TOMOYO Linux Cross Reference
Linux/include/linux/xarray.h

   /* SPDX-License-Identifier: GPL-2.0+ */
   #ifndef _LINUX_XARRAY_H
   #define _LINUX_XARRAY_H
   /*
    * eXtensible Arrays
    * Copyright (c) 2017 Microsoft Corporation
    * Author: Matthew Wilcox <willy@infradead.org>
    *
    * See Documentation/core-api/xarray.rst for how to use the XArray.
   */
  
  #include <linux/bitmap.h>
  #include <linux/bug.h>
  #include <linux/compiler.h>
  #include <linux/err.h>
  #include <linux/gfp.h>
  #include <linux/kconfig.h>
  #include <linux/limits.h>
  #include <linux/lockdep.h>
  #include <linux/rcupdate.h>
  #include <linux/sched/mm.h>
  #include <linux/spinlock.h>
  #include <linux/types.h>
  
  struct list_lru;
  
  /*
   * The bottom two bits of the entry determine how the XArray interprets
   * the contents:
   *
   * 00: Pointer entry
   * 10: Internal entry
   * x1: Value entry or tagged pointer
   *
   * Attempting to store internal entries in the XArray is a bug.
   *
   * Most internal entries are pointers to the next node in the tree.
   * The following internal entries have a special meaning:
   *
   * 0-62: Sibling entries
   * 256: Retry entry
   * 257: Zero entry
   *
   * Errors are also represented as internal entries, but use the negative
   * space (-4094 to -2).  They're never stored in the slots array; only
   * returned by the normal API.
   */
  
  #define BITS_PER_XA_VALUE       (BITS_PER_LONG - 1)
  
  /**
   * xa_mk_value() - Create an XArray entry from an integer.
   * @v: Value to store in XArray.
   *
   * Context: Any context.
   * Return: An entry suitable for storing in the XArray.
   */
  static inline void *xa_mk_value(unsigned long v)
  {
          WARN_ON((long)v < 0);
          return (void *)((v << 1) | 1);
  }
  
  /**
   * xa_to_value() - Get value stored in an XArray entry.
   * @entry: XArray entry.
   *
   * Context: Any context.
   * Return: The value stored in the XArray entry.
   */
  static inline unsigned long xa_to_value(const void *entry)
  {
          return (unsigned long)entry >> 1;
  }
  
  /**
   * xa_is_value() - Determine if an entry is a value.
   * @entry: XArray entry.
   *
   * Context: Any context.
   * Return: True if the entry is a value, false if it is a pointer.
   */
  static inline bool xa_is_value(const void *entry)
  {
          return (unsigned long)entry & 1;
  }
  
  /**
   * xa_tag_pointer() - Create an XArray entry for a tagged pointer.
   * @p: Plain pointer.
   * @tag: Tag value (0, 1 or 3).
   *
   * If the user of the XArray prefers, they can tag their pointers instead
   * of storing value entries.  Three tags are available (0, 1 and 3).
   * These are distinct from the xa_mark_t as they are not replicated up
   * through the array and cannot be searched for.
   *
   * Context: Any context.
   * Return: An XArray entry.
  */
 static inline void *xa_tag_pointer(void *p, unsigned long tag)
 {
         return (void *)((unsigned long)p | tag);
 }
 
 /**
  * xa_untag_pointer() - Turn an XArray entry into a plain pointer.
  * @entry: XArray entry.
  *
  * If you have stored a tagged pointer in the XArray, call this function
  * to get the untagged version of the pointer.
  *
  * Context: Any context.
  * Return: A pointer.
  */
 static inline void *xa_untag_pointer(void *entry)
 {
         return (void *)((unsigned long)entry & ~3UL);
 }
 
 /**
  * xa_pointer_tag() - Get the tag stored in an XArray entry.
  * @entry: XArray entry.
  *
  * If you have stored a tagged pointer in the XArray, call this function
  * to get the tag of that pointer.
  *
  * Context: Any context.
  * Return: A tag.
  */
 static inline unsigned int xa_pointer_tag(void *entry)
 {
         return (unsigned long)entry & 3UL;
 }
 
 /*
  * xa_mk_internal() - Create an internal entry.
  * @v: Value to turn into an internal entry.
  *
  * Internal entries are used for a number of purposes.  Entries 0-255 are
  * used for sibling entries (only 0-62 are used by the current code).  256
  * is used for the retry entry.  257 is used for the reserved / zero entry.
  * Negative internal entries are used to represent errnos.  Node pointers
  * are also tagged as internal entries in some situations.
  *
  * Context: Any context.
  * Return: An XArray internal entry corresponding to this value.
  */
 static inline void *xa_mk_internal(unsigned long v)
 {
         return (void *)((v << 2) | 2);
 }
 
 /*
  * xa_to_internal() - Extract the value from an internal entry.
  * @entry: XArray entry.
  *
  * Context: Any context.
  * Return: The value which was stored in the internal entry.
  */
 static inline unsigned long xa_to_internal(const void *entry)
 {
         return (unsigned long)entry >> 2;
 }
 
 /*
  * xa_is_internal() - Is the entry an internal entry?
  * @entry: XArray entry.
  *
  * Context: Any context.
  * Return: %true if the entry is an internal entry.
  */
 static inline bool xa_is_internal(const void *entry)
 {
         return ((unsigned long)entry & 3) == 2;
 }
 
 #define XA_ZERO_ENTRY           xa_mk_internal(257)
 
 /**
  * xa_is_zero() - Is the entry a zero entry?
  * @entry: Entry retrieved from the XArray
  *
  * The normal API will return NULL as the contents of a slot containing
  * a zero entry.  You can only see zero entries by using the advanced API.
  *
  * Return: %true if the entry is a zero entry.
  */
 static inline bool xa_is_zero(const void *entry)
 {
         return unlikely(entry == XA_ZERO_ENTRY);
 }
 
 /**
  * xa_is_err() - Report whether an XArray operation returned an error
  * @entry: Result from calling an XArray function
  *
  * If an XArray operation cannot complete an operation, it will return
  * a special value indicating an error.  This function tells you
  * whether an error occurred; xa_err() tells you which error occurred.
  *
  * Context: Any context.
  * Return: %true if the entry indicates an error.
  */
 static inline bool xa_is_err(const void *entry)
 {
         return unlikely(xa_is_internal(entry) &&
                         entry >= xa_mk_internal(-MAX_ERRNO));
 }
 
 /**
  * xa_err() - Turn an XArray result into an errno.
  * @entry: Result from calling an XArray function.
  *
  * If an XArray operation cannot complete an operation, it will return
  * a special pointer value which encodes an errno.  This function extracts
  * the errno from the pointer value, or returns 0 if the pointer does not
  * represent an errno.
  *
  * Context: Any context.
  * Return: A negative errno or 0.
  */
 static inline int xa_err(void *entry)
 {
         /* xa_to_internal() would not do sign extension. */
         if (xa_is_err(entry))
                 return (long)entry >> 2;
         return 0;
 }
 
 /**
  * struct xa_limit - Represents a range of IDs.
  * @min: The lowest ID to allocate (inclusive).
  * @max: The maximum ID to allocate (inclusive).
  *
  * This structure is used either directly or via the XA_LIMIT() macro
  * to communicate the range of IDs that are valid for allocation.
  * Three common ranges are predefined for you:
  * * xa_limit_32b       - [0 - UINT_MAX]
  * * xa_limit_31b       - [0 - INT_MAX]
  * * xa_limit_16b       - [0 - USHRT_MAX]
  */
 struct xa_limit {
         u32 max;
         u32 min;
 };
 
 #define XA_LIMIT(_min, _max) (struct xa_limit) { .min = _min, .max = _max }
 
 #define xa_limit_32b    XA_LIMIT(0, UINT_MAX)
 #define xa_limit_31b    XA_LIMIT(0, INT_MAX)
 #define xa_limit_16b    XA_LIMIT(0, USHRT_MAX)
 
 typedef unsigned __bitwise xa_mark_t;
 #define XA_MARK_0               ((__force xa_mark_t)0U)
 #define XA_MARK_1               ((__force xa_mark_t)1U)
 #define XA_MARK_2               ((__force xa_mark_t)2U)
 #define XA_PRESENT              ((__force xa_mark_t)8U)
 #define XA_MARK_MAX             XA_MARK_2
 #define XA_FREE_MARK            XA_MARK_0
 
 enum xa_lock_type {
         XA_LOCK_IRQ = 1,
         XA_LOCK_BH = 2,
 };
 
 /*
  * Values for xa_flags.  The radix tree stores its GFP flags in the xa_flags,
  * and we remain compatible with that.
  */
 #define XA_FLAGS_LOCK_IRQ       ((__force gfp_t)XA_LOCK_IRQ)
 #define XA_FLAGS_LOCK_BH        ((__force gfp_t)XA_LOCK_BH)
 #define XA_FLAGS_TRACK_FREE     ((__force gfp_t)4U)
 #define XA_FLAGS_ZERO_BUSY      ((__force gfp_t)8U)
 #define XA_FLAGS_ALLOC_WRAPPED  ((__force gfp_t)16U)
 #define XA_FLAGS_ACCOUNT        ((__force gfp_t)32U)
 #define XA_FLAGS_MARK(mark)     ((__force gfp_t)((1U << __GFP_BITS_SHIFT) << \
                                                 (__force unsigned)(mark)))
 
 /* ALLOC is for a normal 0-based alloc.  ALLOC1 is for an 1-based alloc */
 #define XA_FLAGS_ALLOC  (XA_FLAGS_TRACK_FREE | XA_FLAGS_MARK(XA_FREE_MARK))
 #define XA_FLAGS_ALLOC1 (XA_FLAGS_TRACK_FREE | XA_FLAGS_ZERO_BUSY)
 
 /**
  * struct xarray - The anchor of the XArray.
  * @xa_lock: Lock that protects the contents of the XArray.
  *
  * To use the xarray, define it statically or embed it in your data structure.
  * It is a very small data structure, so it does not usually make sense to
  * allocate it separately and keep a pointer to it in your data structure.
  *
  * You may use the xa_lock to protect your own data structures as well.
  */
 /*
  * If all of the entries in the array are NULL, @xa_head is a NULL pointer.
  * If the only non-NULL entry in the array is at index 0, @xa_head is that
  * entry.  If any other entry in the array is non-NULL, @xa_head points
  * to an @xa_node.
  */
 struct xarray {
         spinlock_t      xa_lock;
 /* private: The rest of the data structure is not to be used directly. */
         gfp_t           xa_flags;
         void __rcu *    xa_head;
 };
 
 #define XARRAY_INIT(name, flags) {                              \
         .xa_lock = __SPIN_LOCK_UNLOCKED(name.xa_lock),          \
         .xa_flags = flags,                                      \
         .xa_head = NULL,                                        \
 }
 
 /**
  * DEFINE_XARRAY_FLAGS() - Define an XArray with custom flags.
  * @name: A string that names your XArray.
  * @flags: XA_FLAG values.
  *
  * This is intended for file scope definitions of XArrays.  It declares
  * and initialises an empty XArray with the chosen name and flags.  It is
  * equivalent to calling xa_init_flags() on the array, but it does the
  * initialisation at compiletime instead of runtime.
  */
 #define DEFINE_XARRAY_FLAGS(name, flags)                                \
         struct xarray name = XARRAY_INIT(name, flags)
 
 /**
  * DEFINE_XARRAY() - Define an XArray.
  * @name: A string that names your XArray.
  *
  * This is intended for file scope definitions of XArrays.  It declares
  * and initialises an empty XArray with the chosen name.  It is equivalent
  * to calling xa_init() on the array, but it does the initialisation at
  * compiletime instead of runtime.
  */
 #define DEFINE_XARRAY(name) DEFINE_XARRAY_FLAGS(name, 0)
 
 /**
  * DEFINE_XARRAY_ALLOC() - Define an XArray which allocates IDs starting at 0.
  * @name: A string that names your XArray.
  *
  * This is intended for file scope definitions of allocating XArrays.
  * See also DEFINE_XARRAY().
  */
 #define DEFINE_XARRAY_ALLOC(name) DEFINE_XARRAY_FLAGS(name, XA_FLAGS_ALLOC)
 
 /**
  * DEFINE_XARRAY_ALLOC1() - Define an XArray which allocates IDs starting at 1.
  * @name: A string that names your XArray.
  *
  * This is intended for file scope definitions of allocating XArrays.
  * See also DEFINE_XARRAY().
  */
 #define DEFINE_XARRAY_ALLOC1(name) DEFINE_XARRAY_FLAGS(name, XA_FLAGS_ALLOC1)
 
 void *xa_load(struct xarray *, unsigned long index);
 void *xa_store(struct xarray *, unsigned long index, void *entry, gfp_t);
 void *xa_erase(struct xarray *, unsigned long index);
 void *xa_store_range(struct xarray *, unsigned long first, unsigned long last,
                         void *entry, gfp_t);
 bool xa_get_mark(struct xarray *, unsigned long index, xa_mark_t);
 void xa_set_mark(struct xarray *, unsigned long index, xa_mark_t);
 void xa_clear_mark(struct xarray *, unsigned long index, xa_mark_t);
 void *xa_find(struct xarray *xa, unsigned long *index,
                 unsigned long max, xa_mark_t) __attribute__((nonnull(2)));
 void *xa_find_after(struct xarray *xa, unsigned long *index,
                 unsigned long max, xa_mark_t) __attribute__((nonnull(2)));
 unsigned int xa_extract(struct xarray *, void **dst, unsigned long start,
                 unsigned long max, unsigned int n, xa_mark_t);
 void xa_destroy(struct xarray *);
 
 /**
  * xa_init_flags() - Initialise an empty XArray with flags.
  * @xa: XArray.
  * @flags: XA_FLAG values.
  *
  * If you need to initialise an XArray with special flags (eg you need
  * to take the lock from interrupt context), use this function instead
  * of xa_init().
  *
  * Context: Any context.
  */
 static inline void xa_init_flags(struct xarray *xa, gfp_t flags)
 {
         spin_lock_init(&xa->xa_lock);
         xa->xa_flags = flags;
         xa->xa_head = NULL;
 }
 
 /**
  * xa_init() - Initialise an empty XArray.
  * @xa: XArray.
  *
  * An empty XArray is full of NULL entries.
  *
  * Context: Any context.
  */
 static inline void xa_init(struct xarray *xa)
 {
         xa_init_flags(xa, 0);
 }
 
 /**
  * xa_empty() - Determine if an array has any present entries.
  * @xa: XArray.
  *
  * Context: Any context.
  * Return: %true if the array contains only NULL pointers.
  */
 static inline bool xa_empty(const struct xarray *xa)
 {
         return xa->xa_head == NULL;
 }
 
 /**
  * xa_marked() - Inquire whether any entry in this array has a mark set
  * @xa: Array
  * @mark: Mark value
  *
  * Context: Any context.
  * Return: %true if any entry has this mark set.
  */
 static inline bool xa_marked(const struct xarray *xa, xa_mark_t mark)
 {
         return xa->xa_flags & XA_FLAGS_MARK(mark);
 }
 
 /**
  * xa_for_each_range() - Iterate over a portion of an XArray.
  * @xa: XArray.
  * @index: Index of @entry.
  * @entry: Entry retrieved from array.
  * @start: First index to retrieve from array.
  * @last: Last index to retrieve from array.
  *
  * During the iteration, @entry will have the value of the entry stored
  * in @xa at @index.  You may modify @index during the iteration if you
  * want to skip or reprocess indices.  It is safe to modify the array
  * during the iteration.  At the end of the iteration, @entry will be set
  * to NULL and @index will have a value less than or equal to max.
  *
  * xa_for_each_range() is O(n.log(n)) while xas_for_each() is O(n).  You have
  * to handle your own locking with xas_for_each(), and if you have to unlock
  * after each iteration, it will also end up being O(n.log(n)).
  * xa_for_each_range() will spin if it hits a retry entry; if you intend to
  * see retry entries, you should use the xas_for_each() iterator instead.
  * The xas_for_each() iterator will expand into more inline code than
  * xa_for_each_range().
  *
  * Context: Any context.  Takes and releases the RCU lock.
  */
 #define xa_for_each_range(xa, index, entry, start, last)                \
         for (index = start,                                             \
              entry = xa_find(xa, &index, last, XA_PRESENT);             \
              entry;                                                     \
              entry = xa_find_after(xa, &index, last, XA_PRESENT))
 
 /**
  * xa_for_each_start() - Iterate over a portion of an XArray.
  * @xa: XArray.
  * @index: Index of @entry.
  * @entry: Entry retrieved from array.
  * @start: First index to retrieve from array.
  *
  * During the iteration, @entry will have the value of the entry stored
  * in @xa at @index.  You may modify @index during the iteration if you
  * want to skip or reprocess indices.  It is safe to modify the array
  * during the iteration.  At the end of the iteration, @entry will be set
  * to NULL and @index will have a value less than or equal to max.
  *
  * xa_for_each_start() is O(n.log(n)) while xas_for_each() is O(n).  You have
  * to handle your own locking with xas_for_each(), and if you have to unlock
  * after each iteration, it will also end up being O(n.log(n)).
  * xa_for_each_start() will spin if it hits a retry entry; if you intend to
  * see retry entries, you should use the xas_for_each() iterator instead.
  * The xas_for_each() iterator will expand into more inline code than
  * xa_for_each_start().
  *
  * Context: Any context.  Takes and releases the RCU lock.
  */
 #define xa_for_each_start(xa, index, entry, start) \
         xa_for_each_range(xa, index, entry, start, ULONG_MAX)
 
 /**
  * xa_for_each() - Iterate over present entries in an XArray.
  * @xa: XArray.
  * @index: Index of @entry.
  * @entry: Entry retrieved from array.
  *
  * During the iteration, @entry will have the value of the entry stored
  * in @xa at @index.  You may modify @index during the iteration if you want
  * to skip or reprocess indices.  It is safe to modify the array during the
  * iteration.  At the end of the iteration, @entry will be set to NULL and
  * @index will have a value less than or equal to max.
  *
  * xa_for_each() is O(n.log(n)) while xas_for_each() is O(n).  You have
  * to handle your own locking with xas_for_each(), and if you have to unlock
  * after each iteration, it will also end up being O(n.log(n)).  xa_for_each()
  * will spin if it hits a retry entry; if you intend to see retry entries,
  * you should use the xas_for_each() iterator instead.  The xas_for_each()
  * iterator will expand into more inline code than xa_for_each().
  *
  * Context: Any context.  Takes and releases the RCU lock.
  */
 #define xa_for_each(xa, index, entry) \
         xa_for_each_start(xa, index, entry, 0)
 
 /**
  * xa_for_each_marked() - Iterate over marked entries in an XArray.
  * @xa: XArray.
  * @index: Index of @entry.
  * @entry: Entry retrieved from array.
  * @filter: Selection criterion.
  *
  * During the iteration, @entry will have the value of the entry stored
  * in @xa at @index.  The iteration will skip all entries in the array
  * which do not match @filter.  You may modify @index during the iteration
  * if you want to skip or reprocess indices.  It is safe to modify the array
  * during the iteration.  At the end of the iteration, @entry will be set to
  * NULL and @index will have a value less than or equal to max.
  *
  * xa_for_each_marked() is O(n.log(n)) while xas_for_each_marked() is O(n).
  * You have to handle your own locking with xas_for_each(), and if you have
  * to unlock after each iteration, it will also end up being O(n.log(n)).
  * xa_for_each_marked() will spin if it hits a retry entry; if you intend to
  * see retry entries, you should use the xas_for_each_marked() iterator
  * instead.  The xas_for_each_marked() iterator will expand into more inline
  * code than xa_for_each_marked().
  *
  * Context: Any context.  Takes and releases the RCU lock.
  */
 #define xa_for_each_marked(xa, index, entry, filter) \
         for (index = 0, entry = xa_find(xa, &index, ULONG_MAX, filter); \
              entry; entry = xa_find_after(xa, &index, ULONG_MAX, filter))
 
 #define xa_trylock(xa)          spin_trylock(&(xa)->xa_lock)
 #define xa_lock(xa)             spin_lock(&(xa)->xa_lock)
 #define xa_unlock(xa)           spin_unlock(&(xa)->xa_lock)
 #define xa_lock_bh(xa)          spin_lock_bh(&(xa)->xa_lock)
 #define xa_unlock_bh(xa)        spin_unlock_bh(&(xa)->xa_lock)
 #define xa_lock_irq(xa)         spin_lock_irq(&(xa)->xa_lock)
 #define xa_unlock_irq(xa)       spin_unlock_irq(&(xa)->xa_lock)
 #define xa_lock_irqsave(xa, flags) \
                                 spin_lock_irqsave(&(xa)->xa_lock, flags)
 #define xa_unlock_irqrestore(xa, flags) \
                                 spin_unlock_irqrestore(&(xa)->xa_lock, flags)
 #define xa_lock_nested(xa, subclass) \
                                 spin_lock_nested(&(xa)->xa_lock, subclass)
 #define xa_lock_bh_nested(xa, subclass) \
                                 spin_lock_bh_nested(&(xa)->xa_lock, subclass)
 #define xa_lock_irq_nested(xa, subclass) \
                                 spin_lock_irq_nested(&(xa)->xa_lock, subclass)
 #define xa_lock_irqsave_nested(xa, flags, subclass) \
                 spin_lock_irqsave_nested(&(xa)->xa_lock, flags, subclass)
 
 /*
  * Versions of the normal API which require the caller to hold the
  * xa_lock.  If the GFP flags allow it, they will drop the lock to
  * allocate memory, then reacquire it afterwards.  These functions
  * may also re-enable interrupts if the XArray flags indicate the
  * locking should be interrupt safe.
  */
 void *__xa_erase(struct xarray *, unsigned long index);
 void *__xa_store(struct xarray *, unsigned long index, void *entry, gfp_t);
 void *__xa_cmpxchg(struct xarray *, unsigned long index, void *old,
                 void *entry, gfp_t);
 int __must_check __xa_insert(struct xarray *, unsigned long index,
                 void *entry, gfp_t);
 int __must_check __xa_alloc(struct xarray *, u32 *id, void *entry,
                 struct xa_limit, gfp_t);
 int __must_check __xa_alloc_cyclic(struct xarray *, u32 *id, void *entry,
                 struct xa_limit, u32 *next, gfp_t);
 void __xa_set_mark(struct xarray *, unsigned long index, xa_mark_t);
 void __xa_clear_mark(struct xarray *, unsigned long index, xa_mark_t);
 
 /**
  * xa_store_bh() - Store this entry in the XArray.
  * @xa: XArray.
  * @index: Index into array.
  * @entry: New entry.
  * @gfp: Memory allocation flags.
  *
  * This function is like calling xa_store() except it disables softirqs
  * while holding the array lock.
  *
  * Context: Any context.  Takes and releases the xa_lock while
  * disabling softirqs.
  * Return: The old entry at this index or xa_err() if an error happened.
  */
 static inline void *xa_store_bh(struct xarray *xa, unsigned long index,
                 void *entry, gfp_t gfp)
 {
         void *curr;
 
         might_alloc(gfp);
         xa_lock_bh(xa);
         curr = __xa_store(xa, index, entry, gfp);
         xa_unlock_bh(xa);
 
         return curr;
 }
 
 /**
  * xa_store_irq() - Store this entry in the XArray.
  * @xa: XArray.
  * @index: Index into array.
  * @entry: New entry.
  * @gfp: Memory allocation flags.
  *
  * This function is like calling xa_store() except it disables interrupts
  * while holding the array lock.
  *
  * Context: Process context.  Takes and releases the xa_lock while
  * disabling interrupts.
  * Return: The old entry at this index or xa_err() if an error happened.
  */
 static inline void *xa_store_irq(struct xarray *xa, unsigned long index,
                 void *entry, gfp_t gfp)
 {
         void *curr;
 
         might_alloc(gfp);
         xa_lock_irq(xa);
         curr = __xa_store(xa, index, entry, gfp);
         xa_unlock_irq(xa);
 
         return curr;
 }
 
 /**
  * xa_erase_bh() - Erase this entry from the XArray.
  * @xa: XArray.
  * @index: Index of entry.
  *
  * After this function returns, loading from @index will return %NULL.
  * If the index is part of a multi-index entry, all indices will be erased
  * and none of the entries will be part of a multi-index entry.
  *
  * Context: Any context.  Takes and releases the xa_lock while
  * disabling softirqs.
  * Return: The entry which used to be at this index.
  */
 static inline void *xa_erase_bh(struct xarray *xa, unsigned long index)
 {
         void *entry;
 
         xa_lock_bh(xa);
         entry = __xa_erase(xa, index);
         xa_unlock_bh(xa);
 
         return entry;
 }
 
 /**
  * xa_erase_irq() - Erase this entry from the XArray.
  * @xa: XArray.
  * @index: Index of entry.
  *
  * After this function returns, loading from @index will return %NULL.
  * If the index is part of a multi-index entry, all indices will be erased
  * and none of the entries will be part of a multi-index entry.
  *
  * Context: Process context.  Takes and releases the xa_lock while
  * disabling interrupts.
  * Return: The entry which used to be at this index.
  */
 static inline void *xa_erase_irq(struct xarray *xa, unsigned long index)
 {
         void *entry;
 
         xa_lock_irq(xa);
         entry = __xa_erase(xa, index);
         xa_unlock_irq(xa);
 
         return entry;
 }
 
 /**
  * xa_cmpxchg() - Conditionally replace an entry in the XArray.
  * @xa: XArray.
  * @index: Index into array.
  * @old: Old value to test against.
  * @entry: New value to place in array.
  * @gfp: Memory allocation flags.
  *
  * If the entry at @index is the same as @old, replace it with @entry.
  * If the return value is equal to @old, then the exchange was successful.
  *
  * Context: Any context.  Takes and releases the xa_lock.  May sleep
  * if the @gfp flags permit.
  * Return: The old value at this index or xa_err() if an error happened.
  */
 static inline void *xa_cmpxchg(struct xarray *xa, unsigned long index,
                         void *old, void *entry, gfp_t gfp)
 {
         void *curr;
 
         might_alloc(gfp);
         xa_lock(xa);
         curr = __xa_cmpxchg(xa, index, old, entry, gfp);
         xa_unlock(xa);
 
         return curr;
 }
 
 /**
  * xa_cmpxchg_bh() - Conditionally replace an entry in the XArray.
  * @xa: XArray.
  * @index: Index into array.
  * @old: Old value to test against.
  * @entry: New value to place in array.
  * @gfp: Memory allocation flags.
  *
  * This function is like calling xa_cmpxchg() except it disables softirqs
  * while holding the array lock.
  *
  * Context: Any context.  Takes and releases the xa_lock while
  * disabling softirqs.  May sleep if the @gfp flags permit.
  * Return: The old value at this index or xa_err() if an error happened.
  */
 static inline void *xa_cmpxchg_bh(struct xarray *xa, unsigned long index,
                         void *old, void *entry, gfp_t gfp)
 {
         void *curr;
 
         might_alloc(gfp);
         xa_lock_bh(xa);
         curr = __xa_cmpxchg(xa, index, old, entry, gfp);
         xa_unlock_bh(xa);
 
         return curr;
 }
 
 /**
  * xa_cmpxchg_irq() - Conditionally replace an entry in the XArray.
  * @xa: XArray.
  * @index: Index into array.
  * @old: Old value to test against.
  * @entry: New value to place in array.
  * @gfp: Memory allocation flags.
  *
  * This function is like calling xa_cmpxchg() except it disables interrupts
  * while holding the array lock.
  *
  * Context: Process context.  Takes and releases the xa_lock while
  * disabling interrupts.  May sleep if the @gfp flags permit.
  * Return: The old value at this index or xa_err() if an error happened.
  */
 static inline void *xa_cmpxchg_irq(struct xarray *xa, unsigned long index,
                         void *old, void *entry, gfp_t gfp)
 {
         void *curr;
 
         might_alloc(gfp);
         xa_lock_irq(xa);
         curr = __xa_cmpxchg(xa, index, old, entry, gfp);
         xa_unlock_irq(xa);
 
         return curr;
 }
 
 /**
  * xa_insert() - Store this entry in the XArray unless another entry is
  *                      already present.
  * @xa: XArray.
  * @index: Index into array.
  * @entry: New entry.
  * @gfp: Memory allocation flags.
  *
  * Inserting a NULL entry will store a reserved entry (like xa_reserve())
  * if no entry is present.  Inserting will fail if a reserved entry is
  * present, even though loading from this index will return NULL.
  *
  * Context: Any context.  Takes and releases the xa_lock.  May sleep if
  * the @gfp flags permit.
  * Return: 0 if the store succeeded.  -EBUSY if another entry was present.
  * -ENOMEM if memory could not be allocated.
  */
 static inline int __must_check xa_insert(struct xarray *xa,
                 unsigned long index, void *entry, gfp_t gfp)
 {
         int err;
 
         might_alloc(gfp);
         xa_lock(xa);
         err = __xa_insert(xa, index, entry, gfp);
         xa_unlock(xa);
 
         return err;
 }
 
 /**
  * xa_insert_bh() - Store this entry in the XArray unless another entry is
  *                      already present.
  * @xa: XArray.
  * @index: Index into array.
  * @entry: New entry.
  * @gfp: Memory allocation flags.
  *
  * Inserting a NULL entry will store a reserved entry (like xa_reserve())
  * if no entry is present.  Inserting will fail if a reserved entry is
  * present, even though loading from this index will return NULL.
  *
  * Context: Any context.  Takes and releases the xa_lock while
  * disabling softirqs.  May sleep if the @gfp flags permit.
  * Return: 0 if the store succeeded.  -EBUSY if another entry was present.
  * -ENOMEM if memory could not be allocated.
  */
 static inline int __must_check xa_insert_bh(struct xarray *xa,
                 unsigned long index, void *entry, gfp_t gfp)
 {
         int err;
 
         might_alloc(gfp);
         xa_lock_bh(xa);
         err = __xa_insert(xa, index, entry, gfp);
         xa_unlock_bh(xa);
 
         return err;
 }
 
 /**
  * xa_insert_irq() - Store this entry in the XArray unless another entry is
  *                      already present.
  * @xa: XArray.
  * @index: Index into array.
  * @entry: New entry.
  * @gfp: Memory allocation flags.
  *
  * Inserting a NULL entry will store a reserved entry (like xa_reserve())
  * if no entry is present.  Inserting will fail if a reserved entry is
  * present, even though loading from this index will return NULL.
  *
  * Context: Process context.  Takes and releases the xa_lock while
  * disabling interrupts.  May sleep if the @gfp flags permit.
  * Return: 0 if the store succeeded.  -EBUSY if another entry was present.
  * -ENOMEM if memory could not be allocated.
  */
 static inline int __must_check xa_insert_irq(struct xarray *xa,
                 unsigned long index, void *entry, gfp_t gfp)
 {
         int err;
 
         might_alloc(gfp);
         xa_lock_irq(xa);
         err = __xa_insert(xa, index, entry, gfp);
         xa_unlock_irq(xa);
 
         return err;
 }
 
 /**
  * xa_alloc() - Find somewhere to store this entry in the XArray.
  * @xa: XArray.
  * @id: Pointer to ID.
  * @entry: New entry.
  * @limit: Range of ID to allocate.
  * @gfp: Memory allocation flags.
  *
  * Finds an empty entry in @xa between @limit.min and @limit.max,
  * stores the index into the @id pointer, then stores the entry at
  * that index.  A concurrent lookup will not see an uninitialised @id.
  *
  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
  * in xa_init_flags().
  *
  * Context: Any context.  Takes and releases the xa_lock.  May sleep if
  * the @gfp flags permit.
  * Return: 0 on success, -ENOMEM if memory could not be allocated or
  * -EBUSY if there are no free entries in @limit.
  */
 static inline __must_check int xa_alloc(struct xarray *xa, u32 *id,
                 void *entry, struct xa_limit limit, gfp_t gfp)
 {
         int err;
 
         might_alloc(gfp);
         xa_lock(xa);
         err = __xa_alloc(xa, id, entry, limit, gfp);
         xa_unlock(xa);
 
         return err;
 }
 
 /**
  * xa_alloc_bh() - Find somewhere to store this entry in the XArray.
  * @xa: XArray.
  * @id: Pointer to ID.
  * @entry: New entry.
  * @limit: Range of ID to allocate.
  * @gfp: Memory allocation flags.
  *
  * Finds an empty entry in @xa between @limit.min and @limit.max,
  * stores the index into the @id pointer, then stores the entry at
  * that index.  A concurrent lookup will not see an uninitialised @id.
  *
  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
  * in xa_init_flags().
  *
  * Context: Any context.  Takes and releases the xa_lock while
  * disabling softirqs.  May sleep if the @gfp flags permit.
  * Return: 0 on success, -ENOMEM if memory could not be allocated or
  * -EBUSY if there are no free entries in @limit.
  */
 static inline int __must_check xa_alloc_bh(struct xarray *xa, u32 *id,
                 void *entry, struct xa_limit limit, gfp_t gfp)
 {
         int err;
 
         might_alloc(gfp);
         xa_lock_bh(xa);
         err = __xa_alloc(xa, id, entry, limit, gfp);
         xa_unlock_bh(xa);
 
         return err;
 }
 
 /**
  * xa_alloc_irq() - Find somewhere to store this entry in the XArray.
  * @xa: XArray.
  * @id: Pointer to ID.
  * @entry: New entry.
  * @limit: Range of ID to allocate.
  * @gfp: Memory allocation flags.
  *
  * Finds an empty entry in @xa between @limit.min and @limit.max,
  * stores the index into the @id pointer, then stores the entry at
  * that index.  A concurrent lookup will not see an uninitialised @id.
  *
  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
  * in xa_init_flags().
  *
  * Context: Process context.  Takes and releases the xa_lock while
  * disabling interrupts.  May sleep if the @gfp flags permit.
  * Return: 0 on success, -ENOMEM if memory could not be allocated or
  * -EBUSY if there are no free entries in @limit.
  */
 static inline int __must_check xa_alloc_irq(struct xarray *xa, u32 *id,
                 void *entry, struct xa_limit limit, gfp_t gfp)
 {
         int err;
 
         might_alloc(gfp);
         xa_lock_irq(xa);
         err = __xa_alloc(xa, id, entry, limit, gfp);
         xa_unlock_irq(xa);
 
         return err;
 }
 
 /**
  * xa_alloc_cyclic() - Find somewhere to store this entry in the XArray.
  * @xa: XArray.
  * @id: Pointer to ID.
  * @entry: New entry.
  * @limit: Range of allocated ID.
  * @next: Pointer to next ID to allocate.
  * @gfp: Memory allocation flags.
  *
  * Finds an empty entry in @xa between @limit.min and @limit.max,
  * stores the index into the @id pointer, then stores the entry at
  * that index.  A concurrent lookup will not see an uninitialised @id.
  * The search for an empty entry will start at @next and will wrap
  * around if necessary.
  *
  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
  * in xa_init_flags().
  *
  * Context: Any context.  Takes and releases the xa_lock.  May sleep if
  * the @gfp flags permit.
  * Return: 0 if the allocation succeeded without wrapping.  1 if the
  * allocation succeeded after wrapping, -ENOMEM if memory could not be
  * allocated or -EBUSY if there are no free entries in @limit.
  */
 static inline int xa_alloc_cyclic(struct xarray *xa, u32 *id, void *entry,
                 struct xa_limit limit, u32 *next, gfp_t gfp)
 {
         int err;
 
         might_alloc(gfp);
         xa_lock(xa);
         err = __xa_alloc_cyclic(xa, id, entry, limit, next, gfp);
         xa_unlock(xa);
 
         return err;
 }
 
 /**
  * xa_alloc_cyclic_bh() - Find somewhere to store this entry in the XArray.
  * @xa: XArray.
  * @id: Pointer to ID.
  * @entry: New entry.
  * @limit: Range of allocated ID.
  * @next: Pointer to next ID to allocate.
  * @gfp: Memory allocation flags.
  *
  * Finds an empty entry in @xa between @limit.min and @limit.max,
  * stores the index into the @id pointer, then stores the entry at
  * that index.  A concurrent lookup will not see an uninitialised @id.
  * The search for an empty entry will start at @next and will wrap
  * around if necessary.
  *
  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
  * in xa_init_flags().
  *
  * Context: Any context.  Takes and releases the xa_lock while
  * disabling softirqs.  May sleep if the @gfp flags permit.
  * Return: 0 if the allocation succeeded without wrapping.  1 if the
  * allocation succeeded after wrapping, -ENOMEM if memory could not be
  * allocated or -EBUSY if there are no free entries in @limit.
  */
 static inline int xa_alloc_cyclic_bh(struct xarray *xa, u32 *id, void *entry,
                 struct xa_limit limit, u32 *next, gfp_t gfp)
 {
         int err;
 
         might_alloc(gfp);
         xa_lock_bh(xa);
         err = __xa_alloc_cyclic(xa, id, entry, limit, next, gfp);
         xa_unlock_bh(xa);
 
         return err;
 }
 
 /**
  * xa_alloc_cyclic_irq() - Find somewhere to store this entry in the XArray.
  * @xa: XArray.
  * @id: Pointer to ID.
  * @entry: New entry.
  * @limit: Range of allocated ID.
  * @next: Pointer to next ID to allocate.
  * @gfp: Memory allocation flags.
  *
  * Finds an empty entry in @xa between @limit.min and @limit.max,
  * stores the index into the @id pointer, then stores the entry at
  * that index.  A concurrent lookup will not see an uninitialised @id.
  * The search for an empty entry will start at @next and will wrap
  * around if necessary.
  *
  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
  * in xa_init_flags().
  *
  * Context: Process context.  Takes and releases the xa_lock while
  * disabling interrupts.  May sleep if the @gfp flags permit.
  * Return: 0 if the allocation succeeded without wrapping.  1 if the
  * allocation succeeded after wrapping, -ENOMEM if memory could not be
  * allocated or -EBUSY if there are no free entries in @limit.
  */
 static inline int xa_alloc_cyclic_irq(struct xarray *xa, u32 *id, void *entry,
                 struct xa_limit limit, u32 *next, gfp_t gfp)
 {
         int err;
 
         might_alloc(gfp);
         xa_lock_irq(xa);
         err = __xa_alloc_cyclic(xa, id, entry, limit, next, gfp);
         xa_unlock_irq(xa);
 
         return err;
 }
 
 /**
  * xa_reserve() - Reserve this index in the XArray.
  * @xa: XArray.
  * @index: Index into array.
  * @gfp: Memory allocation flags.
  *
  * Ensures there is somewhere to store an entry at @index in the array.
  * If there is already something stored at @index, this function does
  * nothing.  If there was nothing there, the entry is marked as reserved.
  * Loading from a reserved entry returns a %NULL pointer.
  *
  * If you do not use the entry that you have reserved, call xa_release()
  * or xa_erase() to free any unnecessary memory.
  *
  * Context: Any context.  Takes and releases the xa_lock.
  * May sleep if the @gfp flags permit.
  * Return: 0 if the reservation succeeded or -ENOMEM if it failed.
  */
 static inline __must_check
 int xa_reserve(struct xarray *xa, unsigned long index, gfp_t gfp)
 {
         return xa_err(xa_cmpxchg(xa, index, NULL, XA_ZERO_ENTRY, gfp));
 }
 
 /**
  * xa_reserve_bh() - Reserve this index in the XArray.
  * @xa: XArray.
  * @index: Index into array.
  * @gfp: Memory allocation flags.
  *
  * A softirq-disabling version of xa_reserve().
  *
  * Context: Any context.  Takes and releases the xa_lock while
  * disabling softirqs.
  * Return: 0 if the reservation succeeded or -ENOMEM if it failed.
  */
 static inline __must_check
 int xa_reserve_bh(struct xarray *xa, unsigned long index, gfp_t gfp)
 {
         return xa_err(xa_cmpxchg_bh(xa, index, NULL, XA_ZERO_ENTRY, gfp));
 }
 
 /**
  * xa_reserve_irq() - Reserve this index in the XArray.
  * @xa: XArray.
  * @index: Index into array.
  * @gfp: Memory allocation flags.
  *
  * An interrupt-disabling version of xa_reserve().
  *
  * Context: Process context.  Takes and releases the xa_lock while
  * disabling interrupts.
  * Return: 0 if the reservation succeeded or -ENOMEM if it failed.
  */
 static inline __must_check
 int xa_reserve_irq(struct xarray *xa, unsigned long index, gfp_t gfp)
 {
         return xa_err(xa_cmpxchg_irq(xa, index, NULL, XA_ZERO_ENTRY, gfp));
 }
 
 /**
  * xa_release() - Release a reserved entry.
  * @xa: XArray.
  * @index: Index of entry.
  *
  * After calling xa_reserve(), you can call this function to release the
  * reservation.  If the entry at @index has been stored to, this function
  * will do nothing.
  */
 static inline void xa_release(struct xarray *xa, unsigned long index)
 {
         xa_cmpxchg(xa, index, XA_ZERO_ENTRY, NULL, 0);
 }
 
 /* Everything below here is the Advanced API.  Proceed with caution. */
 
 /*
  * The xarray is constructed out of a set of 'chunks' of pointers.  Choosing
  * the best chunk size requires some tradeoffs.  A power of two recommends
  * itself so that we can walk the tree based purely on shifts and masks.
  * Generally, the larger the better; as the number of slots per level of the
  * tree increases, the less tall the tree needs to be.  But that needs to be
  * balanced against the memory consumption of each node.  On a 64-bit system,
  * xa_node is currently 576 bytes, and we get 7 of them per 4kB page.  If we
  * doubled the number of slots per node, we'd get only 3 nodes per 4kB page.
  */
 #ifndef XA_CHUNK_SHIFT
 #define XA_CHUNK_SHIFT          (IS_ENABLED(CONFIG_BASE_SMALL) ? 4 : 6)
 #endif
 #define XA_CHUNK_SIZE           (1UL << XA_CHUNK_SHIFT)
 #define XA_CHUNK_MASK           (XA_CHUNK_SIZE - 1)
 #define XA_MAX_MARKS            3
 #define XA_MARK_LONGS           BITS_TO_LONGS(XA_CHUNK_SIZE)
 
 /*
  * @count is the count of every non-NULL element in the ->slots array
  * whether that is a value entry, a retry entry, a user pointer,
  * a sibling entry or a pointer to the next level of the tree.
  * @nr_values is the count of every element in ->slots which is
  * either a value entry or a sibling of a value entry.
  */
 struct xa_node {
         unsigned char   shift;          /* Bits remaining in each slot */
         unsigned char   offset;         /* Slot offset in parent */
         unsigned char   count;          /* Total entry count */
         unsigned char   nr_values;      /* Value entry count */
         struct xa_node __rcu *parent;   /* NULL at top of tree */
         struct xarray   *array;         /* The array we belong to */
         union {
                 struct list_head private_list;  /* For tree user */
                 struct rcu_head rcu_head;       /* Used when freeing node */
         };
         void __rcu      *slots[XA_CHUNK_SIZE];
         union {
                 unsigned long   tags[XA_MAX_MARKS][XA_MARK_LONGS];
                 unsigned long   marks[XA_MAX_MARKS][XA_MARK_LONGS];
         };
 };
 
 void xa_dump(const struct xarray *);
 void xa_dump_node(const struct xa_node *);
 
 #ifdef XA_DEBUG
 #define XA_BUG_ON(xa, x) do {                                   \
                 if (x) {                                        \
                         xa_dump(xa);                            \
                         BUG();                                  \
                 }                                               \
         } while (0)
 #define XA_NODE_BUG_ON(node, x) do {                            \
                 if (x) {                                        \
                         if (node) xa_dump_node(node);           \
                         BUG();                                  \
                 }                                               \
         } while (0)
 #else
 #define XA_BUG_ON(xa, x)        do { } while (0)
 #define XA_NODE_BUG_ON(node, x) do { } while (0)
 #endif
 
 /* Private */
 static inline void *xa_head(const struct xarray *xa)
 {
         return rcu_dereference_check(xa->xa_head,
                                                 lockdep_is_held(&xa->xa_lock));
 }
 
 /* Private */
 static inline void *xa_head_locked(const struct xarray *xa)
 {
         return rcu_dereference_protected(xa->xa_head,
                                                 lockdep_is_held(&xa->xa_lock));
 }
 
 /* Private */
 static inline void *xa_entry(const struct xarray *xa,
                                 const struct xa_node *node, unsigned int offset)
 {
         XA_NODE_BUG_ON(node, offset >= XA_CHUNK_SIZE);
         return rcu_dereference_check(node->slots[offset],
                                                 lockdep_is_held(&xa->xa_lock));
 }
 
 /* Private */
 static inline void *xa_entry_locked(const struct xarray *xa,
                                 const struct xa_node *node, unsigned int offset)
 {
         XA_NODE_BUG_ON(node, offset >= XA_CHUNK_SIZE);
         return rcu_dereference_protected(node->slots[offset],
                                                 lockdep_is_held(&xa->xa_lock));
 }
 
 /* Private */
 static inline struct xa_node *xa_parent(const struct xarray *xa,
                                         const struct xa_node *node)
 {
         return rcu_dereference_check(node->parent,
                                                 lockdep_is_held(&xa->xa_lock));
 }
 
 /* Private */
 static inline struct xa_node *xa_parent_locked(const struct xarray *xa,
                                         const struct xa_node *node)
 {
         return rcu_dereference_protected(node->parent,
                                                 lockdep_is_held(&xa->xa_lock));
 }
 
 /* Private */
 static inline void *xa_mk_node(const struct xa_node *node)
 {
         return (void *)((unsigned long)node | 2);
 }
 
 /* Private */
 static inline struct xa_node *xa_to_node(const void *entry)
 {
         return (struct xa_node *)((unsigned long)entry - 2);
 }
 
 /* Private */
 static inline bool xa_is_node(const void *entry)
 {
         return xa_is_internal(entry) && (unsigned long)entry > 4096;
 }
 
 /* Private */
 static inline void *xa_mk_sibling(unsigned int offset)
 {
         return xa_mk_internal(offset);
 }
 
 /* Private */
 static inline unsigned long xa_to_sibling(const void *entry)
 {
         return xa_to_internal(entry);
 }
 
 /**
  * xa_is_sibling() - Is the entry a sibling entry?
  * @entry: Entry retrieved from the XArray
  *
  * Return: %true if the entry is a sibling entry.
  */
 static inline bool xa_is_sibling(const void *entry)
 {
         return IS_ENABLED(CONFIG_XARRAY_MULTI) && xa_is_internal(entry) &&
                 (entry < xa_mk_sibling(XA_CHUNK_SIZE - 1));
 }
 
 #define XA_RETRY_ENTRY          xa_mk_internal(256)
 
 /**
  * xa_is_retry() - Is the entry a retry entry?
  * @entry: Entry retrieved from the XArray
  *
  * Return: %true if the entry is a retry entry.
  */
 static inline bool xa_is_retry(const void *entry)
 {
         return unlikely(entry == XA_RETRY_ENTRY);
 }
 
 /**
  * xa_is_advanced() - Is the entry only permitted for the advanced API?
  * @entry: Entry to be stored in the XArray.
  *
  * Return: %true if the entry cannot be stored by the normal API.
  */
 static inline bool xa_is_advanced(const void *entry)
 {
         return xa_is_internal(entry) && (entry <= XA_RETRY_ENTRY);
 }
 
 /**
  * typedef xa_update_node_t - A callback function from the XArray.
  * @node: The node which is being processed
  *
  * This function is called every time the XArray updates the count of
  * present and value entries in a node.  It allows advanced users to
  * maintain the private_list in the node.
  *
  * Context: The xa_lock is held and interrupts may be disabled.
  *          Implementations should not drop the xa_lock, nor re-enable
  *          interrupts.
  */
 typedef void (*xa_update_node_t)(struct xa_node *node);
 
 void xa_delete_node(struct xa_node *, xa_update_node_t);
 
 /*
  * The xa_state is opaque to its users.  It contains various different pieces
  * of state involved in the current operation on the XArray.  It should be
  * declared on the stack and passed between the various internal routines.
  * The various elements in it should not be accessed directly, but only
  * through the provided accessor functions.  The below documentation is for
  * the benefit of those working on the code, not for users of the XArray.
  *
  * @xa_node usually points to the xa_node containing the slot we're operating
  * on (and @xa_offset is the offset in the slots array).  If there is a
  * single entry in the array at index 0, there are no allocated xa_nodes to
  * point to, and so we store %NULL in @xa_node.  @xa_node is set to
  * the value %XAS_RESTART if the xa_state is not walked to the correct
  * position in the tree of nodes for this operation.  If an error occurs
  * during an operation, it is set to an %XAS_ERROR value.  If we run off the
  * end of the allocated nodes, it is set to %XAS_BOUNDS.
  */
 struct xa_state {
         struct xarray *xa;
         unsigned long xa_index;
         unsigned char xa_shift;
         unsigned char xa_sibs;
         unsigned char xa_offset;
         unsigned char xa_pad;           /* Helps gcc generate better code */
         struct xa_node *xa_node;
         struct xa_node *xa_alloc;
         xa_update_node_t xa_update;
         struct list_lru *xa_lru;
 };
 
 /*
  * We encode errnos in the xas->xa_node.  If an error has happened, we need to
  * drop the lock to fix it, and once we've done so the xa_state is invalid.
  */
 #define XA_ERROR(errno) ((struct xa_node *)(((unsigned long)errno << 2) | 2UL))
 #define XAS_BOUNDS      ((struct xa_node *)1UL)
 #define XAS_RESTART     ((struct xa_node *)3UL)
 
 #define __XA_STATE(array, index, shift, sibs)  {        \
         .xa = array,                                    \
         .xa_index = index,                              \
         .xa_shift = shift,                              \
         .xa_sibs = sibs,                                \
         .xa_offset = 0,                                 \
         .xa_pad = 0,                                    \
         .xa_node = XAS_RESTART,                         \
         .xa_alloc = NULL,                               \
         .xa_update = NULL,                              \
         .xa_lru = NULL,                                 \
 }
 
 /**
  * XA_STATE() - Declare an XArray operation state.
  * @name: Name of this operation state (usually xas).
  * @array: Array to operate on.
  * @index: Initial index of interest.
  *
  * Declare and initialise an xa_state on the stack.
  */
 #define XA_STATE(name, array, index)                            \
         struct xa_state name = __XA_STATE(array, index, 0, 0)
 
 /**
  * XA_STATE_ORDER() - Declare an XArray operation state.
  * @name: Name of this operation state (usually xas).
  * @array: Array to operate on.
  * @index: Initial index of interest.
  * @order: Order of entry.
  *
  * Declare and initialise an xa_state on the stack.  This variant of
  * XA_STATE() allows you to specify the 'order' of the element you
  * want to operate on.`
  */
 #define XA_STATE_ORDER(name, array, index, order)               \
         struct xa_state name = __XA_STATE(array,                \
                         (index >> order) << order,              \
                         order - (order % XA_CHUNK_SHIFT),       \
                         (1U << (order % XA_CHUNK_SHIFT)) - 1)
 
 #define xas_marked(xas, mark)   xa_marked((xas)->xa, (mark))
 #define xas_trylock(xas)        xa_trylock((xas)->xa)
 #define xas_lock(xas)           xa_lock((xas)->xa)
 #define xas_unlock(xas)         xa_unlock((xas)->xa)
 #define xas_lock_bh(xas)        xa_lock_bh((xas)->xa)
 #define xas_unlock_bh(xas)      xa_unlock_bh((xas)->xa)
 #define xas_lock_irq(xas)       xa_lock_irq((xas)->xa)
 #define xas_unlock_irq(xas)     xa_unlock_irq((xas)->xa)
 #define xas_lock_irqsave(xas, flags) \
                                 xa_lock_irqsave((xas)->xa, flags)
 #define xas_unlock_irqrestore(xas, flags) \
                                 xa_unlock_irqrestore((xas)->xa, flags)
 
 /**
  * xas_error() - Return an errno stored in the xa_state.
  * @xas: XArray operation state.
  *
  * Return: 0 if no error has been noted.  A negative errno if one has.
  */
 static inline int xas_error(const struct xa_state *xas)
 {
         return xa_err(xas->xa_node);
 }
 
 /**
  * xas_set_err() - Note an error in the xa_state.
  * @xas: XArray operation state.
  * @err: Negative error number.
  *
  * Only call this function with a negative @err; zero or positive errors
  * will probably not behave the way you think they should.  If you want
  * to clear the error from an xa_state, use xas_reset().
  */
 static inline void xas_set_err(struct xa_state *xas, long err)
 {
         xas->xa_node = XA_ERROR(err);
 }
 
 /**
  * xas_invalid() - Is the xas in a retry or error state?
  * @xas: XArray operation state.
  *
  * Return: %true if the xas cannot be used for operations.
  */
 static inline bool xas_invalid(const struct xa_state *xas)
 {
         return (unsigned long)xas->xa_node & 3;
 }
 
 /**
  * xas_valid() - Is the xas a valid cursor into the array?
  * @xas: XArray operation state.
  *
  * Return: %true if the xas can be used for operations.
  */
 static inline bool xas_valid(const struct xa_state *xas)
 {
         return !xas_invalid(xas);
 }
 
 /**
  * xas_is_node() - Does the xas point to a node?
  * @xas: XArray operation state.
  *
  * Return: %true if the xas currently references a node.
  */
 static inline bool xas_is_node(const struct xa_state *xas)
 {
         return xas_valid(xas) && xas->xa_node;
 }
 
 /* True if the pointer is something other than a node */
 static inline bool xas_not_node(struct xa_node *node)
 {
         return ((unsigned long)node & 3) || !node;
 }
 
 /* True if the node represents RESTART or an error */
 static inline bool xas_frozen(struct xa_node *node)
 {
         return (unsigned long)node & 2;
 }
 
 /* True if the node represents head-of-tree, RESTART or BOUNDS */
 static inline bool xas_top(struct xa_node *node)
 {
         return node <= XAS_RESTART;
 }
 
 /**
  * xas_reset() - Reset an XArray operation state.
  * @xas: XArray operation state.
  *
  * Resets the error or walk state of the @xas so future walks of the
  * array will start from the root.  Use this if you have dropped the
  * xarray lock and want to reuse the xa_state.
  *
  * Context: Any context.
  */
 static inline void xas_reset(struct xa_state *xas)
 {
         xas->xa_node = XAS_RESTART;
 }
 
 /**
  * xas_retry() - Retry the operation if appropriate.
  * @xas: XArray operation state.
  * @entry: Entry from xarray.
  *
  * The advanced functions may sometimes return an internal entry, such as
  * a retry entry or a zero entry.  This function sets up the @xas to restart
  * the walk from the head of the array if needed.
  *
  * Context: Any context.
  * Return: true if the operation needs to be retried.
  */
 static inline bool xas_retry(struct xa_state *xas, const void *entry)
 {
         if (xa_is_zero(entry))
                 return true;
         if (!xa_is_retry(entry))
                 return false;
         xas_reset(xas);
         return true;
 }
 
 void *xas_load(struct xa_state *);
 void *xas_store(struct xa_state *, void *entry);
 void *xas_find(struct xa_state *, unsigned long max);
 void *xas_find_conflict(struct xa_state *);
 
 bool xas_get_mark(const struct xa_state *, xa_mark_t);
 void xas_set_mark(const struct xa_state *, xa_mark_t);
 void xas_clear_mark(const struct xa_state *, xa_mark_t);
 void *xas_find_marked(struct xa_state *, unsigned long max, xa_mark_t);
 void xas_init_marks(const struct xa_state *);
 
 bool xas_nomem(struct xa_state *, gfp_t);
 void xas_destroy(struct xa_state *);
 void xas_pause(struct xa_state *);
 
 void xas_create_range(struct xa_state *);
 
 #ifdef CONFIG_XARRAY_MULTI
 int xa_get_order(struct xarray *, unsigned long index);
 int xas_get_order(struct xa_state *xas);
 void xas_split(struct xa_state *, void *entry, unsigned int order);
 void xas_split_alloc(struct xa_state *, void *entry, unsigned int order, gfp_t);
 #else
 static inline int xa_get_order(struct xarray *xa, unsigned long index)
 {
         return 0;
 }
 
 static inline int xas_get_order(struct xa_state *xas)
 {
         return 0;
 }
 
 static inline void xas_split(struct xa_state *xas, void *entry,
                 unsigned int order)
 {
         xas_store(xas, entry);
 }
 
 static inline void xas_split_alloc(struct xa_state *xas, void *entry,
                 unsigned int order, gfp_t gfp)
 {
 }
 #endif
 
 /**
  * xas_reload() - Refetch an entry from the xarray.
  * @xas: XArray operation state.
  *
  * Use this function to check that a previously loaded entry still has
  * the same value.  This is useful for the lockless pagecache lookup where
  * we walk the array with only the RCU lock to protect us, lock the page,
  * then check that the page hasn't moved since we looked it up.
  *
  * The caller guarantees that @xas is still valid.  If it may be in an
  * error or restart state, call xas_load() instead.
  *
  * Return: The entry at this location in the xarray.
  */
 static inline void *xas_reload(struct xa_state *xas)
 {
         struct xa_node *node = xas->xa_node;
         void *entry;
         char offset;
 
         if (!node)
                 return xa_head(xas->xa);
         if (IS_ENABLED(CONFIG_XARRAY_MULTI)) {
                 offset = (xas->xa_index >> node->shift) & XA_CHUNK_MASK;
                 entry = xa_entry(xas->xa, node, offset);
                 if (!xa_is_sibling(entry))
                         return entry;
                 offset = xa_to_sibling(entry);
         } else {
                 offset = xas->xa_offset;
         }
         return xa_entry(xas->xa, node, offset);
 }
 
 /**
  * xas_set() - Set up XArray operation state for a different index.
  * @xas: XArray operation state.
  * @index: New index into the XArray.
  *
  * Move the operation state to refer to a different index.  This will
  * have the effect of starting a walk from the top; see xas_next()
  * to move to an adjacent index.
  */
 static inline void xas_set(struct xa_state *xas, unsigned long index)
 {
         xas->xa_index = index;
         xas->xa_node = XAS_RESTART;
 }
 
 /**
  * xas_advance() - Skip over sibling entries.
  * @xas: XArray operation state.
  * @index: Index of last sibling entry.
  *
  * Move the operation state to refer to the last sibling entry.
  * This is useful for loops that normally want to see sibling
  * entries but sometimes want to skip them.  Use xas_set() if you
  * want to move to an index which is not part of this entry.
  */
 static inline void xas_advance(struct xa_state *xas, unsigned long index)
 {
         unsigned char shift = xas_is_node(xas) ? xas->xa_node->shift : 0;
 
         xas->xa_index = index;
         xas->xa_offset = (index >> shift) & XA_CHUNK_MASK;
 }
 
 /**
  * xas_set_order() - Set up XArray operation state for a multislot entry.
  * @xas: XArray operation state.
  * @index: Target of the operation.
  * @order: Entry occupies 2^@order indices.
  */
 static inline void xas_set_order(struct xa_state *xas, unsigned long index,
                                         unsigned int order)
 {
 #ifdef CONFIG_XARRAY_MULTI
         xas->xa_index = order < BITS_PER_LONG ? (index >> order) << order : 0;
         xas->xa_shift = order - (order % XA_CHUNK_SHIFT);
         xas->xa_sibs = (1 << (order % XA_CHUNK_SHIFT)) - 1;
         xas->xa_node = XAS_RESTART;
 #else
         BUG_ON(order > 0);
         xas_set(xas, index);
 #endif
 }
 
 /**
  * xas_set_update() - Set up XArray operation state for a callback.
  * @xas: XArray operation state.
  * @update: Function to call when updating a node.
  *
  * The XArray can notify a caller after it has updated an xa_node.
  * This is advanced functionality and is only needed by the page
  * cache and swap cache.
  */
 static inline void xas_set_update(struct xa_state *xas, xa_update_node_t update)
 {
         xas->xa_update = update;
 }
 
 static inline void xas_set_lru(struct xa_state *xas, struct list_lru *lru)
 {
         xas->xa_lru = lru;
 }
 
 /**
  * xas_next_entry() - Advance iterator to next present entry.
  * @xas: XArray operation state.
  * @max: Highest index to return.
  *
  * xas_next_entry() is an inline function to optimise xarray traversal for
  * speed.  It is equivalent to calling xas_find(), and will call xas_find()
  * for all the hard cases.
  *
  * Return: The next present entry after the one currently referred to by @xas.
  */
 static inline void *xas_next_entry(struct xa_state *xas, unsigned long max)
 {
         struct xa_node *node = xas->xa_node;
         void *entry;
 
         if (unlikely(xas_not_node(node) || node->shift ||
                         xas->xa_offset != (xas->xa_index & XA_CHUNK_MASK)))
                 return xas_find(xas, max);
 
         do {
                 if (unlikely(xas->xa_index >= max))
                         return xas_find(xas, max);
                 if (unlikely(xas->xa_offset == XA_CHUNK_MASK))
                         return xas_find(xas, max);
                 entry = xa_entry(xas->xa, node, xas->xa_offset + 1);
                 if (unlikely(xa_is_internal(entry)))
                         return xas_find(xas, max);
                 xas->xa_offset++;
                 xas->xa_index++;
         } while (!entry);
 
         return entry;
 }
 
 /* Private */
 static inline unsigned int xas_find_chunk(struct xa_state *xas, bool advance,
                 xa_mark_t mark)
 {
         unsigned long *addr = xas->xa_node->marks[(__force unsigned)mark];
         unsigned int offset = xas->xa_offset;
 
         if (advance)
                 offset++;
         if (XA_CHUNK_SIZE == BITS_PER_LONG) {
                 if (offset < XA_CHUNK_SIZE) {
                         unsigned long data = *addr & (~0UL << offset);
                         if (data)
                                 return __ffs(data);
                 }
                 return XA_CHUNK_SIZE;
         }
 
         return find_next_bit(addr, XA_CHUNK_SIZE, offset);
 }
 
 /**
  * xas_next_marked() - Advance iterator to next marked entry.
  * @xas: XArray operation state.
  * @max: Highest index to return.
  * @mark: Mark to search for.
  *
  * xas_next_marked() is an inline function to optimise xarray traversal for
  * speed.  It is equivalent to calling xas_find_marked(), and will call
  * xas_find_marked() for all the hard cases.
  *
  * Return: The next marked entry after the one currently referred to by @xas.
  */
 static inline void *xas_next_marked(struct xa_state *xas, unsigned long max,
                                                                 xa_mark_t mark)
 {
         struct xa_node *node = xas->xa_node;
         void *entry;
         unsigned int offset;
 
         if (unlikely(xas_not_node(node) || node->shift))
                 return xas_find_marked(xas, max, mark);
         offset = xas_find_chunk(xas, true, mark);
         xas->xa_offset = offset;
         xas->xa_index = (xas->xa_index & ~XA_CHUNK_MASK) + offset;
         if (xas->xa_index > max)
                 return NULL;
         if (offset == XA_CHUNK_SIZE)
                 return xas_find_marked(xas, max, mark);
         entry = xa_entry(xas->xa, node, offset);
         if (!entry)
                 return xas_find_marked(xas, max, mark);
         return entry;
 }
 
 /*
  * If iterating while holding a lock, drop the lock and reschedule
  * every %XA_CHECK_SCHED loops.
  */
 enum {
         XA_CHECK_SCHED = 4096,
 };
 
 /**
  * xas_for_each() - Iterate over a range of an XArray.
  * @xas: XArray operation state.
  * @entry: Entry retrieved from the array.
  * @max: Maximum index to retrieve from array.
  *
  * The loop body will be executed for each entry present in the xarray
  * between the current xas position and @max.  @entry will be set to
  * the entry retrieved from the xarray.  It is safe to delete entries
  * from the array in the loop body.  You should hold either the RCU lock
  * or the xa_lock while iterating.  If you need to drop the lock, call
  * xas_pause() first.
  */
 #define xas_for_each(xas, entry, max) \
         for (entry = xas_find(xas, max); entry; \
              entry = xas_next_entry(xas, max))
 
 /**
  * xas_for_each_marked() - Iterate over a range of an XArray.
  * @xas: XArray operation state.
  * @entry: Entry retrieved from the array.
  * @max: Maximum index to retrieve from array.
  * @mark: Mark to search for.
  *
  * The loop body will be executed for each marked entry in the xarray
  * between the current xas position and @max.  @entry will be set to
  * the entry retrieved from the xarray.  It is safe to delete entries
  * from the array in the loop body.  You should hold either the RCU lock
  * or the xa_lock while iterating.  If you need to drop the lock, call
  * xas_pause() first.
  */
 #define xas_for_each_marked(xas, entry, max, mark) \
         for (entry = xas_find_marked(xas, max, mark); entry; \
              entry = xas_next_marked(xas, max, mark))
 
 /**
  * xas_for_each_conflict() - Iterate over a range of an XArray.
  * @xas: XArray operation state.
  * @entry: Entry retrieved from the array.
  *
  * The loop body will be executed for each entry in the XArray that
  * lies within the range specified by @xas.  If the loop terminates
  * normally, @entry will be %NULL.  The user may break out of the loop,
  * which will leave @entry set to the conflicting entry.  The caller
  * may also call xa_set_err() to exit the loop while setting an error
  * to record the reason.
  */
 #define xas_for_each_conflict(xas, entry) \
         while ((entry = xas_find_conflict(xas)))
 
 void *__xas_next(struct xa_state *);
 void *__xas_prev(struct xa_state *);
 
 /**
  * xas_prev() - Move iterator to previous index.
  * @xas: XArray operation state.
  *
  * If the @xas was in an error state, it will remain in an error state
  * and this function will return %NULL.  If the @xas has never been walked,
  * it will have the effect of calling xas_load().  Otherwise one will be
  * subtracted from the index and the state will be walked to the correct
  * location in the array for the next operation.
  *
  * If the iterator was referencing index 0, this function wraps
  * around to %ULONG_MAX.
  *
  * Return: The entry at the new index.  This may be %NULL or an internal
  * entry.
  */
 static inline void *xas_prev(struct xa_state *xas)
 {
         struct xa_node *node = xas->xa_node;
 
         if (unlikely(xas_not_node(node) || node->shift ||
                                 xas->xa_offset == 0))
                 return __xas_prev(xas);
 
         xas->xa_index--;
         xas->xa_offset--;
         return xa_entry(xas->xa, node, xas->xa_offset);
 }
 
 /**
  * xas_next() - Move state to next index.
  * @xas: XArray operation state.
  *
  * If the @xas was in an error state, it will remain in an error state
  * and this function will return %NULL.  If the @xas has never been walked,
  * it will have the effect of calling xas_load().  Otherwise one will be
  * added to the index and the state will be walked to the correct
  * location in the array for the next operation.
  *
  * If the iterator was referencing index %ULONG_MAX, this function wraps
  * around to 0.
  *
  * Return: The entry at the new index.  This may be %NULL or an internal
  * entry.
  */
 static inline void *xas_next(struct xa_state *xas)
 {
         struct xa_node *node = xas->xa_node;
 
         if (unlikely(xas_not_node(node) || node->shift ||
                                 xas->xa_offset == XA_CHUNK_MASK))
                 return __xas_next(xas);
 
         xas->xa_index++;
         xas->xa_offset++;
         return xa_entry(xas->xa, node, xas->xa_offset);
 }
 
 #endif /* _LINUX_XARRAY_H */
 

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.