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