#include <linux/kernel.h>#include <linux/module.h>#include <linux/list_sort.h>#include <linux/slab.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; 	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.		 */		(*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 passed to"					" list_sort() 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); #ifdef DEBUG_LIST_SORTstruct debug_el {	struct list_head l_h;	int value;	unsigned serial;}; static int cmp(void *priv, struct list_head *a, struct list_head *b){	return container_of(a, struct debug_el, l_h)->value	     - container_of(b, struct debug_el, l_h)->value;} /* * The pattern of set bits in the list length determines which cases * are hit in list_sort(). */#define LIST_SORT_TEST_LENGTH (512+128+2) /* not including head */ static int __init list_sort_test(void){	int i, r = 1, count;	struct list_head *head = kmalloc(sizeof(*head), GFP_KERNEL);	struct list_head *cur; 	printk(KERN_WARNING "testing list_sort()\n"); 	cur = head;	for (i = 0; i < LIST_SORT_TEST_LENGTH; i++) {		struct debug_el *el = kmalloc(sizeof(*el), GFP_KERNEL);		BUG_ON(!el);		 /* force some equivalencies */		el->value = (r = (r * 725861) % 6599) % (LIST_SORT_TEST_LENGTH/3);		el->serial = i; 		el->l_h.prev = cur;		cur->next = &el->l_h;		cur = cur->next;	}	head->prev = cur; 	list_sort(NULL, head, cmp); 	count = 1;	for (cur = head->next; cur->next != head; cur = cur->next) {		struct debug_el *el = container_of(cur, struct debug_el, l_h);		int cmp_result = cmp(NULL, cur, cur->next);		if (cur->next->prev != cur) {			printk(KERN_EMERG "list_sort() returned "						"a corrupted list!\n");			return 1;		} else if (cmp_result > 0) {			printk(KERN_EMERG "list_sort() failed to sort!\n");			return 1;		} else if (cmp_result == 0 &&				el->serial >= container_of(cur->next,					struct debug_el, l_h)->serial) {			printk(KERN_EMERG "list_sort() failed to preserve order"						 " of equivalent elements!\n");			return 1;		}		kfree(cur->prev);		count++;	}	kfree(cur);	if (count != LIST_SORT_TEST_LENGTH) {		printk(KERN_EMERG "list_sort() returned list of"						"different length!\n");		return 1;	}	return 0;}module_init(list_sort_test);#endif