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 * A direct pointer (root->rnode pointing directly to a data item, 30 * rather than another radix_tree_node) is signalled by the low bit 31 * set in the root->rnode pointer. 32 * 33 * In this case root->height is also NULL, but the direct pointer tests are 34 * needed for RCU lookups when root->height is unreliable. 35 */ 36 #define RADIX_TREE_DIRECT_PTR 1 37 38 static inline void *radix_tree_ptr_to_direct(void *ptr) 39 { 40 return (void *)((unsigned long)ptr | RADIX_TREE_DIRECT_PTR); 41 } 42 43 static inline void *radix_tree_direct_to_ptr(void *ptr) 44 { 45 return (void *)((unsigned long)ptr & ~RADIX_TREE_DIRECT_PTR); 46 } 47 48 static inline int radix_tree_is_direct_ptr(void *ptr) 49 { 50 return (int)((unsigned long)ptr & RADIX_TREE_DIRECT_PTR); 51 } 52 53 /*** radix-tree API starts here ***/ 54 55 #define RADIX_TREE_MAX_TAGS 2 56 57 /* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */ 58 struct radix_tree_root { 59 unsigned int height; 60 gfp_t gfp_mask; 61 struct radix_tree_node *rnode; 62 }; 63 64 #define RADIX_TREE_INIT(mask) { \ 65 .height = 0, \ 66 .gfp_mask = (mask), \ 67 .rnode = NULL, \ 68 } 69 70 #define RADIX_TREE(name, mask) \ 71 struct radix_tree_root name = RADIX_TREE_INIT(mask) 72 73 #define INIT_RADIX_TREE(root, mask) \ 74 do { \ 75 (root)->height = 0; \ 76 (root)->gfp_mask = (mask); \ 77 (root)->rnode = NULL; \ 78 } while (0) 79 80 /** 81 * Radix-tree synchronization 82 * 83 * The radix-tree API requires that users provide all synchronisation (with 84 * specific exceptions, noted below). 85 * 86 * Synchronization of access to the data items being stored in the tree, and 87 * management of their lifetimes must be completely managed by API users. 88 * 89 * For API usage, in general, 90 * - any function _modifying_ the the tree or tags (inserting or deleting 91 * items, setting or clearing tags must exclude other modifications, and 92 * exclude any functions reading the tree. 93 * - any function _reading_ the the tree or tags (looking up items or tags, 94 * gang lookups) must exclude modifications to the tree, but may occur 95 * concurrently with other readers. 96 * 97 * The notable exceptions to this rule are the following functions: 98 * radix_tree_lookup 99 * radix_tree_tag_get 100 * radix_tree_gang_lookup 101 * radix_tree_gang_lookup_tag 102 * radix_tree_tagged 103 * 104 * The first 4 functions are able to be called locklessly, using RCU. The 105 * caller must ensure calls to these functions are made within rcu_read_lock() 106 * regions. Other readers (lock-free or otherwise) and modifications may be 107 * running concurrently. 108 * 109 * It is still required that the caller manage the synchronization and lifetimes 110 * of the items. So if RCU lock-free lookups are used, typically this would mean 111 * that the items have their own locks, or are amenable to lock-free access; and 112 * that the items are freed by RCU (or only freed after having been deleted from 113 * the radix tree *and* a synchronize_rcu() grace period). 114 * 115 * (Note, rcu_assign_pointer and rcu_dereference are not needed to control 116 * access to data items when inserting into or looking up from the radix tree) 117 * 118 * radix_tree_tagged is able to be called without locking or RCU. 119 */ 120 121 /** 122 * radix_tree_deref_slot - dereference a slot 123 * @pslot: pointer to slot, returned by radix_tree_lookup_slot 124 * Returns: item that was stored in that slot with any direct pointer flag 125 * removed. 126 * 127 * For use with radix_tree_lookup_slot(). Caller must hold tree at least read 128 * locked across slot lookup and dereference. More likely, will be used with 129 * radix_tree_replace_slot(), as well, so caller will hold tree write locked. 130 */ 131 static inline void *radix_tree_deref_slot(void **pslot) 132 { 133 return radix_tree_direct_to_ptr(*pslot); 134 } 135 /** 136 * radix_tree_replace_slot - replace item in a slot 137 * @pslot: pointer to slot, returned by radix_tree_lookup_slot 138 * @item: new item to store in the slot. 139 * 140 * For use with radix_tree_lookup_slot(). Caller must hold tree write locked 141 * across slot lookup and replacement. 142 */ 143 static inline void radix_tree_replace_slot(void **pslot, void *item) 144 { 145 BUG_ON(radix_tree_is_direct_ptr(item)); 146 rcu_assign_pointer(*pslot, 147 (void *)((unsigned long)item | 148 ((unsigned long)*pslot & RADIX_TREE_DIRECT_PTR))); 149 } 150 151 int radix_tree_insert(struct radix_tree_root *, unsigned long, void *); 152 void *radix_tree_lookup(struct radix_tree_root *, unsigned long); 153 void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long); 154 void *radix_tree_delete(struct radix_tree_root *, unsigned long); 155 unsigned int 156 radix_tree_gang_lookup(struct radix_tree_root *root, void **results, 157 unsigned long first_index, unsigned int max_items); 158 int radix_tree_preload(gfp_t gfp_mask); 159 void radix_tree_init(void); 160 void *radix_tree_tag_set(struct radix_tree_root *root, 161 unsigned long index, unsigned int tag); 162 void *radix_tree_tag_clear(struct radix_tree_root *root, 163 unsigned long index, unsigned int tag); 164 int radix_tree_tag_get(struct radix_tree_root *root, 165 unsigned long index, unsigned int tag); 166 unsigned int 167 radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results, 168 unsigned long first_index, unsigned int max_items, 169 unsigned int tag); 170 int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag); 171 172 static inline void radix_tree_preload_end(void) 173 { 174 preempt_enable(); 175 } 176 177 #endif /* _LINUX_RADIX_TREE_H */ 178