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 /* 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/gfp_types.h>
 #include <linux/list.h>
 #include <linux/lockdep.h>
 #include <linux/math.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 */

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