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- radix-tree.h
/*
* Copyright (C) 2001 Momchil Velikov
* Portions Copyright (C) 2001 Christoph Hellwig
* Copyright (C) 2006 Nick Piggin
* Copyright (C) 2012 Konstantin Khlebnikov
*
* 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/bug.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
/*
* 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
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();
}
/**
* struct radix_tree_iter - radix tree iterator state
*
* @index: index of current slot
* @next_index: next-to-last index for this chunk
* @tags: bit-mask for tag-iterating
*
* This radix tree iterator works in terms of "chunks" of slots. A chunk is a
* subinterval of slots contained within one radix tree leaf node. It is
* described by a pointer to its first slot and a struct radix_tree_iter
* which holds the chunk's position in the tree and its size. For tagged
* iteration radix_tree_iter also holds the slots' bit-mask for one chosen
* radix tree tag.
*/
struct radix_tree_iter {
unsigned long index;
unsigned long next_index;
unsigned long tags;
};
#define RADIX_TREE_ITER_TAG_MASK 0x00FF /* tag index in lower byte */
#define RADIX_TREE_ITER_TAGGED 0x0100 /* lookup tagged slots */
#define RADIX_TREE_ITER_CONTIG 0x0200 /* stop at first hole */
/**
* radix_tree_iter_init - initialize radix tree iterator
*
* @iter: pointer to iterator state
* @start: iteration starting index
* Returns: NULL
*/
static __always_inline void **
radix_tree_iter_init(struct radix_tree_iter *iter, unsigned long start)
{
/*
* Leave iter->tags uninitialized. radix_tree_next_chunk() will fill it
* in the case of a successful tagged chunk lookup. If the lookup was
* unsuccessful or non-tagged then nobody cares about ->tags.
*
* Set index to zero to bypass next_index overflow protection.
* See the comment in radix_tree_next_chunk() for details.
*/
iter->index = 0;
iter->next_index = start;
return NULL;
}
/**
* radix_tree_next_chunk - find next chunk of slots for iteration
*
* @root: radix tree root
* @iter: iterator state
* @flags: RADIX_TREE_ITER_* flags and tag index
* Returns: pointer to chunk first slot, or NULL if there no more left
*
* This function looks up the next chunk in the radix tree starting from
* @iter->next_index. It returns a pointer to the chunk's first slot.
* Also it fills @iter with data about chunk: position in the tree (index),
* its end (next_index), and constructs a bit mask for tagged iterating (tags).
*/
void **radix_tree_next_chunk(struct radix_tree_root *root,
struct radix_tree_iter *iter, unsigned flags);
/**
* radix_tree_chunk_size - get current chunk size
*
* @iter: pointer to radix tree iterator
* Returns: current chunk size
*/
static __always_inline unsigned
radix_tree_chunk_size(struct radix_tree_iter *iter)
{
return iter->next_index - iter->index;
}
/**
* radix_tree_next_slot - find next slot in chunk
*
* @slot: pointer to current slot
* @iter: pointer to interator state
* @flags: RADIX_TREE_ITER_*, should be constant
* Returns: pointer to next slot, or NULL if there no more left
*
* This function updates @iter->index in the case of a successful lookup.
* For tagged lookup it also eats @iter->tags.
*/
static __always_inline void **
radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
{
if (flags & RADIX_TREE_ITER_TAGGED) {
iter->tags >>= 1;
if (likely(iter->tags & 1ul)) {
iter->index++;
return slot + 1;
}
if (!(flags & RADIX_TREE_ITER_CONTIG) && likely(iter->tags)) {
unsigned offset = __ffs(iter->tags);
iter->tags >>= offset;
iter->index += offset + 1;
return slot + offset + 1;
}
} else {
unsigned size = radix_tree_chunk_size(iter) - 1;
while (size--) {
slot++;
iter->index++;
if (likely(*slot))
return slot;
if (flags & RADIX_TREE_ITER_CONTIG) {
/* forbid switching to the next chunk */
iter->next_index = 0;
break;
}
}
}
return NULL;
}
/**
* radix_tree_for_each_chunk - iterate over chunks
*
* @slot: the void** variable for pointer to chunk first slot
* @root: the struct radix_tree_root pointer
* @iter: the struct radix_tree_iter pointer
* @start: iteration starting index
* @flags: RADIX_TREE_ITER_* and tag index
*
* Locks can be released and reacquired between iterations.
*/
#define radix_tree_for_each_chunk(slot, root, iter, start, flags) \
for (slot = radix_tree_iter_init(iter, start) ; \
(slot = radix_tree_next_chunk(root, iter, flags)) ;)
/**
* radix_tree_for_each_chunk_slot - iterate over slots in one chunk
*
* @slot: the void** variable, at the beginning points to chunk first slot
* @iter: the struct radix_tree_iter pointer
* @flags: RADIX_TREE_ITER_*, should be constant
*
* This macro is designed to be nested inside radix_tree_for_each_chunk().
* @slot points to the radix tree slot, @iter->index contains its index.
*/
#define radix_tree_for_each_chunk_slot(slot, iter, flags) \
for (; slot ; slot = radix_tree_next_slot(slot, iter, flags))
/**
* radix_tree_for_each_slot - iterate over non-empty slots
*
* @slot: the void** variable for pointer to slot
* @root: the struct radix_tree_root pointer
* @iter: the struct radix_tree_iter pointer
* @start: iteration starting index
*
* @slot points to radix tree slot, @iter->index contains its index.
*/
#define radix_tree_for_each_slot(slot, root, iter, start) \
for (slot = radix_tree_iter_init(iter, start) ; \
slot || (slot = radix_tree_next_chunk(root, iter, 0)) ; \
slot = radix_tree_next_slot(slot, iter, 0))
/**
* radix_tree_for_each_contig - iterate over contiguous slots
*
* @slot: the void** variable for pointer to slot
* @root: the struct radix_tree_root pointer
* @iter: the struct radix_tree_iter pointer
* @start: iteration starting index
*
* @slot points to radix tree slot, @iter->index contains its index.
*/
#define radix_tree_for_each_contig(slot, root, iter, start) \
for (slot = radix_tree_iter_init(iter, start) ; \
slot || (slot = radix_tree_next_chunk(root, iter, \
RADIX_TREE_ITER_CONTIG)) ; \
slot = radix_tree_next_slot(slot, iter, \
RADIX_TREE_ITER_CONTIG))
/**
* radix_tree_for_each_tagged - iterate over tagged slots
*
* @slot: the void** variable for pointer to slot
* @root: the struct radix_tree_root pointer
* @iter: the struct radix_tree_iter pointer
* @start: iteration starting index
* @tag: tag index
*
* @slot points to radix tree slot, @iter->index contains its index.
*/
#define radix_tree_for_each_tagged(slot, root, iter, start, tag) \
for (slot = radix_tree_iter_init(iter, start) ; \
slot || (slot = radix_tree_next_chunk(root, iter, \
RADIX_TREE_ITER_TAGGED | tag)) ; \
slot = radix_tree_next_slot(slot, iter, \
RADIX_TREE_ITER_TAGGED))
#endif /* _LINUX_RADIX_TREE_H */