/* * Copyright (C) 2001 Momchil Velikov * Portions Copyright (C) 2001 Christoph Hellwig * Copyright (C) 2006 Nick Piggin * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License as * published by the Free Software Foundation; either version 2, or (at * your option) any later version. * * This program is distributed in the hope that it will be useful, but * WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ #ifndef _LINUX_RADIX_TREE_H #define _LINUX_RADIX_TREE_H #include #include #include #include /* * An indirect pointer (root->rnode pointing to a radix_tree_node, rather * than a data item) is signalled by the low bit set in the root->rnode * pointer. * * In this case root->height is > 0, but the indirect pointer tests are * needed for RCU lookups (because root->height is unreliable). The only * time callers need worry about this is when doing a lookup_slot under * RCU. * * Indirect pointer in fact is also used to tag the last pointer of a node * when it is shrunk, before we rcu free the node. See shrink code for * details. */ #define RADIX_TREE_INDIRECT_PTR 1 /* * A common use of the radix tree is to store pointers to struct pages; * but shmem/tmpfs needs also to store swap entries in the same tree: * those are marked as exceptional entries to distinguish them. * EXCEPTIONAL_ENTRY tests the bit, EXCEPTIONAL_SHIFT shifts content past it. */ #define RADIX_TREE_EXCEPTIONAL_ENTRY 2 #define RADIX_TREE_EXCEPTIONAL_SHIFT 2 #define radix_tree_indirect_to_ptr(ptr) \ radix_tree_indirect_to_ptr((void __force *)(ptr)) static inline int radix_tree_is_indirect_ptr(void *ptr) { return (int)((unsigned long)ptr & RADIX_TREE_INDIRECT_PTR); } /*** radix-tree API starts here ***/ #define RADIX_TREE_MAX_TAGS 3 /* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */ struct radix_tree_root { unsigned int height; gfp_t gfp_mask; struct radix_tree_node __rcu *rnode; }; #define RADIX_TREE_INIT(mask) { \ .height = 0, \ .gfp_mask = (mask), \ .rnode = NULL, \ } #define RADIX_TREE(name, mask) \ struct radix_tree_root name = RADIX_TREE_INIT(mask) #define INIT_RADIX_TREE(root, mask) \ do { \ (root)->height = 0; \ (root)->gfp_mask = (mask); \ (root)->rnode = NULL; \ } while (0) /** * Radix-tree synchronization * * The radix-tree API requires that users provide all synchronisation (with * specific exceptions, noted below). * * Synchronization of access to the data items being stored in the tree, and * management of their lifetimes must be completely managed by API users. * * For API usage, in general, * - any function _modifying_ the tree or tags (inserting or deleting * items, setting or clearing tags) must exclude other modifications, and * exclude any functions reading the tree. * - any function _reading_ the tree or tags (looking up items or tags, * gang lookups) must exclude modifications to the tree, but may occur * concurrently with other readers. * * The notable exceptions to this rule are the following functions: * radix_tree_lookup * radix_tree_lookup_slot * radix_tree_tag_get * radix_tree_gang_lookup * radix_tree_gang_lookup_slot * radix_tree_gang_lookup_tag * radix_tree_gang_lookup_tag_slot * radix_tree_tagged * * The first 7 functions are able to be called locklessly, using RCU. The * caller must ensure calls to these functions are made within rcu_read_lock() * regions. Other readers (lock-free or otherwise) and modifications may be * running concurrently. * * It is still required that the caller manage the synchronization and lifetimes * of the items. So if RCU lock-free lookups are used, typically this would mean * that the items have their own locks, or are amenable to lock-free access; and * that the items are freed by RCU (or only freed after having been deleted from * the radix tree *and* a synchronize_rcu() grace period). * * (Note, rcu_assign_pointer and rcu_dereference are not needed to control * access to data items when inserting into or looking up from the radix tree) * * Note that the value returned by radix_tree_tag_get() may not be relied upon * if only the RCU read lock is held. Functions to set/clear tags and to * delete nodes running concurrently with it may affect its result such that * two consecutive reads in the same locked section may return different * values. If reliability is required, modification functions must also be * excluded from concurrency. * * radix_tree_tagged is able to be called without locking or RCU. */ /** * radix_tree_deref_slot - dereference a slot * @pslot: pointer to slot, returned by radix_tree_lookup_slot * Returns: item that was stored in that slot with any direct pointer flag * removed. * * For use with radix_tree_lookup_slot(). Caller must hold tree at least read * locked across slot lookup and dereference. Not required if write lock is * held (ie. items cannot be concurrently inserted). * * radix_tree_deref_retry must be used to confirm validity of the pointer if * only the read lock is held. */ static inline void *radix_tree_deref_slot(void **pslot) { return rcu_dereference(*pslot); } /** * radix_tree_deref_slot_protected - dereference a slot without RCU lock but with tree lock held * @pslot: pointer to slot, returned by radix_tree_lookup_slot * Returns: item that was stored in that slot with any direct pointer flag * removed. * * Similar to radix_tree_deref_slot but only used during migration when a pages * mapping is being moved. The caller does not hold the RCU read lock but it * must hold the tree lock to prevent parallel updates. */ static inline void *radix_tree_deref_slot_protected(void **pslot, spinlock_t *treelock) { return rcu_dereference_protected(*pslot, lockdep_is_held(treelock)); } /** * radix_tree_deref_retry - check radix_tree_deref_slot * @arg: pointer returned by radix_tree_deref_slot * Returns: 0 if retry is not required, otherwise retry is required * * radix_tree_deref_retry must be used with radix_tree_deref_slot. */ static inline int radix_tree_deref_retry(void *arg) { return unlikely((unsigned long)arg & RADIX_TREE_INDIRECT_PTR); } /** * radix_tree_exceptional_entry - radix_tree_deref_slot gave exceptional entry? * @arg: value returned by radix_tree_deref_slot * Returns: 0 if well-aligned pointer, non-0 if exceptional entry. */ static inline int radix_tree_exceptional_entry(void *arg) { /* Not unlikely because radix_tree_exception often tested first */ return (unsigned long)arg & RADIX_TREE_EXCEPTIONAL_ENTRY; } /** * radix_tree_exception - radix_tree_deref_slot returned either exception? * @arg: value returned by radix_tree_deref_slot * Returns: 0 if well-aligned pointer, non-0 if either kind of exception. */ static inline int radix_tree_exception(void *arg) { return unlikely((unsigned long)arg & (RADIX_TREE_INDIRECT_PTR | RADIX_TREE_EXCEPTIONAL_ENTRY)); } /** * radix_tree_replace_slot - replace item in a slot * @pslot: pointer to slot, returned by radix_tree_lookup_slot * @item: new item to store in the slot. * * For use with radix_tree_lookup_slot(). Caller must hold tree write locked * across slot lookup and replacement. */ static inline void radix_tree_replace_slot(void **pslot, void *item) { BUG_ON(radix_tree_is_indirect_ptr(item)); rcu_assign_pointer(*pslot, item); } int radix_tree_insert(struct radix_tree_root *, unsigned long, void *); void *radix_tree_lookup(struct radix_tree_root *, unsigned long); void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long); void *radix_tree_delete(struct radix_tree_root *, unsigned long); unsigned int radix_tree_gang_lookup(struct radix_tree_root *root, void **results, unsigned long first_index, unsigned int max_items); unsigned int radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results, unsigned long *indices, unsigned long first_index, unsigned int max_items); unsigned long radix_tree_next_hole(struct radix_tree_root *root, unsigned long index, unsigned long max_scan); unsigned long radix_tree_prev_hole(struct radix_tree_root *root, unsigned long index, unsigned long max_scan); int radix_tree_preload(gfp_t gfp_mask); void radix_tree_init(void); void *radix_tree_tag_set(struct radix_tree_root *root, unsigned long index, unsigned int tag); void *radix_tree_tag_clear(struct radix_tree_root *root, unsigned long index, unsigned int tag); int radix_tree_tag_get(struct radix_tree_root *root, unsigned long index, unsigned int tag); unsigned int radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results, unsigned long first_index, unsigned int max_items, unsigned int tag); unsigned int radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results, unsigned long first_index, unsigned int max_items, unsigned int tag); unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root, unsigned long *first_indexp, unsigned long last_index, unsigned long nr_to_tag, unsigned int fromtag, unsigned int totag); int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag); unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item); static inline void radix_tree_preload_end(void) { preempt_enable(); } #endif /* _LINUX_RADIX_TREE_H */