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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#define RADIX_TREE_INDIRECT_PTR 1
39#define RADIX_TREE_RETRY ((void *)-1UL)
40
41static inline void *radix_tree_ptr_to_indirect(void *ptr)
42{
43 return (void *)((unsigned long)ptr | RADIX_TREE_INDIRECT_PTR);
44}
45
46static inline void *radix_tree_indirect_to_ptr(void *ptr)
47{
48 return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_PTR);
49}
50
51static inline int radix_tree_is_indirect_ptr(void *ptr)
52{
53 return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR);
54}
55
56/*** radix-tree API starts here ***/
57
58#define RADIX_TREE_MAX_TAGS 2
59
60/* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
61struct radix_tree_root {
62 unsigned int height;
63 gfp_t gfp_mask;
64 struct radix_tree_node *rnode;
65};
66
67#define RADIX_TREE_INIT(mask) { \
68 .height = 0, \
69 .gfp_mask = (mask), \
70 .rnode = NULL, \
71}
72
73#define RADIX_TREE(name, mask) \
74 struct radix_tree_root name = RADIX_TREE_INIT(mask)
75
76#define INIT_RADIX_TREE(root, mask) \
77do { \
78 (root)->height = 0; \
79 (root)->gfp_mask = (mask); \
80 (root)->rnode = NULL; \
81} while (0)
82
83/**
84 * Radix-tree synchronization
85 *
86 * The radix-tree API requires that users provide all synchronisation (with
87 * specific exceptions, noted below).
88 *
89 * Synchronization of access to the data items being stored in the tree, and
90 * management of their lifetimes must be completely managed by API users.
91 *
92 * For API usage, in general,
93 * - any function _modifying_ the tree or tags (inserting or deleting
94 * items, setting or clearing tags) must exclude other modifications, and
95 * exclude any functions reading the tree.
96 * - any function _reading_ the tree or tags (looking up items or tags,
97 * gang lookups) must exclude modifications to the tree, but may occur
98 * concurrently with other readers.
99 *
100 * The notable exceptions to this rule are the following functions:
101 * radix_tree_lookup
102 * radix_tree_lookup_slot
103 * radix_tree_tag_get
104 * radix_tree_gang_lookup
105 * radix_tree_gang_lookup_slot
106 * radix_tree_gang_lookup_tag
107 * radix_tree_gang_lookup_tag_slot
108 * radix_tree_tagged
109 *
110 * The first 7 functions are able to be called locklessly, using RCU. The
111 * caller must ensure calls to these functions are made within rcu_read_lock()
112 * regions. Other readers (lock-free or otherwise) and modifications may be
113 * running concurrently.
114 *
115 * It is still required that the caller manage the synchronization and lifetimes
116 * of the items. So if RCU lock-free lookups are used, typically this would mean
117 * that the items have their own locks, or are amenable to lock-free access; and
118 * that the items are freed by RCU (or only freed after having been deleted from
119 * the radix tree *and* a synchronize_rcu() grace period).
120 *
121 * (Note, rcu_assign_pointer and rcu_dereference are not needed to control
122 * access to data items when inserting into or looking up from the radix tree)
123 *
124 * Note that the value returned by radix_tree_tag_get() may not be relied upon
125 * if only the RCU read lock is held. Functions to set/clear tags and to
126 * delete nodes running concurrently with it may affect its result such that
127 * two consecutive reads in the same locked section may return different
128 * values. If reliability is required, modification functions must also be
129 * excluded from concurrency.
130 *
131 * radix_tree_tagged is able to be called without locking or RCU.
132 */
133
134/**
135 * radix_tree_deref_slot - dereference a slot
136 * @pslot: pointer to slot, returned by radix_tree_lookup_slot
137 * Returns: item that was stored in that slot with any direct pointer flag
138 * removed.
139 *
140 * For use with radix_tree_lookup_slot(). Caller must hold tree at least read
141 * locked across slot lookup and dereference. More likely, will be used with
142 * radix_tree_replace_slot(), as well, so caller will hold tree write locked.
143 */
144static inline void *radix_tree_deref_slot(void **pslot)
145{
146 void *ret = rcu_dereference(*pslot);
147 if (unlikely(radix_tree_is_indirect_ptr(ret)))
148 ret = RADIX_TREE_RETRY;
149 return ret;
150}
151/**
152 * radix_tree_replace_slot - replace item in a slot
153 * @pslot: pointer to slot, returned by radix_tree_lookup_slot
154 * @item: new item to store in the slot.
155 *
156 * For use with radix_tree_lookup_slot(). Caller must hold tree write locked
157 * across slot lookup and replacement.
158 */
159static inline void radix_tree_replace_slot(void **pslot, void *item)
160{
161 BUG_ON(radix_tree_is_indirect_ptr(item));
162 rcu_assign_pointer(*pslot, item);
163}
164
165int radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
166void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
167void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
168void *radix_tree_delete(struct radix_tree_root *, unsigned long);
169unsigned int
170radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
171 unsigned long first_index, unsigned int max_items);
172unsigned int
173radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
174 unsigned long first_index, unsigned int max_items);
175unsigned long radix_tree_next_hole(struct radix_tree_root *root,
176 unsigned long index, unsigned long max_scan);
177unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
178 unsigned long index, unsigned long max_scan);
179int radix_tree_preload(gfp_t gfp_mask);
180void radix_tree_init(void);
181void *radix_tree_tag_set(struct radix_tree_root *root,
182 unsigned long index, unsigned int tag);
183void *radix_tree_tag_clear(struct radix_tree_root *root,
184 unsigned long index, unsigned int tag);
185int radix_tree_tag_get(struct radix_tree_root *root,
186 unsigned long index, unsigned int tag);
187unsigned int
188radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
189 unsigned long first_index, unsigned int max_items,
190 unsigned int tag);
191unsigned int
192radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
193 unsigned long first_index, unsigned int max_items,
194 unsigned int tag);
195int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);
196
197static inline void radix_tree_preload_end(void)
198{
199 preempt_enable();
200}
201
202#endif /* _LINUX_RADIX_TREE_H */