xref: /linux/include/linux/xarray.h (revision f73a058be5d70dd81a43f16b2bbff4b1576a7af8)
1 /* SPDX-License-Identifier: GPL-2.0+ */
2 #ifndef _LINUX_XARRAY_H
3 #define _LINUX_XARRAY_H
4 /*
5  * eXtensible Arrays
6  * Copyright (c) 2017 Microsoft Corporation
7  * Author: Matthew Wilcox <willy@infradead.org>
8  *
9  * See Documentation/core-api/xarray.rst for how to use the XArray.
10  */
11 
12 #include <linux/bitmap.h>
13 #include <linux/bug.h>
14 #include <linux/compiler.h>
15 #include <linux/err.h>
16 #include <linux/gfp.h>
17 #include <linux/kconfig.h>
18 #include <linux/limits.h>
19 #include <linux/lockdep.h>
20 #include <linux/rcupdate.h>
21 #include <linux/sched/mm.h>
22 #include <linux/spinlock.h>
23 #include <linux/types.h>
24 
25 struct list_lru;
26 
27 /*
28  * The bottom two bits of the entry determine how the XArray interprets
29  * the contents:
30  *
31  * 00: Pointer entry
32  * 10: Internal entry
33  * x1: Value entry or tagged pointer
34  *
35  * Attempting to store internal entries in the XArray is a bug.
36  *
37  * Most internal entries are pointers to the next node in the tree.
38  * The following internal entries have a special meaning:
39  *
40  * 0-62: Sibling entries
41  * 256: Retry entry
42  * 257: Zero entry
43  *
44  * Errors are also represented as internal entries, but use the negative
45  * space (-4094 to -2).  They're never stored in the slots array; only
46  * returned by the normal API.
47  */
48 
49 #define BITS_PER_XA_VALUE	(BITS_PER_LONG - 1)
50 
51 /**
52  * xa_mk_value() - Create an XArray entry from an integer.
53  * @v: Value to store in XArray.
54  *
55  * Context: Any context.
56  * Return: An entry suitable for storing in the XArray.
57  */
58 static inline void *xa_mk_value(unsigned long v)
59 {
60 	WARN_ON((long)v < 0);
61 	return (void *)((v << 1) | 1);
62 }
63 
64 /**
65  * xa_to_value() - Get value stored in an XArray entry.
66  * @entry: XArray entry.
67  *
68  * Context: Any context.
69  * Return: The value stored in the XArray entry.
70  */
71 static inline unsigned long xa_to_value(const void *entry)
72 {
73 	return (unsigned long)entry >> 1;
74 }
75 
76 /**
77  * xa_is_value() - Determine if an entry is a value.
78  * @entry: XArray entry.
79  *
80  * Context: Any context.
81  * Return: True if the entry is a value, false if it is a pointer.
82  */
83 static inline bool xa_is_value(const void *entry)
84 {
85 	return (unsigned long)entry & 1;
86 }
87 
88 /**
89  * xa_tag_pointer() - Create an XArray entry for a tagged pointer.
90  * @p: Plain pointer.
91  * @tag: Tag value (0, 1 or 3).
92  *
93  * If the user of the XArray prefers, they can tag their pointers instead
94  * of storing value entries.  Three tags are available (0, 1 and 3).
95  * These are distinct from the xa_mark_t as they are not replicated up
96  * through the array and cannot be searched for.
97  *
98  * Context: Any context.
99  * Return: An XArray entry.
100  */
101 static inline void *xa_tag_pointer(void *p, unsigned long tag)
102 {
103 	return (void *)((unsigned long)p | tag);
104 }
105 
106 /**
107  * xa_untag_pointer() - Turn an XArray entry into a plain pointer.
108  * @entry: XArray entry.
109  *
110  * If you have stored a tagged pointer in the XArray, call this function
111  * to get the untagged version of the pointer.
112  *
113  * Context: Any context.
114  * Return: A pointer.
115  */
116 static inline void *xa_untag_pointer(void *entry)
117 {
118 	return (void *)((unsigned long)entry & ~3UL);
119 }
120 
121 /**
122  * xa_pointer_tag() - Get the tag stored in an XArray entry.
123  * @entry: XArray entry.
124  *
125  * If you have stored a tagged pointer in the XArray, call this function
126  * to get the tag of that pointer.
127  *
128  * Context: Any context.
129  * Return: A tag.
130  */
131 static inline unsigned int xa_pointer_tag(void *entry)
132 {
133 	return (unsigned long)entry & 3UL;
134 }
135 
136 /*
137  * xa_mk_internal() - Create an internal entry.
138  * @v: Value to turn into an internal entry.
139  *
140  * Internal entries are used for a number of purposes.  Entries 0-255 are
141  * used for sibling entries (only 0-62 are used by the current code).  256
142  * is used for the retry entry.  257 is used for the reserved / zero entry.
143  * Negative internal entries are used to represent errnos.  Node pointers
144  * are also tagged as internal entries in some situations.
145  *
146  * Context: Any context.
147  * Return: An XArray internal entry corresponding to this value.
148  */
149 static inline void *xa_mk_internal(unsigned long v)
150 {
151 	return (void *)((v << 2) | 2);
152 }
153 
154 /*
155  * xa_to_internal() - Extract the value from an internal entry.
156  * @entry: XArray entry.
157  *
158  * Context: Any context.
159  * Return: The value which was stored in the internal entry.
160  */
161 static inline unsigned long xa_to_internal(const void *entry)
162 {
163 	return (unsigned long)entry >> 2;
164 }
165 
166 /*
167  * xa_is_internal() - Is the entry an internal entry?
168  * @entry: XArray entry.
169  *
170  * Context: Any context.
171  * Return: %true if the entry is an internal entry.
172  */
173 static inline bool xa_is_internal(const void *entry)
174 {
175 	return ((unsigned long)entry & 3) == 2;
176 }
177 
178 #define XA_ZERO_ENTRY		xa_mk_internal(257)
179 
180 /**
181  * xa_is_zero() - Is the entry a zero entry?
182  * @entry: Entry retrieved from the XArray
183  *
184  * The normal API will return NULL as the contents of a slot containing
185  * a zero entry.  You can only see zero entries by using the advanced API.
186  *
187  * Return: %true if the entry is a zero entry.
188  */
189 static inline bool xa_is_zero(const void *entry)
190 {
191 	return unlikely(entry == XA_ZERO_ENTRY);
192 }
193 
194 /**
195  * xa_is_err() - Report whether an XArray operation returned an error
196  * @entry: Result from calling an XArray function
197  *
198  * If an XArray operation cannot complete an operation, it will return
199  * a special value indicating an error.  This function tells you
200  * whether an error occurred; xa_err() tells you which error occurred.
201  *
202  * Context: Any context.
203  * Return: %true if the entry indicates an error.
204  */
205 static inline bool xa_is_err(const void *entry)
206 {
207 	return unlikely(xa_is_internal(entry) &&
208 			entry >= xa_mk_internal(-MAX_ERRNO));
209 }
210 
211 /**
212  * xa_err() - Turn an XArray result into an errno.
213  * @entry: Result from calling an XArray function.
214  *
215  * If an XArray operation cannot complete an operation, it will return
216  * a special pointer value which encodes an errno.  This function extracts
217  * the errno from the pointer value, or returns 0 if the pointer does not
218  * represent an errno.
219  *
220  * Context: Any context.
221  * Return: A negative errno or 0.
222  */
223 static inline int xa_err(void *entry)
224 {
225 	/* xa_to_internal() would not do sign extension. */
226 	if (xa_is_err(entry))
227 		return (long)entry >> 2;
228 	return 0;
229 }
230 
231 /**
232  * struct xa_limit - Represents a range of IDs.
233  * @min: The lowest ID to allocate (inclusive).
234  * @max: The maximum ID to allocate (inclusive).
235  *
236  * This structure is used either directly or via the XA_LIMIT() macro
237  * to communicate the range of IDs that are valid for allocation.
238  * Three common ranges are predefined for you:
239  * * xa_limit_32b	- [0 - UINT_MAX]
240  * * xa_limit_31b	- [0 - INT_MAX]
241  * * xa_limit_16b	- [0 - USHRT_MAX]
242  */
243 struct xa_limit {
244 	u32 max;
245 	u32 min;
246 };
247 
248 #define XA_LIMIT(_min, _max) (struct xa_limit) { .min = _min, .max = _max }
249 
250 #define xa_limit_32b	XA_LIMIT(0, UINT_MAX)
251 #define xa_limit_31b	XA_LIMIT(0, INT_MAX)
252 #define xa_limit_16b	XA_LIMIT(0, USHRT_MAX)
253 
254 typedef unsigned __bitwise xa_mark_t;
255 #define XA_MARK_0		((__force xa_mark_t)0U)
256 #define XA_MARK_1		((__force xa_mark_t)1U)
257 #define XA_MARK_2		((__force xa_mark_t)2U)
258 #define XA_PRESENT		((__force xa_mark_t)8U)
259 #define XA_MARK_MAX		XA_MARK_2
260 #define XA_FREE_MARK		XA_MARK_0
261 
262 enum xa_lock_type {
263 	XA_LOCK_IRQ = 1,
264 	XA_LOCK_BH = 2,
265 };
266 
267 /*
268  * Values for xa_flags.  The radix tree stores its GFP flags in the xa_flags,
269  * and we remain compatible with that.
270  */
271 #define XA_FLAGS_LOCK_IRQ	((__force gfp_t)XA_LOCK_IRQ)
272 #define XA_FLAGS_LOCK_BH	((__force gfp_t)XA_LOCK_BH)
273 #define XA_FLAGS_TRACK_FREE	((__force gfp_t)4U)
274 #define XA_FLAGS_ZERO_BUSY	((__force gfp_t)8U)
275 #define XA_FLAGS_ALLOC_WRAPPED	((__force gfp_t)16U)
276 #define XA_FLAGS_ACCOUNT	((__force gfp_t)32U)
277 #define XA_FLAGS_MARK(mark)	((__force gfp_t)((1U << __GFP_BITS_SHIFT) << \
278 						(__force unsigned)(mark)))
279 
280 /* ALLOC is for a normal 0-based alloc.  ALLOC1 is for an 1-based alloc */
281 #define XA_FLAGS_ALLOC	(XA_FLAGS_TRACK_FREE | XA_FLAGS_MARK(XA_FREE_MARK))
282 #define XA_FLAGS_ALLOC1	(XA_FLAGS_TRACK_FREE | XA_FLAGS_ZERO_BUSY)
283 
284 /**
285  * struct xarray - The anchor of the XArray.
286  * @xa_lock: Lock that protects the contents of the XArray.
287  *
288  * To use the xarray, define it statically or embed it in your data structure.
289  * It is a very small data structure, so it does not usually make sense to
290  * allocate it separately and keep a pointer to it in your data structure.
291  *
292  * You may use the xa_lock to protect your own data structures as well.
293  */
294 /*
295  * If all of the entries in the array are NULL, @xa_head is a NULL pointer.
296  * If the only non-NULL entry in the array is at index 0, @xa_head is that
297  * entry.  If any other entry in the array is non-NULL, @xa_head points
298  * to an @xa_node.
299  */
300 struct xarray {
301 	spinlock_t	xa_lock;
302 /* private: The rest of the data structure is not to be used directly. */
303 	gfp_t		xa_flags;
304 	void __rcu *	xa_head;
305 };
306 
307 #define XARRAY_INIT(name, flags) {				\
308 	.xa_lock = __SPIN_LOCK_UNLOCKED(name.xa_lock),		\
309 	.xa_flags = flags,					\
310 	.xa_head = NULL,					\
311 }
312 
313 /**
314  * DEFINE_XARRAY_FLAGS() - Define an XArray with custom flags.
315  * @name: A string that names your XArray.
316  * @flags: XA_FLAG values.
317  *
318  * This is intended for file scope definitions of XArrays.  It declares
319  * and initialises an empty XArray with the chosen name and flags.  It is
320  * equivalent to calling xa_init_flags() on the array, but it does the
321  * initialisation at compiletime instead of runtime.
322  */
323 #define DEFINE_XARRAY_FLAGS(name, flags)				\
324 	struct xarray name = XARRAY_INIT(name, flags)
325 
326 /**
327  * DEFINE_XARRAY() - Define an XArray.
328  * @name: A string that names your XArray.
329  *
330  * This is intended for file scope definitions of XArrays.  It declares
331  * and initialises an empty XArray with the chosen name.  It is equivalent
332  * to calling xa_init() on the array, but it does the initialisation at
333  * compiletime instead of runtime.
334  */
335 #define DEFINE_XARRAY(name) DEFINE_XARRAY_FLAGS(name, 0)
336 
337 /**
338  * DEFINE_XARRAY_ALLOC() - Define an XArray which allocates IDs starting at 0.
339  * @name: A string that names your XArray.
340  *
341  * This is intended for file scope definitions of allocating XArrays.
342  * See also DEFINE_XARRAY().
343  */
344 #define DEFINE_XARRAY_ALLOC(name) DEFINE_XARRAY_FLAGS(name, XA_FLAGS_ALLOC)
345 
346 /**
347  * DEFINE_XARRAY_ALLOC1() - Define an XArray which allocates IDs starting at 1.
348  * @name: A string that names your XArray.
349  *
350  * This is intended for file scope definitions of allocating XArrays.
351  * See also DEFINE_XARRAY().
352  */
353 #define DEFINE_XARRAY_ALLOC1(name) DEFINE_XARRAY_FLAGS(name, XA_FLAGS_ALLOC1)
354 
355 void *xa_load(struct xarray *, unsigned long index);
356 void *xa_store(struct xarray *, unsigned long index, void *entry, gfp_t);
357 void *xa_erase(struct xarray *, unsigned long index);
358 void *xa_store_range(struct xarray *, unsigned long first, unsigned long last,
359 			void *entry, gfp_t);
360 bool xa_get_mark(struct xarray *, unsigned long index, xa_mark_t);
361 void xa_set_mark(struct xarray *, unsigned long index, xa_mark_t);
362 void xa_clear_mark(struct xarray *, unsigned long index, xa_mark_t);
363 void *xa_find(struct xarray *xa, unsigned long *index,
364 		unsigned long max, xa_mark_t) __attribute__((nonnull(2)));
365 void *xa_find_after(struct xarray *xa, unsigned long *index,
366 		unsigned long max, xa_mark_t) __attribute__((nonnull(2)));
367 unsigned int xa_extract(struct xarray *, void **dst, unsigned long start,
368 		unsigned long max, unsigned int n, xa_mark_t);
369 void xa_destroy(struct xarray *);
370 
371 /**
372  * xa_init_flags() - Initialise an empty XArray with flags.
373  * @xa: XArray.
374  * @flags: XA_FLAG values.
375  *
376  * If you need to initialise an XArray with special flags (eg you need
377  * to take the lock from interrupt context), use this function instead
378  * of xa_init().
379  *
380  * Context: Any context.
381  */
382 static inline void xa_init_flags(struct xarray *xa, gfp_t flags)
383 {
384 	spin_lock_init(&xa->xa_lock);
385 	xa->xa_flags = flags;
386 	xa->xa_head = NULL;
387 }
388 
389 /**
390  * xa_init() - Initialise an empty XArray.
391  * @xa: XArray.
392  *
393  * An empty XArray is full of NULL entries.
394  *
395  * Context: Any context.
396  */
397 static inline void xa_init(struct xarray *xa)
398 {
399 	xa_init_flags(xa, 0);
400 }
401 
402 /**
403  * xa_empty() - Determine if an array has any present entries.
404  * @xa: XArray.
405  *
406  * Context: Any context.
407  * Return: %true if the array contains only NULL pointers.
408  */
409 static inline bool xa_empty(const struct xarray *xa)
410 {
411 	return xa->xa_head == NULL;
412 }
413 
414 /**
415  * xa_marked() - Inquire whether any entry in this array has a mark set
416  * @xa: Array
417  * @mark: Mark value
418  *
419  * Context: Any context.
420  * Return: %true if any entry has this mark set.
421  */
422 static inline bool xa_marked(const struct xarray *xa, xa_mark_t mark)
423 {
424 	return xa->xa_flags & XA_FLAGS_MARK(mark);
425 }
426 
427 /**
428  * xa_for_each_range() - Iterate over a portion of an XArray.
429  * @xa: XArray.
430  * @index: Index of @entry.
431  * @entry: Entry retrieved from array.
432  * @start: First index to retrieve from array.
433  * @last: Last index to retrieve from array.
434  *
435  * During the iteration, @entry will have the value of the entry stored
436  * in @xa at @index.  You may modify @index during the iteration if you
437  * want to skip or reprocess indices.  It is safe to modify the array
438  * during the iteration.  At the end of the iteration, @entry will be set
439  * to NULL and @index will have a value less than or equal to max.
440  *
441  * xa_for_each_range() is O(n.log(n)) while xas_for_each() is O(n).  You have
442  * to handle your own locking with xas_for_each(), and if you have to unlock
443  * after each iteration, it will also end up being O(n.log(n)).
444  * xa_for_each_range() will spin if it hits a retry entry; if you intend to
445  * see retry entries, you should use the xas_for_each() iterator instead.
446  * The xas_for_each() iterator will expand into more inline code than
447  * xa_for_each_range().
448  *
449  * Context: Any context.  Takes and releases the RCU lock.
450  */
451 #define xa_for_each_range(xa, index, entry, start, last)		\
452 	for (index = start,						\
453 	     entry = xa_find(xa, &index, last, XA_PRESENT);		\
454 	     entry;							\
455 	     entry = xa_find_after(xa, &index, last, XA_PRESENT))
456 
457 /**
458  * xa_for_each_start() - Iterate over a portion of an XArray.
459  * @xa: XArray.
460  * @index: Index of @entry.
461  * @entry: Entry retrieved from array.
462  * @start: First index to retrieve from array.
463  *
464  * During the iteration, @entry will have the value of the entry stored
465  * in @xa at @index.  You may modify @index during the iteration if you
466  * want to skip or reprocess indices.  It is safe to modify the array
467  * during the iteration.  At the end of the iteration, @entry will be set
468  * to NULL and @index will have a value less than or equal to max.
469  *
470  * xa_for_each_start() is O(n.log(n)) while xas_for_each() is O(n).  You have
471  * to handle your own locking with xas_for_each(), and if you have to unlock
472  * after each iteration, it will also end up being O(n.log(n)).
473  * xa_for_each_start() will spin if it hits a retry entry; if you intend to
474  * see retry entries, you should use the xas_for_each() iterator instead.
475  * The xas_for_each() iterator will expand into more inline code than
476  * xa_for_each_start().
477  *
478  * Context: Any context.  Takes and releases the RCU lock.
479  */
480 #define xa_for_each_start(xa, index, entry, start) \
481 	xa_for_each_range(xa, index, entry, start, ULONG_MAX)
482 
483 /**
484  * xa_for_each() - Iterate over present entries in an XArray.
485  * @xa: XArray.
486  * @index: Index of @entry.
487  * @entry: Entry retrieved from array.
488  *
489  * During the iteration, @entry will have the value of the entry stored
490  * in @xa at @index.  You may modify @index during the iteration if you want
491  * to skip or reprocess indices.  It is safe to modify the array during the
492  * iteration.  At the end of the iteration, @entry will be set to NULL and
493  * @index will have a value less than or equal to max.
494  *
495  * xa_for_each() is O(n.log(n)) while xas_for_each() is O(n).  You have
496  * to handle your own locking with xas_for_each(), and if you have to unlock
497  * after each iteration, it will also end up being O(n.log(n)).  xa_for_each()
498  * will spin if it hits a retry entry; if you intend to see retry entries,
499  * you should use the xas_for_each() iterator instead.  The xas_for_each()
500  * iterator will expand into more inline code than xa_for_each().
501  *
502  * Context: Any context.  Takes and releases the RCU lock.
503  */
504 #define xa_for_each(xa, index, entry) \
505 	xa_for_each_start(xa, index, entry, 0)
506 
507 /**
508  * xa_for_each_marked() - Iterate over marked entries in an XArray.
509  * @xa: XArray.
510  * @index: Index of @entry.
511  * @entry: Entry retrieved from array.
512  * @filter: Selection criterion.
513  *
514  * During the iteration, @entry will have the value of the entry stored
515  * in @xa at @index.  The iteration will skip all entries in the array
516  * which do not match @filter.  You may modify @index during the iteration
517  * if you want to skip or reprocess indices.  It is safe to modify the array
518  * during the iteration.  At the end of the iteration, @entry will be set to
519  * NULL and @index will have a value less than or equal to max.
520  *
521  * xa_for_each_marked() is O(n.log(n)) while xas_for_each_marked() is O(n).
522  * You have to handle your own locking with xas_for_each(), and if you have
523  * to unlock after each iteration, it will also end up being O(n.log(n)).
524  * xa_for_each_marked() will spin if it hits a retry entry; if you intend to
525  * see retry entries, you should use the xas_for_each_marked() iterator
526  * instead.  The xas_for_each_marked() iterator will expand into more inline
527  * code than xa_for_each_marked().
528  *
529  * Context: Any context.  Takes and releases the RCU lock.
530  */
531 #define xa_for_each_marked(xa, index, entry, filter) \
532 	for (index = 0, entry = xa_find(xa, &index, ULONG_MAX, filter); \
533 	     entry; entry = xa_find_after(xa, &index, ULONG_MAX, filter))
534 
535 #define xa_trylock(xa)		spin_trylock(&(xa)->xa_lock)
536 #define xa_lock(xa)		spin_lock(&(xa)->xa_lock)
537 #define xa_unlock(xa)		spin_unlock(&(xa)->xa_lock)
538 #define xa_lock_bh(xa)		spin_lock_bh(&(xa)->xa_lock)
539 #define xa_unlock_bh(xa)	spin_unlock_bh(&(xa)->xa_lock)
540 #define xa_lock_irq(xa)		spin_lock_irq(&(xa)->xa_lock)
541 #define xa_unlock_irq(xa)	spin_unlock_irq(&(xa)->xa_lock)
542 #define xa_lock_irqsave(xa, flags) \
543 				spin_lock_irqsave(&(xa)->xa_lock, flags)
544 #define xa_unlock_irqrestore(xa, flags) \
545 				spin_unlock_irqrestore(&(xa)->xa_lock, flags)
546 #define xa_lock_nested(xa, subclass) \
547 				spin_lock_nested(&(xa)->xa_lock, subclass)
548 #define xa_lock_bh_nested(xa, subclass) \
549 				spin_lock_bh_nested(&(xa)->xa_lock, subclass)
550 #define xa_lock_irq_nested(xa, subclass) \
551 				spin_lock_irq_nested(&(xa)->xa_lock, subclass)
552 #define xa_lock_irqsave_nested(xa, flags, subclass) \
553 		spin_lock_irqsave_nested(&(xa)->xa_lock, flags, subclass)
554 
555 /*
556  * Versions of the normal API which require the caller to hold the
557  * xa_lock.  If the GFP flags allow it, they will drop the lock to
558  * allocate memory, then reacquire it afterwards.  These functions
559  * may also re-enable interrupts if the XArray flags indicate the
560  * locking should be interrupt safe.
561  */
562 void *__xa_erase(struct xarray *, unsigned long index);
563 void *__xa_store(struct xarray *, unsigned long index, void *entry, gfp_t);
564 void *__xa_cmpxchg(struct xarray *, unsigned long index, void *old,
565 		void *entry, gfp_t);
566 int __must_check __xa_insert(struct xarray *, unsigned long index,
567 		void *entry, gfp_t);
568 int __must_check __xa_alloc(struct xarray *, u32 *id, void *entry,
569 		struct xa_limit, gfp_t);
570 int __must_check __xa_alloc_cyclic(struct xarray *, u32 *id, void *entry,
571 		struct xa_limit, u32 *next, gfp_t);
572 void __xa_set_mark(struct xarray *, unsigned long index, xa_mark_t);
573 void __xa_clear_mark(struct xarray *, unsigned long index, xa_mark_t);
574 
575 /**
576  * xa_store_bh() - Store this entry in the XArray.
577  * @xa: XArray.
578  * @index: Index into array.
579  * @entry: New entry.
580  * @gfp: Memory allocation flags.
581  *
582  * This function is like calling xa_store() except it disables softirqs
583  * while holding the array lock.
584  *
585  * Context: Any context.  Takes and releases the xa_lock while
586  * disabling softirqs.
587  * Return: The old entry at this index or xa_err() if an error happened.
588  */
589 static inline void *xa_store_bh(struct xarray *xa, unsigned long index,
590 		void *entry, gfp_t gfp)
591 {
592 	void *curr;
593 
594 	might_alloc(gfp);
595 	xa_lock_bh(xa);
596 	curr = __xa_store(xa, index, entry, gfp);
597 	xa_unlock_bh(xa);
598 
599 	return curr;
600 }
601 
602 /**
603  * xa_store_irq() - Store this entry in the XArray.
604  * @xa: XArray.
605  * @index: Index into array.
606  * @entry: New entry.
607  * @gfp: Memory allocation flags.
608  *
609  * This function is like calling xa_store() except it disables interrupts
610  * while holding the array lock.
611  *
612  * Context: Process context.  Takes and releases the xa_lock while
613  * disabling interrupts.
614  * Return: The old entry at this index or xa_err() if an error happened.
615  */
616 static inline void *xa_store_irq(struct xarray *xa, unsigned long index,
617 		void *entry, gfp_t gfp)
618 {
619 	void *curr;
620 
621 	might_alloc(gfp);
622 	xa_lock_irq(xa);
623 	curr = __xa_store(xa, index, entry, gfp);
624 	xa_unlock_irq(xa);
625 
626 	return curr;
627 }
628 
629 /**
630  * xa_erase_bh() - Erase this entry from the XArray.
631  * @xa: XArray.
632  * @index: Index of entry.
633  *
634  * After this function returns, loading from @index will return %NULL.
635  * If the index is part of a multi-index entry, all indices will be erased
636  * and none of the entries will be part of a multi-index entry.
637  *
638  * Context: Any context.  Takes and releases the xa_lock while
639  * disabling softirqs.
640  * Return: The entry which used to be at this index.
641  */
642 static inline void *xa_erase_bh(struct xarray *xa, unsigned long index)
643 {
644 	void *entry;
645 
646 	xa_lock_bh(xa);
647 	entry = __xa_erase(xa, index);
648 	xa_unlock_bh(xa);
649 
650 	return entry;
651 }
652 
653 /**
654  * xa_erase_irq() - Erase this entry from the XArray.
655  * @xa: XArray.
656  * @index: Index of entry.
657  *
658  * After this function returns, loading from @index will return %NULL.
659  * If the index is part of a multi-index entry, all indices will be erased
660  * and none of the entries will be part of a multi-index entry.
661  *
662  * Context: Process context.  Takes and releases the xa_lock while
663  * disabling interrupts.
664  * Return: The entry which used to be at this index.
665  */
666 static inline void *xa_erase_irq(struct xarray *xa, unsigned long index)
667 {
668 	void *entry;
669 
670 	xa_lock_irq(xa);
671 	entry = __xa_erase(xa, index);
672 	xa_unlock_irq(xa);
673 
674 	return entry;
675 }
676 
677 /**
678  * xa_cmpxchg() - Conditionally replace an entry in the XArray.
679  * @xa: XArray.
680  * @index: Index into array.
681  * @old: Old value to test against.
682  * @entry: New value to place in array.
683  * @gfp: Memory allocation flags.
684  *
685  * If the entry at @index is the same as @old, replace it with @entry.
686  * If the return value is equal to @old, then the exchange was successful.
687  *
688  * Context: Any context.  Takes and releases the xa_lock.  May sleep
689  * if the @gfp flags permit.
690  * Return: The old value at this index or xa_err() if an error happened.
691  */
692 static inline void *xa_cmpxchg(struct xarray *xa, unsigned long index,
693 			void *old, void *entry, gfp_t gfp)
694 {
695 	void *curr;
696 
697 	might_alloc(gfp);
698 	xa_lock(xa);
699 	curr = __xa_cmpxchg(xa, index, old, entry, gfp);
700 	xa_unlock(xa);
701 
702 	return curr;
703 }
704 
705 /**
706  * xa_cmpxchg_bh() - Conditionally replace an entry in the XArray.
707  * @xa: XArray.
708  * @index: Index into array.
709  * @old: Old value to test against.
710  * @entry: New value to place in array.
711  * @gfp: Memory allocation flags.
712  *
713  * This function is like calling xa_cmpxchg() except it disables softirqs
714  * while holding the array lock.
715  *
716  * Context: Any context.  Takes and releases the xa_lock while
717  * disabling softirqs.  May sleep if the @gfp flags permit.
718  * Return: The old value at this index or xa_err() if an error happened.
719  */
720 static inline void *xa_cmpxchg_bh(struct xarray *xa, unsigned long index,
721 			void *old, void *entry, gfp_t gfp)
722 {
723 	void *curr;
724 
725 	might_alloc(gfp);
726 	xa_lock_bh(xa);
727 	curr = __xa_cmpxchg(xa, index, old, entry, gfp);
728 	xa_unlock_bh(xa);
729 
730 	return curr;
731 }
732 
733 /**
734  * xa_cmpxchg_irq() - Conditionally replace an entry in the XArray.
735  * @xa: XArray.
736  * @index: Index into array.
737  * @old: Old value to test against.
738  * @entry: New value to place in array.
739  * @gfp: Memory allocation flags.
740  *
741  * This function is like calling xa_cmpxchg() except it disables interrupts
742  * while holding the array lock.
743  *
744  * Context: Process context.  Takes and releases the xa_lock while
745  * disabling interrupts.  May sleep if the @gfp flags permit.
746  * Return: The old value at this index or xa_err() if an error happened.
747  */
748 static inline void *xa_cmpxchg_irq(struct xarray *xa, unsigned long index,
749 			void *old, void *entry, gfp_t gfp)
750 {
751 	void *curr;
752 
753 	might_alloc(gfp);
754 	xa_lock_irq(xa);
755 	curr = __xa_cmpxchg(xa, index, old, entry, gfp);
756 	xa_unlock_irq(xa);
757 
758 	return curr;
759 }
760 
761 /**
762  * xa_insert() - Store this entry in the XArray unless another entry is
763  *			already present.
764  * @xa: XArray.
765  * @index: Index into array.
766  * @entry: New entry.
767  * @gfp: Memory allocation flags.
768  *
769  * Inserting a NULL entry will store a reserved entry (like xa_reserve())
770  * if no entry is present.  Inserting will fail if a reserved entry is
771  * present, even though loading from this index will return NULL.
772  *
773  * Context: Any context.  Takes and releases the xa_lock.  May sleep if
774  * the @gfp flags permit.
775  * Return: 0 if the store succeeded.  -EBUSY if another entry was present.
776  * -ENOMEM if memory could not be allocated.
777  */
778 static inline int __must_check xa_insert(struct xarray *xa,
779 		unsigned long index, void *entry, gfp_t gfp)
780 {
781 	int err;
782 
783 	might_alloc(gfp);
784 	xa_lock(xa);
785 	err = __xa_insert(xa, index, entry, gfp);
786 	xa_unlock(xa);
787 
788 	return err;
789 }
790 
791 /**
792  * xa_insert_bh() - Store this entry in the XArray unless another entry is
793  *			already present.
794  * @xa: XArray.
795  * @index: Index into array.
796  * @entry: New entry.
797  * @gfp: Memory allocation flags.
798  *
799  * Inserting a NULL entry will store a reserved entry (like xa_reserve())
800  * if no entry is present.  Inserting will fail if a reserved entry is
801  * present, even though loading from this index will return NULL.
802  *
803  * Context: Any context.  Takes and releases the xa_lock while
804  * disabling softirqs.  May sleep if the @gfp flags permit.
805  * Return: 0 if the store succeeded.  -EBUSY if another entry was present.
806  * -ENOMEM if memory could not be allocated.
807  */
808 static inline int __must_check xa_insert_bh(struct xarray *xa,
809 		unsigned long index, void *entry, gfp_t gfp)
810 {
811 	int err;
812 
813 	might_alloc(gfp);
814 	xa_lock_bh(xa);
815 	err = __xa_insert(xa, index, entry, gfp);
816 	xa_unlock_bh(xa);
817 
818 	return err;
819 }
820 
821 /**
822  * xa_insert_irq() - Store this entry in the XArray unless another entry is
823  *			already present.
824  * @xa: XArray.
825  * @index: Index into array.
826  * @entry: New entry.
827  * @gfp: Memory allocation flags.
828  *
829  * Inserting a NULL entry will store a reserved entry (like xa_reserve())
830  * if no entry is present.  Inserting will fail if a reserved entry is
831  * present, even though loading from this index will return NULL.
832  *
833  * Context: Process context.  Takes and releases the xa_lock while
834  * disabling interrupts.  May sleep if the @gfp flags permit.
835  * Return: 0 if the store succeeded.  -EBUSY if another entry was present.
836  * -ENOMEM if memory could not be allocated.
837  */
838 static inline int __must_check xa_insert_irq(struct xarray *xa,
839 		unsigned long index, void *entry, gfp_t gfp)
840 {
841 	int err;
842 
843 	might_alloc(gfp);
844 	xa_lock_irq(xa);
845 	err = __xa_insert(xa, index, entry, gfp);
846 	xa_unlock_irq(xa);
847 
848 	return err;
849 }
850 
851 /**
852  * xa_alloc() - Find somewhere to store this entry in the XArray.
853  * @xa: XArray.
854  * @id: Pointer to ID.
855  * @entry: New entry.
856  * @limit: Range of ID to allocate.
857  * @gfp: Memory allocation flags.
858  *
859  * Finds an empty entry in @xa between @limit.min and @limit.max,
860  * stores the index into the @id pointer, then stores the entry at
861  * that index.  A concurrent lookup will not see an uninitialised @id.
862  *
863  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
864  * in xa_init_flags().
865  *
866  * Context: Any context.  Takes and releases the xa_lock.  May sleep if
867  * the @gfp flags permit.
868  * Return: 0 on success, -ENOMEM if memory could not be allocated or
869  * -EBUSY if there are no free entries in @limit.
870  */
871 static inline __must_check int xa_alloc(struct xarray *xa, u32 *id,
872 		void *entry, struct xa_limit limit, gfp_t gfp)
873 {
874 	int err;
875 
876 	might_alloc(gfp);
877 	xa_lock(xa);
878 	err = __xa_alloc(xa, id, entry, limit, gfp);
879 	xa_unlock(xa);
880 
881 	return err;
882 }
883 
884 /**
885  * xa_alloc_bh() - Find somewhere to store this entry in the XArray.
886  * @xa: XArray.
887  * @id: Pointer to ID.
888  * @entry: New entry.
889  * @limit: Range of ID to allocate.
890  * @gfp: Memory allocation flags.
891  *
892  * Finds an empty entry in @xa between @limit.min and @limit.max,
893  * stores the index into the @id pointer, then stores the entry at
894  * that index.  A concurrent lookup will not see an uninitialised @id.
895  *
896  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
897  * in xa_init_flags().
898  *
899  * Context: Any context.  Takes and releases the xa_lock while
900  * disabling softirqs.  May sleep if the @gfp flags permit.
901  * Return: 0 on success, -ENOMEM if memory could not be allocated or
902  * -EBUSY if there are no free entries in @limit.
903  */
904 static inline int __must_check xa_alloc_bh(struct xarray *xa, u32 *id,
905 		void *entry, struct xa_limit limit, gfp_t gfp)
906 {
907 	int err;
908 
909 	might_alloc(gfp);
910 	xa_lock_bh(xa);
911 	err = __xa_alloc(xa, id, entry, limit, gfp);
912 	xa_unlock_bh(xa);
913 
914 	return err;
915 }
916 
917 /**
918  * xa_alloc_irq() - Find somewhere to store this entry in the XArray.
919  * @xa: XArray.
920  * @id: Pointer to ID.
921  * @entry: New entry.
922  * @limit: Range of ID to allocate.
923  * @gfp: Memory allocation flags.
924  *
925  * Finds an empty entry in @xa between @limit.min and @limit.max,
926  * stores the index into the @id pointer, then stores the entry at
927  * that index.  A concurrent lookup will not see an uninitialised @id.
928  *
929  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
930  * in xa_init_flags().
931  *
932  * Context: Process context.  Takes and releases the xa_lock while
933  * disabling interrupts.  May sleep if the @gfp flags permit.
934  * Return: 0 on success, -ENOMEM if memory could not be allocated or
935  * -EBUSY if there are no free entries in @limit.
936  */
937 static inline int __must_check xa_alloc_irq(struct xarray *xa, u32 *id,
938 		void *entry, struct xa_limit limit, gfp_t gfp)
939 {
940 	int err;
941 
942 	might_alloc(gfp);
943 	xa_lock_irq(xa);
944 	err = __xa_alloc(xa, id, entry, limit, gfp);
945 	xa_unlock_irq(xa);
946 
947 	return err;
948 }
949 
950 /**
951  * xa_alloc_cyclic() - Find somewhere to store this entry in the XArray.
952  * @xa: XArray.
953  * @id: Pointer to ID.
954  * @entry: New entry.
955  * @limit: Range of allocated ID.
956  * @next: Pointer to next ID to allocate.
957  * @gfp: Memory allocation flags.
958  *
959  * Finds an empty entry in @xa between @limit.min and @limit.max,
960  * stores the index into the @id pointer, then stores the entry at
961  * that index.  A concurrent lookup will not see an uninitialised @id.
962  * The search for an empty entry will start at @next and will wrap
963  * around if necessary.
964  *
965  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
966  * in xa_init_flags().
967  *
968  * Context: Any context.  Takes and releases the xa_lock.  May sleep if
969  * the @gfp flags permit.
970  * Return: 0 if the allocation succeeded without wrapping.  1 if the
971  * allocation succeeded after wrapping, -ENOMEM if memory could not be
972  * allocated or -EBUSY if there are no free entries in @limit.
973  */
974 static inline int xa_alloc_cyclic(struct xarray *xa, u32 *id, void *entry,
975 		struct xa_limit limit, u32 *next, gfp_t gfp)
976 {
977 	int err;
978 
979 	might_alloc(gfp);
980 	xa_lock(xa);
981 	err = __xa_alloc_cyclic(xa, id, entry, limit, next, gfp);
982 	xa_unlock(xa);
983 
984 	return err;
985 }
986 
987 /**
988  * xa_alloc_cyclic_bh() - Find somewhere to store this entry in the XArray.
989  * @xa: XArray.
990  * @id: Pointer to ID.
991  * @entry: New entry.
992  * @limit: Range of allocated ID.
993  * @next: Pointer to next ID to allocate.
994  * @gfp: Memory allocation flags.
995  *
996  * Finds an empty entry in @xa between @limit.min and @limit.max,
997  * stores the index into the @id pointer, then stores the entry at
998  * that index.  A concurrent lookup will not see an uninitialised @id.
999  * The search for an empty entry will start at @next and will wrap
1000  * around if necessary.
1001  *
1002  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
1003  * in xa_init_flags().
1004  *
1005  * Context: Any context.  Takes and releases the xa_lock while
1006  * disabling softirqs.  May sleep if the @gfp flags permit.
1007  * Return: 0 if the allocation succeeded without wrapping.  1 if the
1008  * allocation succeeded after wrapping, -ENOMEM if memory could not be
1009  * allocated or -EBUSY if there are no free entries in @limit.
1010  */
1011 static inline int xa_alloc_cyclic_bh(struct xarray *xa, u32 *id, void *entry,
1012 		struct xa_limit limit, u32 *next, gfp_t gfp)
1013 {
1014 	int err;
1015 
1016 	might_alloc(gfp);
1017 	xa_lock_bh(xa);
1018 	err = __xa_alloc_cyclic(xa, id, entry, limit, next, gfp);
1019 	xa_unlock_bh(xa);
1020 
1021 	return err;
1022 }
1023 
1024 /**
1025  * xa_alloc_cyclic_irq() - Find somewhere to store this entry in the XArray.
1026  * @xa: XArray.
1027  * @id: Pointer to ID.
1028  * @entry: New entry.
1029  * @limit: Range of allocated ID.
1030  * @next: Pointer to next ID to allocate.
1031  * @gfp: Memory allocation flags.
1032  *
1033  * Finds an empty entry in @xa between @limit.min and @limit.max,
1034  * stores the index into the @id pointer, then stores the entry at
1035  * that index.  A concurrent lookup will not see an uninitialised @id.
1036  * The search for an empty entry will start at @next and will wrap
1037  * around if necessary.
1038  *
1039  * Must only be operated on an xarray initialized with flag XA_FLAGS_ALLOC set
1040  * in xa_init_flags().
1041  *
1042  * Context: Process context.  Takes and releases the xa_lock while
1043  * disabling interrupts.  May sleep if the @gfp flags permit.
1044  * Return: 0 if the allocation succeeded without wrapping.  1 if the
1045  * allocation succeeded after wrapping, -ENOMEM if memory could not be
1046  * allocated or -EBUSY if there are no free entries in @limit.
1047  */
1048 static inline int xa_alloc_cyclic_irq(struct xarray *xa, u32 *id, void *entry,
1049 		struct xa_limit limit, u32 *next, gfp_t gfp)
1050 {
1051 	int err;
1052 
1053 	might_alloc(gfp);
1054 	xa_lock_irq(xa);
1055 	err = __xa_alloc_cyclic(xa, id, entry, limit, next, gfp);
1056 	xa_unlock_irq(xa);
1057 
1058 	return err;
1059 }
1060 
1061 /**
1062  * xa_reserve() - Reserve this index in the XArray.
1063  * @xa: XArray.
1064  * @index: Index into array.
1065  * @gfp: Memory allocation flags.
1066  *
1067  * Ensures there is somewhere to store an entry at @index in the array.
1068  * If there is already something stored at @index, this function does
1069  * nothing.  If there was nothing there, the entry is marked as reserved.
1070  * Loading from a reserved entry returns a %NULL pointer.
1071  *
1072  * If you do not use the entry that you have reserved, call xa_release()
1073  * or xa_erase() to free any unnecessary memory.
1074  *
1075  * Context: Any context.  Takes and releases the xa_lock.
1076  * May sleep if the @gfp flags permit.
1077  * Return: 0 if the reservation succeeded or -ENOMEM if it failed.
1078  */
1079 static inline __must_check
1080 int xa_reserve(struct xarray *xa, unsigned long index, gfp_t gfp)
1081 {
1082 	return xa_err(xa_cmpxchg(xa, index, NULL, XA_ZERO_ENTRY, gfp));
1083 }
1084 
1085 /**
1086  * xa_reserve_bh() - Reserve this index in the XArray.
1087  * @xa: XArray.
1088  * @index: Index into array.
1089  * @gfp: Memory allocation flags.
1090  *
1091  * A softirq-disabling version of xa_reserve().
1092  *
1093  * Context: Any context.  Takes and releases the xa_lock while
1094  * disabling softirqs.
1095  * Return: 0 if the reservation succeeded or -ENOMEM if it failed.
1096  */
1097 static inline __must_check
1098 int xa_reserve_bh(struct xarray *xa, unsigned long index, gfp_t gfp)
1099 {
1100 	return xa_err(xa_cmpxchg_bh(xa, index, NULL, XA_ZERO_ENTRY, gfp));
1101 }
1102 
1103 /**
1104  * xa_reserve_irq() - Reserve this index in the XArray.
1105  * @xa: XArray.
1106  * @index: Index into array.
1107  * @gfp: Memory allocation flags.
1108  *
1109  * An interrupt-disabling version of xa_reserve().
1110  *
1111  * Context: Process context.  Takes and releases the xa_lock while
1112  * disabling interrupts.
1113  * Return: 0 if the reservation succeeded or -ENOMEM if it failed.
1114  */
1115 static inline __must_check
1116 int xa_reserve_irq(struct xarray *xa, unsigned long index, gfp_t gfp)
1117 {
1118 	return xa_err(xa_cmpxchg_irq(xa, index, NULL, XA_ZERO_ENTRY, gfp));
1119 }
1120 
1121 /**
1122  * xa_release() - Release a reserved entry.
1123  * @xa: XArray.
1124  * @index: Index of entry.
1125  *
1126  * After calling xa_reserve(), you can call this function to release the
1127  * reservation.  If the entry at @index has been stored to, this function
1128  * will do nothing.
1129  */
1130 static inline void xa_release(struct xarray *xa, unsigned long index)
1131 {
1132 	xa_cmpxchg(xa, index, XA_ZERO_ENTRY, NULL, 0);
1133 }
1134 
1135 /* Everything below here is the Advanced API.  Proceed with caution. */
1136 
1137 /*
1138  * The xarray is constructed out of a set of 'chunks' of pointers.  Choosing
1139  * the best chunk size requires some tradeoffs.  A power of two recommends
1140  * itself so that we can walk the tree based purely on shifts and masks.
1141  * Generally, the larger the better; as the number of slots per level of the
1142  * tree increases, the less tall the tree needs to be.  But that needs to be
1143  * balanced against the memory consumption of each node.  On a 64-bit system,
1144  * xa_node is currently 576 bytes, and we get 7 of them per 4kB page.  If we
1145  * doubled the number of slots per node, we'd get only 3 nodes per 4kB page.
1146  */
1147 #ifndef XA_CHUNK_SHIFT
1148 #define XA_CHUNK_SHIFT		(IS_ENABLED(CONFIG_BASE_SMALL) ? 4 : 6)
1149 #endif
1150 #define XA_CHUNK_SIZE		(1UL << XA_CHUNK_SHIFT)
1151 #define XA_CHUNK_MASK		(XA_CHUNK_SIZE - 1)
1152 #define XA_MAX_MARKS		3
1153 #define XA_MARK_LONGS		BITS_TO_LONGS(XA_CHUNK_SIZE)
1154 
1155 /*
1156  * @count is the count of every non-NULL element in the ->slots array
1157  * whether that is a value entry, a retry entry, a user pointer,
1158  * a sibling entry or a pointer to the next level of the tree.
1159  * @nr_values is the count of every element in ->slots which is
1160  * either a value entry or a sibling of a value entry.
1161  */
1162 struct xa_node {
1163 	unsigned char	shift;		/* Bits remaining in each slot */
1164 	unsigned char	offset;		/* Slot offset in parent */
1165 	unsigned char	count;		/* Total entry count */
1166 	unsigned char	nr_values;	/* Value entry count */
1167 	struct xa_node __rcu *parent;	/* NULL at top of tree */
1168 	struct xarray	*array;		/* The array we belong to */
1169 	union {
1170 		struct list_head private_list;	/* For tree user */
1171 		struct rcu_head	rcu_head;	/* Used when freeing node */
1172 	};
1173 	void __rcu	*slots[XA_CHUNK_SIZE];
1174 	union {
1175 		unsigned long	tags[XA_MAX_MARKS][XA_MARK_LONGS];
1176 		unsigned long	marks[XA_MAX_MARKS][XA_MARK_LONGS];
1177 	};
1178 };
1179 
1180 void xa_dump(const struct xarray *);
1181 void xa_dump_node(const struct xa_node *);
1182 
1183 #ifdef XA_DEBUG
1184 #define XA_BUG_ON(xa, x) do {					\
1185 		if (x) {					\
1186 			xa_dump(xa);				\
1187 			BUG();					\
1188 		}						\
1189 	} while (0)
1190 #define XA_NODE_BUG_ON(node, x) do {				\
1191 		if (x) {					\
1192 			if (node) xa_dump_node(node);		\
1193 			BUG();					\
1194 		}						\
1195 	} while (0)
1196 #else
1197 #define XA_BUG_ON(xa, x)	do { } while (0)
1198 #define XA_NODE_BUG_ON(node, x)	do { } while (0)
1199 #endif
1200 
1201 /* Private */
1202 static inline void *xa_head(const struct xarray *xa)
1203 {
1204 	return rcu_dereference_check(xa->xa_head,
1205 						lockdep_is_held(&xa->xa_lock));
1206 }
1207 
1208 /* Private */
1209 static inline void *xa_head_locked(const struct xarray *xa)
1210 {
1211 	return rcu_dereference_protected(xa->xa_head,
1212 						lockdep_is_held(&xa->xa_lock));
1213 }
1214 
1215 /* Private */
1216 static inline void *xa_entry(const struct xarray *xa,
1217 				const struct xa_node *node, unsigned int offset)
1218 {
1219 	XA_NODE_BUG_ON(node, offset >= XA_CHUNK_SIZE);
1220 	return rcu_dereference_check(node->slots[offset],
1221 						lockdep_is_held(&xa->xa_lock));
1222 }
1223 
1224 /* Private */
1225 static inline void *xa_entry_locked(const struct xarray *xa,
1226 				const struct xa_node *node, unsigned int offset)
1227 {
1228 	XA_NODE_BUG_ON(node, offset >= XA_CHUNK_SIZE);
1229 	return rcu_dereference_protected(node->slots[offset],
1230 						lockdep_is_held(&xa->xa_lock));
1231 }
1232 
1233 /* Private */
1234 static inline struct xa_node *xa_parent(const struct xarray *xa,
1235 					const struct xa_node *node)
1236 {
1237 	return rcu_dereference_check(node->parent,
1238 						lockdep_is_held(&xa->xa_lock));
1239 }
1240 
1241 /* Private */
1242 static inline struct xa_node *xa_parent_locked(const struct xarray *xa,
1243 					const struct xa_node *node)
1244 {
1245 	return rcu_dereference_protected(node->parent,
1246 						lockdep_is_held(&xa->xa_lock));
1247 }
1248 
1249 /* Private */
1250 static inline void *xa_mk_node(const struct xa_node *node)
1251 {
1252 	return (void *)((unsigned long)node | 2);
1253 }
1254 
1255 /* Private */
1256 static inline struct xa_node *xa_to_node(const void *entry)
1257 {
1258 	return (struct xa_node *)((unsigned long)entry - 2);
1259 }
1260 
1261 /* Private */
1262 static inline bool xa_is_node(const void *entry)
1263 {
1264 	return xa_is_internal(entry) && (unsigned long)entry > 4096;
1265 }
1266 
1267 /* Private */
1268 static inline void *xa_mk_sibling(unsigned int offset)
1269 {
1270 	return xa_mk_internal(offset);
1271 }
1272 
1273 /* Private */
1274 static inline unsigned long xa_to_sibling(const void *entry)
1275 {
1276 	return xa_to_internal(entry);
1277 }
1278 
1279 /**
1280  * xa_is_sibling() - Is the entry a sibling entry?
1281  * @entry: Entry retrieved from the XArray
1282  *
1283  * Return: %true if the entry is a sibling entry.
1284  */
1285 static inline bool xa_is_sibling(const void *entry)
1286 {
1287 	return IS_ENABLED(CONFIG_XARRAY_MULTI) && xa_is_internal(entry) &&
1288 		(entry < xa_mk_sibling(XA_CHUNK_SIZE - 1));
1289 }
1290 
1291 #define XA_RETRY_ENTRY		xa_mk_internal(256)
1292 
1293 /**
1294  * xa_is_retry() - Is the entry a retry entry?
1295  * @entry: Entry retrieved from the XArray
1296  *
1297  * Return: %true if the entry is a retry entry.
1298  */
1299 static inline bool xa_is_retry(const void *entry)
1300 {
1301 	return unlikely(entry == XA_RETRY_ENTRY);
1302 }
1303 
1304 /**
1305  * xa_is_advanced() - Is the entry only permitted for the advanced API?
1306  * @entry: Entry to be stored in the XArray.
1307  *
1308  * Return: %true if the entry cannot be stored by the normal API.
1309  */
1310 static inline bool xa_is_advanced(const void *entry)
1311 {
1312 	return xa_is_internal(entry) && (entry <= XA_RETRY_ENTRY);
1313 }
1314 
1315 /**
1316  * typedef xa_update_node_t - A callback function from the XArray.
1317  * @node: The node which is being processed
1318  *
1319  * This function is called every time the XArray updates the count of
1320  * present and value entries in a node.  It allows advanced users to
1321  * maintain the private_list in the node.
1322  *
1323  * Context: The xa_lock is held and interrupts may be disabled.
1324  *	    Implementations should not drop the xa_lock, nor re-enable
1325  *	    interrupts.
1326  */
1327 typedef void (*xa_update_node_t)(struct xa_node *node);
1328 
1329 void xa_delete_node(struct xa_node *, xa_update_node_t);
1330 
1331 /*
1332  * The xa_state is opaque to its users.  It contains various different pieces
1333  * of state involved in the current operation on the XArray.  It should be
1334  * declared on the stack and passed between the various internal routines.
1335  * The various elements in it should not be accessed directly, but only
1336  * through the provided accessor functions.  The below documentation is for
1337  * the benefit of those working on the code, not for users of the XArray.
1338  *
1339  * @xa_node usually points to the xa_node containing the slot we're operating
1340  * on (and @xa_offset is the offset in the slots array).  If there is a
1341  * single entry in the array at index 0, there are no allocated xa_nodes to
1342  * point to, and so we store %NULL in @xa_node.  @xa_node is set to
1343  * the value %XAS_RESTART if the xa_state is not walked to the correct
1344  * position in the tree of nodes for this operation.  If an error occurs
1345  * during an operation, it is set to an %XAS_ERROR value.  If we run off the
1346  * end of the allocated nodes, it is set to %XAS_BOUNDS.
1347  */
1348 struct xa_state {
1349 	struct xarray *xa;
1350 	unsigned long xa_index;
1351 	unsigned char xa_shift;
1352 	unsigned char xa_sibs;
1353 	unsigned char xa_offset;
1354 	unsigned char xa_pad;		/* Helps gcc generate better code */
1355 	struct xa_node *xa_node;
1356 	struct xa_node *xa_alloc;
1357 	xa_update_node_t xa_update;
1358 	struct list_lru *xa_lru;
1359 };
1360 
1361 /*
1362  * We encode errnos in the xas->xa_node.  If an error has happened, we need to
1363  * drop the lock to fix it, and once we've done so the xa_state is invalid.
1364  */
1365 #define XA_ERROR(errno) ((struct xa_node *)(((unsigned long)errno << 2) | 2UL))
1366 #define XAS_BOUNDS	((struct xa_node *)1UL)
1367 #define XAS_RESTART	((struct xa_node *)3UL)
1368 
1369 #define __XA_STATE(array, index, shift, sibs)  {	\
1370 	.xa = array,					\
1371 	.xa_index = index,				\
1372 	.xa_shift = shift,				\
1373 	.xa_sibs = sibs,				\
1374 	.xa_offset = 0,					\
1375 	.xa_pad = 0,					\
1376 	.xa_node = XAS_RESTART,				\
1377 	.xa_alloc = NULL,				\
1378 	.xa_update = NULL,				\
1379 	.xa_lru = NULL,					\
1380 }
1381 
1382 /**
1383  * XA_STATE() - Declare an XArray operation state.
1384  * @name: Name of this operation state (usually xas).
1385  * @array: Array to operate on.
1386  * @index: Initial index of interest.
1387  *
1388  * Declare and initialise an xa_state on the stack.
1389  */
1390 #define XA_STATE(name, array, index)				\
1391 	struct xa_state name = __XA_STATE(array, index, 0, 0)
1392 
1393 /**
1394  * XA_STATE_ORDER() - Declare an XArray operation state.
1395  * @name: Name of this operation state (usually xas).
1396  * @array: Array to operate on.
1397  * @index: Initial index of interest.
1398  * @order: Order of entry.
1399  *
1400  * Declare and initialise an xa_state on the stack.  This variant of
1401  * XA_STATE() allows you to specify the 'order' of the element you
1402  * want to operate on.`
1403  */
1404 #define XA_STATE_ORDER(name, array, index, order)		\
1405 	struct xa_state name = __XA_STATE(array,		\
1406 			(index >> order) << order,		\
1407 			order - (order % XA_CHUNK_SHIFT),	\
1408 			(1U << (order % XA_CHUNK_SHIFT)) - 1)
1409 
1410 #define xas_marked(xas, mark)	xa_marked((xas)->xa, (mark))
1411 #define xas_trylock(xas)	xa_trylock((xas)->xa)
1412 #define xas_lock(xas)		xa_lock((xas)->xa)
1413 #define xas_unlock(xas)		xa_unlock((xas)->xa)
1414 #define xas_lock_bh(xas)	xa_lock_bh((xas)->xa)
1415 #define xas_unlock_bh(xas)	xa_unlock_bh((xas)->xa)
1416 #define xas_lock_irq(xas)	xa_lock_irq((xas)->xa)
1417 #define xas_unlock_irq(xas)	xa_unlock_irq((xas)->xa)
1418 #define xas_lock_irqsave(xas, flags) \
1419 				xa_lock_irqsave((xas)->xa, flags)
1420 #define xas_unlock_irqrestore(xas, flags) \
1421 				xa_unlock_irqrestore((xas)->xa, flags)
1422 
1423 /**
1424  * xas_error() - Return an errno stored in the xa_state.
1425  * @xas: XArray operation state.
1426  *
1427  * Return: 0 if no error has been noted.  A negative errno if one has.
1428  */
1429 static inline int xas_error(const struct xa_state *xas)
1430 {
1431 	return xa_err(xas->xa_node);
1432 }
1433 
1434 /**
1435  * xas_set_err() - Note an error in the xa_state.
1436  * @xas: XArray operation state.
1437  * @err: Negative error number.
1438  *
1439  * Only call this function with a negative @err; zero or positive errors
1440  * will probably not behave the way you think they should.  If you want
1441  * to clear the error from an xa_state, use xas_reset().
1442  */
1443 static inline void xas_set_err(struct xa_state *xas, long err)
1444 {
1445 	xas->xa_node = XA_ERROR(err);
1446 }
1447 
1448 /**
1449  * xas_invalid() - Is the xas in a retry or error state?
1450  * @xas: XArray operation state.
1451  *
1452  * Return: %true if the xas cannot be used for operations.
1453  */
1454 static inline bool xas_invalid(const struct xa_state *xas)
1455 {
1456 	return (unsigned long)xas->xa_node & 3;
1457 }
1458 
1459 /**
1460  * xas_valid() - Is the xas a valid cursor into the array?
1461  * @xas: XArray operation state.
1462  *
1463  * Return: %true if the xas can be used for operations.
1464  */
1465 static inline bool xas_valid(const struct xa_state *xas)
1466 {
1467 	return !xas_invalid(xas);
1468 }
1469 
1470 /**
1471  * xas_is_node() - Does the xas point to a node?
1472  * @xas: XArray operation state.
1473  *
1474  * Return: %true if the xas currently references a node.
1475  */
1476 static inline bool xas_is_node(const struct xa_state *xas)
1477 {
1478 	return xas_valid(xas) && xas->xa_node;
1479 }
1480 
1481 /* True if the pointer is something other than a node */
1482 static inline bool xas_not_node(struct xa_node *node)
1483 {
1484 	return ((unsigned long)node & 3) || !node;
1485 }
1486 
1487 /* True if the node represents RESTART or an error */
1488 static inline bool xas_frozen(struct xa_node *node)
1489 {
1490 	return (unsigned long)node & 2;
1491 }
1492 
1493 /* True if the node represents head-of-tree, RESTART or BOUNDS */
1494 static inline bool xas_top(struct xa_node *node)
1495 {
1496 	return node <= XAS_RESTART;
1497 }
1498 
1499 /**
1500  * xas_reset() - Reset an XArray operation state.
1501  * @xas: XArray operation state.
1502  *
1503  * Resets the error or walk state of the @xas so future walks of the
1504  * array will start from the root.  Use this if you have dropped the
1505  * xarray lock and want to reuse the xa_state.
1506  *
1507  * Context: Any context.
1508  */
1509 static inline void xas_reset(struct xa_state *xas)
1510 {
1511 	xas->xa_node = XAS_RESTART;
1512 }
1513 
1514 /**
1515  * xas_retry() - Retry the operation if appropriate.
1516  * @xas: XArray operation state.
1517  * @entry: Entry from xarray.
1518  *
1519  * The advanced functions may sometimes return an internal entry, such as
1520  * a retry entry or a zero entry.  This function sets up the @xas to restart
1521  * the walk from the head of the array if needed.
1522  *
1523  * Context: Any context.
1524  * Return: true if the operation needs to be retried.
1525  */
1526 static inline bool xas_retry(struct xa_state *xas, const void *entry)
1527 {
1528 	if (xa_is_zero(entry))
1529 		return true;
1530 	if (!xa_is_retry(entry))
1531 		return false;
1532 	xas_reset(xas);
1533 	return true;
1534 }
1535 
1536 void *xas_load(struct xa_state *);
1537 void *xas_store(struct xa_state *, void *entry);
1538 void *xas_find(struct xa_state *, unsigned long max);
1539 void *xas_find_conflict(struct xa_state *);
1540 
1541 bool xas_get_mark(const struct xa_state *, xa_mark_t);
1542 void xas_set_mark(const struct xa_state *, xa_mark_t);
1543 void xas_clear_mark(const struct xa_state *, xa_mark_t);
1544 void *xas_find_marked(struct xa_state *, unsigned long max, xa_mark_t);
1545 void xas_init_marks(const struct xa_state *);
1546 
1547 bool xas_nomem(struct xa_state *, gfp_t);
1548 void xas_destroy(struct xa_state *);
1549 void xas_pause(struct xa_state *);
1550 
1551 void xas_create_range(struct xa_state *);
1552 
1553 #ifdef CONFIG_XARRAY_MULTI
1554 int xa_get_order(struct xarray *, unsigned long index);
1555 int xas_get_order(struct xa_state *xas);
1556 void xas_split(struct xa_state *, void *entry, unsigned int order);
1557 void xas_split_alloc(struct xa_state *, void *entry, unsigned int order, gfp_t);
1558 #else
1559 static inline int xa_get_order(struct xarray *xa, unsigned long index)
1560 {
1561 	return 0;
1562 }
1563 
1564 static inline int xas_get_order(struct xa_state *xas)
1565 {
1566 	return 0;
1567 }
1568 
1569 static inline void xas_split(struct xa_state *xas, void *entry,
1570 		unsigned int order)
1571 {
1572 	xas_store(xas, entry);
1573 }
1574 
1575 static inline void xas_split_alloc(struct xa_state *xas, void *entry,
1576 		unsigned int order, gfp_t gfp)
1577 {
1578 }
1579 #endif
1580 
1581 /**
1582  * xas_reload() - Refetch an entry from the xarray.
1583  * @xas: XArray operation state.
1584  *
1585  * Use this function to check that a previously loaded entry still has
1586  * the same value.  This is useful for the lockless pagecache lookup where
1587  * we walk the array with only the RCU lock to protect us, lock the page,
1588  * then check that the page hasn't moved since we looked it up.
1589  *
1590  * The caller guarantees that @xas is still valid.  If it may be in an
1591  * error or restart state, call xas_load() instead.
1592  *
1593  * Return: The entry at this location in the xarray.
1594  */
1595 static inline void *xas_reload(struct xa_state *xas)
1596 {
1597 	struct xa_node *node = xas->xa_node;
1598 	void *entry;
1599 	char offset;
1600 
1601 	if (!node)
1602 		return xa_head(xas->xa);
1603 	if (IS_ENABLED(CONFIG_XARRAY_MULTI)) {
1604 		offset = (xas->xa_index >> node->shift) & XA_CHUNK_MASK;
1605 		entry = xa_entry(xas->xa, node, offset);
1606 		if (!xa_is_sibling(entry))
1607 			return entry;
1608 		offset = xa_to_sibling(entry);
1609 	} else {
1610 		offset = xas->xa_offset;
1611 	}
1612 	return xa_entry(xas->xa, node, offset);
1613 }
1614 
1615 /**
1616  * xas_set() - Set up XArray operation state for a different index.
1617  * @xas: XArray operation state.
1618  * @index: New index into the XArray.
1619  *
1620  * Move the operation state to refer to a different index.  This will
1621  * have the effect of starting a walk from the top; see xas_next()
1622  * to move to an adjacent index.
1623  */
1624 static inline void xas_set(struct xa_state *xas, unsigned long index)
1625 {
1626 	xas->xa_index = index;
1627 	xas->xa_node = XAS_RESTART;
1628 }
1629 
1630 /**
1631  * xas_advance() - Skip over sibling entries.
1632  * @xas: XArray operation state.
1633  * @index: Index of last sibling entry.
1634  *
1635  * Move the operation state to refer to the last sibling entry.
1636  * This is useful for loops that normally want to see sibling
1637  * entries but sometimes want to skip them.  Use xas_set() if you
1638  * want to move to an index which is not part of this entry.
1639  */
1640 static inline void xas_advance(struct xa_state *xas, unsigned long index)
1641 {
1642 	unsigned char shift = xas_is_node(xas) ? xas->xa_node->shift : 0;
1643 
1644 	xas->xa_index = index;
1645 	xas->xa_offset = (index >> shift) & XA_CHUNK_MASK;
1646 }
1647 
1648 /**
1649  * xas_set_order() - Set up XArray operation state for a multislot entry.
1650  * @xas: XArray operation state.
1651  * @index: Target of the operation.
1652  * @order: Entry occupies 2^@order indices.
1653  */
1654 static inline void xas_set_order(struct xa_state *xas, unsigned long index,
1655 					unsigned int order)
1656 {
1657 #ifdef CONFIG_XARRAY_MULTI
1658 	xas->xa_index = order < BITS_PER_LONG ? (index >> order) << order : 0;
1659 	xas->xa_shift = order - (order % XA_CHUNK_SHIFT);
1660 	xas->xa_sibs = (1 << (order % XA_CHUNK_SHIFT)) - 1;
1661 	xas->xa_node = XAS_RESTART;
1662 #else
1663 	BUG_ON(order > 0);
1664 	xas_set(xas, index);
1665 #endif
1666 }
1667 
1668 /**
1669  * xas_set_update() - Set up XArray operation state for a callback.
1670  * @xas: XArray operation state.
1671  * @update: Function to call when updating a node.
1672  *
1673  * The XArray can notify a caller after it has updated an xa_node.
1674  * This is advanced functionality and is only needed by the page
1675  * cache and swap cache.
1676  */
1677 static inline void xas_set_update(struct xa_state *xas, xa_update_node_t update)
1678 {
1679 	xas->xa_update = update;
1680 }
1681 
1682 static inline void xas_set_lru(struct xa_state *xas, struct list_lru *lru)
1683 {
1684 	xas->xa_lru = lru;
1685 }
1686 
1687 /**
1688  * xas_next_entry() - Advance iterator to next present entry.
1689  * @xas: XArray operation state.
1690  * @max: Highest index to return.
1691  *
1692  * xas_next_entry() is an inline function to optimise xarray traversal for
1693  * speed.  It is equivalent to calling xas_find(), and will call xas_find()
1694  * for all the hard cases.
1695  *
1696  * Return: The next present entry after the one currently referred to by @xas.
1697  */
1698 static inline void *xas_next_entry(struct xa_state *xas, unsigned long max)
1699 {
1700 	struct xa_node *node = xas->xa_node;
1701 	void *entry;
1702 
1703 	if (unlikely(xas_not_node(node) || node->shift ||
1704 			xas->xa_offset != (xas->xa_index & XA_CHUNK_MASK)))
1705 		return xas_find(xas, max);
1706 
1707 	do {
1708 		if (unlikely(xas->xa_index >= max))
1709 			return xas_find(xas, max);
1710 		if (unlikely(xas->xa_offset == XA_CHUNK_MASK))
1711 			return xas_find(xas, max);
1712 		entry = xa_entry(xas->xa, node, xas->xa_offset + 1);
1713 		if (unlikely(xa_is_internal(entry)))
1714 			return xas_find(xas, max);
1715 		xas->xa_offset++;
1716 		xas->xa_index++;
1717 	} while (!entry);
1718 
1719 	return entry;
1720 }
1721 
1722 /* Private */
1723 static inline unsigned int xas_find_chunk(struct xa_state *xas, bool advance,
1724 		xa_mark_t mark)
1725 {
1726 	unsigned long *addr = xas->xa_node->marks[(__force unsigned)mark];
1727 	unsigned int offset = xas->xa_offset;
1728 
1729 	if (advance)
1730 		offset++;
1731 	if (XA_CHUNK_SIZE == BITS_PER_LONG) {
1732 		if (offset < XA_CHUNK_SIZE) {
1733 			unsigned long data = *addr & (~0UL << offset);
1734 			if (data)
1735 				return __ffs(data);
1736 		}
1737 		return XA_CHUNK_SIZE;
1738 	}
1739 
1740 	return find_next_bit(addr, XA_CHUNK_SIZE, offset);
1741 }
1742 
1743 /**
1744  * xas_next_marked() - Advance iterator to next marked entry.
1745  * @xas: XArray operation state.
1746  * @max: Highest index to return.
1747  * @mark: Mark to search for.
1748  *
1749  * xas_next_marked() is an inline function to optimise xarray traversal for
1750  * speed.  It is equivalent to calling xas_find_marked(), and will call
1751  * xas_find_marked() for all the hard cases.
1752  *
1753  * Return: The next marked entry after the one currently referred to by @xas.
1754  */
1755 static inline void *xas_next_marked(struct xa_state *xas, unsigned long max,
1756 								xa_mark_t mark)
1757 {
1758 	struct xa_node *node = xas->xa_node;
1759 	void *entry;
1760 	unsigned int offset;
1761 
1762 	if (unlikely(xas_not_node(node) || node->shift))
1763 		return xas_find_marked(xas, max, mark);
1764 	offset = xas_find_chunk(xas, true, mark);
1765 	xas->xa_offset = offset;
1766 	xas->xa_index = (xas->xa_index & ~XA_CHUNK_MASK) + offset;
1767 	if (xas->xa_index > max)
1768 		return NULL;
1769 	if (offset == XA_CHUNK_SIZE)
1770 		return xas_find_marked(xas, max, mark);
1771 	entry = xa_entry(xas->xa, node, offset);
1772 	if (!entry)
1773 		return xas_find_marked(xas, max, mark);
1774 	return entry;
1775 }
1776 
1777 /*
1778  * If iterating while holding a lock, drop the lock and reschedule
1779  * every %XA_CHECK_SCHED loops.
1780  */
1781 enum {
1782 	XA_CHECK_SCHED = 4096,
1783 };
1784 
1785 /**
1786  * xas_for_each() - Iterate over a range of an XArray.
1787  * @xas: XArray operation state.
1788  * @entry: Entry retrieved from the array.
1789  * @max: Maximum index to retrieve from array.
1790  *
1791  * The loop body will be executed for each entry present in the xarray
1792  * between the current xas position and @max.  @entry will be set to
1793  * the entry retrieved from the xarray.  It is safe to delete entries
1794  * from the array in the loop body.  You should hold either the RCU lock
1795  * or the xa_lock while iterating.  If you need to drop the lock, call
1796  * xas_pause() first.
1797  */
1798 #define xas_for_each(xas, entry, max) \
1799 	for (entry = xas_find(xas, max); entry; \
1800 	     entry = xas_next_entry(xas, max))
1801 
1802 /**
1803  * xas_for_each_marked() - Iterate over a range of an XArray.
1804  * @xas: XArray operation state.
1805  * @entry: Entry retrieved from the array.
1806  * @max: Maximum index to retrieve from array.
1807  * @mark: Mark to search for.
1808  *
1809  * The loop body will be executed for each marked entry in the xarray
1810  * between the current xas position and @max.  @entry will be set to
1811  * the entry retrieved from the xarray.  It is safe to delete entries
1812  * from the array in the loop body.  You should hold either the RCU lock
1813  * or the xa_lock while iterating.  If you need to drop the lock, call
1814  * xas_pause() first.
1815  */
1816 #define xas_for_each_marked(xas, entry, max, mark) \
1817 	for (entry = xas_find_marked(xas, max, mark); entry; \
1818 	     entry = xas_next_marked(xas, max, mark))
1819 
1820 /**
1821  * xas_for_each_conflict() - Iterate over a range of an XArray.
1822  * @xas: XArray operation state.
1823  * @entry: Entry retrieved from the array.
1824  *
1825  * The loop body will be executed for each entry in the XArray that
1826  * lies within the range specified by @xas.  If the loop terminates
1827  * normally, @entry will be %NULL.  The user may break out of the loop,
1828  * which will leave @entry set to the conflicting entry.  The caller
1829  * may also call xa_set_err() to exit the loop while setting an error
1830  * to record the reason.
1831  */
1832 #define xas_for_each_conflict(xas, entry) \
1833 	while ((entry = xas_find_conflict(xas)))
1834 
1835 void *__xas_next(struct xa_state *);
1836 void *__xas_prev(struct xa_state *);
1837 
1838 /**
1839  * xas_prev() - Move iterator to previous index.
1840  * @xas: XArray operation state.
1841  *
1842  * If the @xas was in an error state, it will remain in an error state
1843  * and this function will return %NULL.  If the @xas has never been walked,
1844  * it will have the effect of calling xas_load().  Otherwise one will be
1845  * subtracted from the index and the state will be walked to the correct
1846  * location in the array for the next operation.
1847  *
1848  * If the iterator was referencing index 0, this function wraps
1849  * around to %ULONG_MAX.
1850  *
1851  * Return: The entry at the new index.  This may be %NULL or an internal
1852  * entry.
1853  */
1854 static inline void *xas_prev(struct xa_state *xas)
1855 {
1856 	struct xa_node *node = xas->xa_node;
1857 
1858 	if (unlikely(xas_not_node(node) || node->shift ||
1859 				xas->xa_offset == 0))
1860 		return __xas_prev(xas);
1861 
1862 	xas->xa_index--;
1863 	xas->xa_offset--;
1864 	return xa_entry(xas->xa, node, xas->xa_offset);
1865 }
1866 
1867 /**
1868  * xas_next() - Move state to next index.
1869  * @xas: XArray operation state.
1870  *
1871  * If the @xas was in an error state, it will remain in an error state
1872  * and this function will return %NULL.  If the @xas has never been walked,
1873  * it will have the effect of calling xas_load().  Otherwise one will be
1874  * added to the index and the state will be walked to the correct
1875  * location in the array for the next operation.
1876  *
1877  * If the iterator was referencing index %ULONG_MAX, this function wraps
1878  * around to 0.
1879  *
1880  * Return: The entry at the new index.  This may be %NULL or an internal
1881  * entry.
1882  */
1883 static inline void *xas_next(struct xa_state *xas)
1884 {
1885 	struct xa_node *node = xas->xa_node;
1886 
1887 	if (unlikely(xas_not_node(node) || node->shift ||
1888 				xas->xa_offset == XA_CHUNK_MASK))
1889 		return __xas_next(xas);
1890 
1891 	xas->xa_index++;
1892 	xas->xa_offset++;
1893 	return xa_entry(xas->xa, node, xas->xa_offset);
1894 }
1895 
1896 #endif /* _LINUX_XARRAY_H */
1897