radix-tree: fix the comment of radix_tree_next_slot()

[mirror_ubuntu-hirsute-kernel.git] / include / linux / radix-tree.h

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
 * Copyright (C) 2001 Momchil Velikov
 * Portions Copyright (C) 2001 Christoph Hellwig
 * Copyright (C) 2006 Nick Piggin
 * Copyright (C) 2012 Konstantin Khlebnikov
 */
#ifndef _LINUX_RADIX_TREE_H
#define _LINUX_RADIX_TREE_H

#include <linux/bitops.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/percpu.h>
#include <linux/preempt.h>
#include <linux/rcupdate.h>
#include <linux/spinlock.h>
#include <linux/types.h>
#include <linux/xarray.h>
#include <linux/local_lock.h>

/* Keep unconverted code working */
#define radix_tree_root         xarray
#define radix_tree_node         xa_node

struct radix_tree_preload {
        local_lock_t lock;
        unsigned nr;
        /* nodes->parent points to next preallocated node */
        struct radix_tree_node *nodes;
};
DECLARE_PER_CPU(struct radix_tree_preload, radix_tree_preloads);

/*
 * The bottom two bits of the slot determine how the remaining bits in the
 * slot are interpreted:
 *
 * 00 - data pointer
 * 10 - internal entry
 * x1 - value entry
 *
 * The internal entry may be a pointer to the next level in the tree, a
 * sibling entry, or an indicator that the entry in this slot has been moved
 * to another location in the tree and the lookup should be restarted.  While
 * NULL fits the 'data pointer' pattern, it means that there is no entry in
 * the tree for this index (no matter what level of the tree it is found at).
 * This means that storing a NULL entry in the tree is the same as deleting
 * the entry from the tree.
 */
#define RADIX_TREE_ENTRY_MASK           3UL
#define RADIX_TREE_INTERNAL_NODE        2UL

static inline bool radix_tree_is_internal_node(void *ptr)
{
        return ((unsigned long)ptr & RADIX_TREE_ENTRY_MASK) ==
                                RADIX_TREE_INTERNAL_NODE;
}

/*** radix-tree API starts here ***/

#define RADIX_TREE_MAP_SHIFT    XA_CHUNK_SHIFT
#define RADIX_TREE_MAP_SIZE     (1UL << RADIX_TREE_MAP_SHIFT)
#define RADIX_TREE_MAP_MASK     (RADIX_TREE_MAP_SIZE-1)

#define RADIX_TREE_MAX_TAGS     XA_MAX_MARKS
#define RADIX_TREE_TAG_LONGS    XA_MARK_LONGS

#define RADIX_TREE_INDEX_BITS  (8 /* CHAR_BIT */ * sizeof(unsigned long))
#define RADIX_TREE_MAX_PATH (DIV_ROUND_UP(RADIX_TREE_INDEX_BITS, \
                                          RADIX_TREE_MAP_SHIFT))

/* The IDR tag is stored in the low bits of xa_flags */
#define ROOT_IS_IDR     ((__force gfp_t)4)
/* The top bits of xa_flags are used to store the root tags */
#define ROOT_TAG_SHIFT  (__GFP_BITS_SHIFT)

#define RADIX_TREE_INIT(name, mask)     XARRAY_INIT(name, mask)

#define RADIX_TREE(name, mask) \
        struct radix_tree_root name = RADIX_TREE_INIT(name, mask)

#define INIT_RADIX_TREE(root, mask) xa_init_flags(root, mask)

static inline bool radix_tree_empty(const struct radix_tree_root *root)
{
        return root->xa_head == NULL;
}

/**
 * struct radix_tree_iter - radix tree iterator state
 *
 * @index:      index of current slot
 * @next_index: one beyond the last index for this chunk
 * @tags:       bit-mask for tag-iterating
 * @node:       node that contains current slot
 *
 * 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;
        struct radix_tree_node *node;
};

/**
 * 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
 * radix_tree_lookup_slot
 * radix_tree_tag_get
 * radix_tree_gang_lookup
 * 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
 * @slot: slot pointer, returned by radix_tree_lookup_slot
 *
 * 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.
 *
 * Return: entry stored in that slot.
 */
static inline void *radix_tree_deref_slot(void __rcu **slot)
{
        return rcu_dereference(*slot);
}

/**
 * radix_tree_deref_slot_protected - dereference a slot with tree lock held
 * @slot: slot pointer, returned by radix_tree_lookup_slot
 *
 * Similar to radix_tree_deref_slot.  The caller does not hold the RCU read
 * lock but it must hold the tree lock to prevent parallel updates.
 *
 * Return: entry stored in that slot.
 */
static inline void *radix_tree_deref_slot_protected(void __rcu **slot,
                                                        spinlock_t *treelock)
{
        return rcu_dereference_protected(*slot, 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(radix_tree_is_internal_node(arg));
}

/**
 * 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_ENTRY_MASK);
}

int radix_tree_insert(struct radix_tree_root *, unsigned long index,
                        void *);
void *__radix_tree_lookup(const struct radix_tree_root *, unsigned long index,
                          struct radix_tree_node **nodep, void __rcu ***slotp);
void *radix_tree_lookup(const struct radix_tree_root *, unsigned long);
void __rcu **radix_tree_lookup_slot(const struct radix_tree_root *,
                                        unsigned long index);
void __radix_tree_replace(struct radix_tree_root *, struct radix_tree_node *,
                          void __rcu **slot, void *entry);
void radix_tree_iter_replace(struct radix_tree_root *,
                const struct radix_tree_iter *, void __rcu **slot, void *entry);
void radix_tree_replace_slot(struct radix_tree_root *,
                             void __rcu **slot, void *entry);
void radix_tree_iter_delete(struct radix_tree_root *,
                        struct radix_tree_iter *iter, void __rcu **slot);
void *radix_tree_delete_item(struct radix_tree_root *, unsigned long, void *);
void *radix_tree_delete(struct radix_tree_root *, unsigned long);
unsigned int radix_tree_gang_lookup(const struct radix_tree_root *,
                        void **results, unsigned long first_index,
                        unsigned int max_items);
int radix_tree_preload(gfp_t gfp_mask);
int radix_tree_maybe_preload(gfp_t gfp_mask);
void radix_tree_init(void);
void *radix_tree_tag_set(struct radix_tree_root *,
                        unsigned long index, unsigned int tag);
void *radix_tree_tag_clear(struct radix_tree_root *,
                        unsigned long index, unsigned int tag);
int radix_tree_tag_get(const struct radix_tree_root *,
                        unsigned long index, unsigned int tag);
void radix_tree_iter_tag_clear(struct radix_tree_root *,
                const struct radix_tree_iter *iter, unsigned int tag);
unsigned int radix_tree_gang_lookup_tag(const struct radix_tree_root *,
                void **results, unsigned long first_index,
                unsigned int max_items, unsigned int tag);
unsigned int radix_tree_gang_lookup_tag_slot(const struct radix_tree_root *,
                void __rcu ***results, unsigned long first_index,
                unsigned int max_items, unsigned int tag);
int radix_tree_tagged(const struct radix_tree_root *, unsigned int tag);

static inline void radix_tree_preload_end(void)
{
        local_unlock(&radix_tree_preloads.lock);
}

void __rcu **idr_get_free(struct radix_tree_root *root,
                              struct radix_tree_iter *iter, gfp_t gfp,
                              unsigned long max);

enum {
        RADIX_TREE_ITER_TAG_MASK = 0x0f,        /* tag index in lower nybble */
        RADIX_TREE_ITER_TAGGED   = 0x10,        /* lookup tagged slots */
        RADIX_TREE_ITER_CONTIG   = 0x20,        /* 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 __rcu **
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 __rcu **radix_tree_next_chunk(const struct radix_tree_root *,
                             struct radix_tree_iter *iter, unsigned flags);

/**
 * radix_tree_iter_lookup - look up an index in the radix tree
 * @root: radix tree root
 * @iter: iterator state
 * @index: key to look up
 *
 * If @index is present in the radix tree, this function returns the slot
 * containing it and updates @iter to describe the entry.  If @index is not
 * present, it returns NULL.
 */
static inline void __rcu **
radix_tree_iter_lookup(const struct radix_tree_root *root,
                        struct radix_tree_iter *iter, unsigned long index)
{
        radix_tree_iter_init(iter, index);
        return radix_tree_next_chunk(root, iter, RADIX_TREE_ITER_CONTIG);
}

/**
 * radix_tree_iter_retry - retry this chunk of the iteration
 * @iter:       iterator state
 *
 * If we iterate over a tree protected only by the RCU lock, a race
 * against deletion or creation may result in seeing a slot for which
 * radix_tree_deref_retry() returns true.  If so, call this function
 * and continue the iteration.
 */
static inline __must_check
void __rcu **radix_tree_iter_retry(struct radix_tree_iter *iter)
{
        iter->next_index = iter->index;
        iter->tags = 0;
        return NULL;
}

static inline unsigned long
__radix_tree_iter_add(struct radix_tree_iter *iter, unsigned long slots)
{
        return iter->index + slots;
}

/**
 * radix_tree_iter_resume - resume iterating when the chunk may be invalid
 * @slot: pointer to current slot
 * @iter: iterator state
 * Returns: New slot pointer
 *
 * If the iterator needs to release then reacquire a lock, the chunk may
 * have been invalidated by an insertion or deletion.  Call this function
 * before releasing the lock to continue the iteration from the next index.
 */
void __rcu **__must_check radix_tree_iter_resume(void __rcu **slot,
                                        struct radix_tree_iter *iter);

/**
 * radix_tree_chunk_size - get current chunk size
 *
 * @iter:       pointer to radix tree iterator
 * Returns:     current chunk size
 */
static __always_inline long
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 iterator 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.
 *
 * There are several cases where 'slot' can be passed in as NULL to this
 * function.  These cases result from the use of radix_tree_iter_resume() or
 * radix_tree_iter_retry().  In these cases we don't end up dereferencing
 * 'slot' because either:
 * a) we are doing tagged iteration and iter->tags has been set to 0, or
 * b) we are doing non-tagged iteration, and iter->index and iter->next_index
 *    have been set up so that radix_tree_chunk_size() returns 1 or 0.
 */
static __always_inline void __rcu **radix_tree_next_slot(void __rcu **slot,
                                struct radix_tree_iter *iter, unsigned flags)
{
        if (flags & RADIX_TREE_ITER_TAGGED) {
                iter->tags >>= 1;
                if (unlikely(!iter->tags))
                        return NULL;
                if (likely(iter->tags & 1ul)) {
                        iter->index = __radix_tree_iter_add(iter, 1);
                        slot++;
                        goto found;
                }
                if (!(flags & RADIX_TREE_ITER_CONTIG)) {
                        unsigned offset = __ffs(iter->tags);

                        iter->tags >>= offset++;
                        iter->index = __radix_tree_iter_add(iter, offset);
                        slot += offset;
                        goto found;
                }
        } else {
                long count = radix_tree_chunk_size(iter);

                while (--count > 0) {
                        slot++;
                        iter->index = __radix_tree_iter_add(iter, 1);

                        if (likely(*slot))
                                goto found;
                        if (flags & RADIX_TREE_ITER_CONTIG) {
                                /* forbid switching to the next chunk */
                                iter->next_index = 0;
                                break;
                        }
                }
        }
        return NULL;

 found:
        return slot;
}

/**
 * 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_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 | tag))

#endif /* _LINUX_RADIX_TREE_H */