1 #include <linux/kernel.h>
3 #include <linux/compiler.h>
4 #include <linux/export.h>
5 #include <linux/string.h>
6 #include <linux/list_sort.h>
7 #include <linux/list.h>
9 #define MAX_LIST_LENGTH_BITS 20
12 * Returns a list organized in an intermediate format suited
13 * to chaining of merge() calls: null-terminated, no reserved or
14 * sentinel head node, "prev" links not maintained.
16 static struct list_head *merge(void *priv,
17 int (*cmp)(void *priv, struct list_head *a,
19 struct list_head *a, struct list_head *b)
21 struct list_head head, *tail = &head;
24 /* if equal, take 'a' -- important for sort stability */
25 if ((*cmp)(priv, a, b) <= 0) {
39 * Combine final list merge with restoration of standard doubly-linked
40 * list structure. This approach duplicates code from merge(), but
41 * runs faster than the tidier alternatives of either a separate final
42 * prev-link restoration pass, or maintaining the prev links
45 static void merge_and_restore_back_links(void *priv,
46 int (*cmp)(void *priv, struct list_head *a,
48 struct list_head *head,
49 struct list_head *a, struct list_head *b)
51 struct list_head *tail = head;
55 /* if equal, take 'a' -- important for sort stability */
56 if ((*cmp)(priv, a, b) <= 0) {
71 * In worst cases this loop may run many iterations.
72 * Continue callbacks to the client even though no
73 * element comparison is needed, so the client's cmp()
74 * routine can invoke cond_resched() periodically.
76 if (unlikely(!(++count)))
77 (*cmp)(priv, tail->next, tail->next);
79 tail->next->prev = tail;
88 * list_sort - sort a list
89 * @priv: private data, opaque to list_sort(), passed to @cmp
90 * @head: the list to sort
91 * @cmp: the elements comparison function
93 * This function implements "merge sort", which has O(nlog(n))
96 * The comparison function @cmp must return a negative value if @a
97 * should sort before @b, and a positive value if @a should sort after
98 * @b. If @a and @b are equivalent, and their original relative
99 * ordering is to be preserved, @cmp must return 0.
101 void list_sort(void *priv, struct list_head *head,
102 int (*cmp)(void *priv, struct list_head *a,
103 struct list_head *b))
105 struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
106 -- last slot is a sentinel */
107 int lev; /* index into part[] */
109 struct list_head *list;
111 if (list_empty(head))
114 memset(part, 0, sizeof(part));
116 head->prev->next = NULL;
120 struct list_head *cur = list;
124 for (lev = 0; part[lev]; lev++) {
125 cur = merge(priv, cmp, part[lev], cur);
129 if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
130 printk_once(KERN_DEBUG "list too long for efficiency\n");
138 for (lev = 0; lev < max_lev; lev++)
140 list = merge(priv, cmp, part[lev], list);
142 merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
144 EXPORT_SYMBOL(list_sort);