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Diffstat (limited to 'include/linux/radix-tree.h')
| -rw-r--r-- | include/linux/radix-tree.h | 231 |
1 files changed, 231 insertions, 0 deletions
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h new file mode 100644 index 00000000..23241c2f --- /dev/null +++ b/include/linux/radix-tree.h @@ -0,0 +1,231 @@ +/* + * 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 <linux/preempt.h> +#include <linux/types.h> +#include <linux/kernel.h> +#include <linux/rcupdate.h> + +/* + * 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 + +#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_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 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); + +static inline void radix_tree_preload_end(void) +{ + preempt_enable(); +} + +#endif /* _LINUX_RADIX_TREE_H */ |