1 #include <linux/kernel.h>
2 #include <linux/module.h>
3 #include <linux/list_sort.h>
4 #include <linux/slab.h>
5 #include <linux/list.h>
7 #define MAX_LIST_LENGTH_BITS 20
10 * Returns a list organized in an intermediate format suited
11 * to chaining of merge() calls: null-terminated, no reserved or
12 * sentinel head node, "prev" links not maintained.
14 static struct list_head *merge(void *priv,
15 int (*cmp)(void *priv, struct list_head *a,
17 struct list_head *a, struct list_head *b)
19 struct list_head head, *tail = &head;
22 /* if equal, take 'a' -- important for sort stability */
23 if ((*cmp)(priv, a, b) <= 0) {
37 * Combine final list merge with restoration of standard doubly-linked
38 * list structure. This approach duplicates code from merge(), but
39 * runs faster than the tidier alternatives of either a separate final
40 * prev-link restoration pass, or maintaining the prev links
43 static void merge_and_restore_back_links(void *priv,
44 int (*cmp)(void *priv, struct list_head *a,
46 struct list_head *head,
47 struct list_head *a, struct list_head *b)
49 struct list_head *tail = head;
52 /* if equal, take 'a' -- important for sort stability */
53 if ((*cmp)(priv, a, b) <= 0) {
68 * In worst cases this loop may run many iterations.
69 * Continue callbacks to the client even though no
70 * element comparison is needed, so the client's cmp()
71 * routine can invoke cond_resched() periodically.
73 (*cmp)(priv, tail->next, tail->next);
75 tail->next->prev = tail;
84 * list_sort - sort a list
85 * @priv: private data, opaque to list_sort(), passed to @cmp
86 * @head: the list to sort
87 * @cmp: the elements comparison function
89 * This function implements "merge sort", which has O(nlog(n))
92 * The comparison function @cmp must return a negative value if @a
93 * should sort before @b, and a positive value if @a should sort after
94 * @b. If @a and @b are equivalent, and their original relative
95 * ordering is to be preserved, @cmp must return 0.
97 void list_sort(void *priv, struct list_head *head,
98 int (*cmp)(void *priv, struct list_head *a,
101 struct list_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
102 -- last slot is a sentinel */
103 int lev; /* index into part[] */
105 struct list_head *list;
107 if (list_empty(head))
110 memset(part, 0, sizeof(part));
112 head->prev->next = NULL;
116 struct list_head *cur = list;
120 for (lev = 0; part[lev]; lev++) {
121 cur = merge(priv, cmp, part[lev], cur);
125 if (unlikely(lev >= ARRAY_SIZE(part)-1)) {
126 printk_once(KERN_DEBUG "list passed to"
127 " list_sort() too long for"
136 for (lev = 0; lev < max_lev; lev++)
138 list = merge(priv, cmp, part[lev], list);
140 merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
142 EXPORT_SYMBOL(list_sort);
144 #ifdef CONFIG_TEST_LIST_SORT
146 #include <linux/random.h>
149 struct list_head list;
154 static int cmp(void *priv, struct list_head *a, struct list_head *b)
156 return container_of(a, struct debug_el, list)->value
157 - container_of(b, struct debug_el, list)->value;
161 * The pattern of set bits in the list length determines which cases
162 * are hit in list_sort().
164 #define TEST_LIST_LEN (512+128+2) /* not including head */
166 static int __init list_sort_test(void)
169 struct list_head *head = kmalloc(sizeof(*head), GFP_KERNEL);
170 struct list_head *cur;
172 printk(KERN_DEBUG "testing list_sort()\n");
175 for (i = 0; i < TEST_LIST_LEN; i++) {
176 struct debug_el *el = kmalloc(sizeof(*el), GFP_KERNEL);
178 /* force some equivalencies */
179 el->value = random32() % (TEST_LIST_LEN/3);
183 cur->next = &el->list;
188 list_sort(NULL, head, cmp);
191 for (cur = head->next; cur->next != head; cur = cur->next) {
192 struct debug_el *el = container_of(cur, struct debug_el, list);
193 int cmp_result = cmp(NULL, cur, cur->next);
194 if (cur->next->prev != cur) {
195 printk(KERN_ERR "list_sort() returned "
196 "a corrupted list!\n");
198 } else if (cmp_result > 0) {
199 printk(KERN_ERR "list_sort() failed to sort!\n");
201 } else if (cmp_result == 0 &&
202 el->serial >= container_of(cur->next,
203 struct debug_el, list)->serial) {
204 printk(KERN_ERR "list_sort() failed to preserve order "
205 "of equivalent elements!\n");
212 if (count != TEST_LIST_LEN) {
213 printk(KERN_ERR "list_sort() returned list of "
214 "different length!\n");
219 module_init(list_sort_test);
220 #endif /* CONFIG_TEST_LIST_SORT */