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 41 static inline void *radix_tree_ptr_to_indirect(void *ptr) 42 { 43 return (void *)((unsigned long)ptr | RADIX_TREE_INDIRECT_PTR); 44 } 45 46 static inline void *radix_tree_indirect_to_ptr(void *ptr) 47 { 48 return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_PTR); 49 } 50 #define radix_tree_indirect_to_ptr(ptr) \ 51 radix_tree_indirect_to_ptr((void __force *)(ptr)) 52 53 static inline int radix_tree_is_indirect_ptr(void *ptr) 54 { 55 return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR); 56 } 57 58 /*** radix-tree API starts here ***/ 59 60 #define RADIX_TREE_MAX_TAGS 3 61 62 /* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */ 63 struct radix_tree_root { 64 unsigned int height; 65 gfp_t gfp_mask; 66 struct radix_tree_node __rcu *rnode; 67 }; 68 69 #define RADIX_TREE_INIT(mask) { \ 70 .height = 0, \ 71 .gfp_mask = (mask), \ 72 .rnode = NULL, \ 73 } 74 75 #define RADIX_TREE(name, mask) \ 76 struct radix_tree_root name = RADIX_TREE_INIT(mask) 77 78 #define INIT_RADIX_TREE(root, mask) \ 79 do { \ 80 (root)->height = 0; \ 81 (root)->gfp_mask = (mask); \ 82 (root)->rnode = NULL; \ 83 } while (0) 84 85 /** 86 * Radix-tree synchronization 87 * 88 * The radix-tree API requires that users provide all synchronisation (with 89 * specific exceptions, noted below). 90 * 91 * Synchronization of access to the data items being stored in the tree, and 92 * management of their lifetimes must be completely managed by API users. 93 * 94 * For API usage, in general, 95 * - any function _modifying_ the tree or tags (inserting or deleting 96 * items, setting or clearing tags) must exclude other modifications, and 97 * exclude any functions reading the tree. 98 * - any function _reading_ the tree or tags (looking up items or tags, 99 * gang lookups) must exclude modifications to the tree, but may occur 100 * concurrently with other readers. 101 * 102 * The notable exceptions to this rule are the following functions: 103 * radix_tree_lookup 104 * radix_tree_lookup_slot 105 * radix_tree_tag_get 106 * radix_tree_gang_lookup 107 * radix_tree_gang_lookup_slot 108 * radix_tree_gang_lookup_tag 109 * radix_tree_gang_lookup_tag_slot 110 * radix_tree_tagged 111 * 112 * The first 7 functions are able to be called locklessly, using RCU. The 113 * caller must ensure calls to these functions are made within rcu_read_lock() 114 * regions. Other readers (lock-free or otherwise) and modifications may be 115 * running concurrently. 116 * 117 * It is still required that the caller manage the synchronization and lifetimes 118 * of the items. So if RCU lock-free lookups are used, typically this would mean 119 * that the items have their own locks, or are amenable to lock-free access; and 120 * that the items are freed by RCU (or only freed after having been deleted from 121 * the radix tree *and* a synchronize_rcu() grace period). 122 * 123 * (Note, rcu_assign_pointer and rcu_dereference are not needed to control 124 * access to data items when inserting into or looking up from the radix tree) 125 * 126 * Note that the value returned by radix_tree_tag_get() may not be relied upon 127 * if only the RCU read lock is held. Functions to set/clear tags and to 128 * delete nodes running concurrently with it may affect its result such that 129 * two consecutive reads in the same locked section may return different 130 * values. If reliability is required, modification functions must also be 131 * excluded from concurrency. 132 * 133 * radix_tree_tagged is able to be called without locking or RCU. 134 */ 135 136 /** 137 * radix_tree_deref_slot - dereference a slot 138 * @pslot: pointer to slot, returned by radix_tree_lookup_slot 139 * Returns: item that was stored in that slot with any direct pointer flag 140 * removed. 141 * 142 * For use with radix_tree_lookup_slot(). Caller must hold tree at least read 143 * locked across slot lookup and dereference. More likely, will be used with 144 * radix_tree_replace_slot(), as well, so caller will hold tree write locked. 145 */ 146 static inline void *radix_tree_deref_slot(void **pslot) 147 { 148 void *ret = rcu_dereference(*pslot); 149 if (unlikely(radix_tree_is_indirect_ptr(ret))) 150 ret = RADIX_TREE_RETRY; 151 return ret; 152 } 153 /** 154 * radix_tree_replace_slot - replace item in a slot 155 * @pslot: pointer to slot, returned by radix_tree_lookup_slot 156 * @item: new item to store in the slot. 157 * 158 * For use with radix_tree_lookup_slot(). Caller must hold tree write locked 159 * across slot lookup and replacement. 160 */ 161 static inline void radix_tree_replace_slot(void **pslot, void *item) 162 { 163 BUG_ON(radix_tree_is_indirect_ptr(item)); 164 rcu_assign_pointer(*pslot, item); 165 } 166 167 int radix_tree_insert(struct radix_tree_root *, unsigned long, void *); 168 void *radix_tree_lookup(struct radix_tree_root *, unsigned long); 169 void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long); 170 void *radix_tree_delete(struct radix_tree_root *, unsigned long); 171 unsigned int 172 radix_tree_gang_lookup(struct radix_tree_root *root, void **results, 173 unsigned long first_index, unsigned int max_items); 174 unsigned int 175 radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results, 176 unsigned long first_index, unsigned int max_items); 177 unsigned long radix_tree_next_hole(struct radix_tree_root *root, 178 unsigned long index, unsigned long max_scan); 179 unsigned long radix_tree_prev_hole(struct radix_tree_root *root, 180 unsigned long index, unsigned long max_scan); 181 int radix_tree_preload(gfp_t gfp_mask); 182 void radix_tree_init(void); 183 void *radix_tree_tag_set(struct radix_tree_root *root, 184 unsigned long index, unsigned int tag); 185 void *radix_tree_tag_clear(struct radix_tree_root *root, 186 unsigned long index, unsigned int tag); 187 int radix_tree_tag_get(struct radix_tree_root *root, 188 unsigned long index, unsigned int tag); 189 unsigned int 190 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results, 191 unsigned long first_index, unsigned int max_items, 192 unsigned int tag); 193 unsigned int 194 radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results, 195 unsigned long first_index, unsigned int max_items, 196 unsigned int tag); 197 unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root, 198 unsigned long *first_indexp, unsigned long last_index, 199 unsigned long nr_to_tag, 200 unsigned int fromtag, unsigned int totag); 201 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag); 202 203 static inline void radix_tree_preload_end(void) 204 { 205 preempt_enable(); 206 } 207 208 #endif /* _LINUX_RADIX_TREE_H */ 209