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/*
* 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.
*/
#define RADIX_TREE_INDIRECT_PTR 1
#define RADIX_TREE_RETRY ((void *)-1UL)
static inline void *radix_tree_ptr_to_indirect(void *ptr)
{
return (void *)((unsigned long)ptr | RADIX_TREE_INDIRECT_PTR);
}
static inline void *radix_tree_indirect_to_ptr(void *ptr)
{
return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_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 2
/* 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 *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. More likely, will be used with
* radix_tree_replace_slot(), as well, so caller will hold tree write locked.
*/
static inline void *radix_tree_deref_slot(void **pslot)
{
void *ret = rcu_dereference(*pslot);
if (unlikely(radix_tree_is_indirect_ptr(ret)))
ret = RADIX_TREE_RETRY;
return ret;
}
/**
* 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);
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 */
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