREE_H
22
23#include <linux/preempt.h>
24#include <linux/types.h>
25#include <linux/kernel.h>
26#include <linux/rcupdate.h>
27
28/*
29 * An indirect pointer (root->rnode pointing to a radix_tree_node, rather
30 * than a data item) is signalled by the low bit set in the root->rnode
31 * pointer.
32 *
33 * In this case root->height is > 0, but the indirect pointer tests are
34 * needed for RCU lookups (because root->height is unreliable). The only
35 * time callers need worry about this is when doing a lookup_slot under
36 * RCU.
37 *
38 * Indirect pointer in fact is also used to tag the last pointer of a node
39 * when it is shrunk, before we rcu free the node. See shrink code for
40 * details.
41 */
42#define RADIX_TREE_INDIRECT_PTR 1
43
44#define radix_tree_indirect_to_ptr(ptr) \
45 radix_tree_indirect_to_ptr((void __force *)(ptr))
46
47static inline int radix_tree_is_indirect_ptr(void *ptr)
48{
49 return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
50}
51
52/*** radix-tree API starts here ***/
53
54#define RADIX_TREE_MAX_TAGS 3
55
56/* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
57struct radix_tree_root {
58 unsigned int height;
59 gfp_t gfp_mask;
60 struct radix_tree_node __rcu *rnode;
61};
62
63#define RADIX_TREE_INIT(mask) { \
64 .height = 0, \
65 .gfp_mask = (mask), \
66 .rnode = NULL, \
67}
68
69#define RADIX_TREE(name, mask) \
70 struct radix_tree_root name = RADIX_TREE_INIT(mask)
71
72#define INIT_RADIX_TREE(root, mask) \
73do { \
74 (root)->height = 0; \
75 (root)->gfp_mask = (mask); \
76 (root)->rnode = NULL; \
77} while (0)
78
79/**
80 * Radix-tree synchronization
81 *
82 * The radix-tree API requires that users provide all synchronisation (with
83 * specific exceptions, noted below).
84 *
85 * Synchronization of access to the data items being stored in the tree, and
86 * management of their lifetimes must be completely managed by API users.
87 *
88 * For API usage, in general,
89 * - any function _modifying_ the tree or tags (inserting or deleting
90 * items, setting or clearing tags) must exclude other modifications, and
91 * exclude any functions reading the tree.
92 * - any function _reading_ the tree or tags (looking up items or tags,
93 * gang lookups) must exclude modifications to the tree, but may occur
94 * concurrently with other readers.
95 *
96 * The notable exceptions to this rule are the following functions:
97 * radix_tree_lookup
98 * radix_tree_lookup_slot
99 * radix_tree_tag_get
100 * radix_tree_gang_lookup
101 * radix_tree_gang_lookup_slot
102 * radix_tree_gang_lookup_tag
103 * radix_tree_gang_lookup_tag_slot
104 * radix_tree_tagged
105 *
106 * The first 7 functions are able to be called locklessly, using RCU. The
107 * caller must ensure calls to these functions are made within rcu_read_lock()
108 * regions. Other readers (lock-free or otherwise) and modifications may be
109 * running concurrently.
110 *
111 * It is still required that the caller manage the synchronization and lifetimes
112 * of the items. So if RCU lock-free lookups are used, typically this would mean
113 * that the items have their own locks, or are amenable to lock-free access; and
114 * that the items are freed by RCU (or only freed after having been deleted from
115 * the radix tree *and* a synchronize_rcu() grace period).
116 *
117 * (Note, rcu_assign_pointer and rcu_dereference are not needed to control
118 * access to data items when inserting into or looking up from the radix tree)
119 *
120 * Note that the value returned by radix_tree_tag_get() may not be relied upon
121 * if only the RCU read lock is held. Functions to set/clear tags and to
122 * delete nodes running concurrently with it may affect its result such that
123 * two consecutive reads in the same locked section may return different
124 * values. If reliability is required, modification functions must also be
125 * excluded from concurrency.
126 *
127 * radix_tree_tagged is able to be called without locking or RCU.
128 */
129
130/**
131 * radix_tree_deref_slot - dereference a slot
132 * @pslot: pointer to slot, returned by radix_tree_lookup_slot
133 * Returns: item that was stored in that slot with any direct pointer flag
134 * removed.
135 *
136 * For use with radix_tree_lookup_slot(). Caller must hold tree at least read
137 * locked across slot lookup and dereference. Not required if write lock is
138 * held (ie. items cannot be concurrently inserted).
139 *
140 * radix_tree_deref_retry must be used to confirm validity of the pointer if
141 * only the read lock is held.
142 */
143static inline void *radix_tree_deref_slot(void **pslot)
144{
145 return rcu_dereference(*pslot);
146}
147
148/**
149 * radix_tree_deref_retry - check radix_tree_deref_slot
150 * @arg: pointer returned by radix_tree_deref_slot
151 * Returns: 0 if retry is not required, otherwise retry is required
152 *
153 * radix_tree_deref_retry must be used with radix_tree_deref_slot.
154 */
155static inline int radix_tree_deref_retry(void *arg)
156{
157 return unlikely((unsigned long)arg & RADIX_TREE_INDIRECT_PTR);
158}
159
160/**
161 * radix_tree_replace_slot - replace item in a slot
162 * @pslot: pointer to slot, returned by radix_tree_lookup_slot
163 * @item: new item to store in the slot.
164 *
165 * For use with radix_tree_lookup_slot(). Caller must hold tree write locked
166 * across slot lookup and replacement.
167 */
168static inline void radix_tree_replace_slot(void **pslot, void *item)
169{
170 BUG_ON(radix_tree_is_indirect_ptr(item));
171 rcu_assign_pointer(*pslot, item);
172}
173
174int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
175void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
176void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
177void *radix_tree_delete(struct radix_tree_root *, unsigned long);
178unsigned int
179radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
180 unsigned long first_index, unsigned int max_items);
181unsigned int
182radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
183 unsigned long first_index, unsigned int max_items);
184unsigned long radix_tree_next_hole(struct radix_tree_root *root,
185 unsigned long index, unsigned long max_scan);
186unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
187 unsigned long index, unsigned long max_scan);
188int radix_tree_preload(gfp_t gfp_mask);
189void radix_tree_init(void);
190void *radix_tree_tag_set(struct radix_tree_root *root,
191 unsigned long index, unsigned int tag);
192void *radix_tree_tag_clear(struct radix_tree_root *root,
193 unsigned long index, unsigned int tag);
194int radix_tree_tag_get(struct radix_tree_root *root,
195 unsigned long index, unsigned int tag);
196unsigned int
197radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
198 unsigned long first_index, unsigned int max_items,
199 unsigned int tag);
200unsigned int
201radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
202 unsigned long first_index, unsigned int max_items,
203 unsigned int tag);
204unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
205 unsigned long *first_indexp, unsigned long last_index,
206 unsigned long nr_to_tag,
207 unsigned int fromtag, unsigned int totag);
208int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);
209
210static inline void radix_tree_preload_end(void)
211{
212 preempt_enable();
213}
214
215#endif /* _LINUX_RADIX_TREE_H */