// SPDX-License-Identifier: GPL-2.0#include <linux/kernel.h>#include <linux/bug.h>#include <linux/compiler.h>#include <linux/export.h>#include <linux/string.h>#include <linux/list_sort.h>#include <linux/list.h> #define MAX_LIST_LENGTH_BITS 20 /* * Returns a list organized in an intermediate format suited * to chaining of merge() calls: null-terminated, no reserved or * sentinel head node, "prev" links not maintained. */static struct list_head *merge(void *priv,				int (*cmp)(void *priv, struct list_head *a,					struct list_head *b),				struct list_head *a, struct list_head *b){	struct list_head head, *tail = &head; 	while (a && b) {		/* if equal, take 'a' -- important for sort stability */		if ((*cmp)(priv, a, b) <= 0) {			tail->next = a;			a = a->next;		} else {			tail->next = b;			b = b->next;		}		tail = tail->next;	}	tail->next = a?:b;	return head.next;} /* * Combine final list merge with restoration of standard doubly-linked * list structure.  This approach duplicates code from merge(), but * runs faster than the tidier alternatives of either a separate final * prev-link restoration pass, or maintaining the prev links * throughout. */static void merge_and_restore_back_links(void *priv,				int (*cmp)(void *priv, struct list_head *a,					struct list_head *b),				struct list_head *head,				struct list_head *a, struct list_head *b){	struct list_head *tail = head;	u8 count = 0; 	while (a && b) {		/* if equal, take 'a' -- important for sort stability */		if ((*cmp)(priv, a, b) <= 0) {			tail->next = a;			a->prev = tail;			a = a->next;		} else {			tail->next = b;			b->prev = tail;			b = b->next;		}		tail = tail->next;	}	tail->next = a ? : b; 	do {		/*		 * In worst cases this loop may run many iterations.		 * Continue callbacks to the client even though no		 * element comparison is needed, so the client's cmp()		 * routine can invoke cond_resched() periodically.		 */		if (unlikely(!(++count)))			(*cmp)(priv, tail->next, tail->next); 		tail->next->prev = tail;		tail = tail->next;	} while (tail->next); 	tail->next = head;	head->prev = tail;} /** * list_sort - sort a list * @priv: private data, opaque to list_sort(), passed to @cmp * @head: the list to sort * @cmp: the elements comparison function * * This function implements "merge sort", which has O(nlog(n)) * complexity. * * The comparison function @cmp must return a negative value if @a * should sort before @b, and a positive value if @a should sort after * @b. If @a and @b are equivalent, and their original relative * ordering is to be preserved, @cmp must return 0. */void list_sort(void *priv, struct list_head *head,		int (*cmp)(void *priv, struct list_head *a,			struct list_head *b)){	struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists						-- last slot is a sentinel */	int lev;  /* index into part[] */	int max_lev = 0;	struct list_head *list; 	if (list_empty(head))		return; 	memset(part, 0, sizeof(part)); 	head->prev->next = NULL;	list = head->next; 	while (list) {		struct list_head *cur = list;		list = list->next;		cur->next = NULL; 		for (lev = 0; part[lev]; lev++) {			cur = merge(priv, cmp, part[lev], cur);			part[lev] = NULL;		}		if (lev > max_lev) {			if (unlikely(lev >= ARRAY_SIZE(part)-1)) {				printk_once(KERN_DEBUG "list too long for efficiency\n");				lev--;			}			max_lev = lev;		}		part[lev] = cur;	} 	for (lev = 0; lev < max_lev; lev++)		if (part[lev])			list = merge(priv, cmp, part[lev], list); 	merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);}EXPORT_SYMBOL(list_sort);